Piping Design - Chem Eng

April 14, 2018 | Author: Anonymous | Category: Documents
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T his is the first in a series of ar- ticles that will cover a wide range of piping topics. The topics will cross process-industry lines, per- taining to, for example, the chemical, petroleum-refining, pulp-and-paper and pharmaceutical and other indus- tries.The main intent of these articles to address questions and misunder- standings as they relate to use of pip- ing on a general basis. Typical of the topics that will be cov- ered in this series are the following: • With respect to ASME flange rat- ings — Is the correct terminology 150- and 300-pound flange, or is it Class 150 and Class 300 flange? And do the 150 and 300 actually mean anything, or are they simply identifiers? Similarly, with respect to forged fittings, is the terminology 2,000-pound and 3,000-pound, or is it Class 2000 and Class 3000? • How do you determine which Class of forged fitting to select for your specification? • How do you determine and then assign corrosion allowance for pip- ing? • How do you select the proper bolts and gaskets for a service? • How is pipe wall thickness estab- lished? • What is MAWP? • What is operating and design pres- sure, and how do they differ? Simi- larly, what are operating and de- sign temperature? How do design pressure and temperature relate to a PSV set point and leak testing? • For a given process application, under what Code should the design be carried out? • What kind of problems might be ex- pected with sanitary clamp fittings, and how can they be avoided or al- leviated? • What is ASME-BPE? And how do ASME B31.3 and ASME-BPE work in concert with one another? What is ASME BPE doing to bring ac- creditation to the pharmaceutical industry? The catch-all terminology for pipe and tubing is “tubular products.” This term includes pipe, tube and their respec- tive fittings. The term, “piping,” itself refers to a system of pipe, fittings, flanges, valves, bolts, gaskets and other inline components that make up an entire system used to convey a fluid. As for the simple distinction be- tween pipe and tubing, it is that tub- ing is thin-walled pipe with a diam- eter different from that of nominally comparable pipe. PiPing and tubing Piping and tubing can basically be grouped into three broad classifica- tions: pipe, pressure tube and mechan- ical tube. Based on user requirements, these classifications come in various types, such as standard pipe, pressure pipe, line pipe, water well pipe, oil- country tubular goods, conduit, piles, nipple pipe and sprinkler pipe. The two types of main relevance to the chemical process industries are standard and pressure pipe. Distin- guishable only from the standpoint of use, standard pipe is intended for low- pressure, non-volatile use, whereas pressure pipe is intended for use in higher-integrity services, namely, ser- vices in which the pipe is required to convey high-pressure, volatile or non- volatile liquids and gases, particularly at sub-zero or elevated temperatures. Pipe (standard or pressure) is man- ufactured to a nominal pipe size (NPS) in which the outside diameter (OD) of 42 ChemiCal engineering www.Che.Com FeBrUarY 2007 W. M. Huitt W. M. Huitt Co. Feature Report Piping for Process Plants Part 1: The Basics Pipe, fittings and related equipment are fundamental to the operation of chemical process plants. The series of articles beginning with this one spells out the details 42-47 CHE 2-07.indd 42 1/24/07 2:28:12 PM a given nominal size remains constant while any change in wall thickness is reflected in the inside diameter (ID). Pipe wall thicknesses are specified by Schedule (Sch.) Numbers 5, 10, 20, 30, 40, 60, 80, 100, 120, 140 and 160. Add the suffix ‘s’ when specifying stainless steel or other alloys. Wall thickness is also specified by the symbols Std. (Standard), XS (Extra Strong) and XX (Double Extra Strong). Pipe of NPS 12 in. and smaller has an OD that is nominally larger than that specified, whereas pipe with a NPS 14 in. and larger has an OD equal to the size specified. Steel and alloy tubing is manufac- tured to an OD equal to that speci- fied; this means, for example, that ¼-in. tubing will in fact have a ¼-in. OD, and that 2-in. tubing will have a 2-in. OD. This practice also pertains to copper tubing for air conditioning and refrigeration. Copper tubing for other purposes has an OD that is always 1/8 in. larger than the diameter specified. As an example, ½-in. copper tubing will have a 5/8-in. OD, and 1-in. tubing will have a 1 1/8-in. OD.Wall thickness for tubing is specified in the actual decimal equivalent of its thickness. Manufacturing methods Pipe is manufactured in three basic forms: cast, welded and seamless. Tubing is manufactured in two basic forms: welded and seamless. Cast Pipe: Cast pipe is available in four basic types: white iron, malleable iron, gray iron and ductile iron. White iron has a high content of carbon in the carbide form. Carbides give it a high compressive strength and a hard- ness that provides added resistance to wear, but leaves it very brittle. The absence of graphite bestows a light colored appearance. Malleable iron is white cast iron that has been heat treated for added ductility. If white cast iron is reheated in the presence of oxygen-containing materials such as an iron oxide, and allowed it to cool very slowly, the free carbon forms small graphite particles. This gives malleable iron excellent machinability and ductility proper- ties, along with good shock resistant properties. Gray iron is the oldest form of cast iron pipe and is synonymous with the name, “cast iron.” It contains carbon in the form of flake graphite, which gives it its characteristic gray color. Gray cast iron has virtually no elastic or plastic properties, but has excellent machining and self-lubricating prop- erties due to the graphite content Ductile iron is arguably the most versatile of the cast irons. It has ex- cellent ductile and machinable prop- erties while also having high strength characteristics. Welded Steel Pipe (and Tubing): Statements made about pipe in the this section also pertain to tubing. ChemiCal engineering www.Che.Com FeBrUarY 2007 43 IndustrIes and standards “P ipe is pipe”. This is a euphemism quite often used among piping designers and engineers. Taken at face value, this is a true statement — pipe is certainly pipe. However, taken in context, the statement means that no matter which pro- cerss industry you work in when designing piping systems, the issues are all the same. And in that context, it could not be further from the truth. Consider in particular the pharmaceutical industry. Although not new per se, it is a relative newcomer to the idea of dedicated design, engineering and construction principles, when compared to other process industries, such as petroleum refining, bulk chemi- cals, and pulp and paper industries; indeed, even in comparison with nuclear power, and with semiconductor manufacture. Here is a frame of reference, in terms of relevant standard-setting orga- nizations: the American Society of Mechanical Engineers (ASME) was established in 1880; the American Petroleum Institute (API) was established in 1919; 3-A Standards (for the food and dairy industry) were first developed in the 1920’s; the ASME commit- tee for BPVC (Boiler Pressure Vessel Code) Section III for nuclear power was proposed in 1963; the Semiconductor Equipment and Materials Institute (SEMI) was established in 1973; the Interna- tional Society of Pharmaceutical Engineers (ISPE) was established in 1980; and ASME Biopharmaceutical Equipment (BPE) issued its first standard in 1997. Prior to ASME-BPE, the aforementioned 3- A piping standards were the common recourse for facilitating the design of pharmaceutical facilities. While some of the above standards organizations, and their re- sulting codes and standards, are specific to a particular industry, others are more generalized in their use and are utilized across the various industries. For example, the design and construction of a large pharmaceutical facility depends upon not only pharma- ceutical-based standards, codes, guidelines and industry practices such as those generated by ISPE and ASME-BPE; it also avails itself of standards created for other industries. In other words, when designing and constructing a bulk pharmaceutical finishing facility, or a bulk Active Pharmaceutical Ingredient (API) facility, the engineers and constructors will be working under some of the same standards and guidelines as they would when designing and building in other industries such as a petroleum refinery or bulk chemical facility. The point is not that the pharmaceutical industry itself is young; as already stated, it is not. The point is that the standards and accepted practices appropriate for state-of-the-art design, en- gineering and manufacture are. As recently as the past fifteen or so years, industry practice, including dimensional standards for high purity fittings, were left to the resources of the phar- maceutical company owner or their engineering firm (engineer of record). The same point applied to construction methods and procedures, including materials of construction. These require- ments were basically established for each project and were very dependent upon what the owner’s personnel and the engineering firm brought to the table. Industry standards did not exist. With regard to materials of construction, the ongoing evolution of technology (science and engineering alike) has raised expec- tations throughout industry. For instance, out of the research and development that went into the Hubble Space Telescope came new methodology and technology to better measure and define the limits of surface roughness required in material used in hy- gienic-fluid-service contact piping. This capability is of particular interest to the pharmaceutical and biopharmaceutical industries (as well as the semiconductor industry), where cross-contamina- tion at the molecular level cannot be tolerated in many cases. This requires surfaces to be very cleanable. Surface roughness used to be expressed as polish numbers (i.e., #4 or #7) then grit numbers such as 150, 180 or 240). The prob- lem with either of these two methods lay in their subjectivity and their generality. These indicators were not specific enough and the accept/reject result relied too much on a subjective visual verification. There will be more on surface finish requirements in a subsequent installment. With acute awareness of the ongoing problems currently faced in the pharmaceutical industry and, for altogether different rea- sons, the semiconductor industry, various standards organiza- tions have taken steps to alleviate the consistent problems that have plagued the industry in the past with, for instasnce, high purity welding issues, standardization of fittings, and guidelines for industry practice. This series of articles will discuss some of the finer points of these issues, and, in some cases, what the standards organizations, are doing to promote and consolidate some of the better thinking in this industry and in this field. ❏ 42-47 CHE 2-07.indd 43 1/24/07 2:28:57 PM Welded steel pipe is manufactured by furnace welding or by fusion weld- ing. Furnace welding is achieved by heating strip steel, also referred as skelp, to welding temperature then forming it into pipe. The continuous weld, or buttweld, is forged at the time the strip is formed into pipe. This is a process generally used to manufacture low-cost pipe 3 ½ in. OD and below. Fusion Welded pipe is formed from skelp that is cold rolled into pipe and the edges welded together by resis- tance welding, induction welding or arc welding. Electric resistance welding (ERW) can be accomplished by flash welding, high-frequency or low-fre- quency resistance welding. A scarfing tool is used to remove upset material along the seam of flash-welded pipe. Flash welding produces a high- strength steel pipe in NPS 4 in. through 36 in. Low-frequency resis- tance welding can be used to manu- facture pipe through NPS 22 in. High- frequency resistance welding can be used to manufacture pipe through NPS 42 in. High-frequency induction welding can be used for high-rate production of small-NPS (6 in. and less) pipe. This is a cleaner form of welding in which scarfing, or the cleaning of upset ma- terial along the seam, is normally not required. Arc welding the longitudinal seam of production pipe is accomplished with submerged arc welding (SAW), inert gas tungsten arc welding (GTAW) also called tungsten inert gas weld- ing (TIG), or gas shielded consumable metal arc welding (MIG). As will be discussed later in this series, the type of weld seam used in the manufacture of pipe is a factor when calculating the Pressure Design Thickness (t) of the pipe wall. Some types of longitudinal pipe seam weld- ing are not as strong as others, reduc- ing the overall integrity of the pipe wall by a percentage factyor given in ASME B31.3 based on the type of lon- gitudinal seam weld. Seamless Steel Pipe and Tubing: Statements in the following also per- tain to tubing. Seamless steel pipe, made using various extrusion and mandrel mill methods, is manufactured by first cre- ating a tube hollow from a steel billet, which is a solid steel round. The billet is heated to its hot metal forming temperature, then pierced by a rotary piercer or by a press piercer to cre- ate the tube hollow, which will have a larger diam- eter and thicker wall than its final pipe form. The tube hollow is then hot-worked by the mandrel mill process, the Mannesmann plug-mill process, or the Ugine Sejournet extru- sion process. Upon completion of these processes, the pipe is referred to as hot-finished. If further work is required to achieve more accuracy in the diameter or wall thickness or improve its finish, the pipe can be cold-finished, or cold- worked. If the pipe is cold-finished, it will then require heat treating to re- move pipe-wall stress created during the working in its cold state. There are also two forging processes used in the manufacture of large di- ameter (10 to 30 inch) pipe with heavy wall thickness (1.5 to 4 inch). The two forging methods are called forged and bored, and hollow forged. PiPe Fittings Pipe fittings are manufactured by the following processes: cast, forged and wrought. Cast fittings Cast fittings are available in cast iron, malleable iron, ordinary steel, stain- less steel, brass, bronze, and other alloy material as follows: Cast Iron: Cast iron threaded fittings, covered by ASME B16.4, are available in Class 125 and Class 250 for sizes NPS ¼ in. through 12 in. Cast iron flanged fittings, under ASME B16.1, are available in Class 25, 125 and 250 in sizes NPS 1 in. through 48 in. Malleable Iron: Malleable iron fit- tings, under ASME B16.3, are avail- able in Class 150 and Class 300 in sizes NPS 1/8 in. though 6 in. for Class 150, and ¼ in. through 3 in. for Class 300. Be aware that Classifications such as 150 and 300 are not universal through- out the ASME Standards. They are instead specific to the Standard with which they are associated. One thus cannot, for instance, automatically transfer the pressure/temperature lim- its of a flange joint in ASME B16.5 to that of a fitting in B16.3. Cast Steel: Cast steel, stainless steel and alloy steel flanged fittings, under ASME B16.5, are available in Class 150, 300, 400, 600, 900, 1500 & 2500 in sizes ½ in. though 24 in. Cast Brass: Cast brass, as well as bronze, threaded fittings, under ASME B16.15, are available in Class 125 and 250, in sizes NPS 1/8 in. through 4 in. for Class 125, and 1/4” through 4 in. for Class 250. Cast Copper: Cast copper solder joints, under ASME B16.18, are avail- able in sizes ¼ in. through 6 in. Forged fittings Before discussion of forged fittings, it is illuminating to consider the dif- ference between forged and wrought fittings. The term, forging, actually dates from the times when metal was worked by hand. A bar of steel would be placed into a forge and heated until it reached its plastic state, at which time the metal would be pulled out of the forge and hammered into some desired shape. Today, forging metal basically means working the metal by means of hydraulic hammers to achieve the desired shape. Wrought iron is corrosion resistant, has excellent tensile strength and welds easily, and in its plastic range is said to be like working taffy candy. What gives wrought iron these attri- butes is the iron silicate fibers, or slag added to the molten iron with a small percentage of carbon, whereas cast iron, having a high carbon content, is more brittle and not as easily worked. The smelters, where the iron ore was melted to produce wrought iron, were called bloomeries. In a bloomery, the process did not completely melt the iron ore; rather the semi-finished Feature Report 44 ChemiCal engineering www.Che.Com FeBrUarY 2007 $ Y $ Y U NominaI pipe waII thickness $ Y (Min.) = 1.09U but not Iess than 0.12 in. (3.0 mm) Approx. 0.06 in. (2.0 mm) before weIding Minimum fIat - 0.75 $ Y See 7.7.1 Figure 1. Socketweld fittings are available in a wide range of sizes 42-47 CHE 2-07.indd 44 1/24/07 2:31:23 PM product was a spongy molten mass called a bloom, a term derived from the red glow of the molten metal, which is likewise how the process gets its name. The slag and impuri- ties were then mechanically removed from the molten mass by twisting and hammering, which is where the term wrought originates. Today forged and wrought are al- most synonymous. ASTM A234, “Stan- dard Specification for Piping Fittings of Wrought Carbon Steel and Alloy Steel for Moderate and High Tem- perature Service” states in Para 4.1 and in Para 5.1 that wrought fittings made under A234 are actually manu- factured or fabricated from material pre-formed by one of the methods listed previously, which includes forg- ing. In ASTM A961, “Standard Specifi- cation for Common Requirements for Steel Flanges, Forged Fittings, Valves and Parts for Piping Applications,” the definition for the term Forged is, “the product of a substantially compres- sive hot or cold plastic working op- eration that consolidates the material and produces the required shape. The plastic working must be performed by a forging machine, such as a hammer, press, or ring rolling machine, and must deform the material to produce a wrought structure throughout the material cross section.” The difference, therefore, between forged and wrought fittings is that forged fittings, simply put, are manu- factured from bar, which while in its plastic state is formed into a fitting with the use of a hammer, press or rolling machine. Wrought fittings, on the other hand, are manufactured from killed steel, forgings, bars, plates and seamless or fusion welded tubu- lar products that are shaped by ham- mering, pressing, piercing, extruding, upsetting, rolling, bending, fusion welding, machining, or by a combina- tion of two or more of these operations. In simpler terms wrought signifies “worked”. There are exceptions in the manufacture of both, but that is the general difference.* ChemiCal engineering www.Che.Com FeBrUarY 2007 45 Plastic-lined PiPe I n the main body of this article, we have touched on just some of the key points related to metal pipe and fittings, while not consider- ing plastic lined pipe systems and nonmetallic piping. Nonmetallic piping merits a discussion on its own, and should not be relegated to a paragraph or two here. On the other hand, since plastic lined pipe is steel pipe with a liner, and is so widely used in the process industries, it is worthwhile to present the relevant basics here. When first introduced, plastic lined pipe filled a large fluid-han- dling gap in industry, but brought with it some technical issues. In particular, when various manufacturers began producing lined pipe and fittings, industry standards for them did not exist. Conse- quently, there were no standard fitting dimensions, and the avail- ability of size and type of fittings would vary from one company to another (as they still do, to a much lesser degree). Due to the auton- omous nature of lined pipe manufacturing during its initial stages, the piping designer for a process plant would have to know early in the design process which manufacturer he or she were going to use. Particularly in fitting-makeup situations, in which a 90-deg elbow might be bolted to a tee, which in turn might br bolted to another 90-deg elbow it was important to know in advance what those makeup dimensions were going to be, and thus the identity of the fitting manufacturer. While the lack of industry standard dimensions was a design problem, other operational type problems existed as well. Some of the fluid services for which these lined pipe systems were specified for (and still are) would normally be expected to operate under a positive pressure, but at times would phase into a negative pres- sure. The liners in the early systems were not necessarily vacuum- rated, and consequently would collapse at times under the negative internal pressure, plugging the pipeline. There was an added problem when gaskets were thrown into the mix. Gaskets were not normally required unless frequent dis- mantling was planned; even so, many firms, both engineering and manufacturers, felt more secure in specifying gaskets at every joint. When required, the gasket of choice, in many cases, was an en- velope type gasket made of PTFE (polytetrafluoroethylene) with an inner core of various filler material, such as EPDM. These gaskets had a tendency to creep under required bolt-torque pressure at ambient conditions. From the time at which a system was installed to the time it was ready to hydrotest, the gaskets would, on many occasion, creep, or relax to the point of reducing the compressive bolt load of the joint enough to where it would not stand up to the hydrotest pressure. Quite often, leaks would become apparent dur- ing the fill cycle prior to testing. Other problems that still exist are those of permeation with regard to PTFE liner material, as well as that of internal and external triboelectric charge generation and accumulation (static electricity). But, due to the diligent efforts of the lined pipe and gasket industries, these types of problems have either been largely eliminated or controlled. Even so, the designer employing lined pipe should keep the poten- tial for static-electricity problems in mind. If electrical charge gen- eration is allowed to continually dissipate to ground, then there is no charge buildup and no problem. That is what occurs with steel pipe in contact with a flowing fluid: charge generation has a path to ground, and does not have an opportunity to build up. With regard to thermoplastic lined pipe, there are two issues to be considered: external charge accumulation and internal charge accumulation. Ex- perience and expertise are needed in order to analyze a particular situation. A subsequent installment of this series will provide basic information that will at least allow you to be familiar with the subject, and help you to understand the issues. Fitting dimensions for lined pipe have been standardized through ASTM F1545 in referencing ASME B16.1 (cast iron fittings), B16.5 (steel fittings) and B16.42 (ductile iron fittings). Note 3 under Sub- Para. 4.2.4 of ASTM F1545 states, “Center-to-face dimensions include the plastic lining,” which means that the dimensions given in the referenced ASME standards are to the bare metal face of the fittings. However, when lined fittings are manufactured, the metal casting is modified to accommodate the liner thickness being in- cluded in that same specified center-to-face dimension. With regard to vacuum rating, liner specifications have been greatly improved, but it is prudent to check the vacuum ratings of available pipe and fittings with each manufacturer under consid- eration. This rating is likely to vary from manufacturer to manu- facturer depending on diameter, fitting, liner type, pressure and temperature. Gasket materials such as PTFE/Silicate composite or 100% expanded PTFE, have been developed to reduce the gasket creep rate in a gasket material. Permeation issues with PTFE liners (these issues also arise, to a lesser extent, with other liner material) have been accommodated more than resolved with the use of vents in the steel pipe casing, the application of vent components at the flange joint, and increased liner thickness. Standard sizes of plastic lined pipe and fittings range from NPS 1 in. through 12 in. And at least one lined-pipe manufacturer, also manufactures larger-diameter pipe and fittings: from NPS 14 in. through 24 in., and when requested can manufacture spools to 144 in. diameter. ❏ *A point concerning the ASTM specifications is worth noting. In referring to ASTM A961 above, I am quoting from what ASTM refers to as a General Requirement Specification. Such a spec- ification is one that covers requirements typical for multiple individual Product Specifications. In this case, the individual Product Specifications covered by A961 are A105, A181, A182, A360, A694, A707, A727 and A836. The reason I point this out is that many de- signers and engineers are not aware that when reviewing an A105 or any of the other ASTM individual Product Specifications you may need to include the associated General Requirement Specification in that review. Reference to a Gen- eral Requirement Specification can be found in the respective Product Specification. 42-47 CHE 2-07.indd 45 1/24/07 2:32:10 PM Forged steel and alloy steel sock- etweld (Figure 1) and threaded fit- tings, under ASME B16.11, are avail- able in sizes NPS 1/8 in. through 4 in. Forged socketweld fittings are avail- able in pressure rating Classes 3000, 6000 and 9000. Forged threaded fit- tings are available in pressure rating Classes 2000, 3000 and 6000. Misapplication of the pressure rat- ing in these forged socketweld and threaded fittings is not infrequent; the person specifying components on many cases does not fully understand the relationship between the pressure Class of these fittings and the pipe they are to be used with. In ASME B16.11 is a table that as- sociates, as a recommendation, fitting pressure Class with pipe wall thick- ness, as follows: Table 1. Correlation of PiPe Wall thiCkness & Pressure rating Pipe wall thickness. threaded socket- weld 80 or XS 2000 3000 160 3000 6000 XXS 6000 9000 The ASME recommendation is based on matching the I.D. of the barrel of the fitting with the I.D. of the pipe. The shoulder of the fitting (the area of the fitting against which the end of the pipe butts), whether socketweld, as shown in Fig. 1, or threaded, is approximately the same width as the specified mating pipe wall thickness, with allowance for fabrication tolerances. As an exam- ple, referring to Table 1, if you had a specified pipe wall thickness of Sch. 160 the matching threaded forged fitting would be a Class 3000, for socketweld it would be a Class 6000. The fitting pressure class is selected based on the pipe wall thickness. Referring to Fig. 1, one can readily see that by not matching the fitting class to the pipe wall thickness it will create either a recessed area or a protruding area the length of the barrel of the fitting, depending on which side you error on. For forged reinforced branch fittings refer to MSS Standard SP-97 – “Integrally Reinforced Forged Branch Outlet Fittings - Socket Welding, Threaded and Buttwelding Ends.” Wrought fittings Wrought steel butt-weld fittings under ASME B16.9 (standard-radius 1.5D elbows and other fittings) are available in sizes ½ in. through 48 in. Wrought steel butt-weld fittings under B16.28 (short-radius 1D elbows), are available in sizes ½ in. through 24 in. There is no pressure/temperature rat- ing classification for these fittings. In lieu of fitting pressure classifications, both B16.9 and B16.28 require that the fitting material be the same as or comparable to the pipe material speci- fication and wall thickness. Under ASME B16.9, given the same material composition, the fittings will have the same allowable pressure/temperature as the pipe. ASME requires that the fittings under B16.28, short radius el- bows, be strength-rated at 80% of the value calculated for straight seamless pipe of the same material and wall thickness. These fittings can be manufactured from seamless or welded pipe or tub- ing, plate or forgings. Laterals, because of the elongated opening cut from the run pipe section are strength-rated at 40% of the strength calculated for Feature Report 46 ChemiCal engineering www.Che.Com FeBrUarY 2007 HygienicPiPing M ajor characteristics of piping for the pharmaceutical and semiconductor industries are the requirements for high- purity, or hygienic, fluid services. These requirements, as dictated by current Good Manufacturing Practices (cGMP) and defined and quantified by the International Soc. of Pharmaceutical Engineers (ISPE) and by ASME Bio Processing Equipment (ASME- BPE), are stringent with regard to the manufacture, documentation, fabrication, installation, qualification, validation and quality con- trol of hygienic piping systems and components. The hours that the engineer or designer requires in generating, maintaining and controlling the added documentation required for hygienic fabrication and installation addds up to 30% to 40% of the overall cost of fabrication and installation. A subsequent in- stallment in this series will cover in more detail the specific require- ments of hygienic fabrication, and, accordingly, where that added cost comes from. Hygienic is a term defined in ASME-BPE as: “of or pertaining to equipment and piping systems that by design, materials of con- struction, and operation provide for the maintenance of cleanliness so that products produced by these systems will not adversely af- fect animal or human health.” While system components such as tube, fittings, valves, as well as the hygienic aspects of the design itself, can apply to the semi- conductor industry, the term “hygienic” itself does not; it instead pertains strictly to the health aspects of a clean and cleanable sys- tem for pharmaceuticals manufacture. The semiconductor industry requires a high, or in some cases higher, degree of cleanliness and cleanability than do the hygienic systems in the pharmaceutical in- dustry, for altogether different reasons. A term that can more ap- propriately be interchanged between these two industries is “high- purity;” this implies a high degree of cleanliness and cleanability without being implicitly connected with one industry or the other. For what is referred to as product contact material, the absence of surface roughness, minimal dead-legs and an easily cleanable system are all imperative. Therefore, the pharmaceutical industry had to make a departure from the 3-A standards (created for the food and dairy industries) of which it had availed itself early on, in order to develop a set of guidelines and standards that better suit its industry. Enter ASME-BPE, which has taken on the task of providing a forum for engineers, pharmaceutical manufacturers, component and equipment manufacturers, and inspectors in an effort to develop consensus standards for the industry where none existed before. Hygienic piping was, up until just recently, referred to as sani- tary piping. Because this term has been so closely associated with the plumbing industry and with sanitary drain piping, it is felt by the pharmaceutical industry that the change in terminology to hy- gienic is more appropriate. In both the pharmaceutical and semiconductor industries, the need for crevicefree, drainable systems is a necessity. This trans- lates into weld joint quality, mechanical joint design requirements, interior pipe surface roughness limits, system drainability and dead-leg limitations. There are two basic types of fitting joints in hygienic piping: welded and clamp. The welded fittings, unlike standard buttweld pipe fittings, have an added tangent length to accommodate the orbital welding machine. The orbital welding machine allows the welding operator to make consistent high-quality autogenous welds (welds made without filler metal). Fusion is made between 42-47 CHE 2-07.indd 46 1/24/07 2:32:47 PM straight seamless pipe of the same material and wall thickness. If a full strength lateral is required, either the wall thickness of the lateral itself can be increased or a reinforcement pad can be added at the branch to com- pensate for the loss of material at the branch opening. Wrought copper solder joint fittings, under ASTM B88 and ASME B16.22, are available in sizes ¼ in. through 6 in. These fittings can be brazed as well as soldered. The pressure/temperature rating for copper fittings are based on the type of solder or brazing material and the tubing size. The rating will vary too, depending on whether the fitting is a standard fitting or a DWV (Drain, Waste, Vent) fitting, which has a re- duced pressure rating. As an example, using alloy Sn50, 50-50 Tin-Lead Solder, at 100ºF, fit- tings ½ in. through 1 in. have a pres- sure rating of 200 psig, and fittings 1½ in. through 2 in. have a pressure rating of 175 psig. DWV fittings 1½ in. through 2 in. have a pressure rating of 95 psig. Using alloy HB, which is a Tin-Anti- mony-Silver-Copper-Nickel (Sn-Sb-Ag- Cu-Ni) solder, having 0.10% maximum lead (Pb) content, at 100ºF, fittings ½ in. through 1 in. have a pressure rat- ing of 1,035 psig and fittings 1½ in. through 2 in. have a pressure rating of 805 psig. DWV fittings 1½ in. through 2 in. would have a pressure rating of 370 psig. It can be seen that, within a given type of fitting, there is a significant difference in the pressure ratings of soldered joints, depending on the type of filler metal composition. Much of the difference is in the temperature at which the solder or brazing filler metal fully melts. This is referred to as its liq- uidus state. The temperature at which the filler starts to melt is referred to as its solidus temperature. The higher the liquidus temperature, the higher the pressure rating of the joint. Acknowledgement I wish to thank Earl Lamson, senior Project Manager with Eli Lilly and Co., for taking time out of a busy schedule to read through the draft of this article. He obliged me by review- ing this article with the same skill, in- telligence and insight he brings to ev- erything he does. His comments kept me concise and on target. ■ Edited by Nicholas P. Chopey Recommended Reading 1. Cox, John, Avoid Leakage in Pipe Systems, Chem. Eng., January 2006, pp. 40–43. 2. Sahoo, Trinath, Gaskets: The Weakest Link, Chem. Eng., June 2005, pp. 38–40. ChemiCal engineering www.Che.Com FeBrUarY 2007 47 Author W. M. (Bill) Huitt has been involved in industrial pip- ing design, engineering and construction since 1965. Posi- tions have included design en- gineer, piping design instruc- tor, project engineer, project supervisor, piping depart- ment supervisor, engineering manager and president of W. M. Huitt Co. a piping con- sulting firm founded in 1987. His experience covers both the engineering and construction fields and crosses industrial lines to include petroleum refining, chemical, petro- chemical, pharmaceutical, pulp & paper, nuclear power, and coal gasification. He has written nu- merous specifications including engineering and construction guidelines to ensure that design and construction comply with code requirements, Owner expectations and good design practices. Bill is a member of ISPE (International Society of Pharmaceutical Engineers), CSI (Construction Specifications Institute) and ASME (American Society of Mechanical Engineers). He is a con- tributor to ASME-BPE and sets on two corporate specification review boards. He can be reached at: W. M. Huitt Co., P O Box 31154, St. Louis, MO 63131-0154, (314)966-8919 HygienicPiPing the parent metals of the two components being welded by means of tungsten inert gas welding. Pipe welding will be covered in more detail in an upcom- ing installment. The photograph shows an example of an orbital, or automatic, welding machine mounted on its work- piece. In this example, the piece happens to be a 90-deg elbow being welded to a cross. One can see in this example why the additional straight tangent section of automatic weld fittings is needed — that extra length provides a mounting surface for attach- ing the automatic welding machine. As for the clamp connection, it is a mechanical con- nection whose design originated in the food and dairy industry, but whose standardization has been under development by ASME- BPE. Due to a lack of definitive standardization, most companies that use this type connection require in their specifications that both the ferrule (the component upon which the clamp fits) and the clamp itself come from the same manufacturer. This precaution is to ensure a competent fit. There are no specific dimensions and tolerances for the clamp assembly, except for those being developed by ASME-BPE. Cur- rently, it is possible to take a set of ferrules from one manufacturer, mate them together with a gasket, attach a clamp from a different manufacturer and tighten up on the clamp nut. In some cases, one can literally rotate the clamp by hand about the ferrules, with no significant force being applied on the joint seal. The clamp joint is the clamp that applies the force that holds the ferrules together. The fact that this can occur begs the need for standardization to a greater degree than what cur- rently exists. Another issue that currently exists with the clamp joint is gasket intrusion into the pipe inside wall, due to inadequate compression control of the gasket. Gasket intrusion is a problem in pharmaceutical service for two reasons: • Depending on the hygienic fluid service and the gasket material, the gasket protruding into the fluid stream can break down and slough off into the fluid flow, contaminating the hygienic fluid • The intrusion of the gasket into pipe on a horizon- tal line can also cause fluid holdup. This can result in the loss of residual product, cause potential cross-contamina- tion of product, and promote microbial growth. Some manufacturers are attempting to overcome these issues by improving on the concept of the clamp joint. One company has developed ferrules whose design provides compression control of the gasket while also controlling the creep tendency that is inherent in, arguably, the most prevalent gasket material used in high purity piping, namely,Teflon. Another firm manufactures a clamp joint (also provided as a bolted connection) that does not require a gasket.This type of joint is currently in use in Europe. While this connection alleviates the issues that are present with a gasketed joint, added care would need to be applied in its handling. Any scratch or ding to the faced part of the sealing surface could compromise its sealing integrity. Nevertheless this is a connection design worth consider- ation. ❏ 42-47 CHE 2-07.indd 47 1/24/07 2:33:20 PM P ipe flanges are used to me- chanically connect pipe sections to other pipe sections, inline components, and equipment. Flanges also allow pipe to be assem- bled and disassembled without cut- ting or welding, which eliminates the need for those two operations when dismantling is required. In providing a breakable joint, however, flanges unfortunately provide a potential leak path for the process fluid contained in the pipe. Because of this, the usage of flanges needs to be minimized where possible, as with all other joints. The most prevalent flange stan- dards to be used in the process in- dustries are based on those of the American Soc. of Mechanical Engi- neers (ASME). These include: B16.1 – Cast Iron Pipe Flanges and Flanged Fittings B16.5 - Pipe Flanges and Flanged Fit- tings (NPS 1/2 through NPS 24, where NPS is nominal pipe size; see Part 1 of this series, CE, February, pp. 42–47) B16.24 – Cast Copper Alloy Pipe Flanges and Flanged Fittings B16.36 – Orifice Flanges B16.42 – Ductile Iron Pipe Flanges and Flanged Fittings Large Diameter Steel Flanges (NPS* 26 through NPS 60) B16.47 – Large Diameter steel flanges (NPS 26 through NPS 60) Flanges are available with various contact facings (the flange-to-flange contact surface) and methods of con- necting to the pipe itself. The flanges under B16.5, a standard widely rel- evant to the process industries, are available in a variety of styles and pressure classifications. The differ- ent styles, or types, are denoted by the way each connects to the pipe itself and/or by the type of face. The types of pipe-to-flange connections include the following: • Threaded • Socket welding (or socket weld) • Slip-on welding (or slip on) • Lapped (or lap joint) • Welding neck (or weld neck) • Blind Flange types Threaded: The threaded flange (Fig- ure 1), through Class 400, is connected to threaded pipe in which the pipe thread conforms to ASME B1.20.1. For threaded flanges in Class 600 and higher, the length through the hub of the flange exceeds the limitations of ASME B1.20.1. ASME B16.5 requires that when using threaded flanges in Class 600 or higher, Schedule 80 or heavier pipe wall thickness be used, and that the end of the pipe be reason- ably close to the mating surface of the flange. Note that the term “reasonably close” is taken, in context, from Annex A of ASME B16.5; it is not quantified. In order to achieve this “reasonably close” requirement, the flange thread has to be longer and the diameters of the smaller threads must be smaller than that indicated in ASME B1.20.1. When installing threaded flanges Class 600 and higher, ASME B16.5 recommends using power equipment to obtain the proper engagement. Sim- ply using arm strength with a hand wrench is not recommended. The primary benefit of threaded flanges is in eliminating the need for welding. In this regard, these flanges are sometimes used in high-pressure service in which the operating temper- ature is ambient. They are not suit- able where high temperatures, cyclic conditions or bending stresses can be potential problems. Socketweld: The socketweld flange is made so that the pipe is inserted into the socket of the flange until it hits the shoulder of the socket. The pipe is then backed away from the shoulder approximately 1/16 in. before being welded to the flange hub. 56 ChemiCal engineering www.Che.Com marCh 2007 W. M. Huitt W. M. Huitt Co. Engineering Practice Piping Design, Part 2 — Flanges The engineer or designer must choose among several flange options. Additional decisions involve facing and surface finishes, and the appropriate gaskets, bolts and nuts *NPS, indicated above, is an acronym for Nomi- nal Pipe Size. 56-61 CHE 3-07.indd 56 2/27/07 6:45:01 PM If the pipe were resting against the shoulder (this is the flat shelf area depicted in Figure 2 as the differ- ence between diameters B and B 2 ) of the socket joint during welding, heat from the weld would expand the pipe longitudinally into the shoulder of the socket, forcing the pipe-to-flange weld area to move. This could cause the weld to crack. The socketweld flange was initially developed for use on small size, high- pressure piping in which both a back- side hub weld and an internal shoul- der weld was made. This provided a static strength equal to the slip-on flange (discussed below), with a fa- tigue strength 1.5 times that of the slip-on flange. Because having two welds was labor intensive, it became the prac- tice to weld only at the hub of the flange. This practice relegated the socketweld flange to be more fre- quently used for small pipe sizes (NPS 2 in. and below) in non-high- pressure, utility type service piping. The socketweld flange is not ap- proved above Class 1500. Slip on: Unlike the socketweld flange, the slip-on flange (Figure 3) allows the pipe to be inserted completely through its hub opening. Two welds are made to secure the flange to the pipe. One fillet weld is made at the hub of the flange, and the second weld is made at the inside diameter of the flange near the flange face. The end of the pipe is offset from the face of the flange by a distance equal to the lesser of the pipe wall thickness or ¼ in. plus approximately 1/16 in. This is to allow for enough room to make the internal fillet weld without damag- ing the flange face. The slip-on flange is a pre- ferred flange for many appli- cations because of its initial lower cost, the reduced need for cut length accuracy and the reduction in end prep time. However, the final in- stalled cost is probably not much less than that of a weld-neck flange. The strength of a slip- on flange under internal pressure is about 40% less than that of a weld-neck flange, and the fatigue rate is about 66% less. The slip- on flange is not approved above Class 1500. Lap joint: The lap-joint flange (Figure 4) requires a compan- ion lap joint, or Type A stub end (stub ends are described below) to complete the joint. The installer is then able to rotate the flange. This capability al- lows for quick bolthole alignment of the mating flange during installation without taking the extra precautions required during prefabrication of a welded flange. Their pressure holding ability is about the same as that of a slip-on flange. The fatigue life of a lap-joint/ stub-end combination is about 10% that of a weld-neck flange, with an initial cost that is a little higher than that of a weld-neck flange. The real cost benefit in using a lap- joint flange assembly is realized when installing a stainless-steel or other costly alloy piping system. In many cases, the designer can elect to use a stub end specified with the same ma- terial as the pipe, but use a less costly, perhaps carbon-steel, lap-joint flange. This strategy prevents the need of having to weld a more costly compat- ible alloy flange to the end of the pipe. Stub ends are prefabricated or cast pipe flares that are welded directly to the pipe. They are available in three different types (Figure 5): Type A, (which is the lap-joint stub end), Type B and Type C. Type A is forged or cast with an outside radius where the flare be- gins. This radius conforms to the radius on the inside of the lap-joint flange. The mating side of the flare has a serrated surface. Type B is forged or cast without the radius where the flare begins. It ChemiCal engineering www.Che.Com marCh 2007 57 2 $ : 5 3 0 5ISFBEFE 9 # $ 5 3 0 4MJQPO 9 0% Type A S U O U - Length 0% Type B Types B and C (type C shown) Types A S U O U - Length 0% Type C ANSI SIip-on fIange S U O U - ANSI Iap-joint fIange Length Figure 1. Threaded flanges need not be welded # $ 5 S 0 Lap joint 9 Figure 3. Slip-on flanges offer an initial lower cost Figure 4. A lap-joint flange can yield savings in material costs Figure 5. Stub-ends serve to complete lap joints # 2 # % $ 5 3 0 Socket weId 9 Figure 2. Socketweld flanges have been commonly used for small pipe sizes 56-61 CHE 3-07.indd 57 2/27/07 6:46:15 PM is used to accommodate the slip-on flange or plate flange as a back-up flange. Type C is fabricated from pipe using five suggested methods indicated in ASME B31.3. The most prevalent of these is the machine flare. This method consists of placing a section of pipe into a flaring machine, flaring the end of the pipe and then cutting it to length. As you can see in the assembly de- tail of Figure 5, stub-end Types B & C have no radius at the flare, while Type A does. This allows Type A to conform to the lap-joint flange. Due to the ra- dius of the Type A stub end, a slip-on flange would have a poor fit, creating non-uniform loading of the flare face as well as an undesirable point load at the radius of the flare. Weld neck: The reinforcement area of the weld-neck flange (Figure 6) dis- tinguishes it from other flanges. This reinforcement area is formed by the added metal thickness, which tapers from the hub of the flange to the weld end. The bore of the flange needs to be specified in order to obtain the same wall thickness at the weld end as the pipe it will be welded to. This will give it the same ID bore as the pipe. The weld-neck flange is the most versatile flange in the ASME stable of flanges. Much of its use is for fit- ting-to-fitting fabrication, in which the flange can be welded directly to a fitting, such as an elbow, without the need for a short piece of pipe, as would be required with a slip-on flange. It can be used in low-pressure, non-haz- ardous fluid services as well as high- pressure, high-cyclic and hazardous fluid services. While the initial cost of the weld- neck flange may be higher than that of a slip-on flange, the installed cost reduces that differential. And for conditions of possible high thermal loading, either cryogenic or elevated temperatures, the weld-neck flange is essential. Blind: While the blind flange (Fig- ure 7) is used to cap off the end of a pipeline or a future branch con- nection, it is also used for other pur- poses. It can be drilled and tapped for a threaded reducing flange or machined out for a slip-on reducing flange. The reduced opening can be either on-center or eccentric. Flange pressure ratings ASME B16.5 flange pressure ratings have been categorized into material groupings. These groupings are for- mulated based on both the material composition and the process by which the flange is manufactured. The available pressure Classifica- tions under ASME B16.5 are: 150, 300, 400, 600, 900, 1500 and 2500. The correct terminology for this designa- tion is Class 150, Class 300, and so on. The term 150 pound, 300 pound and so on is a carryover from the old ASA (American Standards Association) Classification. ASA is the precursor to the American National Standards In- stitute (ANSI).* Development of ASME B16.5 began in 1920. In 1927 the American Tenta- tive Standard B16e was approved. This eventually became what we know today as ASME B16.5. Until the 1960s, the pressure classifications, as addressed earlier, were referred to as 150 pound, 300 pound, etc. It was at this point the pressure clas- sification was changed to the class designation. These designations have no direct correlation with pounds of pressure. Rather, they are a factor in the pressure rating calculation found in B16.5. In a subsequent part of this series, we will discuss how these des- ignations are factored into the design of the flange. Flanges, whether manufactured to ASME, API (American Petroleum In- stitute), MSS (Manufacturer’s Stan- dardization Soc.), AWWA (American Water Works Assn.) or any other stan- dard, are grouped into pressure rat- ings. In ASME, these pressure ratings are a sub-group of the various mate- rial groups designated in B16.5. Tables 1 and 2 in this article break out information from the Table 2 se- ries in ASME B16.5. The Table 2 se- ries is a series of tables that list the working pressures of flanges based on material groupings, temperature and classification. There are 34 such tables, segregated into three material categories: carbon and low alloy steels, austenitic stain- less steels, and nickel alloys. These are further segregated into more defined material sub-groups. Tables 1 and 2 of this article show Table 2-1.1 from B16.5, which indicates, in reverse sequence, Subcategory 1 of Material group 1 (carbon and low alloy steels). If you had an ASME B16.5, Class 150, ASTM A105 flange, this is the table you would use to determine the working pressure limit of the flange. To find the working pressure of the Engineering Practice 58 ChemiCal engineering www.Che.Com marCh 2007 # $ : " 9 WeIding neck 3 0 Figure 6. Weld-neck flanges are highly versatile *ANSI was founded as a committee whose responsibility was to coordinate the development of stan- dards and to act as a standards traffic cop for the various organizations that develop standards. Its basic function is not to develop standards, but rather to provide accreditation of those standards Originating as the American Engineering Standards Committee (AESC) in 1918, ANSI had, over its first ten years, outgrown its Committee status and in 1928 was reorganized and renamed as the American Standards Association (ASA). In 1966 the ASA was reorganized again under the name of the United States of America Standards Institute (USASI). In 1969 ANSI adopted its present name. While the B16 and B31 Standards have previously carried the ASA and ANSI prefix with its vari- ous standards titles, ASME has always been the administrative sponsor in the development of those standards. In the 1970s the prefix designation changed to ANSI/ASME and finally to ASME. Referring to ANSI B16. or ANSI B31. is no longer correct. Instead, it is correct to refer to a standard as ANSI/ASME B16. in that it indicates an ANSI-accredited ASME standard. Or one can simply refer to the standard as ASME B16. or ASME B31. $ #MJOE 3 0 Figure 7. Blind flanges are commonly used to cap off pipe- line ends 56-61 CHE 3-07.indd 58 2/27/07 6:47:38 PM abovementioned flange, enter the col- umn of this table designated as 150 then move down the column to the op- erating temperature. For intermedi- ate temperatures, linear interpolation is permitted. The previous paragraph refers to “operating temperature” when one is looking to determine the working pressure of a flange. “Operating” and “working” are synonymous. The indi- cation of a working pressure and tem- perature of a fluid service is the same as indicating the operating pressure and temperature. There exists some confusion in this area. That confusion becomes appar- ent when the engineer is determining design pressure and temperature and applying them to the flange rating. On the surface, there appears to be a con- flict in rating a flange for design con- ditions when Table 2 only indicates working pressures. Operating and design pressures and temperatures will be explained in more detail in a subsequent article in this series. For now, be aware that every service should have an operat- ing pressure/temperature as well as a design pressure/temperature. A de- sign condition is the maximum coinci- dental pressure and temperature con- dition that the system is expected or allowed to see. This then becomes the condition to which you should design for, and to which the leak test is based on, not the operating condition. Table 2, as it indicates, represents the working or operating pressures of the flange at an indicated tempera- ture for a specific class. The maximum hydrostatic leak-test pressure for a Class 150 flange in Table 2-1.1 is 1.5 times the rated working pressure at 100°F, or 285 x 1.5 = 427.5 rounded off to the next higher 25 psi, or 450 psig. We can extrapolate that piece of information to say that since hydro- static leak-test pressure is based on 1.5 times design pressure, the work- ing pressure limit given in the Table 2 matrix ostensibly becomes the design pressure limit. When one is working with ASME B31.3 Category D fluid services, and initial service leak testing is per- formed, the working pressure limit then remains the working pressure limit because testing is performed at operating or working pressures. However, there are caveats that ad- dress the fact that not all Category D fluid services (see next paragraph) should waive the hydrostatic leak test for an initial service leak test. These conditions, such as steam service, will also be discussed in a subsequent article. Category D fluid services are those fluid services that are nonflammable, non- toxic and not damaging to human tissue. Additionally, Category D fluids do not exceed 150 psig and 366º F. In initial service leak testing, the test fluid is the service fluid. Leak test- ing occurs during or prior to initial operation of the system. As the service fluid is introduced to the piping system and brought to op- erating pressure, in pres- sure increments, all joints are observed for possible leaks. If no leaks are de- tected, the pipeline simply remains in service. Other ASME B31.3 fluid services may be expected to operate at one set of conditions, but are designed for another set. For those systems, which might include periodic steam- out (cleaning, sterilization, sanitiza- tion) or passivation, you therefore want to base your flange-rating selec- tion on those more-extreme, periodic design conditions. To clarify “periodic” in this context, the sanitization pro- cess may be done as frequently as once per week and last for up to one-and-a- half shifts in duration. Facings and surface finishes Standard flange-facing designations (Figure 8) are as follows: flat face, raised face, ring joint, tongue and groove, large and small male and fe- male, small male and female on end of pipe, and large and small tongue and groove. The height of the raised face for Class 150 and 300 flanges is 0.06 in. The height of the raised face for Class 400 and above is 0.25 in. Industry wide, not discounting the lap-joint flange and stub-end com- bination, the two most widely used flange facings are the flat face and the raised face. The surface finish of standard raised-face and flat-face flanges has a serrated concentric or serrated spiral ChemiCal engineering www.Che.Com marCh 2007 59 Figure 8. Flange facings are available in several varieties 56-61 CHE 3-07.indd 59 2/28/07 9:58:07 AM surface finish with an average rough- ness of 125 × 10 –6 in. to 250 × 10 –6 in. The cutting tool used for the ser- rations will have a 0.06 in. or larger radius, and there should be from 45 to 55 grooves per inch. Bolts, nuts and gaskets Sealing of the flange joint and the hygienic-clamp joint (as discussed last month in Part 1) is paramount in providing integrity to the overall piping system. This is achieved with the use of bolts, nuts and gaskets. Making the right selection for the application can mean the difference between a joint with integrity and one without. ASME B16.5 provides a list of ap- propriate bolting material for ASME flanges. The bolting material is grouped into three strength catego- ries — high, intermediate and low — that are based on the minimum yield strength of the specified bolt material. The high-strength category in- cludes bolt material with a minimum yield strength of not less than 105 kilopounds per square inch (ksi). The intermediate-strength category in- cludes bolt material with a minimum yield strength of between 30 ksi and 105 ksi. The low-strength category in- cludes bolt material with a minimum yield strength no greater than 30 ksi. As defined in ASME B16.5, the high-strength bolting materials “. . . . may be used with all listed materials and all gaskets.” The intermediate- strength bolting materials “. . . . may be used with all listed materials and all gaskets, provided it has been veri- fied that a sealed joint can be main- tained under rated working pressure and temperature”. The low-strength bolting materials “. . . . may be used with all listed materials but are lim- ited to Class 150 and Class 300 joints,” and can only be used with selected gaskets as defined in ASME B16.5. ASME B31.3 further clarifies in Paragraph 309.2.1, “Bolting having not more than 30 ksi specified mini- mum yield strength shall not be used for flanged joints rated ASME B16.5 Class 400 and higher, nor for flanged joints using metallic gaskets, unless calculations have been made showing adequate strength to maintain joint tightness.” B31.3 additionally states in Paragraph 309.2.3, “…If either flange is to the ASME B16.1 (cast iron), ASME B16.24 (cast copper alloy), MSS SP- 42 (valves with flanged and buttweld ends), or MSS SP-51 (cast flanges and fittings) specifications, the bolting ma- terial shall be no stronger than low yield strength bolting unless: (a) both flanges have flat faces and a full face gasket is used: or, (b) sequence and torque limits for bolt-up are specified, with consideration of sustained loads, displacement strains, and occasional loads (see Paragraphs. 302.3.5 and 302.3.6), and strength of the flanges.” In specifying flange bolts, as well as the gasket, it is necessary to consider not only design pressure and temper- ature but also fluid service compat- ibility, the critical nature (if any) of the fluid service, and environmental conditions, all in conjunction with one another. To aid in understanding the relationships among these criteria, some clarification follows: • The design pressure and tempera- ture jointly determine the pressure class of a flange set. That in turn, along with flange size, will deter- mine the number and size of the flange bolts. The flange class will also determine the compressibility range of the gasket material • Fluid service compatibility will help determine the most suitable gasket material. The critical nature of the fluid will determine the degree of integrity re- quired in the joint. This requirement will help determine bolt strength and material as well as gasket type • Environmental conditions (corrosive atmosphere, wash-down chemicals, other) will also help determine the best bolt material In short, all of the variables that come together in making up a flange-joint specification have to do so in a com- plementary fashion. Simply selecting a gasket based on material selection and not taking into account the pres- sure rating requirement could provide a gasket that would get crushed under necessary torque requirements rather than withstand the bolt load and cre- ate a seal. Selecting a low-strength bolt to be used with a Class 600 flange joint with proper gasketing will require the bolts to be torqued beyond their yield point, or, at the very least, beyond their elas- tic range. To explain this briefly, bolts act as springs when they are installed and loaded properly. In order for the flange joint to maintain a gasket seal, it requires dynamic loading. Dynamic loading of flange bolts allows expan- sion and contraction movement in and Engineering Practice 60 ChemiCal engineering www.Che.Com marCh 2007 Table 1. Pressure TemPeraTure raTings for grouPs 1.1 Through 3.16 maTerials raTings for grouP 1.1 maTerials nominal designation forgings Castings Plates C-Si A 105 (1) A 216 Gr. WCB (1) A 515 Gr. 70 (1) C-Mn-Si A 350 Gr. LF2 (1) A 516 Gr. 70 (1)(2) A 537 Cl. 1 (3) Notes: (1) Upon prolonged exposure to temperature above 800°F, the carbide phase of steel may be converted to graphite. Permissible, but not recommended for prolonged use above 800°F. (2) Not to be used over 850°F (3) Not to be used over 700°F Table 2. Working Pressures by Classes, Psig Temp., °F Class 150 300 400 600 900 1,500 2,500 -20 to 100 285 740 990 1,480 2,220 3,705 6,170 200 260 675 900 1,350 2,025 3,375 5,625 300 230 655 875 1,315 1,970 3,280 5,470 400 200 635 845 1,270 1,900 3,170 5,280 500 170 600 800 1,200 1,795 2,995 4,990 600 140 550 730 1,095 1,640 2,735 4,560 650 125 535 715 1,075 1,610 2,685 4,475 700 110 535 710 1,065 1,600 2,665 4,440 750 95 505 670 1,010 1,510 2,520 4,200 800 80 410 550 825 1,235 2,060 3,430 850 65 270 355 535 805 1,340 2,230 900 50 170 230 345 515 860 1,430 950 35 105 140 205 310 515 860 1,000 20 50 70 105 155 260 430 56-61 CHE 3-07.indd 60 2/27/07 6:50:11 PM around the joint while maintaining a seal. This is achieved by applying suf- ficient stress to the bolt to take it into the material’s elastic range. If the bolts are not stressed suffi- ciently into their elastic range, any re- laxation in the gasket could reduce the sealing ability of the joint. To the other extreme, if the bolts were stressed be- yond their elastic range and into the plastic range of their material of con- struction the same issue would apply; they would lose their dynamic load on the gasket. In that case, if they did not shear, they would take a set. Any re- laxation in the gasket will then result in the reduction or elimination of the joints sealing ability. The nut should be selected to com- plement the bolt. The bolt material specification will steer you, either partially or completely, into the proper nut selection. ASTM A307, a material standard for bolts in the low-strength category, states that the proper grade for bolts to be used for pipe flange applications is Grade B. The standard goes fur- ther to state that when used for pipe flanges, Grade B bolts require a Heavy Hex Grade A nut under ASTM A563. In writing a pipe specification that included the A307 bolt, you would not need to specify the nut, since it is al- ready defined in A307. However, ASTM A193, alloy and stainless-steel bolts, goes only so far when it states that nuts shall conform to ASTM A194 — there are several grades of A194 nuts to select among. This is an example of where the match- ing nut is not always explicitly called out in the ASTM standard. Because the ASTM standards are inconsistent in that regard, the specification writer must make sure that the nut is cov- ered in a specification. In summary, all four components — flanges, bolts, nuts and gaskets — have to be selected in conjunction with one another in order for the joint assembly to perform in a way that it is expected to for a given application. ■ Edited by Nicholas P. Chopey ChemiCal engineering www.Che.Com marCh 2007 61 Author W. M. (Bill) Huitt has been involved in industrial pip- ing design, engineering and construction since 1965. Posi- tions have included design en- gineer, piping design instruc- tor, project engineer, project supervisor, piping depart- ment supervisor, engineering manager and president of W. M. Huitt Co. a piping con- sulting firm founded in 1987. His experience covers both the engineering and construction fields and crosses industrial lines to include petroleum refining, chemical, petro- chemical, pharmaceutical, pulp & paper, nuclear power, and coal gasification. He has written nu- merous specifications including engineering and construction guidelines to ensure that design and construction comply with code requirements, Owner expectations and good design practices. Bill is a member of ISPE (International Society of Pharmaceutical Engineers), CSI (Construction Specifications Institute) and ASME (American Society of Mechanical Engineers). He is a con- tributor to ASME-BPE and sets on two corporate specification review boards. He can be reached at: W. M. Huitt Co., P O Box 31154, St. Louis, MO 63131-0154, (314)966-8919. His email address is [email protected] MANUFACTURERS OF PROCESS MACHINERY CHEMICALS & PETROCHEMICALS • FOOD PROCESSING • PULP & PAPER PHARMACEUTICALS • PLASTICS AND MORE 128 Market Street • Kenilworth, New Jersey 07033 Phone: 908-259-9292 • Fax: 908-259-9280 www.gocrushers.com ATLANTIC COAST CRUSHERS, INC The Flow-Sentry Crusher is a versatile heavy-duty, in-line machine designed to reduce oversized lumps as they travel through liquid, slurry or powder piping systems. The patented design works well in pressure, gravity or pneumatic applications. Visit us at www.gocrushers.com or contact an ACC representative for additional information on our complete line of standard crushers or to discuss a custom design suitable for your company’s unique requirements. Circle 35 on p. 78 or go to adlinks.che.com/6893-35 XXXDIFDPN I|e we|:||e ler C|| |rele::|eaa|: www.t|e.tem eller:. M /tte:: |e ||e me:| retea| |::ce el $& M $& /rt||ºe: ÷ eºer¡ ar||t|e cc|||:|e¢ |a $& lrem ||e ca:| IJ ¡ear: M $& New:|e||er: M $& We||aar: M |a¢c:|r¡ eºea| |alerma||ea M /a¢ mct| merel 'PSNPSFJOGPSNBUJPO tea|at| !e|a '|ratta a| ZIZ-âZI-+âSJ, j:|ratta@t|e.tem XXXDIFDPN 98I8 CE Web House Ad.indd I S/?4/0¬ II.·0.IS AM 56-61 CHE 3-07.indd 61 2/27/07 6:51:05 PM P iping design is the job of con- figuring the physical aspects of pipe and components in an effort to conform with piping and instrumentation diagrams (P&IDs), fluid-service requirements, associated material specifications, equipment-data sheets, and current good manufacturing practices (GMP) while meeting owner expectations. All of this must be accomplished within a pre-determined, three-dimensional assigned space, while coordinating the activity with that of the architecture, structural steel, HVAC (heating, ven- tilation air conditioning), electrical, video, data-and-security conduit and trays, and operational requirements. Pulling together and coordinating these activities to achieve such a com- pilation of design requires a system- atic methodology, planning, technical ability, interdisciplinary coordination, foresight, and above all, experience. This third part in a series on piping design* discusses a number of key elements, including how to prepare specifications and guidelines, and some insights on flanges, surface fin- ish, design temperature and pressure, and charge accumulation. Although computer-aided design (CAD) has be- come an integral part of piping design, it will not be discussed in this article. SpecS and guidelineS One of the first activities the piping engineer will be involved with is devel- opment of piping specifications (specs) and guidelines on design and construc- tion. Piping specifications, as an over- view, should provide essential material detail for design, procurement and fab- rication. Guidelines, both design and construction, should provide sufficient definition in a well organized manner to allow the designer and constructor the insight and direction they need in order to provide a facility that will meet the expectation of the owner with minimal in-process direction from the owner or construction manager. Piping specifications A piping specification is the document that will describe the physical char- acteristics and specific material at- tributes of pipe, fittings and manual valves necessary to the needs of both design and procurement personnel. These documents also become contrac- tual to the project and the contractors that work under them. Designers will require a sufficient degree of informa- tion in a specification that will allow for determining the service limitations of the specification and what fluid ser- vices the specification’s material is compatible with. For example, a proj- ect may have, among other fluid ser- vices, sulfuric acid and chilled water. The economic and technical feasibility of the material selection for chilled water service would not be technically feasible for sulfuric acid. Inversely, the economic and technical material selec- tion for sulfuric acid service would not be economically feasible for chilled water service. Procurement personnel, too, will need detailed specifications to limit the assumptions they will have to make or the questions they will have to ask in preparing purchase orders. The piping specification should make clear exactly what the material of construction is for each component, and to what standard that component is manufactured. Also included in the component description should be pressure rating, end-connection type and surface finish where required. There are a few rather common mis- takes that companies make in devel- oping or maintaining specifications: 1. The specification itself is either not definitive enough or too definitive; 2. The specifications are not updated in a timely manner; and 3. The specifica- tions are too broad in their content. Let’s consider each of these points in more detail. Point 1. When defining pipe and com- ponents in a specification, you should provide enough information to identify each component without “hamstring- ing” yourself or procurement person- nel in the process. In other words, do not get so specific or proprietary with the specification that only one manu- facturer is qualified to provide the component (unless that is the actual intent). With standard pipe and fit- tings, it’s difficult to provide too much information. However, with valves and other inline equipment, overspecifica- tion can happen quite easily. A common practice is to write a Feature Report 50 ChemiCal engineering www.Che.Com July 2007 engineeering practice Piping Design, Part 3 — Design Elements Design requires a systematic methodology, planning, technical ability, interdisciplinary coordination, foresight and, above all, experience W. M. Huitt W. M. Huitt Co. *Part 1: The Basics, CE February, pp. 42–47; Part 2: Flanges, CE March, pp. 56–61 50-57 CHE 7-07.indd 50 6/28/07 8:29:11 PM specification for a generic type valve, one that can be bid on by multiple potential suppliers, by using the de- scription of one particular valve as a template. What happens is that pro- prietary manufacturer trade names, such as some of the trim materials, are carried over to the generic valve spec. When the procurement person for the mechanical contractor, or whoever is buying the valves for the project, gets ready to purchase this valve, the only manufacturer that can supply it with the specified proprietary trim is the one from which the spec was copied. You would think that doing this would eliminate multiple bids for the valve based on the unintentional pro- prietary requirements in the spec. In- stead, it creates confusion and propa- gates questions. The valve bidders, other than the one the spec was based on, will bid the valve with an excep- tion to the proprietary material, or they will contact the purchasing agent for clarification. Since the purchas- ing agent won’t have the answer, the question or clarification goes back to the engineer and/or the owner. The time necessary for responding to these types of issues is better spent on more pressing matters. When developing a spec, be specific, but try not to include proprietary data unless you intend to. For example, when specifying Viton you are speci- fying a generic DuPont product — ge- neric in that there are several differ- ent types of Viton, such as Viton A, Viton B, Viton GF, Viton GFLT and so on. Each of these has a specific formu- lation, which gives it different fluid- service compatibility and pressure and temperature ranges. Viton is a type of fluorocarbon. Fluo- rocarbons are designated FKM under ASTM D-1418, so when specifying “Viton” you are identifying a specific product from a specific manufacturer — almost. By almost, what is meant is that, if you write the spec as Viton you would most likely get the original formulation, which is Viton A. The fluid service may be more suited for an FKM with polytetrafluoroethylene in it (Viton GF) or an FKM suitable for colder temperatures may be a bet- ter choice (Viton GFLT). Be specific for those who have to use the specs for de- sign and purchase of the material. If, in developing a specification, you wish to establish minimum require- ments for a component or a material, it is certainly acceptable to identify a specific proprietary item as a bench- mark. In doing this — and we’ll stay with the fluorocarbon gasket or seal example — you could identify Viton GF or equal, which would indicate that a comparable material from one of the other fluorocarbon manufactur- ers would be acceptable so long as the fluid service compatibility and pres- sure/temperature ranges were equal to or greater than the Viton GF material. Point 2. All too often after a specifica- tion is developed it will reside in the company’s database without being pe- riodically reviewed and updated. How- ever, industry standards change, part numbers change, manufacturers are bought and sold, manufacturers im- prove their products, and so on. All of these things constitute the need and necessity to review and revise specifi- cations on a timely basis. A company that houses its own set of specifications should review them at least every two years. This timing works out for a couple reasons. Firstly, industry standards, on average, pub- lish every two years, and secondly, capital projects, from design through close-out, will arguably have an aver- age duration of two years. Lessons- learned from projects can then be considered for adoption into company specs, prompting a new revision. Point 3. Specs that are too broad in their content refers to an attempt at making the specs all-inclusive. A pip- ing specification should contain only those components and information that would typically be used from job to job. That would include the follow- ing (as an example): 1. Pressure and temperature limit of the specification 2. Limiting factor for pressure and temperature 3. Pipe material 4. Fitting type, rating and material 5. Flange type, rating and material 6. Gasket type, rating and material 7. Bolt and nut type and material 8. Manual valves, grouped by type 9. Notes 10. Branch chart matrix with corro- sion allowance These ten line items provide the pri- mary component information and notations required for a typical pip- ing system. Some specifications are written to include components, such as steam traps, sight glasses, three- or four-way valves, strainers, and other miscellaneous items. These miscella- neous items are better referred to as specialty items (or some other simi- larly descriptive name) and are sized and specified for each particular appli- cation. This does not make them good candidates for inclusion into a basic pipe specification. To explain the above we can use, as an example, a carbon-steel piping system that is specified to be used in a 150-psig steam service. The pipe, flanges, fittings, bolts, gaskets and valves can all be used at any point in the system as specified. The specifica- tion for a steam trap, however, will vary depending on its intended appli- cation. And depending on its applica- ChemiCal engineering www.Che.Com July 2007 51 Piping Design, Part 3 — Design Elements Figure 1. Shown here is a magnified image (2,000x) of a bio- film [1] 1 0.9 0.8 0.7 0.6 0.5 P r o b a b i I i t y 0.4 0.3 0.2 0.1 0 -1 0 1 2 3 Surface roughness, Ra (µm) 4 5 6 7 ProbabiIity of Attachment vs Surface Roughness Figure 2. The proper surface roughness can maximize the cleaning of biofilm from a pipe [1] 50-57 CHE 7-07.indd 51 6/28/07 8:29:49 PM tion, the load requirements for each trap may vary. For example, a steam- trap application at a drip leg will have a light steady load, whereas a steam- trap application at a shell-and-tube heat exchanger may have a heavier modulating load. And that doesn’t take into account the need for the different types of traps, including F&T (float- and-thermostatic), inverted bucket, and thermodynamic. You could, depending on the size of the project, have multiple variations of the four basic types of steam traps with anywhere from 30 to 300 or more traps in multiple sizes and various load requirements. I think you can see why this type of requirement needs to be its own specification and not a part of the piping specification. A piping specification should be con- cise, definitive and repeatable. Adding specialty type items to the specifica- tion makes it convoluted and difficult to control and interpret. Users of these specifications are designers, bidders, procurement personnel, fabricators, receipt verification clerks, validation and maintenance personnel. With this in mind, you can better understand, or at least value the fact, that these documents have to be in- terpreted and used by a wide range of personnel. These personnel are look- ing for particular information, written in a concise manner that will allow them to design and order or verify components within that specification. Inclusion of the specialty type items will, at the very least, complicate and exacerbate the process. Design/construction guidelines In conjunction with the piping speci- fications, the design and construction guidelines should convey to the de- signer and constructor point-by-point requirements as to how a facility is to be designed and constructed. The guidelines should not be a rhetorical essay, but instead should follow an in- dustry standard format, preferably a CSI (Construction Specifications In- stitute) format. Look at it this way: the material specifications tell the designer and constructor what material to use; the guidelines should tell them how to assimilate and use the material specifications in applying them to good design practice. Without these guidelines as part of any bid pack- age or request-for-proposal package, the owner is essentially leaving it up to the engineer and/or constructor to bring their own set of guidelines to the table. And this may or may not be a good thing. Leaving the full facil- ity’s delivery to the engineer and con- structor depends a great deal on the qualifications of the engineer and the constructor, and whether or not consis- tency from plant to plant and project to project is an issue. If the owner approaches a proj- ect with expectations as to how they would like their plant or facility de- signed and built, then some prepara- tion, on the owner’s part, is in order. Preparation should include, not only material specifications as described earlier, but also the guidelines and narratives (yes, narratives) necessary to define the design and construction requirements. I mention the use of narratives here because a narrative helps facilitate the understanding and conveys the magnitude of the, in most cases, reams of specifications and guidelines neces- sary to build an industrial facility of any appreciable size. In general, a narrative should ex- plain in simple, straight-forward lan- guage, for each discipline: the number- ing scheme used for the specifications and guidelines; association between the material specifications and the guidelines; an explanation as to why the project is governed by a particular code or codes; and a brief description of expectation. The narrative allows you to be more explanatory and descriptive than a formal point-by-point specification. It gives the bidder/engineer a “Readers Digest” version of the stacks of speci- fications and guidelines they are ex- pected to read through and assimilate within a matter of a few weeks. How piping specifications are deliv- ered to a project can have a significant impact on the project itself. There are, generally speaking, three scenarios in which project specifications and guide- lines are delivered to a project. In Sce- nario 1, the owner, or customer, has developed a complete arsenal of speci- fications and guidelines. In the older, more established petroleum-refining and chemical companies you will see entire departments whose mission is to create, maintain and refine all of the specifications and guidelines nec- essary to execute a project. When a project is approved to go out for bid to an engineer, the necessary specifi- cations and guidelines along with the requisite drawings are assembled, packaged and provided to the engineer as bid documents, and beyond that as working documents in the design, en- gineering and construction efforts. In Scenario 2, the owner, or cus- tomer, has some specifications and guidelines that have possibly not been updated for several years. These are provided to the engineer with the un- derstanding and stipulation that any errors or omissions in the documents should be addressed and corrected by the engineer. These, too, would be used in the bid process as well as on the project itself. In Scenario 3, the owner, or cus- tomer, brings no specifications or guidelines to the project table. Speci- fication development becomes part of the overall project engineering effort. Scenarios 1 and 3 are at opposite ends of the spectrum, but afford the best situation for both the owner and engineer/constructor. By providing the engineer and constructor, as in Scenario 1, with a full set of current specifications and well articulated guidelines, the assumption is made that both the engineer and construc- tor are qualified for the level of work required, and can very effectively ex- ecute the design, engineering and con- struction for the project. Scenario 3 allows the engineer and constructor to bring their own game- plan to the project. This too is effective, due only to the fact that the learning curve is minimal. Most engineering firms will be prepared to execute a project with their own set of specifi- cations and guidelines. This applies Engineeering Practice 52 ChemiCal engineering www.Che.Com July 2007 Grounding Iug Iocation 4 in. typicaI Figure 3. Incorporating a grounding lug into the pipe will ensure proper ground- ing, even if the pipe has been painted 50-57 CHE 7-07.indd 52 6/28/07 8:30:18 PM to qualified constructors as well. The down side of this is in the project-to- project inconsistency in specifications and methodology when using different engineers and constructors. Scenario 2 is a worse case situation. Ineffective and outdated owner speci- fications create confusion and ineffi- cient iterations in both the bid process and the execution of a project. Sce- nario 2 additionally creates the great- est opportunity for conflicts between owner documents and the engineer’s documents. For project management, this translates into change orders at some point in a project. A guideline should explain to the engineering firm or constructor, in a concise, definitive manner, just what the owner expects in executing the design and construction of a facility. By actively and methodically devel- oping a set of guidelines, an owner or customer does not have to rely on an outside resource, such as an engineer- ing firm or constructor, to provide the facility required and hoped for. Developing guidelines to convey your company’s requirements and expectations can be accomplished using one or both of the following two basic methods: 1. A formal point-by-point format that covers all necessary criteria that you, as the owner, require on a pro- prietary basis, plus a listing and de- scription of the necessary code and GMP requirements 2. A narrative for each discipline that allows the writer to expand and define, in a much more descriptive manner, the points that aren’t made clear enough, or readily apparent in the more formal format The guideline can be structured on one of the CSI formats. The format exam- ples provided by CSI give a company sufficient flexibility in writing guide- lines, or specifications for that matter, to allow the document to conform to its own particular brand of requirements and nuances. The format also lends a degree of intra-industry conformity to the guidelines and specifications, pro- viding a degree of familiarity to the engineers and constructors who will have to adhere to them. Design elements In the first paragraph of this article, I described the act of designing pip- ing systems for a facility as bringing a number of technical components to- gether to make the pipe conform to a specific set of requirements, within a prescribed area. That’s pretty simplistic, and does not really convey the magnitude of the experience, technical background or the imagination required to ex- ecute such a task. Experience is the essential component here. And that is simply because, aside from whatever innate ability a good designer might possess, the required knowledge is not taught through formal education, but is instead learned by experience. Ongoing learning can be in the form of organized classes, a mentor or any other means available to help learn and understand the physical require- ments and restraints of various sys- tems and industries. Since we do not have enough space here to cover all of the design elements, I will key in on a few topics for clarifi- cation. (And this doesn’t even scratch the surface.) We will discuss flanges, pipe internal-surface finish, weld seam factor, pipe wall thickness, MAWP and MADP, design pressure and tempera- ture, and charge accumulation. Flanges In Parts 1 and 2 of this series of ar- ticles (see footnote on first page), we discussed ASME flanges and their classifications. Most designers are familiar with ASME flange classifica- tions such as 150, 300, 400, and so on. And even though verbally stating 150 pound flange (the origin of this term is discussed in Part 2) rolls off the tongue much easier and is still an industry accepted term, Class 150 is the proper terminology and designation. What may be less familiar is that the class designation is a factor in the calculation for determining the rated working pressure of a flange. That cal- culation is: P P S P T r c b 1 8 750 / , (1) where P c = Ceiling pressure, psig, as speci- fied in ASME B16.5, paragraph D3, at temperature T P T = Rated working pressure, psig, for the specified material at temper- ature T P r = Pressure rating class index, psi (for instance, P r = 300 psi for Class 300). Note: This definition of P r does not apply to Class 150. See ASME B16.5, paragraphs D2.2, D2.3 and D2.4 S 1 = Selected stress, psi, for the speci- fied material at temperature T. See ASME B16.5, paragraphs D2.2, D2.3 and D2.4 Pipe internal-surface finish Internal surface roughness is a topic that is specific to the pharmaceutical, bio-pharmaceutical and semiconduc- ChemiCal engineering www.Che.Com July 2007 53 Figure 4. Nonconducting gaskets between flanges can lead to improper ground- ing between pipes. Introducing a continuity plate between the flanges is one way to ensure proper grounding Continuity pIate (see detaiI) Continuity fIange pIate Continuity pIate detaiI 1/4-in. x 1/2-in. Iarge hex. head screw 0.321-in. dia. sIotted hoIes DriII & tap 1/4-in. x 3/8-in. deep FIange Lock washer FIange PIate A A 3/4-in. wide 50-57 CHE 7-07.indd 53 6/28/07 8:30:46 PM tor sectors, but can also be an issue throughout the CPI. Quantifying and specifying a maximum surface rough- ness for internal pipe wall for use in what is referred to as direct impact fluid services, is a necessity in the above-mentioned sectors. Direct im- pact piping systems are those systems that carry product or carry a fluid ser- vice that ultimately comes in contact with product. The need for a relatively smooth in- ternal pipe wall is predicated on three primary issues: 1. Cleanability and drainability; 2. The ability to hinder the growth of biofilm and to enhance the ability to remove it once it does ap- pear; and 3. To reduce, to a microscopic level, crevices in which microscopic particles can reside and at some point dislodge and get carried along in the fluid stream to damage product. Regarding the first point, cleanabil- ity and drainability are associative; in order for a system to be fully cleanable it has to be designed and laid out in a manner that will eliminate any pock- ets and provide enough slope to elimi- nate any residual liquid (drainable). Not only is this residual liquid (or holdup) a contaminant — from both a bacterial standpoint and as a cross batch contaminant — but it can also be expensive due to the high cost of some drug products. Along those lines, the ASME-BPE Standard provides criteria for minimum slope, maximum deadleg, gasket intrusion, gasket con- cavity, and many other criteria for design of cleanable and drainable hy- gienic piping systems. Regarding the second point, biofilm is defined as a bacterial population composed of cells that are firmly at- tached as microcolonies to a solid sur- face (see Figure 1). At a recent ASME-BPE symposium [1], Frank Riedewald, a senior process engineer with Lockwood-Greene IDC Ltd., explained the results of testing that was performed to determine the relationship between the formation of biofilm, pipe wall-surface finish and pipe wall-surface cleanability. One of the many interesting factors that came from these studies is the fact that the internal surface of the pipe wall can actually be too smooth. Referring to the graph in Figure 2, re- sults indicate that the surface finish range best suited to reduce biofilm adherence to the internal pipe wall surface is from 0.4Ra µm to 1.0Ra µm (15.7Ra µin. to 58.8Ra µin.). What this implies is that, while we currently do not have the means to prevent the onset of biofilm on the internal walls of hygienic or semiconductor piping systems, we can facilitate its removal in the cleaning process by specifying the proper surface finish of the inter- nal pipe walls. The accepted maximum surface finish in the pharmaceutical and bio- pharmaceutical industries is 25Ra µin. (0.6 µm). In the semiconductor in- dustry you might typically see surface finishes in the range of 7Ra µin. to 15Ra µin., particularly in gas delivery systems. While the pharmaceutical industry is concerned with bacterial growth and cross contamination, the semiconductor industry is concerned more with particulate damage to prod- uct on the microscopic level. This per- tains to point three above. Pipe weld seam factor Part 2 of this series of articles men- tioned the fact that the weld seam in longitudinally welded pipe is a fac- tor in the pipe-wall-pressure-design thickness calculation. In ASME B31.3, there are two pipe- wall thicknesses for calculations. One is pressure design thickness (t) and the other is minimum required thick- ness (t m ). There are two equations for finding pressure-design thickness for straight pipe under internal pressure. Equa- tion 2 is where t < D/6, where D is the actual pipe outer diameter (OD); this calculation is based on internal pres- sure, the actual (not nominal) OD of the pipe, stress value of the material at design temperature, joint efficiency factor, and the coefficient Y [a factor used to adjust internal pressure (P) for a nominal material at tempera- ture]. Equation 3 is used when t ≥ D/6; this calculation is based on the above- listed criteria except that ID is used instead of OD, and the sum of all me- chanical allowances is included. t PD SE PY = + 2( ) (2) for when t < D/6 t P d c SE P Y = + − − ( ) [ ( )] 2 2 1 (3) for when t ≥ D/6 t t c m = + (4) where t = Pressure design thickness t m = Minimum required thickness, in- cluding mechanical, corrosion and erosion allowances c = Sum of the mechanical allowances (thread or groove depth) plus cor- rosion and erosion allowances. For threaded components, the nominal thread depth (dimension h of ASME B1.20.1, or equivalent) shall apply. For machined surfaces or grooves where the tolerance is not specified, the tolerance shall be assumed to be 0.02 in. (0.5 mm) in addition to the specified depth of the cut D = Actual pipe OD d = Pipe ID P = Internal design gage pressure S = Stress value for material from ASME B31.3 Table A-1, at design temperature E = Quality factor, or joint efficiency factor Y = Coefficient from ASME B31.3 Table 304.1.1 To determine wall thickness for pipe under external pressure conditions, refer to the Boiler and Pressure Ves- sel Code (BPVC) Section VIII, Division 1, UG-28 through UG-30 and ASME B31.3, paragraph 304.1.3. Keep in mind that for seamless pipe, E will be removed from Equations 2 and 3. Determining MAWP Taking a page from the BPVC, we will go through a few brief steps to deter- mine maximum-allowable working pressure (MAWP) for straight pipe. But let me begin by saying that MAWP is not a B31.3 expression, it comes from the BPVC. We will instead transpose this term to MADP (maximum-allow- able design pressure), which is also not a B31.3 term, but more closely re- lates to piping. When a vessel goes into design it is assigned a coincidental design pres- sure and temperature. These are the Engineeering Practice 54 ChemiCal engineering www.Che.Com July 2007 50-57 CHE 7-07.indd 54 6/28/07 8:31:24 PM maximum conditions the vessel is ex- pected to experience while in service, and what the engineers will design the vessel to handle. The material, it’s thickness, welds, nozzles, flanges, and so on are all designed predicated on this predetermined design criteria. Throughout design, the vessel’s in- tended maximum pressure is referred to as its design pressure. All calcula- tions are based on specified material and component tolerances along with fabrication specifics, meaning types and sizes of welds, reinforcement and so on. Not until after the vessel is fab- ricated can the engineer know what the actual material thickness is, the type and size of each weld, thickness of each nozzle neck, and so on. Only when all of the factual data of con- struction is accumulated and entered into vessel engineering programs can the MAWP be determined. This value, once determined, then replaces the design pressure, and is calculated based on the installed configuration of the vessel (that is, mounted vertically or horizontally; mounted on legs; or mounted on lugs). The difference between the design pressure and the MAWP is that the engineer will design to the design pressure, but the final MAWP is the limiting pressure of the vessel. The MAWP may exceed the design pres- sure, but it can never be less than the design pressure. In applying this to piping we will first calculate the burst pressure of the pipe and then determine the MAWP, or, as was mentioned earlier, a term more closely related to piping, the MADP. There are three equations generally used in calculating burst pressure for pipe. They are: The Barlow formula: P T S D BA F T = × × 2 (5) The Boardman formula: P T S D T BO F T = × × − × 2 0 8 ( . ) (6) The Lamè formula: P S D d D d L T = × − + ( ) ( ) 2 2 2 2 (7) where P BA = Burst pressure, psig (Barlow) P BO = Burst pressure, psig (Board- man) P L = Burst pressure, psig (Lamè) D = Actual pipe OD, in. d = Pipe ID, in. T F = Wall thickness (minus factory tolerance), in. S T = Minimum tensile strength, psi, from B31.3 Table A-1 S f = Safety factor, a factor of 3 or 4 is applied to burst pressure to determine MADP Using any of the three results from any one of the above equations we can then determine MADP (M) as fol- lows: (8) M P S i f = where the subscript i is BA, BO, or L, depending on which formula is used. Design pressure & temperature The ASME B31.3 definition for design pressure and design temperature is stated as two separate definitions. I will integrate them into one by stat- ing: The design pressure and tempera- ture of each component in a piping system shall be not less than the most severe condition of coincident internal or external pressure and temperature (minimum or maximum) expected during service. B31.3 goes on to state: The most severe condition is that which results in the greatest required com- ponent thickness and the highest component rating. How do you determine these values and where do you apply them? We’ll cover the where first. The discussion on determin- ing pipe wall thickness was based on design conditions, in which P is the internal design gage pressure and S is the stress value at the design tem- perature. Design conditions are also used to determine component ratings and as a basis for determining leak test pressure. There is no published standard, or genuine industry consensus, on how to determine design conditions. It ba- sically comes down to an owner’s or engineer’s experience. What I will pro- vide here is a resultant philosophy de- veloped from many sources along with my own experiences. To understand what constitutes de- sign conditions, we first need to define them. The following are some accepted terms and their definitions: System operating pressure: The pressure at which a fluid service is ex- pected to normally operate. System design pressure: Unless ex- tenuating process conditions dictate otherwise, the design pressure is the pressure at the most severe coinci- dent of internal or external pressure and temperature (minimum or maxi- mum) expected during service, plus the greater of 30 psi or 10%. System operating temperature: The temperature at which a fluid service is expected to normally operate. System design temperature: Unless extenuating process conditions dictate otherwise, the design temperature, for operating temperatures between 32°F and 750°F, this value shall be equal to the maximum anticipated operating temperature, plus 25°F rounded off to the next higher 5°. Applying a sort of philosophy cre- ated by the above definitions is somewhat straightforward for utility services, such as steam, water, and ChemiCal engineering www.Che.Com July 2007 55 50-57 CHE 7-07.indd 55 6/28/07 8:31:53 PM non-reactive chemicals. However, that part of the above definitions for design conditions that provide the caveat, “…extenuating process conditions…” implies a slightly different set of rules for process systems. Extenuating process conditions can mean increased pressure and temperature, beyond that defined above, due to chemical reaction, loss of temperature control in heat trans- fer, and so on. Charge buildup in lined pipe Internal and external charge accumu- lation, known as static electricity, or more technically known as triboelec- tric charge accumulation, is the result of charge that is unable to dissipate. If a charge generated in a flowing fluid is allowed to dissipate to ground, as it does in grounded metallic pipe, then there is no problem. However, if a charge cannot dissipate and is al- lowed to accumulate, as it may in non- conductive pipe liners, it now becomes a problem by potentially becoming strong enough to create an electro- static discharge (ESD). With regard to thermoplastic lined pipe there are two forms of this to be considered: external charge accumulation (ECA) and inter- nal charge accumulation (ICA). ECA. This is a concern with lined pipe due to the possibility of not achiev- ing spool-to-spool continuity during installation due, in large part, to im- proved paint primer on flanges. When pipe spools (lined or unlined) are joined by flanges using non-metallic gaskets, the only thing that completes the spool-to-spool continuity is the bolting. The improved paint primer on lined pipe flanges makes this more dif- ficult to achieve because normal bolt tightening doesn’t guarantee metal- to-metal contact between the nut and the flange. Pipe generally does not come with a prime coat of paint; however, lined pipe does. Since flange bolts are used to complete continuity from spool to spool, the installer has to make certain, when installing lined pipe, that the bolts, at least one of the bolts, has penetrated the primer and made contact with bare metal. This was achieved in the past by using star washers on at least one flange bolt while assuming pos- sible bare metal contact with the other bolts, allowing the washers, as they were tightened, to scrape away the prime coat so that contact was made with the bare metal of the flange. With improved prime coat material this is no longer a guarantee. If continuity from spool to spool is not achieved, any charge genera- tion resulting from an internal or an external source cannot readily dissipate to ground. The voltage in triboelectric charge generation will build until it is strong enough to jump to the closest grounded object creating an undesired spark of elec- tricity (ESD). ICA. With regard to pipe, ICA is unique to thermoplastic lined pipe and solid thermoplastic pipe. Without being impregnated with a conduc- tive material, thermoplastics are not good conductors of electricity. PTFE (polytetrafluoroethylene), as an ex- ample, has a high (>10 16 Ohms/unit area), resistivity factor. This is a rela- tively high resistance to conductivity, which means that any charge created inside the pipe cannot readily be con- ducted away to ground by way of the PTFE liner. Instead, the charge will be allowed to build until it exceeds its total dielectric strength and burns a pinhole in the liner to the internal metal wall of the casement pipe. It isn’t charge generation itself that is the problem, it’s the charge accumula- tion. When the rate of charge genera- tion is greater than the rate of charge relaxation (the ability of material to conduct away the generated charge), charge accumulation occurs. The dielectric strength of PTFE is 450 to 500 volts/mil. This indicates that for every 0.001 in. of PTFE liner 450 V of triboelectric charge will be required to penetrate the liner. For a 2-in. pipeline with a 0.130-in. thick liner, this translates into 58,500 V of triboelectric charge to burn through the liner thickness. When the liner is penetrated by an accumulated charge, two addi- tional problems are created: 1. Corro- sive fluid (a major use of lined pipe) is now in contact with and corroding the metal pipe wall and at some point, depending on rate of corrosion, will fail locally and cause fluid to leak to the environment, and 2. The initial charge that burned through the liner is now charging the outer metal pipe. If continuity has not been achieved for the outer pipe, a spark of triboelectric charge is, at some point, going to jump to ground and cause a spark. Corrective action ECG. The simplest method to ensure continuity is to sand away any primer on the back side of each flange to en- sure good metal-to-metal contact be- tween nut and flange. Aside from that or the use of a conductive prime paint, the current ready-made solu- tion to the external continuity problem is the addition of stud bolts located in close proximity to flanges on both pipe spools and fittings (see Figure 3). These studs can be applied at the factory or in the field. At each flange joint a ground- ing strap (jumper) is then affixed to a stud on one spool with a nut, extended over the flange joint and attached to a stud on the connecting spool complet- ing continuity throughout the chain of connecting spools and fittings. Another method of creating continu- ity at flange joints, while being less ob- trusive and more integral, is described as follows. Referring to Figure 4, flanges would be purchased pre-drilled and tapped in the center of the outer edge of the flange between the backside of the flange and the face side of the flange. The drilled and tapped hole in each flange will need to be centered between bolt holes so that they line up after the flange bolts are installed. The tapped hole is 1/4-in. dia. x 1/2-in. deep. After a flange set is installed and fully bolted, the continuity plate (Figure 4) can be installed using two 1/4-in. x 1/2-in. long hex-head screws and two lock washers. The Continu- ity Plate has two 0.312-in. slotted TABLE 1. RECOMMENDED VELOCITIES Liquid conductivity BS 5958 recom- mended flow velocity >1,000 pS/m No restriction 50 – 1,000 pS/m Less than 7 m/s Less than 50 pS/m Less than 1 m/s Note: pS/m (picosiemens/meter) Engineeering Practice 56 ChemiCal engineering www.Che.Com July 2007 50-57 CHE 7-07.indd 56 6/28/07 8:32:27 PM Author W. M. (Bill) Huitt has been involved in industrial pip- ing design, engineering and construction since 1965. Positions have included de- sign engineer, piping design instructor, project engineer, project supervisor, pip- ing department supervisor, engineering manager and president of W. M. Huitt Co. (P.O. Box 31154, St. Louis, MO 63131-0154. Phone: 314-966-8919; Email: [email protected]) a piping consulting firm founded in 1987. His experience covers both the engineering and construction fields and crosses industrial lines to include petroleum refining, chemical, petrochemical, pharmaceutical, pulp & paper, nuclear power, and coal gasification. He has written numerous specifications includ- ing engineering and construction guidelines to ensure that design and construction comply with code requirements, owner expectations and good design practices. Bill is a member of ISPE (International Society of Pharmaceutical Engineers), CSI (Construction Specifications Institute) and ASME (American Society of Mechanical Engineers). He is a contributor to ASME-BPE and sits on two corporate specifica- tion review boards. boltholes allowing for misalignment and movement. The entire continuity plate assem- bly is relatively simple to install, un- obtrusive and establishes integral contact with the pipeline. ICG. One of the first options in pre- venting internal charge accumulation is by minimizing charge generation. This can be done by adjusting the flow velocity relative to the liquid’s conduc- tivity. To minimize design impact, cost and even schedule impact on a project, ICG needs to be evaluated early in the project due to the possibility of a change in line size. To retard charge generation by re- ducing flow velocities, British Stan- dard (BS) suggests the values pre- sented Table 1 (per BS 5958). If velocity reduction is not an op- tion, or if further safeguards against charge accumulation are warranted, then a mechanical solution to pro- vide a path to ground for ICG might be nrcessary. One method for conducting charge accumulation from the interior of the pipe to ground is indicated in Figure 5. What is shown is an orifice plate made of conductive (static dissipative) mate- rial that is compatible with the fluid service. The orifice itself is off center to the OD of the plate and the pipeline itself. With the shallow portion of the ID at the invert of the pipe, the orifice allows the piping to drain in horizon- tal runs. The tab portion of the plate extends beyond the flange OD. On the tab is a bolthole for attaching the modified continuity flange plate. The plate is designed to come in contact with the interior surface of the liner wall as well as protrude into the flowing fluid to provide a conduit for inter- nally generated charge. Continuity is achieved by attaching the plate to the flange OD that is in contact with the piping, which is, in turn, grounded through equipment. Recommendations It is difficult to pre-determine what fluid services and systems will be candidates for charge accumulation prevention and electrostatic dis- charge protection. The simplest and most conservative answer is to as- sume that all fluid services in lined pipe systems are susceptible. In say- ing that, we then have to declare that a company’s pipe specifications need to reflect a global resolution that will affect all installations. With regard to ECA, the recommen- dation for future installations with the least impact would be to specify pipe with no prime coat or at least no primer on the flanges, or a prime coat using a conductive paint. The un- primed pipe would be primed prior to installation with care given to primer touchup on flanges after installation. This would better ensure spool-to- spool external continuity. For existing installations, either the studs or the continuity plate installa- tion would work. It can also be sug- gested that the continuity plates can be tacked on to one flange rather than drilling and tapping both flanges. For dissipating ICG, the orifice plate, as shown in Figure 5, is the only recommendation. ■ Edited by Gerald Ondrey References 1. Riedewald, Frank, “Microbial Biofilms — Are they a problem in the pharmaceuti- cal industry?”ASME-BPE Symposium, Cork, Ireland, June 2004. Acknowledgement I wish to thank Earl Lamson, senior project manager at Eli Lilly and Co., for taking time out of a busy schedule to read this article with the same skill, intelligence and insight he brings to everything he does. His comments kept me con- cise and on track. Bioengineering Inversina – the gentle way of mixing. The Inversina mixes solids or liquids thoroughly and efficiently. The process is clean, because mixing takes place in closed containers that can be quickly interchanged. The Inversina mixes a diverse range of components rapidly and in an extremely gentle way. Segregation does not occur, even after extended mixing times, by virtue of the eversion phenomenon ( Paul Schatz principle). Applications for the Inversina: analyti- cal labs, metal finishing shops, powder metallurgy and nuclear industry, manufacture of batteries, cement, ceramics, cosmetics, dental products, diamond tools, dyes and pigments, electrical and electronic devices, explosives and pyrotechnics, foods, homeopathic products, household products, medicines and pharmaceu- ticals, plastics, printing inks and many other products. The Bioengineering Inversina is available with capacities of 2, 20, 50, 100 and 300 L. Bioengineering, Inc. Waltham, MA 02451, USA Bioengineering AG 8636 Wald, Switzerland [email protected] www.bioengineering.ch Circle 44 on p. 82 or go to adlinks.che.com/6897-44 50-57 CHE 7-07.indd 57 6/28/07 8:32:49 PM William M. Huitt W.M. Huitt Co. T his fourth in a series of articles* on piping for process plants ex- amines two topics that may, at first, seem to fall outside the scope of chemical engineering — pip- ing codes and the pipe fabrication. Obviously chemical engineers will not be welding pipes together, but under- standing the benefits and limitations of different types of welding processes, for example, can help the engineer when designing the system that needs to be welded. But before we get into fabrication, a general overview of piping codes is presented in order to answer the fol- lowing questions: Why is it necessary to comply with piping codes? What is the difference between a code and a concensus standard? Which code should I follow? PIPING CODE Codes and standards The querry, “Why do we, as a company, need to comply with a piping code?” is actually a trick question. Code, by defi- nition is law with statutory force. There- fore the reason for complying with a code is because you literally have to, or else be penalized for non-compliance. A better question would be, “Why comply with or adopt a piping con- sensus standard?” When phrased this way, the question supports the au- thor’s contention that many engineers and designers do not fully understand the difference between a code and a standard. And it doesn’t help matters when some standards are published as a code, and some codes are pub- lished as a standard. This is certainly nothing to get excited about, but it is something worth pointing out. My take on the reason for the mis- understanding of these two closely re- lated terms, standard and code, is that they get bounced around so often in the same context that designers and engineers simply begin interchanging the two terms without much consider- ation for their different meanings. The difference between a standard and a code will be explained shortly, but first lets respond to the first question. Why comply? Consensus standards such as those published by ASME (American Soc. of Mechanical Engineering), ANSI (American National Standards Inst.), API (Americal Petroleum Inst.), NFPA (National Fire Protection Assn.), ASTM (American Soc. for Testing and Mate- rials), International Plumbing Code and others are not mandatory in and of themselves. However, federal, state, city and other local codes are manda- tory. In these municipal codes you will find regulations that establish various requirements taken in whole, or in part from the standards published by the above listed organizations, and others, as legally binding requirements. These standards, as adopted, then become code, which is enforceable by law. When not addressed on a municipal level, but included in corporate speci- fications, the standard becomes a legal code on a contractual basis. Compliance with these codes, irre- spective of government regulations or corporate requirements, doesn’t cost the builder any more than if it didn’t comply. It does, however, cost more to fabricate and install piping systems that have a high degree of integrity as opposed to systems that don’t. Hiring non-certified welders and plumbers, bypassing inspections, ex- aminations and testing, using material that may potentially not withstand service pressures and temperatures, 68 ChemiCal engineering www.Che.Com oCtober 2007 Piping for Process Plants, Part 4: Codes and Fabrication Besides flanges, there are also several different types of joints and welding processes to choose from. Additional decisions involve piping codes Feature Report Engineering Practice * Part 1: The Basics, CE February, pp. 42–47; Part 2: Flanges, CE March, pp. 56–61; Part 3: Design Elements, CE July, pp. 50–57) 68-76 CHE 10-07.indd 68 9/29/07 5:38:39 PM and supporting this type of system with potentially inadequate supports is less costly initially, but there’s too much at risk. I don’t think anyone in good conscience would intentionally attempt to do something like that in order to save money. If anyone intends on fabricating and installing a piping system plans to perform any of the following points, then they are essentially complying with code: • Use listed material • Specify material that meets the re- quirements for fluid service, pres- sure and temperature • Inspect the material for MOC (mate- rial of construction), size and rating • Use certified welders and plumbers • Inspect welds and brazing • Adequately support the pipe • Test the pipe for tightness The code simply explains how to do each of these activities in a formal, well thought-out manner. There is not a reason sufficiently good enough to not comply with ap- propriate industry standards and codes. If there was a fee involved for compliance, this might be a stimulus for debate. But there is no fee, and there is usually just too much at stake to ignore them. Even with utility sys- tems in an administration building or an institutional facility, the potential damage from a ruptured pipeline, or a slow leak at an untested joint could easily overshadow any savings gained in non-compliance. That’s without con- sidering the safety risk to personnel. The first thing that someone should do, if they are considering to do oth- erwise, is check local and state codes. They may find regulations that require adherence to ASME, the International Plumbing Code or some of the other consensus standards. If not already included, this should be a requirement within any company’s specifications. Finally, it is worth taking a histori- cal aside to make a point. ASME pub- lished the first edition of the Boiler and Pressure Vessel Code in 1914– 1915. Prior to creation of the code, and what played a large part in insti- gating its creation, was that between 1870 and 1910 approximately 14,000 boilers had exploded. Some were dev- astating to both people and property. Those numbers fell off drastically as the code was adopted. Uniformity and regulation does have its place. Which code to follow? Like the seatbelt law, code compliance is not just the law, it makes good sense. A professional consensus standard is, very simply put, a code waiting to be adopted. Take the ASME Boiler and Pressure Vessel Code (BPVC): since its first publication in 1915 it has been adopted by 49 states, all the provinces of Canada, and accepted by regulatory authorities in over 80 countries. On May 18, 2005, it was finally ad- opted by the 50th state, South Caro- lina. And this doesn’t mean the BPVC is adopted in its entirety. A state, or corporation for that matter, can adopt a single section or multiple sections of the BPVC, or it can adopt the code in its entirety. Until South Carolina adopted the BPVC, it was actually no more than a standard in that state and only required compliance when stipu- lated in a specification. However, in all honesty you would not get a U.S. boiler or pressure vessel manufacturer to by- pass code compliance. That is, unless you wanted to pay their potential at- torneys’ fees. With regard to code compliance, the question often asked is, “How do I determine which piping code, or stan- dard, I should comply with for my par- ticular project?” Determining proper code applica- tion is relatively straightforward and at the same time comes with a certain degree of latitude to the owner in mak- ing the final determination. In some cases that determination is made for the engineer or contractor at the state level, the local level or by an owner company itself. Providing guidelines for code adoption on a project basis is direction that should be included in any company’s set of specifications, but quite often is not. This can cause a number of disconnects through design and construction. In order to answer the question about code assignment some history has to be told. In keeping this brief I will just touch on the high points. In 1942, ASA B31.1 — American Stan- dard Code for Pressure Piping was published by the American Standards Piping for Process Plants, Part 4: Codes and Fabrication Bioengineering Inversina – the gentle way of mixing. The Inversina mixes solids or liquids thoroughly and efficiently. The process is clean, because mixing takes place in closed containers that can be quickly interchanged. The Inversina mixes a diverse range of components rapidly and in an extremely gentle way. Segregation does not occur, even after extended mixing times, by virtue of the eversion phenomenon ( Paul Schatz principle). Applications for the Inversina: analyti- cal labs, metal finishing shops, powder metallurgy and nuclear industry, manufacture of batteries, cement, ceramics, cosmetics, dental products, diamond tools, dyes and pigments, electrical and electronic devices, explosives and pyrotechnics, foods, homeopathic products, household products, medicines and pharmaceu- ticals, plastics, printing inks and many other products. The Bioengineering Inversina is available with capacities of 2, 20, 50, 100 and 300 L. Bioengineering, Inc. Waltham, MA 02451, USA Bioengineering AG 8636 Wald, Switzerland [email protected] www.bioengineering.ch Circle 51 on p. 122 or go to adlinks.che.com/6900-51 68-76 CHE 10-07.indd 69 9/29/07 5:40:07 PM Association (ASA). This would later change to B31.1 — Power Piping. In the early 1950’s the decision was made to create additional B31 Codes in order to better define the require- ments for more specific needs. The first of those Standards was ASA B31.8 — Gas Transmission and Dis- tribution Piping Systems, which was published in 1955. In 1959 the first ASA B31.3 — Petroleum Refinery Pip- ing Standard was published. After some reorganization and or- ganizational name changes the ASA became ANSI. Subsequent code revi- sions were designated as ANSI Codes. In 1978, ASME was granted accredita- tion by ANSI to organize the B31 Com- mittee as the ASME Code for Pressure Piping. This changed the code designa- tion to ANSI/ASME B31. Since 1955 the B31 Committee has continued to categorize, create and better define code requirements for specific segments of the industry. Through the years since then they have created, not necessarily in this order: B31.4 — Liquid Transportation Piping; B31.5 — Refrigeration Piping; B31.9 — Building Services Piping; and B31.11 — Slurry Transportation Piping. Each of these standards is con- sidered a stand-alone section of the ASME Code for Pressure Piping, B31. What the B31 committee has ac- complished, and is continuing to im- prove upon, are standards that are better focused on specific segments of industry. This alleviates the need for a designer or constructor building an in- stitutional type facility from having to familiarize themselves with the more voluminous B31.3 or even a B31.1. They can work within the much less stringent and extensive requirements of B31.9, a standard created for and much more suitable to that type of de- sign and construction. As mentioned above, ASME B31.1 — Power Piping, was first published in 1942. Its general scope reads: “Rules for this Code Section have been devel- oped considering the needs for appli- cations which include piping typically found in electric power generating sta- tions, in industrial and institutional plants, geothermal heating systems, and central and district heating and cooling systems.” The general scope of ASME B31.3 — Process Piping, reads: “Rules for the Process Piping Code have been devel- oped considering piping typically found in petroleum refineries, chemical, phar- maceutical, textile, paper, semiconduc- tor and cryogenic plants; and related processing plants and terminals.” ASME B31.5 — Refrigeration Pip- ing, applies to refrigerant and second- ary coolant piping systems. Closely related to B31.1, but not having the size, pressure or tempera- ture range, B31.9 was first published in 1982. It was created to fill the need for piping in limited service require- ments. Its scope is narrowly focused on only those service conditions that may be required to service the utility needs of operating a commercial, insti- tutional or residential building. From its shear scope of responsibil- ity, B31.3 encompasses virtually all piping, including those also covered by B31.1 (except for boiler external piping), B31.5 and B31.9. The differ- ence, and distinction, as to which code should apply to a particular project, lies with the definition and scope of the project itself. If a project includes only the instal- lation of perhaps a refrigeration sys- tem, B31.5 would apply. If a project’s scope of work consists of an office, lab- oratory, research facility, institutional facility or any combination thereof, B31.1 or B31.9 and possibly B31.5 would apply. A laboratory or research facility could possibly require fluid services beyond the fluid service lim- its of B31.9. In that case, B31.3 would be adopted for those services. In the case of a process manufactur- ing facility, B31.3 would be the govern- ing code. Since B31.3 covers all piping, B31.5 or B31.9 would not need to be included, not even necessarily with as- sociated laboratory, office and research facilities. The only time B31.5 or B31.9 would become governing codes, in as- Engineering Practice 70 ChemiCal engineering www.Che.Com oCtober 2007 S ince 1956 the employees of Mueller Steam Specialty have been dedi- cated to the manufacture of high quality products delivered on time and with superior customer service. Our core line of rugged strainers is available in a wide range of types and materials. Whether you require basket strainers, Y strainers, “Tee” type strainers, duplex strainers, or even temporary strainers, Mueller will deliver your order from stock or custom engineer and manufacture it to your require- ments. In addition to its strainer line, Mueller offers a full line of check valves, butterfly valves, pump protection and specialty products for a variety of industries and applications. Choose Mueller Steam Specialty for your next project. Circle 57 on p. 122 or go to adlinks.che.com/6900-57 68-76 CHE 10-07.indd 70 9/29/07 5:40:38 PM sociation with a manufacturing facil- ity, is if a refrigeration unit, or an of- fice, laboratory and/or research facility were under a separate design/construct contract from the process manufactur- ing facility. Or if it was a substantial part of the overall project. As an example, project XYZ consists of a process manufacturing facility, related office building and lab facili- ties. If the utility service piping for the office and lab facilities is a small per- centage of the overall project, and/or the design and construction contracts for those facilities are a part of the overall process manufacturing facility, all piping, with code exclusions, could be governed by B31.3. If, however, the office and labora- tory facilities were a substantial part of the overall project, or they were to go to a separate constructor, it may be more beneficial to determine bat- tery limits for those facilities and designate anything inside those bat- tery limits as B31.1 or B31.9 and/or B31.5. In such a case, separate pipe specifications may have to be issued for those portions of the project des- ignated as being governed by B31.9. This is due to the range of fluid ser- vices and the corresponding pressure and temperature limits of B31.9 com- pared to those of B31.3. These differ- ences in code assignment and battery limits may be a driver for the project’s contracting strategy. Many piping service requirements, such as steam, air, chilled water and so on, can come under the auspices of multiple codes. These fluid services, which fall within the definition of B31.3 Category D fluid services, can just as easily fall within the require- ments of B31.1 or B31.9 as well. In an effort at maintaining a high degree of continuity in the process of making the determination of which code to apply to a project, company guidelines should be well defined. The final determination as to what constitutes a governing code, within the purview of the above mentioned codes, is left to the owner and/or to the local governing jurisdic- tion. Engineering specifi- cations should clarify and reflect the intent of the owner and the respective codes in an attempt to pro- vide consistency and direction across all projects within a company. PIPE FABRICATION Entering this section on fabrication does not mean that we leave engineer- ing behind. Indeed, the majority, if not all, fabricators (referring to the fabri- cators that are qualified for heavy in- dustrial work) will have an engineer- ing staff. As a project moves from the design phase into the construction phase, anyone with a modicum of project ex- perience can acknowledge the fact that there will most certainly be conflicts, errors and omissions, no matter how diligent one thinks he or she is during design. This is inherent in the meth- odology of today’s design/engineering process. Although there are methods and approaches to design in which this expected result can be minimized, it is always prudent to be prepared for such errors and omissions. If, on the other hand, the assump- tion is made that the Issued for Con- struction design drawings will facili- tate fabrication and installation with minimal problems, then you can ex- pect to compound whatever problems do occur because you weren’t prepared to handle them. The greatest asset a project manager can have is the abil- ity to learn from past experience and the talent to put into practice what he or she has learned. Pipe fabrication, in the context of this article, is defined as the construc- tion of piping systems by forming and assembling pipe and components with the use of flanged, threaded, clamped, grooved, crimped and welded joints. In Part 2 of this series, we dis- cussed the flange joint; the others will be discussed here. There are var- ious factors, or considerations, that prompt the decision as to which type of connection to use in the assembly of a piping system. To start with, any mechanical joint is considered a po- tential leak point and should be mini- mized. Also, the decision as to which type of joint should be specified comes down to accessibility requirements, installation requirements and joint integrity. Using that as our premise, we can continue to discuss the vari- ous joining methods. Threaded joint Pipe thread, designated as NPT (National Pipe Taper) under ASME B1.20.1, is the type of thread used in joining pipe. This is a tapered thread that, with sealant, allows the threads to form a leak-tight seal by jamming them together as the joint is tightened. The same criteria described (in Part 2) for the threaded flange joint apply also to threaded fittings, in which the benefits of the threaded joint is both in cost savings and in eliminating the need for welding. In this regard, threaded components are sometimes used in high-pressure service in which the operating temperature is ambient. They are not suitable where high tem- peratures, cyclic conditions or bending stresses can be potential concerns. Hygienic clamp joint The clamped joint refers to the sanitary or hygienic clamp (Figure 1). Three in- stalled conditions of the hygienic joint, minus the clamp are presented in Fig- ure 1. Joint A represents a clamp con- nection that has been over tightened causing the gasket to intrude into the inner diameter (ID) of the tubing. This creates a damming effect, preventing the system from completely draining. In joint B, the clamp wasn’t tight- ened enough and left a recess at the gasket area. This creates a pocket where residue can accumulate, so cleanability becomes an issue. Joint C represents a joint in which the proper torque was applied to the clamp leaving the ID of the gasket flush with the ID of the tubing. The clamp C representation is the result that we want to achieve with the hygienic clamp. The problem is that this is very difficult to control on a repeatable basis. Even when the gas- ChemiCal engineering www.Che.Com oCtober 2007 71 " # $ Figure 1. Problems can arise with a clamped joint if not properly installed. Overtightening the clamp can cause the gasket to intrude into the tubing (A), whereas undertightening results in pockets where residue can accumulate (B). The ideal situation is joint C 68-76 CHE 10-07.indd 71 9/29/07 5:41:06 PM ket and ferrules are initially lined up with proper assembly and torque on the joint, some gasket materials have a tendency to creep (creep relaxation), or cold flow. Creep relaxation is defined as: A transient stress-strain condition in which strain increases concurrently with the decay of stress. More simply put, it is the loss of tightness in a gas- ket, measurable by torque loss. Cold flow is defined as: Permanent and continual deformation of a ma- terial that occurs as a result of pro- longed compression or extension at or near room temperature. There have been a number of both gasket and fitting manufacturers that have been investing a great deal of research in attempting to resolve this issue with the clamp joint. Some of the solutions regarding fittings were addressed in Part 2 of this se- ries. Additionally, gasket manufac- turers and others have been work- ing on acceptable gasket materials that have reduced creep relaxation factors, as well as compression con- trolled gasket designs. What is meant by acceptable gasket material is a gasket that is not only compatible with the hygienic fluid ser- vice, but also meets certain U.S. FDA (or comparable) requirements. Those requirements include gasket material that complies with USP Biological Re- activity Test #87 & 88 Class VI for Plas- tics and FDA CFR Title 21 Part 177. Grooved joint The grooved joint (Figure 2), from a static internal-pressure-containment stand- point, is as good as or, in some cases, superior to the ASME Class 150 flange joint. In the smaller sizes (1 to 4 in.), the working pressure limit will be equal to that of a Class 300, carbon-steel, ASTM A105, ASME B16.5 flange. The main weakness of the grooved joint is the bending and torsional stress allowable at the coupling. This stress can be alleviated with proper support. Because of this design characteristic, the manufacturers of grooved joint systems have focused their efforts and created a niche in the fire-protection and utility- fluid service requirements, with the ex- ception of steam and steam condensate. The grooved joint is comparatively easy to install, which is particularly important in areas that would require a fire card for welding. Since no weld- ing is required, modifications can be made while operation continues. Some contractors choose to couple at every joint and fitting, while others choose to selectively locate couplings, much as you would selectively locate a flange joint in a system. It’s a decision that should be made based on the particu- lar requirements or preference of a project or facility. Pressed joint The pressed joint (Figure 3) is actually a system that uses thin wall pipe, up through 2-in. NPT, to enable the join- ing of pipe and fittings with the use of a compression tool. Welding is not required, and threading is only neces- sary when required for instrument or equipment connection. These types of systems are available from various manufacturers in carbon steel, 316 and 304 stainless steel and copper. Because of the thin wall pipe, corrosion allowance becomes a big consideration with carbon steel. While the static internal pressure rating of these systems is comparable to an ASME Class 150 flange joint, there are additional fluid-service and installation characteristics that need to be considered. With axial and tor- sional loading being the weak spots in these systems, they are not practical where water hammer is a potential, Engineering Practice 72 ChemiCal engineering www.Che.Com oCtober 2007 Q QUICK UICK AND AND S SIMPLE IMPLE G GET ET R RESUL ESULTS TS IN IN M MINUTES INUTES N NO O H HAZARDOUS AZARDOUS C CHEMICALS HEMICALS OR OR R REAGENTS EAGENTS 600°C 600°C O ONE NE S SIMPLE IMPLE T TEST EST FOR FOR M MOISTURE OISTURE, S , SOLIDS OLIDS AND AND A ASH SH COMPUTRAC COMPUTRAC ® ® MAX MAX ® ® 5000 5000 MOISTURE/SOLIDS/ASH ANALYZER ® EXCLUSIVE MANUFACTURER OF COMPUTRAC ® MOISTURE ANALYZERS AND JEROME ® MERCURY AND HYDROGEN SULFIDE ANALYZERS F FREE REE T TRIALS RIALS F FREE REE A APPLICA PPLICATION TION D DEVELOPMENT EVELOPMENT 24-H 24-HOUR OUR C CUST USTOMER OMER S SUPPORT UPPORT C CALL ALL U US S T TODA ODAY Y T TO O F FIND IND O OUT UT M MORE ORE!! !! (800) 528.741 (800) 528.7411 1 (602) 470.1414 (602) 470.1414 WWW WWW. . AZIC AZIC. . COM COM COME VISIT US AT: C CHEM HEM S SHOW HOW NEW YORK, NY BOOTH #943 OCT. 30-NOV. 1, 2007 Circle 52 on p. 122 or go to adlinks.che.com/6900-52 Groove Gasket Housing BoIt/nut Figure 2. When properly supported, the grooved joint can perform as well as a flanged joint 68-76 CHE 10-07.indd 72 9/29/07 5:41:36 PM such as in steam-condensate service. The axial load consideration carries over to supporting the pipe as well. Ensure that vertical runs of this pipe are supported properly from beneath. Do not allow joints in vertical runs to be under tension. They must be sup- ported properly from the base of the vertical run. Welded joint The welded joint is by far the most in- tegrated and secure joint you can have. When done properly, a welded joint is as strong as the pipe itself. The key to a weld’s integrity lies in the crafts- manship of the welder or welding op- erator, the performance qualification of the welder or welding operator, and the weld procedure specification. Before going further, I want to ex- plain the difference between the terms welder and welding operator. A welder is someone who welds by hand, or manually. A welding operator is someone who operates an automatic welding machine. The ends of the pipe still have to be prepared and aligned manually, and the automatic welding machine has to be programmed. The advantage of machine welding is apparent in doing production welds. This is shop welding in which there is a quantity of welds to be made on the same material type, wall thick- ness and nominal pipe size. Once the machine is set up for a run of typical pipe like this, it is very efficient and consistent in its weld quality. This is another topic that could easily stand alone as an article, but instead, here we will focus on some of the primary types of welding used with pipe. Those types include the fol- lowing: GMAW (gas metal arc weld- ing) or MIG (metal inert gas); GTAW (gas tungsten arc welding) or TIG (tungsten inert gas); SMAW (shielded metal arc welding) or MMA (manual metal arc) or stick welding; and FCAW (flux cored automatic welding). GMAW: Often referred to as MIG, GMAW can be an automatic or semi-automatic welding process. It is a process by which a shield- ing gas and a continuous, consum- able wire electrode is fed through the same gun (Figure 4a). The shielding gas is an inert or semi-inert gas such as argon or CO 2 that protects the weld area from atmospheric gases, which can detrimentally affect the weld area. There are four commonly used methods of metal transfer used in GMAW. They are: • globular • short-circuiting • spray • pulsed-spray With the use of a shielding gas, the GMAW process is better used indoors or in an area protected from the wind. If the shielding gas is disturbed, the weld area can be affected. GTAW: Most often referred to as TIG, welding, GTAW can be automatic or manual. It uses a nonconsumable tungsten electrode to make the weld (Figure 4b), which can be done with filler metal or without filler metal (autogenous). The TIG process is more exacting, but also more complex and slower than MIG welding. In Part 2 of this series, the use of orbital welding was mentioned for hygienic tube welding. Orbital weld- ing uses the GTAW method. Once the orbital welder is programmed for the material it is welding, it will provide excellent welds on a consistent basis — provided, that is, that the chemistry of the base material is within allow- able ranges. A wide differential in sulfur content between the two components being ChemiCal engineering www.Che.Com oCtober 2007 73 LEADING WORLDWIDE IN MIXING TECHNOLOGIES Advanced Pr ocess Sol ut i ons www.ekato.com GROUP Your contact in Europe Tel.: +49 7622 29-0 e-mail: [email protected] Your contact in the USA Tel.: +1 201 825 4684 e-mail: [email protected] The EKATO GROUP provides their customers with the technical excellence and experience of a global market leader. The companies within the EKATO GROUP operate across the spectrum of mixing technologies. From simple laboratory mixers to turnkey production plants, the EKATO GROUP provides a range of engineering services and custom-made solutions for the most challenging customer applications. The synergies within the EKATO GROUP ensure that reliable and cost-effective solutions can be provided to the highest quality standards for every application. This is supported by a global service network. Circle 58 on p. 122 or go to adlinks.che.com/6900-58 O-ring pocket O-ring Unpressed Pressed O-ring Insertion mark Bead Housing Exaggerated for clarity Patented Pressfit tooI indent Pipe stop Groove Gasket Housing BoIt/nut Figure 3. Welding is not required for the pressed joint, but corrosion can be an issue due to the thin walls 68-76 CHE 10-07.indd 73 9/29/07 5:42:12 PM joined can cause the weld to drift into the high sulfur side. This can cause welds to be rejected due to lack of full penetration. SMAW: Also referred to as MMA welding, or just simply stick weld- ing, SMAW is the most common form of welding used. It is a manual form of welding that uses a consum- able electrode, which is coated with a flux (Figure 4c). As the weld is being made, the flux breaks down to form a shielding gas that protects the weld from the atmosphere. The SMAW welding process is ver- satile and simple, which allows it to be the most common weld done today. FCAW: Flux cored arc welding is a semi- automatic or automatic welding process. It is similar to MIG welding, but the continuously fed, consumable wire has a flux core. The flux provides the shield- ing gas that protects the weld area from the atmosphere during welding. Welding pipe The majority of welds you will see in pipe fabrication will be full-penetra- tion circumferential buttwelds, fillet welds or a combination of the two. The circumferential buttwelds are the welds used to weld two pipe ends together or other components with buttweld ends. Fillet welds are used at socketweld joints and at slip-on flanges. Welds in which a combination of the buttweld and fillet weld would be used would be at a stub-in joint or a similar joint. A stub-in joint (not to be confused with a stub-end) is a connection in which the end of a pipe is welded to the longitudinal run of another pipe (Figure 5). Depending on what the de- sign conditions are, this can be a re- inforced connection or an unreinforced connection. The branch connection can be at 90 deg. or less from the longitu- dinal pipe run. Hygenic fabrication Hygienic and semiconductor pipe fabrication uses automatic autog- enous welding in the form of orbital welding. This is a weld without the use of filler metal. It uses the orbital welding TIG process. In some cases, hand welding is required, but this is kept to a minimum, and will gener- ally require pre-approval. When fabricating pipe for hygienic services it will be necessary to com- ply with, not only a specific method of welding, but also an extensive amount of documentation. Developing and maintaining the required documenta- tion for hygienic pipe fabrication and installation can add an additional 30 to 40% to the piping cost of a project. The documentation needed, from the fabrication effort for validation, may include, but is not limited to: 1. Incoming material examination reports 2. Material certification: a. MTRs b. Certification of compliance 3. Weld-gas certification 4. Signature logs 5. WPQs (welder and welding opera tor performance qualification) 6. Welder and welding operator Engineering Practice Gas nozzIe Contact tube Arc WeId metaI ConsumabIe eIectrode Gas shieId WeId pooI Parent metaI NozzIe FiIIer rod Parent pIate WeId pooI Gas shieIding WeId bead Figure 4. Gas metal arc welding (GMAW; top) uses a shielding gas to protect the weld area from atmospheric gases. Gas tungsten arc welding (GTAW; center) is more exacting than GTAW, but also more complex and slower. Shielded metal arc welding (SMAW; bottom) is the most common form of welding. SMAW is performed manually, whereas GMAW and SMAW can be either performed manually or by an automated system WeId metaI EvoIved gas shieId FIux covering SIag ConsumabIe eIectrode WeId pooI Core wire Arc Parent metaI K n o w | e d g e c o u n t s . MI CPOF I LT PAT I ON ULT P A F I LT P AT I ON N A N OF I L T P AT I ON WWW.MICPODYN-NADIP.COM For more than 4 decades now we have been working very successfully on the development and production of membrane products for the chem|ca| and pharmaceut|ca| industry. This long-standing experience is essential for us. lt is not only an indispensable counterpart to our professional competence but also the key to providing you with products of the highest quality and maximum performance. MlCPODYN TECHNOLOGlES lNC P. O. Box 98269 Paleigh, NC. 27624 Phone 001 - 919 - 341-5936 [email protected] 55,6x254_baer_engl.indd 2 16.02.2007 9:35:54 Uhr Please visit us at the Chem Show. Booth #431 4a. 4b. 4c. Circle 53 on p. 122 or go to adlinks.che.com/6900-53 68-76 CHE 10-07.indd 75 9/29/07 5:42:58 PM inspectionsummary 7.Mechanical and electropolishing procedures 8.Examinerqualification 9.Inspectorqualification 10. Welderqualificationsummary 11. Gagecalibrationcertifications 12. Weldcontinuityreport 13. WPSs (weld procedure specifica- tions) 14. PQRs (procedure qualification record) 15. Weldcouponlog 16. Weldmaps 17. Slopemaps 18. Weldlogs 19. Leaktestreports 20. Inspectionreports 21. Passivationrecords 22. Detailmechanicallayouts 23. Technical specifications for com- ponents 24. As-builtisometrics 25. OriginalIFCisometrics 26. Documentation recording any changesfromIFCtoas-built isometrics The above listed documentation, which closely parallels the list in ASME-BPE,isthatwhichisgenerally requiredtomoveaninstalledhygienic system through validation, commis- sioning and qualification (C&Q).And this isn’t all that’s required.There is additional supporting documentation suchasP&ID’s,proceduraldocuments, andsoon,whicharealsorequired.De- pendingonthesizeandtypeofaproj- ectitcanbeamassiveundertaking.If not properly set up and orchestrated, itcanbecomealogisticalnightmare. What you do not want to do is dis- cover during C&Q that you are miss- ingaportionoftherequireddocumen- tation. Resurrecting this information is labor intensive and can delay a project’s turnover significantly. I can- not stress strongly enough just how imperative it is that all necessary documentation be identified up front. Itneedstobeprocuredthroughoutthe processandassimilatedinaturnover (TO)packageinamannerthatmakes it relatively easy to locate needed information while also allowing the information to be cross indexed and traceablewithintheTOpackage. Thetermvalidationisabroad,gener- alized,self-definingtermthatincludes theactofcommissioningandqualifica- tion.Commissioningandqualification, while they go hand in hand, are two activities that are essentially distinct withinthemselves. n Edited by Gerald Ondrey Acknowledgement: TheauthorwishestothankEarlLamson,senior projectmanagerwithEliLillyandCompany,for beingkindenoughintakingtimeoutofabusy scheduletoreadthroughthedraftofthisarticle. Earl has a remarkable set of project and engi- neering skills that set him apart from many I haveworkedwith.ThatandthefactthatIvalue hisopinionarethereasonsIaskedhimtoreview thisarticle. Engineering Practice 76 ChemiCal engineering www.Che.Com oCtober 2007 www.coade.com DOWNLOAD FREE DEMO Plant Focused. Industry Driven. SM +1 281-890-4566 • [email protected] © 2 0 0 7 C O A D E , In c . A u t o d e s k , t h e A u t o d e s k lo g o , a n d A u t o C A D a r e r e g is t e r e d t r a d e m a r k s o f A u t o d e s k , In c . Why is CADWorx one of the fastest growing and most productive plant design suites on the market? Because it has all the tools to produce intelligent plant designs, including: • Piping • Steel • Cable trays/ ducting • Collision detection • Equipment • Bills of material • Isometrics • Flow schematics • Instrument loop diagrams • Bi-directional links to analysis programs • Walkthrough and visualization CADWorx delivers! Contact us to find out how you can improve your design efficiency. Easy Open Scalable PLANT DESIGN SUITE C A D W o r x ® Circle 54 on p. 122 or go to adlinks.che.com/6900-54 Author W. M. (Bill) Huitthasbeen involved in industrial pip- ing design, engineering and construction since 1965. Positions have included de- sign engineer, piping design instructor, project engineer, project supervisor, pip- ing department supervisor, engineering manager and president ofW. M. Huitt Co. (P.O. Box 31154, St. Louis, MO 63131-0154. Phone: 314-966-8919; Email: [email protected]) a piping consulting firm foundedin1987.Hisexperiencecoversboththe engineeringandconstructionfieldsandcrosses industrial lines to include petroleum refining, chemical, petrochemical, pharmaceutical, pulp & paper, nuclear power, and coal gasification. Hehaswrittennumerousspecificationsinclud- ingengineeringandconstructionguidelinesto ensure that design and construction comply with code requirements, owner expectations and good design practices. Huitt is a member of ISPE (International Society of Pharmaceu- tical Engineers), CSI (Construction Specifica- tions Institute) and ASME (American Society of Mechanical Engineers). He is a contributor toASME-BPEandsitsontwocorporatespeci- ficationreviewboards. 5 I 5 C U D 5 I 5 S 5 S 5 C U D 5 I 5 C U D B C D Figure 5. Stub-in joint connections, such as the three samples shown here, are used for welding the end of a pipe to the longitudinal run of another pipe 68-76 CHE 10-07.indd 76 9/29/07 5:44:00 PM T his fifth in a series of articles [1–4] on piping design discusses the practical issues of installa- tion and cleaning. PIPE INSTALLATION The installation of pipe follows its fab- rication and is very frequently a part of it. The installation of pipe can be accomplished in the following four pri- mary ways, or combinations thereof: 1. Field fabricate and install 2.Shop fabricate and field erected 3. Skid fabrication, assembly and in- stallation 4.Modular construction Field fabricate and install In the first method, the pipe is fabri- cated onsite, either in place or in seg- ments, at an onsite field-fabrication area and then erected. A number of factors will dictate whether or not it is feasible to field fabricate, includ- ing the following: the size and type of the project; pipe size and material; the facility itself; weather conditions; availability of qualified personnel; ex- isting building operations; cleanliness requirements; and time available to do the work. Efficiency, quality and safety are the imperatives that are factored in when considering field fabrication. And cost is the fallout of those factors. Logistically speaking, if all pipe could be fabricated onsite in a safe and ef- ficient manner — maintaining qual- ity while doing so — it would make sense to do it in that manner. However, before mak- ing that final decision, let’s look at some of the pros and cons of field fabrication: Pros: • Only raw material (pipe, fit- tings, valves and so on) need to be shipped to the site location. Such materials are much easier to handle and store than multi-plane configu- rations of pre-fabricated pipe • No time-consuming need to carefully crib, tie-down and chock pre-fabri- cated spool* pieces for transport to the job site • Reduced risk of damage to spool pieces • More efficient opportunity to fabri- cate around unexpected obstacles (structural steel, duct, cable tray, and so on) • Fabricate-as-you-install reduces the rework risk assumed when pre-fabricating spools, or the cost related to field verification prior to shop fabrication • The field-routing installation of pipe through an array of insufficiently documented locations of existing pipe and equipment, on a retrofit project, is quite frequently more effective than attempting to pre-fabricate pipe based on dimensional assumptions Cons: • Weather is arguably the biggest deterrent. If the facility under con- struction is not enclosed, then pro- tection from the elements will have to be provided • When welding has to be done in con- ditions that are not environmentally controlled, then pre-heating will be required if the ambient temperature (not the metal surface temperature) is 0°F or below • In a new facility, as opposed to hav- ing to route piping through an array of poorly located existing pipe and equipment, field fabrication of buttwelded pipe is not as efficient and cost effective as shop fabrication • There may be concerns about safety and efficiency when working in a facility while it is in operation in advance of a turnaround or to begin advance work on a plant expansion Generally speaking, threaded, sock- etweld, grooved, and other propri- etary-type joints that do not require buttwelding are field fabricated and installed. Buttwelding of small, 1 1/2-in. NPS and less, are very often field fabricated and installed because Feature Report 48CHEMÌCAL ENGÌNEERÌNG WWW.CHE.COM APRÌL 2008 Engineering Practice W. M. Huitt W. M. Huitt Co. Piping Design Part 5: Installation and These practical guidelines for deciding which installation procedure to follow, and for cleaning a new pipeline system can prevent problems from happening during startup *Spool pieces are the pre-fabricated sections of pipe that are fabricated and numbered in the shop, then shipped to the job site for installa- tion. Cleaning 17_CHE_041508_EP_GSO.indd 48 3/24/08 7:42:52 AM of the added risk of damage during trans- port, in pre-fabricated form, from the shop to the site. Shop fabricate and install Shop fabrication refers to, generally speaking, any pipe, fittings and components that are assembled by welding into spool assemblies at the fabricator’s fa- cility. The spools are then labeled with an identifier and trans- ported to the job site for installation. Each spool piece needs its own identifier marked on the piece itself in some fashion that will make it easy to know where its desti- nation is in the facility and where it belongs in a multi-spool system of pipe. This will allow the installer to ef- ficiently stage the piece and ready it for installation. As part of the process of developing spool sections, field-welded joints need to be designated. These are welded joints that connect the pre-fabricated spools. In doing this the designer or fabricator will identify two different types of field-welded joints: field weld (FW) and field closure weld (FCW). FW indicates a joint in which the end of a pipe segment is prepared for the installer to set in place and weld to its connecting joint without additional modification in the field. This means that the length of pipe that is joined to another in the field is cut precisely to length and the end prepared in the shop for welding. FCW provides the installer with an additional length of pipe, usually 4 to 6 in. longer than what is indicated on the design drawings, to allow for field adjustment. What has to be considered, and what prompts the need for a FCW, is the ac- tual, as-installed, location of both the fixed equipment that the pipe assem- blies may connect to and the actual installed location of the pipe assembly itself. Odds are that all equipment and piping will not be installed exactly where indicated on design drawings. The dimensional location of the equipment items given on design drawings is not a finite location, it is merely an intended location, as are dinensional locations on drawings for building steel, pipe supports and oth- ers. What factors into the installation of shop-fabricated pipe is the actual location of the equipment nozzle it will be connecting to in relation to the pipe’s installed location. In connecting to equipment there is a build-up, or stack-up, of tolerances that will effectively place the actual, or final, location of the nozzle at some point in three-dimensional space, other than where the design drawing indi- cates. The tolerance stack-up results from the following circumstances: • Manufacturing tolerances in mate- rial forming, nozzle location, and vessel support location • The actual set-in-place location of the vessel • Load cell installation (when appli- cable) • The actual set-in-place pipe run- up location In order to allow for these inevitable deviations between the drawing di- mensions used to fabricate the vessel, set the vessel and install the pipe as- sembly and the actual installed loca- tion of the connecting points, a field- closure piece, or two, will be required for that final adjustment. The field-closure piece is a designated section of the pipe assembly in which a field-closure weld has been indicated. Skid (super skid) fabrication A skid is a pre-packaged assembly that may contain all or some of the follow- ing that make up an operating system: vessels, rotating equipment, piping, automation components, operator in- terfaces, instrumentation, gages, elec- trical panels, wiring and connectors, framework, supports, inline piping components, and insulation. A single process or utility system may fit onto one skid or, depending on size re- straints, may comprise multiple skids. After fabrication of a skid is com- plete, it will typically go through fac- tory-acceptance testing (FAT) at the fabricator’s facility. The skid is then shipped to the job site where it is in- stalled in its final location. After in- stallation it would typically go through a follow-up site-acceptance test (SAT), including additional hydrotesting. This is basically a system shake-down to determine that everything is intact, and that those things that did not re- main intact during transport are dis- covered and repaired. Logistics and the necessary skill set required for the installation, connec- tion and startup of a particular skid package will dictate to what extent the skid fabricator will be involved after it is shipped to the job site. Modular construction The term module or modular construc- tion is quite often, in this context, inter- changed with the term skid fabrication. A module can refer to pre-fabricated units that actually form the structure of a facility as each is installed. Or, the units may be smaller sub-assemblies that, when combined, make up a com- plete process or utility system. Modules also consist of all or some of the following: vessels, rotating equip- ment, piping, automation components, HVAC, instrumentation, electrical wir- ing and connectors, framework, walls, architectural components, lighting, supports, inline piping components, and insulation. This, as an example, allows a complete locker-room module to be placed and connected to a com- plete water-treatment module. The smaller sub-assembly modules, in many cases, are interchanged with the term skid. Misconception can be avoided when a company defines these terms, both for internal discussion and for the purpose of making it clear to outside contractors, as to what is meant when using the term module. Installation approach Now that we have a general idea of the four primary approaches to piping installations how do we decide which is the best method, or combination of methods, to use for a particular proj- ect? Each project is unique with its own particular set of decision drivers with regard to a selected execution approach. There are no hard and fast CHEMÌCAL ENGÌNEERÌNG WWW.CHE.COM APRÌL 2008 49 17_CHE_041508_EP_GSO.indd 49 3/19/08 1:05:20 PM rules for determining a best approach. It requires experienced personnel to assign values to the various aspects of project execution, overlay a timeline, and then assess logistics. It sounds simple, but in actuality can be a very complex process. Therefore, the following is a guide- line and not a hard and fast set of rules. There are simply too many project vari- ables and complexities otherwise. When considering an approach, keep in mind that the method of in- stallation needs to be weighed against a contractor’s preferred methodology. This does not imply that the contrac- tor’s preferred methodology should drive your decision on how to execute a job. On the contrary, once you deter- mine how the job needs to be executed, then look to only those contractors whose preferred methodology agrees with your project execution plans. Some contractors prefer to do most, if not all, fabrication in the shop, oth- ers prefer to set up at the job site, while others are flexible enough to utilize the best of both methods. The three main criteria discussed above — efficiency, quality and safety — would apply here as well. Using these three elements as a basis for making a determination, let us look at some common variables. Environment: The environment is only a factor when work has to be done in an open-air structure or other outdoor installation (such as tank farm, pipeline, pipe rack or yard pip- ing). Working in an open-air structure will require protection from the ele- ments (such as rain, snow, wind and cold). In addition, there may also be a requirement to work in elevated areas with the use of scaffolding. All of this can have a potential impact on safety and efficiency. Pipe-rack installation consists mainly of straight runs of pipe, and will not necessarily have a require- ment or need for pre-fabrication. That is, unless it is pre-fabricated as modular-skid units. Depending on the project, it could be cost effective on an overall strategic basis to modularize the pipe rack, steel and all. The big advantage to shop fabrica- tion is the controlled environment in which it’s done. This includes the qual- ity control aspect, better equipment (generally speaking), a routine meth- odology of how a piece of work pro- gresses through the shop, and better control, through a developed routine of required documentation. Industry: The various sectors of the chemical process industries (CPI) can be grouped into two categories: clean/ indoor build and non-clean/outdoor build. Realizing that there will be exceptions to this generalization, we can include in the clean/indoor built category: pharmaceutical, biophar- maceutical, semiconductor and food and dairy. Under non-clean/outdoor build we can include: petroleum refin- ing; bulk chemicals; pulp and paper; off-shore; pipeline (oil and gas); and power generation. The clean-build philosophy comes from the need to construct certain fa- cilities with a more stringent control on construction debris. Those indus- tries included in this category often re- quire a facility — at least a portion of a facility — to be microbial and particu- late free, as stipulated by the design. There can be no debris, organic or inorganic, remaining after construc- tion in accessible or inaccessible spaces of the facility. Of particular concern with pharmaceutical, bio- pharm and food-and-dairy facilities are food waste and hidden moisture. Food waste can entice and support ro- dents and insects, and hidden mois- ture can propagate mold, which can eventually become airborne. If these intruders are not discovered until the facility is in operation, the impact, upon discovery, can potentially be devastating to production. Such contamination can be found in one of two ways. Discovery at the source, possibly behind a wall or some other out-of-the-way place, means that not only does current production have to cease, but product will have to be an- alyzed for possible contamination. Once found, it then has to be remediated. The other method of discovery comes from the continuous testing and validation of the product stream. If a contaminant is discovered in the product, the production line is stopped, and the problem becomes an investigation into finding the source of the contamination. The clean-build philosophy, there- fore, dictates more stringent and strict requirements for controlling and in- specting for debris on an ongoing basis throughout construction and startup. It will be necessary, on a clean-build site, to adhere to the following rather simple rules: • Smoking or smokeless tobacco prod- ucts of any kind are not allowed on the site property • Provide for offsite break and lunch areas; no food or drink, other than water, are allowed on the site premises • Do not begin installing pipe, duct or equipment until, at the very least, a roof is installed • After roof and walls are installed, ensure that there is no standing water remaining in the facility • Prior to and during the construc- tion of hollow walls, such as those framed and dry-walled, ensure on a daily basis that there is no moisture or debris in the wall cavity • Duct work delivered to the job site shall have the ends covered with a plastic sheet material, which shall remain on the ends until connected in place • Fabricated pipe delivered to the job site shall have the ends covered in a suitable fashion with suitable ma- terial, and the cover shall remain on the ends until pipe is ready to be connected in place • During and after flushing and test- ing of pipelines, all water spills shall be controlled to the extent possible and shall be cleaned after each flushing and testing or at the end of the work day Type of project While the type of project is not the main influence in determining how you approach the execution of a proj- ect, it does play a key role. It will help drive the decision as to how the piping should be fabricated and installed. For example, if the project is a ret- rofit, it will require much of the pipe, regardless of size and joint connec- tion, to be field fabricated and in- stalled. This is due simply to the fact that the effort and cost necessary to verify the location of all existing pipe, equipment, walls, columns, duct and Engineering Practice 50 ChemiCal engineering www.Che.Com april 2008 17_CHE_041508_EP_GSO.indd 50 3/19/08 1:06:21 PM so on, in a somewhat precise manner, would not be very practical. You would be bet- ter served by field verifying the approximate location of the above items with existing drawings, for planning and logistic purposes, then shop or field fabricate, verify and install as you go. A fast track project, one that has a compressed schedule, will require parallel activities where possible. Shop and skid fabrication would be utilized as much as possible simply to expend more man-hours over a shorter time period while at- tempting to maintain efficiency, even though there may be added cost to this approach. This approach is time driven and not budgetary driven. A new grassroots facility still re- quires routing verification as you go, but certainly not the much-more in- volved need to locate previously in- stalled obstructions that is necessary when working with an existing facility. If the project is a clean-build project inside an environmentally controlled area, it will be more practical to shop fabricate or utilize skid or modular fab- rication for most, if not all of the piping. This will reduce the number of person- nel and the amount of fabrication de- bris in the facility, and provide better control for keeping it out of the pipe itself. With personnel, you could have food wrappers, drink cans and bottles, food waste, and clothing items. Fabrica- tion debris could include metal filings, cutting oil, pieces of pipe, weld-rod and weld-wire remnants, and so on. If the project is not a clean-build, but is still inside an environmentally con- trolled facility, the same logic does not necessarily apply. The decision to shop fabricate and install or to field fabri- cate and install becomes one based on efficiency rather than how best to maintain a clean area. But that’s not to say that if it doesn’t qualify as a clean- build project then the construction de- bris can just be allowed to pile up. There is still safety and efficiency to consider on any project, and a clean job site is a major part of that. Main- taining a clean job site is an integral component of good project execution. Keeping personnel and equipment to a minimum at the job site is not an absolute, but is one of the key con- siderations to the efficiency of pipe installation. Following that logic, most of the buttwelded pipe should be shop fabricated. A couple of things to consider, when determining which buttwelded pipe to shop fabricate, are size and material. Pipe material and size range Shop-fabricated spools need to be transported to the job site, which re- quires handling. Handling and trans- porting small diameter pipe and thin- wall tubing spools create the potential for damage to those spools. If you are shop fabricating every- thing and the distance from shop to site is across town, the risk to dam- aging small-diameter pipe spools is a great deal less than if they have to be shipped halfway across the U.S., Eu- rope or Asia, or even across an ocean. In transporting spools over long distances, unless there is a great deal of thought and care given to cribbing the load of spools, it may not be ben- eficial to transport buttwelded pipe spools NPS 1 1/2 in. and less. It may be more practical to fabricate these sizes on site, unless you are fabricating hy- gienic or semiconductor piping; these types of systems require a great deal more control and a cleaner fabrication, meaning that pipe fabrication will re- quire a clean shop area onsite, or the pipe will need to be fabricated at an offsite, better controlled shop facility. A practical rule of thumb in deter- mining what to fabricate in the shop or in the field is provided in Table 1. Dictates of the project and a contrac- tors’ standard operating proceedures will determine how best to define what is shop fabricated and what is field fabricated. TABLE 1. SHOP VERSUS FIELD FABRICATION Size (in.) Material Joint Shop or field ≤ 1 ½ Pipe 1, 2, 3, 6 Field ≤ 1 ½ Pipe 4 & 5 Shop ≥ 2 Pipe 3 & 6 Field ≥ 2 Pipe 4 & 5 Shop ≤ 1 Tubing 5 Field ≤ 1 Tubing 5 Shop (a, b) ≥ 1 ½ Tubing 5 Shop Joint Type: 1 = Socketweld 2 = Threaded 3 = Grooved – Fully (Grooved fittings and pipe ends.) 4 = Grooved – Partially (Shop-welded spools with grooved ends.) 5 = Buttweld 6 = Flanged – Lined or unlined Pipe Notes: a. Hygienic tubing b. Special cribbing and support for transport Circle 30 on p. 76 or go to adlinks.che.com/7371-30 17_CHE_041508_EP_GSO.indd 51 3/24/08 8:20:06 AM Petroleum-refining and bulk-chem- ical projects are generally open-air projects in which field fabrication and installation of pipe are exposed to the elements. While a clean build is not a requirement on these types of projects efficiency and, above all, safety are. Because of this, it would make sense to utilize shop fabrication as much as possible. Fabricating pipe spools under better- controlled shop conditions will provide improved efficiency and safer-per-hour working conditions over what you will generally find in the field. This trans- lates into fewer accidents. Referring back to Table 1, with respect to the potential for damage during transport, pipe sizes NPS 2–3 in. and larger ship much better than smaller pipe sizes, particularly when working with thin-wall tubing. Location Job-site location is one of the key markers in determining shop or field fabrication. In many cases, building a facility in a remote location will be a driver for utilizing a disproportionate amount of skid or module fabrication — disproportionate in the sense that project management may look at modu- larizing the entire job, rather than mo- bilize the staffing and facilities needed to fabricate and install on or near the job site. This would constitute a larger amount of modularization over what might normally be expected for the same type project in a more metropoli- tan region, or an area with reasonable access to needed resources. To expand on that thought; it was pointed out to me by Earl Lamson, senior project manager with Eli Lilly and Co., that project resources, even in metropolitan areas, are quite fre- quently siloed around a specific in- dustry segment. In certain regions of the U.S. for example, you may discover that there is an abundance of crafts- man available when building a refin- ery, but that same region may have difficulty, from a trained and experi- enced personnel perspective, in sup- porting the construction of a semicon- ductor facility. Consequently when building a phar- maceutical facility in another region you may find a sufficient population of trained and expe- rienced craftsman for that industry, but may not find resources ad- equate when building a chemical plant. Building a project in a remote location re- quires the project team to rethink the job-as- usual methodology. From a logistics standpoint, mobilization of personnel and material become a major factor in determining the overall execution of such a project. Project planning is a big component in project execution, but is more so when attempting to build in remote areas. And this doesn’t even touch on the security aspect. Nowadays, when constructing in any number of remote areas, security is a real concern that requires real consideration and real resolution. Re- duced onsite staffing is a good counter measure in reducing risk to personnel when building in remote or even non- remote third-world areas. PIPE SYSTEM CLEANING While there are requirements in ASME for leak testing, cleaning re- quirements do not exist. ASTM A 380 and 967 has standards on cleaning, descaling and passivation, but there is nothing in ASTM on simply flush- ing and general cleaning. Defining the requirements for the internal cleaning of piping systems falls within the re- sponsibilities of the owner. The term “cleaning”, in this context, is a catch-all term that also includes flushing, chemical cleaning, and pas- sivation. So before we go further, let me provide some definition for these terms as they apply in this context, be- cause these terms are somewhat flex- ible in their meaning, depending on source and context, and could be used to describe activities other than what is intended here. Definitions Cleaning: This is a process by which water, solvents, acids or proprietary cleaning solutions are flushed through a piping system to remove contami- nants such as cutting oils, metal fil- ings, weld spatter, dirt and other un- wanted debris. Flushing. This is a process by which water, air or an inert gas is forced through a piping system either in preparation for chemical cleaning or as the only cleaning process. Flushing can be accomplished by using dynamic pressure head or released static pres- sure head, as in a fill-and-dump proce- dure. Blow-down can be considered as flushing with a gas. Passivation. In this process, a chemi- cal solution, usually with a base of nitric, phosphoric, citric acid or other mild oxidant, is used to promote or ac- celerate the formation of a thin (25–50 Å), protective oxide layer (a passive layer) on the internal surfaces of pipe, fittings and equipment. In stainless steels — the most commonly used alloy at present — passivation removes any free iron from the pipe surface to form a chromium-rich oxide layer to protect the metal surface from aggressive liq- uids such as high-purity waters. Note that the terms cleaning and flushing can be interchanged when the process only requires water, air or an inert gas to meet the required level of cleanliness. When the term “clean- ing” is used in this context it may infer what is defined as flushing. Cleaning and testing With regard to cleaning and leak test- ing, and which to do first, there are drivers for both and different schools of thought on the overall process. Each contractor will have its preference. It is in the owner’s best interest to deter- mine its preference or be at risk in just leaving it to the contractor. In either case you should have a line of thought on the process, if for no other reason than to be able to understand what the contractor is proposing to do. At the very least, in advance of leak testing, perform either a basic flush of a test circuit, or perform an internal visual examination as the pipe is in- Engineering Practice 52 ChemiCal engineering www.Che.Com april 2008 Table 2. General cleaninG scenarios category Description C-1 Flush only (water, air or inert gas) C-2 Flush, clean with cleaning solution, flush C-3 Clean with cleaning solution, flush C-4 Flush, clean, passivate, flush Table 3. General leak TesTinG scenarios category Description T-1 Initial service leak test T-2 Hydrostatic leak test T-3 Pneumatic leak test T-4 Sensitive leak test T-5 Alternative leak test 17_CHE_041508_EP_GSO.indd 52 3/19/08 1:10:39 PM stalled. A walk-down of the test circuit should be done just prior to filling the system with any liquid. The last thing you want to happen is to discover too late that a joint wasn’t fully connected or an inline component was taken out of the pipeline. In a facility that is not a clean-build, it can simply be a mess that has to be cleaned. In a clean-build facility, an incident such as this can potentially be costly and time consum- ing to remediate. Tables 2 and 3 list general clean- ing and testing procedures along with easy-to-use indicators. Since this article is concerned with new pipe installations, we will not in- clude steam-out cleaning or pipeline pigging in our discussion. These are cleaning procedures that are used on in-service piping to clean the fluid ser- vice residue buildup from interior pipe walls after a period of use. Before subjecting the system to an internal test pressure, you should first perform a walk down of the piping to make certain, as mentioned earlier, that there are no missing or loose com- ponents. The system is then flushed with water or air to make sure that there are no obstacles in the piping. Over the years, we have discovered everything from soda cans to shop towels, work gloves, nuts and bolts, weld rod, Styrofoam cups, candy wrap- pers, and other miscellaneous debris, including dirt and rocks in installed piping systems. After an initial flush, which could also be the only flush and cleaning re- quired, the system is ready for chemi- cal cleaning or leak testing. In large systems, it may be beneficial to leak test smaller test circuits and then per- form a final cleaning once the entire system is installed and tested. This would include a final completed sys- tem leak test that would test all of the joints that connect the test circuits. That is, unless these joints were tested as the assembly progressed. On large systems, if it is decided to leak test smaller segments, or test circuits as they are installed (prior to flushing the entire system), the piping needs to be examined internally as it is installed. This is to prevent any large-debris items from remaining in the piping during the test. Now that we have touched on generali- ties, let’s take a look at each of the clean- ing categories listed in Table 2 and see how to apply them. Cleaning Category C-1: This is simply a flush with water, air or inert gas. The one non-manual assist that water requires in order for it to clean the inside of a piping system is velocity. But what velocity is necessary? The main concept behind flushing a pipeline is to dislodge and remove suspected debris. In order to dislodge, suspend and remove this unwanted material in the piping system, it is necessary that water or air be forced through the piping system at a veloc- ity sufficient to suspend the heaviest suspected particles and move them along the pipeline. The velocity required to suspend the particles and move them along the pipeline for removal is dependent upon their size and weight, and the flush medium. Metal filings, arguably the heaviest particles normally found in newly fabricated pipe, will have a terminal mid-range settling veloc- ity, in water, of approximately 10 ft/s. Therefore, a flushing velocity of ap- proximately 10 ft/s should be achieved during the flush. (This does not apply to acid cleaning.) Table 4 indicates the rate of flow required to achieve ap- proximately 10 ft/s of velocity through various sizes and schedules of pipe. Purging a piping system clear of de- bris with air requires a velocity of ap- proximately 25 ft/s. Table 5 indicates the air flowrate required to achieve ap- proximately 25 ft/s of velocity through various sizes and schedules of pipe. One thing you might notice is that the size range only extends to 4-in. NPS for both the liquid flush and for the air or gas blow-down. The reason for that is the volume of liquid or gas required to achieve the necessary ve- locity through the larger pipe sizes is quite significant. For example, a 6-in. NPS pipeline would require approximately 900 to 1,000 gal/min, depending on wall thickness of the pipe, to achieve a ve- locity of 10 ft/s. This gets a little cum- bersome and costly unless you have pumps or compressors in place that can achieve the necessary flowrate. The alternative for liquid flushing the larger pipe sizes other than using source line pressure or a pump is to perform a fill-and-dump. In this pro- cess, the pipe system is completely filled with liquid and then drained through a full-line-size, quick-open- ing valve. In doing this, there has to be enough static head to generate suf- ficient force and velocity to achieve essentially the same result as the pumped or line pressure liquid. Cleaning Category C-2: This is a three-step process by which the piping system is initially flushed out with a liquid to remove most of the loose de- bris. This is followed by the circulation of a cleaning solution, which is then followed by a final flush of water. Cleaning solutions are, in many cases, proprietary detergent or acid- based solutions each blended for spe- cific uses. Detergent-based solutions are generally used for removing dirt, cutting oils and grease. Acid-based so- lutions are used to remove the same contaminants as the detergent-base plus weld discoloration and residue. The acid-based solution also passiv- ates the pipe wall. As defined earlier, passivation provides a protective oxide barrier against corrosion. The acids used in some cleaning solutions for ferrous and copper materials leave behind a passivated interior pipe surface as a result of the cleaning process. In util- ity water services, such as tower and chilled water, this barrier against cor- rosion is maintained with corrosion inhibitors that are injected into the fluid stream on an ongoing basis. Keep in mind that the formation of passivated surfaces is a natural occur- rence with metals in an oxygen envi- Engineering Practice 54 ChemiCal engineering www.Che.Com april 2008 Table 4. RaTe of flushing liquid (gal/ min) needed To mainTain a velociTy of appRoximaTely 10 fT/s pipe Sch. pipe size (in.) ½ ¾ 1 1 ½ 2 3 4 5S 12 20 34 77 123 272 460 40 10 16 27 64 105 230 397 80 7 13 22 55 92 — — 17_CHE_041508_EP_GSO.indd 54 3/19/08 1:16:50 PM ronment; the acid merely initiates and speeds up the process. When using stainless alloys — usu- ally 316L, in hygienic-water services such as water for injection (WFI), pu- rified water, deionized (DI) water and in some cases soft water — passiv- ation is a final step in the preparation for service of these pipelines. Passivation is also a periodic ongo- ing preventative-maintenance pro- cedure. High-purity water is very corrosive and attacks any free iron found on the surface of stainless-steel pipe. Free iron has a tendency to come out of solution when material is cold worked, as in bending or forming pipe without the benefit of heat. It also oc- curs with the threading of alloy bolts, which are solution annealed (heat treated) after threading. Passivation removes this free iron while also ac- celerating, in the presence of O 2 , the oxidation rate of the stainless steel, providing a chromium-rich, oxide cor- rosion barrier as defined above. Over time (and this is one hypothet- ical thought on the subject), this very thin corrosion barrier tends to get depleted or worn off, particularly at high impingement areas of the piping system, such as elbows, tees and pump casings. Once the passive layer wears through, any free iron exposed to the high purity water will oxidize, or rust. This will show up as surface rouge. Rouging is an unwanted surface dis- coloration that is periodically removed by means of a derouging process. This is an operational, as-needed chemical- cleaning process that will remove all or most of the rouge and also re-pas- sivate the internal pipe surface. Discussions and research on the topic of rouging continue. This is a subject that has more questions than answers at the present time. Currently, the ASME-BPE is looking into this issue. One of the questions to be answered is whether or not rouge is actually detri- mental to product streams. Cleaning Category C-3: This is a two-step cleaning process that uses a detergent- or acid-based solution to clean the pipe interior of any un- wanted residue or debris. This is then followed by a final flush of water. Cleaning Category C-4: This is a three- or four-step process generally [email protected] 973.257.8011 We’ll take you there. API Manufacturing | Clinical Manufacturing | Dosage Form Manufacturing | Scale Up VISIT US AT BIO SAN DIEGO JUNE 17 – 20 Booth #218 www.dsmpharmaceuticals.com BLEED SIZE 5.25 X 11 CHEM ENGINEERING Circle 32 on p. 76 or go to adlinks.che.com/7371-32 17_CHE_041508_EP_GSO.indd 55 3/19/08 1:18:49 PM used in hygienic service piping. In most cases, simply due to the clean fabrication approach used in hygienic pipe fabrication, only a water flush with deionized- (DI) quality water, or better, would be necessary for cleaning ,followed by passivation of the piping system, then a final flush of water. There are variations to each of these primary cleaning functions and it would be in an owner’s best interest to define these requirements, by fluid ser- vice, in advance of the work to be done. Cleaning procedures This section describes some fundamen- tal cleaning procedures as they might appear in a specification or guideline and includes the leak-test procedures that will follow in Part 6. This will give you some idea as to what you might consider developing for your own set of specifications. Assuming that if your company repeatedly executes projects you will have cleaning and testing guidelines, in some form, prepared for your contractor. If not, you may not get what you expect. It’s better to give some forethought to these activities rather than be surprised at the results. Once a menu of these cleaning and testing procedures are developed, using pre-assigned symbols, similar to those given in the following, they can then be specified in the line list with the respec- tive fluid services as you require. In this manner, there is no second guess- ing during construction. Each piping circuit is assigned a specific clean and test protocol in advance. Many pre-developed procedures I have seen over the years, those de- veloped by owners in particular, have been very simplistic, and typically out of date. This is an indicator to most con- tractors that the owner’s representative will most likely not attempt to enforce them. The contractor, in making that assumption, may simply ignore them and perform their own procedures. Your procedural guidelines should be explicit and current to ensure that the contractors know that someone has given some thought to how he or she wants that work accomplished, making it far more likely that the con- tractors will execute your procedure instead of their own. It is certainly acceptable to accom- modate suggestions to a procedure from a contractor when they don’t compromise the intent of the owner’s requirements and are likely to im- prove the efficiency of the contractor. If a submitted alternate procedure does not compromise the intent of the owner, it is recommended that it be accepted. This will allow the owner to see if that efficiency is really there. With that in mind, let’s create a couple of general cleaning procedures. A general practice in the flushing and cleaning process (also indicated in leak testing), is the evacuation of air when using liquids. Always pro- vide high-point vents for evacuating air during the fill cycle and low point drains for clearing out all of the liquid when the process is complete. Using the same terminology in Table 2 these cleaning procedures will be categorized as follows: Category C-1: Flush or blowdown only (water, air or inert gas) C-1.1 — These systems shall be flushed with the fluid that the sys- tem is intended for. There shall be no hydrostatic or pneumatic leak test. An initial-service leak test will be performed. a. Connect system to its permanent supply line. Include a permanent block valve at the supply line con- nection. All outlets shall have tem- porary hoses run to drain. Do not flush through coils, plates, strainers or filter elements. b. Using supply line pressure, flush system through all outlets until water is clear and free of any debris at all outlet points. Flush a quantity of fluid through each branch not less than three times that contained in the system. Use Table 6 to estimate volume of liquid in the system. c. These systems are required only to undergo an initial-service leak test. During the flushing procedure, and as the system is placed into service, all joints shall be checked for leaks. d. Any leaks discovered during the flush- ing process, or during the process of placing the system into service, will require the system to be drained and repaired. After which the process will start over with Step 2. C-1.2 — These systems shall be flushed clean with potable water. a. Connect a flush/test manifold at a designated inlet to the system, and a temporary hose or pipe on the des- ignated outlet(s) of the system. b. Route temporary hose or pipe from potable water supply, approved by owner, and connect to flush/test manifold. Route outlet hose or pipe to sewer, or as directed by owner represenative. Secure end of outlet. c. Using a once through procedure (not a re-circulation), and the rate of flow in Table 4, perform an ini- tial flush through the system with a quantity of potable water not less than three times that contained in the system. Use Table 6 to estimate volume of liquid in the system. Dis- charge to sewer, or as directed by owner representative. d. After the initial flush, insert a coni- cal strainer into a spool piece located between the discharge of the piping system and the outlet hose. Perform a second flush with a volume of po- table water not less than that con- tained in the system. e. After the second flush (Step d), pull the strainer and check for debris; if debris is found repeat Step c. If no debris is found the system is ready for leak testing. Category C2: Flush then clean with cleaning solution, followed by a neu- tralization rinse. Because of the thor- oughness of the flush, clean and rinse process there should be no need to Engineering Practice 56 ChemiCal engineering www.Che.Com april 2008 Table 5. RaTe of aiR flow (fT 3 /s) To mainTain a velociTy of appRoximaTely 25 fT/s pipe sch. pipe sizes (in.) ½ ¾ 1 1 ½ 2 3 4 Press. 15 psig 5S 0.14 0.23 0.39 0.86 1.39 3.06 5.17 40 0.11 0.19 0.30 0.71 1.18 2.59 4.47 80 0.08 0.15 0.25 0.62 1.04 2.32 4.03 Press. 50 psig 5S 0.30 0.51 0.84 1.88 3.02 6.67 11.3 40 0.23 0.41 0.66 1.56 2.56 5.65 9.73 80 0.18 0.33 0.55 1.35 2.26 5.05 8.79 17_CHE_041508_EP_GSO.indd 56 3/19/08 1:19:31 PM check for transient debris, only for neutralization. However, if circum- stances dictate otherwise, then a final check for debris may be warranted. C-2.1 — These systems shall be pre- flushed with potable water, cleaned with (indicate cleaning agent) then a rinse/neutralization followed by leak testing with potable water. If it is determined that the system will be installed and tested progressively in segments, the sequence of cleaning and testing can be altered to follow the segmented installation, thereby leak testing segments of a piping system as they are installed without clean- ing. The entire system would then be cleaned once installed and tested. a. Hook up flush/test manifold at a des- ignated temporary inlet to the sys- tem between the circulating pump discharge and the system inlet. In- stall a temporary hose or pipe on the designated outlet(s) of the system. b. Route temporary hose or pipe from potable water supply, approved by owner, and connect to flush/test manifold. Route outlet hose or pipe to sewer, or as directed by owner’s representative. c. Close valve between the circulating pump (if no valve is included in the system design, insert a line-blind or install a blind flange with a drain valve) discharge and flush/test rig. Open valve between flush/test man- ifold and piping system. d. Using the once-through procedure (meaning the cleaning fluid is not re-circulated), and the rate of flow in Table 4, perform an initial flush through the system, bypassing the circulation pump, with a quantity of potable water equal to not less than three times that contained in the system. Use Table 6 to estimate volume of liquid in the system. (Note: During the water flush, check the system for leaks. Verify no leaks prior to introducing chemical cleaning solution to the piping system.) e. Discharge to sewer, or as directed by owner’s representative. f. After completing the initial flush, drain remaining water in the sys- tem. Or, retain water if cleaning chemicals will be added to the circu- lating water. g. Configure valves and hoses to cir- culate through pump. Connect head tank, or other source containing cleaning agent, to connection pro- vided on circulation loop. h. Fill the system with the pre-mea- sured (indicate preferred clean- ing agent and mixing ratio or per- centage by volume) and circulate through the system for 48 h. To minimize corrosion, if anticipated, circulate cleaning agent at a low- velocity rate prescribed by the cleaning-agent manufacturer. i. Drain cleaning agent to sewer or containment, as directed by owner. j. Reconnect, as in Step a, for the once through flush/neutralization, and flush system with potable water using a quantity not less than three times that of the system volume. Since the (name cleaning agent) so- lution has a neutral pH, the rinse water will have to be visually ex- amined for clarity. Rinse until clear. The rinse must be started as quickly after the cleaning cycle as possible. If cleaning residue is allowed to dry on the interior pipe wall, it will be more difficult to remove by simply flushing. The final rinse and neu- tralization must be accomplished before any possible residue has time to dry. k. Test pH for neutralization. Once neutralization is achieved proceed to Step l. l. Remove pump and temporary circu- lation loop, then configure the system for leak testing. This may include re- moval of some components, insertion of line-blinds, installation of tempo- rary spools pieces and so on. These three examples should pro- vide an idea as to the kind of dialog that needs to be created in providing guidance and direction to the contrac- tor responsible for the work. And, as stated earlier, these procedures, for the most part, are flexible enough to accommodate suggested modifica- tions from the contractor. ■ Edited by Gerald Ondrey Acknowledgement The author’s deep appreciation again goes to Earl Lamson, senior project manager with Eli Lilly and Co., for taking the time to review these arti- cles. His comments help make this ar- ticle, and the others, better documents than they otherwise would have been. He obliged me by applying the same skill, intelligence and insight he brings to everything he does. His comments kept me concise and on target. References 1. Huitt, W.H., Piping for Process Plants: The Ba- sics, Chem. Eng. February 2007, pp. 42–47. 2. Huitt, W.H., Piping for Process Plants: Flanges, Chem. Eng. March 2007, pp. 56–61. 3. Huitt, W.H., Piping for Process Plants: Design Elements, Chem. Eng. July 2007, pp. 50–57. 4. Huitt, W.H., Piping for Process Plants: Codes and Fabrication, Chem. Eng. February 2007, pp. 68–76. Table 6. Volume of waTer (gal) per lineal fooT of pipe pipe Sizes (in.) Sch. 1/2 3/4 1 11/2 2 3 4 6 8 10 12 14 16 18 20 24 5S .021 .035 .058 .129 .207 .455 .771 1.68 — — — — — — — — 20 — — — — — — — — 2.71 4.31 6.16 7.34 9.70 12.4 15.2 22.2 40 .016 .028 .045 .106 .176 .386 .664 1.51 2.61 4.11 5.84 9.22 9.22 14.5 14.5 — 80 .012 .023 .037 .093 .154 .345 .60 1.36 — — — — — — — — Author W. M. (Bill) Huitt has been involved in industrial pip- ing design, engineering and construction since 1965. Posi- tions have included design en- gineer, piping design instruc- tor, project engineer, project supervisor, piping depart- ment supervisor, engineering manager and president of W. M. Huitt Co. (P.O. Box 31154, St. Louis, MO 63131-0154. Phone: 314-966-8919; Email: wmhuitt@aol. com) a piping consulting firm founded in 1987. His experience covers both the engineering and construction fields and crosses industrial lines to include petroleum refining, chemical, petro- chemical, pharmaceutical, pulp & paper, nuclear power, and coal gasification. He has written nu- merous specifications including engineering and construction guidelines to ensure that design and construction comply with code requirements, owner expectations and good design practices. Bill is a member of ISPE (International Society of Pharmaceutical Engineers), CSI (Construction Specifications Institute) and ASME (American Society of Mechanical Engineers). He is a con- tributor to ASME-BPE and sits on two corporate specification review boards. Engineering Practice 58 ChemiCal engineering www.Che.Com april 2008 17_CHE_041508_EP_GSO.indd 58 3/27/08 7:17:16 AM T his sixth and final part of a series of articles [1–5] on piping for pro- cess plants discusses practical is- sues of leak testing and verifica- tion of piping systems. Leak testing Leak testing and pressure testing are often used synonymously. However, pressure testing is a misnomer when referring to leak testing of piping sys- tems. By definition, a pressure test is the procedure performed on a relief valve to test its set-point pressure. The intent, when pressure testing a relief valve, is not to check for leaks, but to test the pressure set point of the valve by gradually adding pressure to the relief valve until it lifts the valve off of the seat. A leak test, on the other hand, is performed to check the sealing integ- rity of a piping system by applying internal pressure to a pre-determined limit, based on design conditions, then checking joints and component seals for leaks. It is not intended that the MAWP (maximum allowable working pressure) of a piping system be veri- fied or validated. Before discussing the various types of leak tests and leak-test procedures I would like to briefly talk about con- trolling and tracking this activity. Testing, like many aspects of a project, should be a controlled process. There should be a formal method of docu- menting and tracking this activity as the contractor proceeds through the leak testing process. Documentation In documenting the leak testing activ- ity there are certain forms that will be needed. They consist of the following: 1. A dedicated set of piping and in- strumentation diagrams (P&IDs) to identify the limits and number the test circuits 2. A form to record components that were either installed or removed prior to testing 3. A checklist form for field supervi- sion to ensure that each step of the test process is accomplished 4. Leak-test data forms The two sets of documents, from those listed above, that need to be retained are the P&ID’s and the leak- test data forms. The other two sets of forms are procedural checklists. The leak-test data forms should con- tain key data such as the following: 1. Test circuit number 2. P&ID number(s) 3. Date of test 4. Project name or number, or both 5. Location within facility 6. Line number(s) 7. Design pressure 8. Test pressure 9. Test fluid 10. Test fluid temperature 11. Time (military) recorded test begins 12. Pressure at start of test 13. Time (military) recorded test ends 14. Pressure at end of test 15. Total elapsed time of test 16. Total pressure differential (plus or minus) from the beginning to the end of test period 17. Comment section (indicate if leaks were found and system was repaired and retested or if system passed) 18. Signatures and dates Also make certain that the testing contractor has current calibration logs of his or her test instruments, such as pressure gages. Primary leak tests ASME B31.3 defines five pri- mary leak tests as follows: Initial service leak test. This applies only to those fluid services meeting the criteria as defined under ASME B31.3 Category D fluid service. This includes fluids in which the following apply: • The fluid handled is nonflamma- ble, nontoxic, and not damaging to human tissue • The design gage pressure does not exceed 1,035 kPa (150 psi) • The design temperature is from –29°C (–20°F) through 186°C (366°F) The initial service leak test is a pro- cess by which the test fluid is the fluid that is to be used in the intended pip- ing system at operating pressure and temperature. It is accomplished by connecting to the fluid source with a valved connection and then gradually opening the source valve and filling the system. In liquid systems, air is purged during the fill cycle through high point vents. A rolling examination of all joints is continually performed during the fill cycle and for a period of time after the system is completely filled and is under line pressure. In a situation in which the pipeline that is being tested has distribution on multiple floors of a facility, there will be pressure differentials between the floors due to static head differ- ences. This will occur in operation Feature Report 48 ChemiCal engineering www.Che.Com June 2008 engineering Practice Proper documentation, determination of the fluid service category and operating conditions are among the factors necessary to perform the correct leak test on a piping system Piping for Process Plants Part 6: Testing & Verification W. M. Huitt W. M. Huitt Co. 17_CHE_061508_EP_GSO.indd 48 5/22/08 2:48:28 PM and is acceptable under initial ser- vice test conditions. The test pressure achieved for ini- tial service testing is what it will be in operation. The only difference is that the flowing fluid during opera- tion will incur an amount of pressure drop that will not be present during the static test. Hydrostatic leak test. This is the most commonly used leak test and is performed by using a liquid, normally water, and in some cases with addi- tives to prevent freezing, under a pres- sure calculated by Equation (1): (1) P P S S T T = ⋅ ⋅ 1 5 . where P T = Test pressure, psi P = Internal design gage pressure, psig S T = Stress value at test temperature, psi (see ASME B31.3, Table A-1) S = Stress value at design tempera- ture, psi (see B31.1, Table A-1) However, as long as the metal tem- perature of S T remains below the temperature at which the allowable stress value for S T begins to dimin- ish and the allowable stress value of S and S T are equal, then S T and S cancel each other leaving the simpler Equation (2): P P T = ⋅ 1 5 . (2) Unlike initial service test- ing, pressure variations due to static head differences in eleva- tion have to be accommodated in hydrostatic testing. That means the calculated test pressure is the minimum pressure required for the system. When hydrostati- cally testing a multi-floor system, the minimum calculated test pressure shall be realized at the highest point. This is not stated, but is inferred in B31.3. Pneumatic leak test. This test is performed using air or a pre- ferred inert gas. This is a rela- tively easy test to perform simply from a preparation and cleanup standpoint. However, this test has a hazardous potential because of the stored energy in the pressur- ized gas. And for that reason alone it should be used very selectively. When pneumatic testing is per- formed, it must be done under a strictly controlled procedure with on- site supervision in addition to coordi- nation with all other crafts and per- sonnel in the test area. The test pressure for pneumatic leak testing under B31.3 is calculated using Equation (3), for B31.9 it is cal- culated using Equation (4), and for B31.1 it is calculated using Equation (5). P P T = ⋅ 1 1 . (3) P P T = ⋅ 1 4 . (4) P P P T = ⋅ ⋅ 1 2 1 5 . . to (5) One misconception with pneumatic leak testing is in its procedure, as de- scribed in B31.3. There is a misconcep- tion that the test pressure should be maintained while the joints are ex- amined. This is not correct. As B31.3 explains, pressure is increased gradu- ally until the test pressure is reached. At that point, the test pressure is held until piping strains equalize through- out the system. After a sufficient amount of time is allowed for piping strains to equalize, the pressure is then reduced to the design pressure (see Reference [3] for a discussion of the design pressure). While design pressure is held, all joints are examined for leaks. It is not required that the examination take place while holding test pressure. There is more to the entire proce- dure that is not included here. Please refer to B31.3 or B31.1 for full details on pneumatic leak testing. Sensitive leak test. This leak test is performed when there is a higher- than-normal potential for fluid leak- age, such as for hydrogen. I also recom- mend its use when a fluid is classified as a Category M fluid service. B31.1 refers to this test as Mass-Spectrom- eter and Halide Testing. In B31.3, the process for sensitive leak testing is as follows: The test shall be in accordance with the gas and bubble test method speci- fied in the BPV Code, Section V, Article 10, or by another method demonstrated to have equal sensitivity. Sensitivity of the test shall be not less than 10 –3 atm . mL/s under test conditions. a. The test pressure shall be at least the lesser of 105 kPa (15 psi) gage, or 25% [of] the design pressure. b. The pressure shall be gradually in- creased until a gage pressure the lesser of one-half the test pressure or 170 kPa (25 psi) gage is attained, at which time a preliminary check shall be made. Then the pressure shall be gradually increased in steps until the test pres- sure is reached, the pressure being held long enough at each step to equal- ize piping strains. In testing fluid services that are extremely difficult to seal against, or fluid services classified as a Category M fluid service, I would suggest the following in preparation for the pro- cess described under B31.3: • Prior to performing the sensitive leak test, perform a low-pressure test (15 psig) with air or an inert gas using the bubble test method. Check every mechanical joint for leakage • After completing the preliminary low-pressure pneumatic test, purge all of the gas from the system using helium. Once the system is thor- oughly purged, and contains no less than 98% He, continue using He to perform the sensitive leak test with a mass spectrometer tuned to He. Helium is the trace gas used in this ChemiCal engineering www.Che.Com June 2008 49 Piping for Process Plants Part 6: Testing & Verification 17_CHE_061508_EP_GSO.indd 49 5/22/08 2:49:25 PM process and has a size that is close to that of the hydrogen molecule; this makes it nearly as difficult to seal against as H 2 without the volatility. Test each mechanical joint using the mass spectrometer to determine leak rate, if any. Alternative leak test. In lieu of per- forming an actual leak test, in which internal pressure is used, the alterna- tive leak test takes the examination and flexibility analysis approach. This test is conducted only when it is determined that either hydrostatic or pneumatic testing would be det- rimental to the piping system or the fluid intended for the piping system, an inherent risk to personnel, or im- practical to achieve. As an alternative to testing with internal pressure, it is acceptable to qualify a system through examination and flexibility analysis. The process calls for the examination of all groove welds, and includes longitudinal welds used in the manufacture of pipe and fittings that have not been previously tested hydrostatically or pneumati- cally. It requires a 100% radiograph or ultrasonic examination of those welds. Where applicable, the sensitive leak test shall be used on any untested me- chanical joints. This alternative leak test also requires a flexibility analysis as applicable. Very briefly, a flexibility analysis verifies, on a theoretical basis, that an installed piping system is within the allowable stress range of the material and components under design con- ditions if a system: (a) duplicates or replaces without significant change, a system operating with a successful service record; (b) can be judged ad- equate by comparison with previously analyzed systems; and (c) is of uni- form size, has no more than two points of fixation, no intermediate restraints, and falls within the limitations of em- pirical Equation (6). (6) D y L U K ⋅ − ( ) ≤ 2 1 where D = Outer dia. of pipe, in. (or mm) y = Resultant of total displacement strains to be absorbed by piping system, in. (or mm) L = Developed length of piping be- tween anchors, in. (or mm) U = Anchor distance, straight line between anchors, ft (or m) K 1 = 208,000 S A /E a , (mm/m) 2 = 30 S A /E a , (in./ft) 2 S A = Allowable displacement stress range per Equation (1a) of ASME B31.3, ksi (MPa) E a = Reference modulus of elasticity at 70°F (21°C), ksi (MPa) One example in which an alternative leak test might be used is in making a branch tie-in to an existing, in-ser- vice line using a saddle with an o-let branch fitting with a weld-neck flange welded to that, and a valve mounted to the flange. Within temperature limitations, the fillet weld used to weld the saddle to the existing pipe can be examined using the dye pen- etrant or magnetic particle method. The circumferential butt or groove weld used in welding the weld neck and the o-let fitting together should be radiographically or ultrasonically examined. And the flange joint con- necting the valve should have the torque of each bolt checked after visu- ally ensuring correct type and place- ment of the gasket. There are circumstances, regarding the tie-in scenario we just discussed for alternative leak testing, in which a hydrostatic or pneumatic test can be used. It depends on what the fluid service is in the existing pipeline. If it is a fluid service that can be con- sidered a Category D, then it is quite possible that a hydrostatic or pneu- matic leak test can be performed on the described tie-in. By capping the valve with a blind flange modified to include a test rig of valves, nipples and hose connectors, you can perform a leak test rather than an alternative leak test. As men- tioned, this does depend on the exist- ing service fluid. If the existing fluid service is steam or a cryogenic fluid, then you might want to consider the alternative leak test. More on documentation As seen in Equations (1–5), the leak test pressure, except for initial service testing, is based on design pressure and design temperature, both of which are described in Reference [3]. A few general procedures for cleaning and testing are presented below. As in all other project functions, control and documentation is a key element in the cleaning and testing of piping systems. It does, however, need to be handled in a manner that is dictated by the type of project. That means you don’t want to bury yourself in unwarranted paperwork and place an unnecessary burden on the contractor. Building a commercial or institu- tional type facility will not require the same level of documentation and stringent controls that an industrial type facility would require. But even within the industrial sector there are varying degrees of required testing and documentation. To begin with, documentation re- quirements in industry standards are simplistic and somewhat generalized, as is apparent in ASME B31.3, which states in Para. 345.2.7: Records shall be made of each piping system during the testing, including: (a) Date of test (b) Identification of piping system tested (c) Test fluid (d) Test pressure (e) Certification of results by examiner These records need not be retained after completion of the test if a certification by the inspector that the piping has satisfactorily passed pressure testing as required by this Code is retained. ASME B31.3 goes on to state, in Para. 346.3: Unless otherwise specified by the engineering design, the following re- cords shall be retained for at least 5 years after the record is generated for the project: (a) Examination procedures; and (b) Examination personnel qualifica- tions Standards that cover such a broad array of industrial manufacturing, do not, as a rule, attempt to get too spe- cific in some of their requirements. Be- yond the essential requirements, such as those indicated above, the owner, engineer or contractor has to assume responsibility and know-how for pro- viding more specific and proprietary requirements for a particular project specific to the particular needs of the Engineering Practice 50 ChemiCal engineering www.Che.Com June 2008 17_CHE_061508_EP_GSO.indd 50 5/22/08 2:50:16 PM owner. The following will help, to some extent, fill that gap. Which fluid service category? While Category-D fluid services qualify for initial service leak testing, there are caveats that should be con- sidered. This is a situation in which ASME provides some flexibility in testing by lowering the bar on require- ments where there is reduced risk in failure, provided that if failure should occur, the results would not cause catastrophic damage to property or ir- reparable harm to personnel. The owner’s responsibility for any fluid service selected for initial ser- vice leak testing lies in determining what fluid services to place into each of the fluid service categories: Nor- mal, Category D, Category M, and High Pressure. Acids, caustics, volatile chemicals and petroleum products are usually easy to identify as those not quali- fying as a Category-D fluid service. Cooling tower water, chilled water, air and nitrogen are all easy to identify as qualifyiers for Category-D fluid services. The fluid services that fall within the acceptable Category D guidelines, but still have the poten- tial for being hazardous to personnel are not so straight forward. Consider water as an example. At ambient conditions, water will sim- ply make you wet if you get dripped or sprayed on. By OSHA standards, once the temperature of water exceeds 140°F (60°C), it starts to become det- rimental to personnel upon contact. At this point, the range of human toler- ance becomes a factor. However, as the temperature continues to elevate, it eventually moves into a range that be- comes scalding upon human contact. Human tolerance is no longer a factor because the water has become hazard- ous and the decision is made for you. Before continuing, a point of clari- fication. The 140ºF temperature men- tioned above is with respect to sim- ply coming in contact with an object at that temperature. Brief contact at that temperature would not be detri- mental. In various litigation related to scalding it has been determined that an approximate one-second ex- posure to 160°F water will result in third degree burns. An approximate half-minute exposure to 130°F water will result in third degree burns. And an approximate ten minute exposure to 120°F water can result in third- degree burns. With the maximum temperature limit of 366°F (185.5°C) for Category- D fluid services, what the owner needs to consider are three factors: (1) within that range of 140°F (60°C), the temperature at which discomfort be- gins to set in, to 366°F (185.5°C), the upper limit of Category-D fluids, what do we consider hazardous; (2) what is the level of opportunity for risk to per- sonnel; and (3) what is the level of as- sured integrity of the installation Assured integrity means that, if there are procedures and protocols in place that require, validate and docu- ment third-party inspection of all pipe fabrication, installation and testing, then there is a high degree of assured integrity in the system. If some or all of these requirements are not in place then there is no assured integrity. All three of these factors — tem- perature, risk of contact and assured integrity — have to be considered to- gether to arrive at a reasonable deter- mination for borderline Category-D fluid services. If, for instance, a fluid service is hot enough to be considered hazardous, but is in an area of a fa- cility that sees very little personnel activity, then the fluid service could still be considered as a Category-D fluid service. One factor I have not included here is the degree of relative importance of a fluid service. If a system failed, how big of a disruption would it cause in plant operation, and how does that factor into this process? For example, if a safety shower water system has to be shut down for leak repair, the downtime to make the repairs has little impact on plant oper- ations. This system would therefore be of relatively low importance and not a factor in this evaluation process. If, on the other hand, a chilled water system has to be shut down for leak re- pair to a main header, this could have a significant impact to operations and production. This could translate into lost production and could be consid- ered a high degree of importance. You could also extend this logic a bit further by assigning normal fluid-ser- vice status to the primary headers of a chilled water system and assigning Category D status to the secondary distribution branches, then leak test accordingly. You need to be cautious in considering this. By applying different category significance to the same pip- ing system it could cause more confu- sion than it is worth. In other words it may be more value added to simply default to the more conservative cat- egory of normal. Once it has been established that there is a high assured integrity value for these piping systems, there are two remaining factors to be considered. First, within the temperature range indicated above, at what temperature should a fluid be considered hazard- ous? Second, how probable is it that personnel could be in the vicinity of a leak, should one occur? For this discussion, let us deter- mine that any fluid at 160°F (71°C) and above is hazardous upon contact with human skin. If the fluid you are considering is within this tempera- ture range, then it has the potential of being considered a normal fluid, as defined in B31.3, pending its location as listed in Table 1. For example, if you have a fluid that is operating at 195°F (90.6°C), it would be considered hazardous in this evalu- ation. But, if the system is located in a Group 5 area (Table 1) it could still qualify as a Category D fluid service. Leak test examples After the above exercise in evaluating a fluid service, we can now continue with a few examples of leak test pro- cedures. Using the designations given in Table 2, these leak test procedures will be categorized as follows: Testing Category T-1. T-1.1 — This category covers liquid piping systems categorized by ASME B31.3 as Category-D fluid service and ChemiCal engineering www.Che.Com June 2008 51 Table 1. areas under ConsideraTion for CaTegory d group description yes no 1 Personnel occupied space √ 2 Corridor frequented by personnel √ 3 Sensitive equipment (MCC, control room, and so on) √ 4 Corridor infrequently used by personnel √ 5 Maintenance & operations personnel only access √ 17_CHE_061508_EP_GSO.indd 51 5/22/08 2:51:36 PM will require initial service leak test- ing only. 1. If the system is not placed into ser- vice or tested immediately after flushing and cleaning, and has set idle for an unspecified period of time, it shall require a preliminary pneumatic test at the discretion of the owner. In doing so, air shall be supplied to the system to a pressure of 10 psig and held there for 15 min to ensure that joints and compo- nents have not been tampered with, and that the system is still intact. After this preliminary pressure check, proceed. 2. After completion of the flushing and cleaning process, connect the sys- tem, if not already connected, to its permanent supply source and to all of its terminal points. Open the block valve at the supply line and gradu- ally feed the liquid into the system. 3. Start and stop the fill process to allow proper high-point venting to be accomplished. Hold pressure to its minimum until the system is completely filled and vented. 4. Once it is determined that the sys- tem has been filled and vented prop- erly, gradually increase pressure until 50% of operating pressure is reached. Hold that pressure for ap- proximately two minutes to allow piping strains to equalize. Continue to supply the system gradually until full operating pressure is achieved. 5. During the process of filling the sys- tem, check all joints for leaks. Should leaks be found at any time during this process, drain the system, re- pair leak(s) and begin again with Step 1. (Caveat: Should the leak be no more than a drip every minute or two on average at a flange joint, it could require simply checking the torque on the bolts without draining the entire system. If someone forgot to fully tighten the bolts, then do so now. If it happens to be a threaded joint you may still need to drain the system, disassemble the joint, clean the threads, add new sealant and re- connect the joint before continuing.) 6. Record test results and fill in all re- quired fields on the leak test form. T-1.2. — This category covers pneu- matic piping systems categorized by ASME B31.3 as Category-D fluid ser- vice and will require initial service leak testing. 1. After completion of the blow-down process, the system shall be connected to its permanent supply source, if not already done so, and to all of its ter- minal points. Open the block valve at the supply line and gradually feed the gas into the system. 2. Increase the pressure to a point equal to the lesser of one-half the operating pressure or 25 psig. Make a preliminary check of all joints by sound or bubble test. If leaks are found, release pressure, repair leak(s) and begin again with Step 1. If no leaks are identified, continue to Step 3. 3. Continue to increase pressure in 25 psi increments, holding that pres- sure momentarily (approximately 2 min) after each increase to allow piping strains to equalize, until the operating pressure is reached. 4. Check for leaks by sound or bubble test, or both. If leaks are found, re- lease pressure, repair leak(s) and begin again with Step 2. If no leaks are found, the system is ready for service. 5. Record test results and fill in all re- quired fields on the leak test form. Category T-3.1 — Hydrostatic Leak Test. T-3.1. — This category covers liquid piping systems categorized by ASME B31.3 as normal fluid service. 1. If the system is not placed into ser- vice or tested immediately after flushing and cleaning, and has set idle for an unspecified period of time, it shall require a preliminary pneumatic test at the discretion of the owner. In doing so, air shall be supplied to the system to a pressure of 10 psig and held there for 15 min- utes to ensure that joints and com- ponents have not been tampered with, and that the system is still in- tact. After this preliminary pressure check, proceed. 2. After completion of the flushing and cleaning process, with the flush/test manifold still in place and the tem- porary potable water supply still connected (reconnect if necessary), open the block valve at the supply line and complete filling the system with potable water. 3. Start and stop the fill process to allow proper high-point venting to be accomplished. Hold pressure to its minimum until the system is completely filled and vented. 4. Once it is determined that the sys- tem has been filled and vented properly, gradually increase pres- sure until 50% of the test pressure is reached. Hold that pressure for approximately two minutes to allow piping strains to equalize. Continue to supply the system gradually until test pressure is achieved. 5. During the process of filling the sys- tem and increasing pressure to 50% of the test pressure, check all joints for leaks. Should any leaks be found, drain system, repair leak(s) and begin again with Step 1. 6. Once the test pressure has been achieved, hold it for a minimum of 30 min or until all joints have been checked for leaks. This includes valve and equipment seals and packing. 7. If leaks are found, evacuate system as required, repair and repeat from Step 2. If no leaks are found, evacu- ate system and replace all items temporarily removed. 8. Record all data and activities on leak test forms. The three examples above should provide an idea as to the kind of guide- line that needs to be created in provid- ing direction to the contractor respon- sible for the work. Preparation For leak testing to be successful on your project, careful preparation is key. This preparation starts with gathering information on test pres- sures, test fluids, and the types of tests that will be required. The most convenient place for this information to reside is the piping line list or pip- ing system list. A piping line list and piping system list achieve the same purpose, only to different degrees of detail. On some projects, it may be more practical to compile the information by entire service fluid systems. Other projects may require a more detailed approach Engineering Practice 52 ChemiCal engineering www.Che.Com June 2008 Table 2. General leak TesTinG scenarios category Description T-1 Initial service leak test T-2 Hydrostatic leak test T-3 Pneumatic leak test T-4 Sensitive leak test T-5 Alternative leak test 17_CHE_061508_EP_GSO.indd 52 5/22/08 2:52:13 PM by listing each to and from line along with the particular data for each line. The line list itself is an excellent control document that might include the following for each line item: 1. Line size 2. Fluid 3. Nominal material of construction 4. Pipe specification 5. Insulation specification 6. P&ID 7. Line sequence number 8. From and to information 9. Pipe code 10. Fluid service category 11. Heat tracing 12. Operating pressure 13. Design pressure 14. Operating temperature 15. Design temperature 16. Type of cleaning 17. Test pressure 18. Test fluid 19. Type of test Developing this type of information on a single form provides everyone involved with the basic information needed for each line. Having access to this line-by- line information in such a concise, well- organized manner reduces guess-work and errors during testing. Test results, documented on the test data forms, will be maintained under separate cover. Together, the line list provides the required information on each line or system, and the test-data forms provide signed verification of the actual test data of the test circuits that make up each line or system. VALIDATION The process of validation has been around for longer than the 40 plus years the author has been in this business. You may know it by its less formal namesakes walk-down and checkout. Compared to validation, walk-down and checkout procedures are not nearly as complex, stringent, or all inclusive. Validation is actually a subset ac- tivity under the umbrella of commis- sioning and qualification (C&Q). It is derived from the need to authenticate and document specifically defined re- quirements for a project and stems in- directly from, and in response to, the Code of Federal Regulation 29CFR Titles 210 and 211 current Good Man- ufacturing Practice (cGMP) and U.S. Food and Drug Administration (FDA) requirements. These CFR Titles and FDA requirements drove the need to demonstrate or prove compliance. These requirements can cover everything from verification of ex- amination and inspection, documen- tation of materials used, software functionality and repeatability to welder qualification, welding ma- chine qualification, and so on. The cGMP requirements under 29CFR Titles 210 and 211 are a vague predecessor of what valida- tion has become, and continues to become. From these basic govern- mental outlines, companies, and the pharmaceutical industry as a whole, have increasingly provided improved interpretation of these guidelines to meet many industry-imposed, as well as self-imposed requirements. To a lesser extent, industrial proj- ects outside the pharmaceutical, food and beverage, and semi-conductor industries, industries not prone to require such in-depth scrutiny, could benefit from adopting some of the es- sential elements of validation, such as: material verification, leak-test re- cords, welder and welding operator- qualification records, and so on. At face value this exercise would pro- vide an assurance that the fabricating and installing contractor is fulfilling its contractual obligation. The added ben- efit is that, in knowing that this degree of scrutiny will take place, the contrac- tor will take extra measures to mini- mize the possibility of any rejects. This is not to imply that all con- tractors are out to get by with as little as they can. Just the opposite is actually true. Most contractors quali- fied to perform at this level of work are in it to perform well and to meet their obligations. Most will already have their own verification proce- dure in place. The bottom line is that the owner is still responsible for the end result. No one wants to head for the litiga- tion table at the end of a project. And the best way to avoid that is for the owner to be proactive in developing its requirements prior to initiating a project. This allows the specifica- tion writers and reviewers the benefit of having time to consider just what those requirements are and how they should be defined without the time pressures imposed when this activity is project driven. Performing this kind of activity while in the heat of a project sched- ule tends to force quick agreement to specifications and requirements writ- ten by parties other than those with the owner’s best interest at heart. Validating a piping system to ensure compliance and acceptability is always beneficial and money well spent. FINAL remArks Before concluding this series of ar- ticles, there are just a couple of final points to be made. Evolving standards We have previously discussed industry standards and how they are selected and applied on a project [4]. What was not covered is the fact that most proj- ects will actually have a need to com- ply with multiple industry standards. In a large grassroots pharmaceuti- cal project you may need to include industry compliance standards for much of the underground utility pip- ing, ASME B31.1 for boiler external piping (if not included with packaged boilers), ASME B31.3 for chemical and utility piping throughout the facility, and ASME-BPE for any hygienic pip- ing requirements. These and other standards, thanks in large part to the cooperation of the standards developers and ANSI, work hand-in-hand with one another by ref- erencing each other where necessary. These standards committees have enough work to do within their de- fined scope of work without inadver- tently duplicating work done by other standards organizations. An integrated set of American Na- tional Standards is the reason that, when used appropriately, these stan- dards can be used as needed on a proj- ect without fear of conflict between those standards. One thing that should be understood with industry standards is the fact that they will always be in a state of flux; al- ways changing. And this is a good thing. These are changes that reflect updating to a new understanding, expanded clar- ChemiCal engineering www.Che.Com June 2008 53 17_CHE_061508_EP_GSO.indd 53 5/22/08 2:52:56 PM ification on the various sections that make up a standard, staying abreast of technology, and simply building the knowledge base of the standard. For example, two new parts are being added to the seven parts cur- rently existing in ASME-BPE. There will be a Metallic Materials of Con- struction Part (MMOC), and a Certi- fication Part (CR). This is all part of the ever-evolving understanding of the needs of the industrial community and improved clarification, through discussion and debate on content. Conclusion This series of articles attempted to cover a wide range of topics on in- dustrial piping in order to provide a basic broad understanding of some key points, without going into great detail on any specific topic. It is hoped that the readers of this series will dig deeper into this subject matter to dis- cover and learn some of the more fi- nite points of what was discussed in this and previous articles. It is hoped that this series provides enough basic knowledge of piping for you to recog- nize when there is more to a piping issue than what you are being told. n Edited by Gerald Ondrey Acknowledgement My deep appreciation again goes to Earl Lamson, senior project manager with Eli Lilly and Co., for taking the time to review each of these articles. His comments help make the articles better documents than they otherwise would have been. He obliged me by applying the same skill, intelligence and insight he brings to everything he does. His comments kept me concise and on target. Author W. M. (Bill) Huitt has been involved in industrial piping design, engineering and con- struction since 1965. Positions have included design engineer, piping design instructor, proj- ect engineer, project supervi- sor, piping department super- visor, engineering manager and president of W. M. Huitt Co. (P.O. Box 31154, St. Louis, MO 63131-0154. Phone: 314- 966-8919; Email: [email protected]) a piping consulting firm founded in 1987. His experience covers both the engineering and construction fields and crosses industrial lines to include petroleum refining, chemical, petrochemical, pharmaceutical, pulp and paper, nuclear power, and coal gasification. He has written numerous specifications including engineering and con- struction guidelines to ensure that design and construction comply with code requirements, owner expectations and good design practices. Bill is a member of ISPE (International Society of Pharmaceutical Engineers), CSI (Construction Specifications Institute) and ASME (American Society of Mechanical Engineers). He is a con- tributor to ASME-BPE and sits on two corporate specification review boards. Engineering Practice 54 ChemiCal engineering www.Che.Com June 2008 Circle 27 on p. 86 or go to adlinks.che.com/7373-27 References 1. Huitt, W.H., Piping for Process Plants: The Basics, Chem. Eng. February 2007, pp. 42–47. 2. Huitt, W.H., Piping for Process Plants: Flanges, Chem. Eng. March 2007, pp. 56–61. 3. Huitt, W.H., Piping for Process Plants: Design Elements, Chem. Eng. July 2007, pp. 50–57. 4. Huitt, W.H., Piping for Process Plants: Codes and Fabrication, Chem. Eng. October 2007, pp. 68–76. 5. Huitt, W.H., Piping for Process Plants: In- stallation and Cleaning, Chem. Eng. April 2008, pp. 48–58. 17_CHE_061508_EP_GSO.indd 54 5/22/08 2:53:34 PM


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