4. 1 - Basics of Condition Based Maintenance

Chapter 1 - Basics of Condition Based Maintenance• Principles of Condition Monitoring Condition monitoring is the science and technology related to assessing machine performance and/or condition (health) based on the following: • • • • Periodic, continuous or semi-continuous data acquisition from samples, sensors, etc. Application of the appropriate tests or related diagnostic techniques Analysis and validation of the data The making of the results into meaningful recommendations for appropriate maintenance action, leading to a reduction in cost and an increase in machine reliability. How to Prevent Problems from Occurring in the First Place with a Proactive Approach Examples of Condition Based Parameters • • • • • • • • Vibration Temperature (e.g., bearings) Thermography Process variables (flows, pressures, PH levels, etc.) Lubricant condition Product quality Motor current Ultrasonic thickness gauging Course Objective This textbook introduces the concepts of condition-based maintenance, with an emphasis on the use of machinery vibration as a tool to determine machine health and identify root cause problems. Subjects discussed include: • • • • • • • • The Basics of Condition-Based Maintenance Fundamentals of Machinery Vibration How to Set Up a Condition Monitoring System Physical Considerations Database Considerations How to Set Up and Use Alarms Vibration Analysis Techniques How to Analyze “Typical” Machinery Problems Virtually any machine health or operability parameter that can be reliably and accurately measured can be used as a condition based maintenance tool. Some provide earlier detection of machinery problems than others do. Often, a change in one parameter may not seem important unless other related parameters also change. Regardless of the parameter selected, condition monitoring programs must adhere to the following standards: • • • • Reliability Accuracy Precision Traceability Condition monitoring programs must utilize meaningful measurement parameters and alarms that are true indicators of machine health. However, there are practical limits on how many measurements can be taken on a machine. The added cost for each measurement may not produce a significant SKF Reliability Systems – Fundamentals of Machine Condition 1-1 Basics of Condition Based Maintenance improvement in the ability to detect a pending machine problem. This textbook will concentrate on vibrationbased condition monitoring as it is one of the most mature of the condition monitoring technologies and is the most widely applied. However, when designing a program, all possible measurements should be considered. For example, oil analysis will typically provide the earliest indication of a developing problem in a sleeve bearing. However, oil analysis cannot determine if unbalance or misalignment is a cause of the premature wear. The combined measurements provide early warning with additional diagnostic abilities. Accurate and extensive data can be collected and analyzed on machines, and accurate diagnoses of problems can be made. However, the most important component of a condition monitoring program is the action directed at the correction of the identified problems. Many times, companies follow the guidelines for proper data collection as outlined above, but their program fails because no actions are taken once alarm limits are exceeded. In a cement plant in North America, only 17% of condition-based related work orders are acted upon. • bearing failure because the root cause has not been identified and corrected Identify a machine problem, write a work order for the repair, production cannot “afford” to shut the machine down, machine runs to failure True condition based maintenance requires much more than data collection. A successful program identifies causes and corrects them. Additionally, the entire plant must participate in the process. Failure to act on identified machinery problems puts the plant in a purely reactive maintenance mode, regardless of the technologies that they have invested in. The Four Basic Steps Detection - Routine vibration data collection, where readings on a machine, machine component, or structure are compared to alarm limits specifically created for the machine. When an alarm is exceeded, basic diagnosis is performed to identify the most likely problem with the machine. A determination is made to either, continue to monitor the machine, reacquire the reading for confirmation, or perform a more complete analysis. Analysis - Mechanical problems or defects generate unique vibration patterns. Vibration analysis utilizes advanced tools and techniques first to confirm the diagnosis of the problem, and second to identify the most likely vibrationbased root cause. Techniques include time waveform analysis, more complete spectrum analysis, phase readings, on-line and off-line tests, and run-up and coast-down test. The goal is to get t o the true root cause, the cause, instead of dealing only with the effect, the current problem that has caused the alarm. Correction / Improvement Repairs - In this text, correction / improvement repairs and correction / improvement maintenance actions are those that can be executed while the machine is operating or when there is an opportune time, such as a planned production outage. Improvement repairs are those that advance the current machine condition, such as oiling, lubrication, bolt tightening, and to the extent of realignment and field balancing. The Ideal Condition Based Model • • • • • Detect a potential problem Verify the problem Identify the problem’s root cause Issue a corrective work order to fix the problem and address the root cause Verify the correction and adjust acceptance limits up or down The ideal condition based maintenance program will follow each of these steps for each machine incident. However, in practice, steps are often skipped. For example, the following two scenarios are often encountered: • Identify a damaged bearing, write a work order, replace the bearing, start the machine, and ultimately find the same 1-2 SKF Reliability Systems - Fundamentals of Machine Condition Basics of Condition Based Maintenance Verification - Once the repairs have been executed, it is important that the vibration analyst be at the machine to ensure that the repair has been made, the root cause has been addressed, and that no new problems were introduced during the repair. Alternatively, mechanics can check their own work with basic overall readings, notifying the analyst if the levels are high. After the machine has reached operating temperature and is operating under normal loads, a new set of baseline data are recorded and, if appropriate, new alarm limits are established. Kiln 5 ID Fan Alignment Case History offset at the coupling in its cold state. A confirmation of the existing cold alignment was done. 081-550 ID Fan as Found. • • 1200 RPM 2600 Hp. DC drive Sleeve oil friction type bearings 081-550 ID Fan Thermal Growth. The alignment was completed by the PPM crew using a laser alignment system. Thermal rise figures were entered into the system, and the laser computer calculated a final alignment position. Further trending showed the misalignment condition to be subsiding as the fan base temperatures increased, a process that took more than 2 weeks. The rest of the story: Condition monitoring showed deterioration of the fan bearings indicating replacement during every annual shutdown. Basic diagnosis of the root cause indicted unbalance as the source of the high loads that were producing premature bearing wear. Each year the symptom, or effect – the worn bearings – were replaced. However, since a comprehensive analysis had never been performed, the true root cause – misalignment – had never been corrected. This plant was performing only the first step of a comprehensive condition based maintenance program – detection – until a comprehensive Condition based and Proactive Maintenance program was established. Another detail is important. Upon startup, the fan vibration was much higher than they had expected. Management and the rest of the maintenance staff questioned the work that was done and were skeptical of the analysis and correction. Two weeks later, after the massive Kiln 5 Fan. Running the fan at only 1100 RPM limited production to only 85% of the design rate. This fan has historically experienced vibration problems usually seen as 1X. Typically, this unit is balanced in a cold running position. It would then show higher 1X when it reached operating temperature of 350 degrees Celsius (662 degrees F). Suspecting that misalignment could be a factor, we decided to complete a thermal growth study on this unit before the March 1998 annual shutdown. An Infra-red distancing theodelite was used to monitor the hot running position. The inboard fan pedestal rose by .069” (1.75 mm), while the outboard grew by .030” (0.76 mm). This required us to raise the motor to achieve a .040” (1.0 mm) SKF Reliability Systems - Fundamentals of Machine Condition 1-3 Basics of Condition Based Maintenance pedestals reached normal operating temperatures, the vibration levels at the fan bearings were the lowest ever recorded. A true success. The downside? With the fan running so smoothly at 1200 RPM, operations now wants to run the fan at higher than design speed to increase production through number 5 kiln! Operating a fan above its design speed involves a degree of risk due to potential blade and rotor stress problems and the possibility that the fan may reach one of its critical speeds. Thorough analysis is required on any machine before increasing its speed. The Condition Based Maintenance Cycle increase measurement frequency adjust alarm levels (improve) Periodic Monitoring repair equipment measurement exceeds no alarm limit? yes schedule repair(s) analyze problem How Deterioration Advances Towards Failure Within a collection of machines, there is a definite pattern of life spans. Most equipment that survives infancy continues to perform with few failures. In time, however, the rates of failures begin to increase and eventually every machine will have failed. Traditional preventive maintenance overhauls would be scheduled where the curve begins to trend upwards. However, this can be costly because it does not address machines that fail prematurely and often requires expensive overhauls on perfectly healthy machines. The goal of a condition based maintenance program is to detect machinery problems early enough to allow time to schedule the most effective repair effort before failure. This is typically accomplished by trending the critical data that measures machinery health over time. The condition based maintenance concept is simple: Using condition based technologies, measure physical parameters like vibration, temperature, pressure, lubricant condition, etc., and determine which combination provides the best indication of machine health. Establish alarm limits that will trigger during routine monitoring. When a machine exceeds a vibration alarm, the problem is diagnosed to determine the severity of the problem, and whether any corrective or remedial action is required. This becomes easier over time, as the characteristics of each machine are learned and the diagnosis becomes more straightforward. Ideally, the alarm limits are set high enough to minimize extraneous alarms, yet conservative enough to not miss a critical excursion in machine condition. Alarm limits are continuously adjusted as more is learned about the machinery in the condition based maintenance program. Periodic or continuous monitoring readings are taken on the machinery. If a measurement exceeds its alarm limit, the system automatically detects the exception and produces plots and reports that help analyze the problem. As the problem is likely detected early in its failure stage, the analyst has time to schedule the most efficient and effective repair prior to component failure. This allows maintenance personnel time to order parts in advance, 1-4 SKF Reliability Systems - Fundamentals of Machine Condition Basics of Condition Based Maintenance schedule manpower, and plan multiple repairs during a scheduled downtime that best fits the plant’s schedule. After the repair is complete, condition based technologies are again used, this time to measure vibration levels on the repaired equipment to create a new baseline reading, quantify repair efforts and ensure quality repair results. Trend Graph This example trend plot shows a material blower’s condition based maintenance history over a 2-1/2 year span. Example Trend Plot. An alert alarm level was established at 0.314 IPS (8 mm/s). When the vibration amplitude first exceeds the alarm, there is a window of approximately three months to schedule a repair before failure based on experience with this machine and its historical performance. Actual repair windows will vary from machine to machine. After the repairs, vibration readings show that the vibration drops to acceptable levels and begins to deteriorate as the machine’s normal wear cycle repeats. From the proactive standpoint, this machine raises some questions. The mean time between repairs (MTBR) is approximately 12 months, which may be excessive. A limestone blower would be prone to blade erosion or corrosion, and the bearings and seals are undoubtedly subjected to contamination. What steps could be taken to try to improve this machine’s performance? Maintenance Philosophies Run-to-failure The premise is simple – run a machine without performing any maintenance on it until it breaks down. There are a number of machines in a plant that should actually be maintained in this fashion. These are machines that typically cost more to maintain than replace and that have little or no impact on production, safety, or the environment. In other words, the risk associated with failure is low. Often, these are referred to as throwaway machines. Preventive It is intuitively obvious that equipment that receives routine and/or necessary maintenance will run longer, better, and more reliably at a SKF Reliability Systems - Fundamentals of Machine Condition 1-5 Basics of Condition Based Maintenance lower cost. Preventive maintenance is also referred to a scheduled, planned, and calendarbased maintenance and its goal is to prevent failures and extend life through cleaning, inspection, routine replacement of lubricants and filters, and scheduled repairs or overhauls based on experience or history. availability, cost, and acceptable equipment risk. Proactive maintenance is planned and directed actions aimed at eliminating or reducing the sources of failures through craftsmanship and the use of the highest quality components and parts available. The implications of this definition are not simple but the premise is. If a problem source can be identified and corrected, or prevented in the first place, the machine, if properly operated, should provide significantly longer service and present fewer maintenance problems. Condition Based The evolution of condition based maintenance is a long one. It is only with the advent of modern measurement devices that it has become a more widely accepted maintenance practice. Condition based maintenance is the application of various technologies to determine the current condition of machinery in order to schedule necessary repairs on a timely basis. It sounds simple, and really, it is. Maintenance is applied only to those machines that require attention and only when needed. Much of the time, condition monitoring is performed while the machinery is running, avoiding downtime. Technologies commonly used in condition based maintenance, or condition monitoring (CM), are: • • • • • • • • • • vibration infrared thermography lube oil analysis temperature measurements ultrasonic noise detection ultrasonic thickness testing motor current analysis product quality/surface finish walk-around inspections other industry or product-specific measurements Condition Monitoring Decisions • • • • What machinery do I monitor? What measurements do I perform on the selected machinery? How often do I perform the selected measurements? What type of condition based equipment do I monitor with? The task of adapting a plant and machinery to a piece of equipment or technology is much more difficult than selecting the proper tools from a well designed and well thought out condition monitoring program. Even an existing program can benefit from a review starting at the top of this list. Fine tuning of the program will increase effectiveness and efficiency and often reduce the cost of operating the program. Selecting Machinery to Monitor • • • • • • Problem machinery Affect on production Probability of failure Personnel safety Manning level Payback Proactive Run-to-failure, preventive, and condition based programs are all reactive. In practice, a good maintenance program blends all of these practices to provide the best mix of machine 1-6 SKF Reliability Systems - Fundamentals of Machine Condition Basics of Condition Based Maintenance Machinery monitoring should be implemented on a priority basis. The first machines to be included in a condition based maintenance program should be those with known problems or a history of problems – the bad actors. Solving problems on high-profile machinery not only provides potentially rapid financial paybacks but also proves the long-term effectiveness and benefits of condition based maintenance. Machinery Classifications Critical Equipment – On-Line Protection Systems • • • • • • • Essential, un-spared machines High maintenance dollars High impact on production output Progress very rapidly toward catastrophic failure Critical failure causes high safety risk Vibration/TSI monitoring is an integral part of operating critical equipment Run up / Run down Critical equipment is typically essential, unspared machinery. Should a failure occur, it might progress very rapidly toward catastrophic failure (e.g., turbines, generators). Machinery in this classification requires the protection offered by On-Line Protection Systems. Cost and Effect of an Unexpected Shutdown or Failure Would loss of this machine create a catastrophic failure, or be financially disruptive? Probability of Failure Equipment operating at design limits and/or handling aggressive material should be monitored more closely than equipment in light, routine service. Personnel Safety Can machinery failure or abnormal operating condition create unsafe conditions for personnel, the environment, or the public? Manning Level Is the equipment in a continuously manned facility or is it operating unattended in a remote location? Equipment operating unattended normally requires automated/continuous condition based maintenance. While protection systems provide an important function for critical rotating machinery, they are generally not designed to provide a condition based maintenance function. They operate based on the current condition of the machine, and many systems do not trend historical data or forecast future problems. On-line Protection Systems perform Vibration, Thermal, and TSI measurements very quickly and, if pre-set alarms levels are exceeded, provide relays to shut down the problem machine before catastrophic failure occurs. Critical machinery operators are typically “tuned into” their equipment and On-Line Protection Systems, and can mentally note minor changes in operating parameters before alarm levels are exceeded. Fully integrated condition monitoring systems provide an interface module that can be added to On-Line Protection Systems to provide trending, forecasting, and analysis features from the measurements they routinely acquire. SKF Reliability Systems - Fundamentals of Machine Condition 1-7 Basics of Condition Based Maintenance Toxic, un-spared, high polling requirement (no shut-down protection required) – Surveillance Systems • Sites with power plants utilize combinations of on-line and surveillance systems Petrochemical • • • On-line monitoring for critical non-spared machinery Walk-around systems for support equipment such as lube oil pumps Surveillance systems utilized in hazardous environments • • • • • • Hazardous/unsafe environments Lack of manpower More frequent monitoring (continuous data collection) Network capabilities Consistent data collection Permanently mounted sensors No automatic shut-down features • Paper machines are examples of machinery requiring automated on-line surveillance systems. Instead of continuous data collection, data are collected every few minutes, compared to alarm settings, and the stored for trending purposes. Automatic data collection is preferred due to potentially hazardous environments and the need for early detection of machinery problems. Balance of Plant - Portable Systems • Require less frequent monitoring (every week, month, quarter) Non-critical machinery Low safety risk Failure has little effect on production The best way to determine monitoring requirements is to assess the requirements of each machine and it’s location, environment, and accessibility. Also, determine whether the machine already has a monitoring system. Redundant data collection for trending and analysis purposes is often a good alternative when the protection system is limited. An assessment will also identify machinery that does not require condition monitoring due to the cost of monitoring versus the cost of the machine running to failure. Often, these machines are only checked at startup to identify assembly or installation problems. The final condition monitoring system in any industry will consist of combinations of on-line protection, on-line surveillance, and walkaround monitoring equipment. Innovations in data collection technology may improve monitoring options on some machinery. Therefore, a reassessment of the system every five years is recommended. • • • Industry Systems Overview Power generation • • • Protection systems on large equipment such as turbines and feed pumps Walk-around systems for balance of plant machinery Use vibration monitoring (TSI) to start up and operate machinery What Measurements Do I Perform? The secret to effective maintenance based on condition is in choosing measurements that effectively identify changes in machinery condition over time. At this stage, careful thought provides a large return. Measurements such as vibration and temperature are the best indicators of rotating machinery condition. Oil condition is often equally useful. Each of these is discussed in detail on later pages. Information available in a machine's control system such as pressure, flow, and speed; or Pulp and paper • • On-line monitoring used in production and quality control systems Walk-around systems for pumps, fans, etc. 1-8 SKF Reliability Systems - Fundamentals of Machine Condition Basics of Condition Based Maintenance from machine gauges can be incorporated into a condition based maintenance program for assessment and historical trending. This additional data helps with machinery condition analysis. Monitoring performance parameters separately from a machine's control system also serves as a backup to the accuracy of the control system and provides additional alarm and report control. The “key” to detecting and isolating specific faults is to perform the appropriate measurement (or measurements) that best detects the expected faults. The technologies employed in condition monitoring must be integrated into the plant environment, as opposed to attempting to adapt a plant and the machines to the tools. The task of adapting a plant and machinery to a piece of equipment or technology is much more difficult than selecting the proper tools from a well designed and well thought out condition monitoring program. Even an existing program can benefit from periodic reviews. Fine-tuning the program will increase effectiveness and efficiency and often reduce the cost of operating the program. More detailed measurement parameters for machinery will be discussed later in this course. Experience provides excellent guidance for selecting measurement intervals. Machinery that has experienced past problems, or for which problems have historically developed quickly, requires shorter measurement intervals. For machinery with a good, reliable operating history, measurement intervals are longer. Continuous Monitoring - Examines measurements taken on a continuous basis. With continuous monitoring, an automated data collection system logs measurements from permanently installed sensors. Continuous monitoring requires a relatively large initial expenditure, but once installed, cost of operation is low. Periodic Monitoring – Is based on measurements taken at regular time intervals. Measurements are usually obtained manually with a portable instrument when the data collection intervals are greater than a week. More frequent periodic data collection is generally handled with a surveillance system. What Type of Monitoring Do I Perform? Lubrication Wear Particle Analysis - Monitoring oil condition warns of an increase in foreign substances, such as water, which can degrade the lubricating properties of the oil and cause bearing failures. Particle size and concentration of ferrous materials are measured. These metallic particles are analyzed to determine which part of the machine is wearing and how fast. Ferrography - The study and analysis of particles contained in the lubricating oil. The composition, size, and relative quantities of particles can be recorded, trended, and analyzed to deduce problems associated with wear and contamination. Oil Degradation - Typically monitors viscosity and acidity. Viscosity is the most important characteristic. How Often Do I Measure? • Machinery that have experienced past problems, or for which problems have historically developed quickly, require shorter measurement intervals. For machinery with a good, reliable operating history, measurement intervals are longer. • Much of the same thought process and criteria used in selecting machinery and measurement types is used in selecting measurement intervals. For example, equipment where damages proceed very rapidly from inception to failure and the consequences are great requires continuous protection with very short time intervals (on the order of 1 reading per second). SKF Reliability Systems - Fundamentals of Machine Condition 1-9 Basics of Condition Based Maintenance reduce the effective viscosity of the lubricant by 50% and will reduce the bearing life by 90%! Temperature In General - Temperature measurement is a useful indicator of mechanical condition or the load applied to a specific component, such as a thrust bearing. As a bearing fails, friction causes its temperature to rise. Installing thermocouple sensors in the housing of a bearing and measuring temperature changes within the bearing or lubricant allows problems to be detected in the early stages and to schedule maintenance before a more serious and expensive failure occurs. For electric motors, a 10 degree Celsius (50 degree Fahrenheit) increase causes a 50% drop in the life of the windings. Infrared - Infrared Thermometry (IR) is being used extensively in a variety of manufacturing facilities and power plants to detect energy losses and monitor temperatures of motors, other equipment, and processes. Simple “point and shoot” models make this technology easy to use. A major advantage of this technology is that measurements can be taken instantly and safely from a distance without having to touch hot, hazardous, or moving objects or to access hard-to-reach surfaces. Viscosity is affected by: • • • • Change in oxidation characteristics Excessive Mechanical Stress Contamination A 20% increase or decrease in oil viscosity indicates a problem that should be investigated! Spectrochemical & Physical Properties Analysis • • • Indicates quality of lubricant. Categorizes and quantifies wear metals and additives Reported in parts per million (ppm) Wear Particle Analysis • • Indicates wear mechanism. Wear particle analysis characterizes particle size and concentration of ferrous materials, and provides visual inspection of particle formation Wear particle concentration characterizes particle size and concentration of wear particles • Particle Count • • • Provides information of particle size vs. concentration Units are counts per 100 ml fluid, categorized by particle size 5–10 u/100 ml; 10–25 u/100 ml; 25–50 u/100 ml; 50–100 u/100 ml; >100 u/100 ml There are three basic methods of using a portable IR thermometer: spot measuring, scanning, and determining temperature differentials. Spot measuring determines the absolute surface temperature of an object, while scanning identifies hot spots as the thermometer is moved along the selected target. The temperature-differential method compares two or more separate spot Water The maximum water allowed is 200 ppm (parts per million). 0.1% (1000 ppm) of water will 1-10 SKF Reliability Systems - Fundamentals of Machine Condition Basics of Condition Based Maintenance measurements, either in different locations or at the same location over time. Infrared thermometers only measure surface temperatures, and they cannot read through panels, covers, or glass. It is also recommended that black paint or masking tape be applied to shiny or polished metal surfaces in order to obtain accurate measurements. Airborne particles such as steam, dust, and smoke may also reduce accuracy. Thermography - Thermography is the use of an infrared imaging and measurement camera to "see" and "measure" thermal energy emitted from an object. Thermal, or infrared energy is light that is not visible because its wavelength is too long to be detected by the human eye; it's the part of the electromagnetic spectrum that we perceive as heat. Unlike visible light, in the infrared world, everything with a temperature above absolute zero emits heat. Even very cold objects, like ice cubes, emit infrared. The higher the object's temperature, the greater the IR radiation emitted. Infrared allows us to see what our eyes cannot. Infrared thermography cameras produce images of invisible infrared or "heat" radiation and provide precise non-contact temperature measurement capabilities. Nearly everything gets hot before it fails, making infrared cameras extremely cost-effective, valuable diagnostic tools in many diverse applications. In addition, as industry strives to improve manufacturing efficiencies, manage energy, improve product quality, and enhance worker safety, new applications for infrared cameras continually emerge. Ultrasonic - Some of the most common plant applications are: leak detection in pressure and vacuum systems (i.e., boilers, heat exchangers, condensers, chillers, distillation columns, vacuum furnaces, specialty gas systems), bearing inspection, steam trap inspection, valve blow-by, pump cavitations, detection of corona in switch gear, compressor valve analysis, integrity of seals and gaskets in tanks, pipe systems and large walk-in boxes. All operating equipment and most leakage problems produce a broad range of sound. The high frequency ultrasonic components of these sounds are extremely short wave in nature, and a short wave signal tends to be fairly directional. It is therefore to isolate these signals from background noises and detect their exact location. In addition, as subtle changes begin to occur in mechanical equipment, the nature of ultrasound allows these potential warning signals to be detected early, before actual failure. Airborne ultrasound instruments, often referred to as "ultrasonic translators", provide information two ways: qualitatively, due to the ability to "hear" ultrasounds through a noise isolating headphone, and quantitatively, via incremental readings on a meter. This is accomplished in most ultrasonic translators by an electronic process called "heterodyning", which accurately converts the ultrasounds sensed by the instrument into the audible range where users can hear and recognize them through headphones. Although the ability to gauge intensity and view sonic patterns is important, it is equally important to be able to "hear" the ultrasounds produced by various equipment. That is precisely what makes these instruments so useful; they allow inspectors to confirm a diagnosis on the spot by being able to discriminate among various equipment sounds. The reason users can accurately pinpoint the location of a particular ultrasonic signal in a machine or from a leak is due to its high frequency short wave. Most of the sounds sensed by humans range between 20 Hz and 20 kHz (20 cycles per second to 20,000 cycles per second). They tend to be relatively gross when compared with the sound waves sensed by ultrasonic translators. Low frequency sounds SKF Reliability Systems - Fundamentals of Machine Condition 1-11 Basics of Condition Based Maintenance in the audible range are approximately 1.9 cm. to 17 meters in length, whereas ultrasounds sensed by ultrasonic translators are only 0.3 1.6 cm long. Since ultrasound wavelengths are magnitudes smaller, the ultrasonic environment is much more conducive to locating and isolating the source of problems in loud plant environments. The advantages of a hand-held vibration meters are low price, convenience and flexibility in use. They have limited analysis capabilities and should be used as a supplement to a program rather than the only tool. Some companies have had great success in early detection by having operators take these simple instruments into the field when performing their routine shift inspections. Hand-Held Meters with Storage Capabilities Vibration Vibration is considered the most valuable tool available for monitoring rotating machinery condition. Vibration technology has a sound technical and historical background and there is extensive data available on its application. There are many vibration tools that can be used to monitor a machine’s condition that range from basic instruments where the readings are manually recorded to full-function instruments that are capable of performing sophisticated analysis in addition to routine data collection. Hand-Held Instruments Data Collectors. Hand-Held Instruments. A hand-held vibration meter is an inexpensive and simple to use instrument that should be a part of any vibration monitoring program. Hand-held meters are carried by machinery maintenance personnel and, when placed in contact with vibrating machinery, provide a display of vibration data. Vibration levels are assessed on the spot for normal or abnormal machinery vibration conditions. Typical hand-held vibration meters are battery powered and use an accelerometer pickup because of its wide range and rugged construction. Vibration meters should be as small and lightweight as possible, and ruggedly packaged for maximum resistance to abuse. Plants are finding it beneficial to have machine or process operators participate in the program. Data collection devices have been developed that allow operators to not only easily record important operating parameters from gauges and other indicators, but to also easily collect overall vibration data. These operating parameters are stored in the same database as the vibration data for easy trending, reporting, and cross-referencing. A typical operatorbased collection device is shown in Figure 6. Hand-held instruments combine compact size with data storage capabilities, providing an inexpensive starting point for a periodic condition based maintenance program. User defined measurements are downloaded to the instrument. An operator or mechanic then walks a route through the plant, collecting vibration, temperature, and process data, along with visual inspections. As each measurement is collected, its results are automatically recorded in the collection instrument. After the route is complete, measurement data is easily uploaded to database analysis 1-12 SKF Reliability Systems - Fundamentals of Machine Condition Basics of Condition Based Maintenance software for reporting, long term trending and analysis. Portable Data Collectors/Analyzers instruments and entered through the data collector's keypad. Visual observations such as leaks and dirty oil are also entered through the keypad. Machinery measurements display on the portable data collector’s display screen and can be analyzed in the field, or when the route is complete, the operator can connect the data collector to a host computer and transfer the measurements and observations to database management software for analysis. On-Line Surveillance Systems Portable Data Collector / Analyzers. Portable Data Collectors / Analyzers perform all the functions necessary for a periodic machinery condition program and are considered the “work horse” of most vibration condition monitoring programs. Based on a machine’s historical performance, industry and insurance recommendations, and manufacturer recommendations, vibration data is acquired on a periodic basis (e.g., weekly, monthly, quarterly) to detect changes in machine health or condition. Some systems, known as on-line surveillance systems, may acquire data every few minutes on critical machinery and/or machines that progress rapidly from the first indications of failure to total failure. A variety of data is acquired, including overall vibration trend information, vibration spectra, time waveform readings; and special bearing failure detection measurements. Portable data collectors / analyzers collect and record machinery vibration data and display high-resolution FFT frequency spectra and time domain waveforms on an LCD screen. Collected vibration measurements can be analyzed on the spot, or downloaded to a host computer's database management program for analysis and long term trending. The data collector is carried by an operator to each measurement point, and vibration measurements are made with a temporarily attached probe or from sensors permanently attached to the machinery. Other measurements such as process pressure, temperature, and flow can be read from LMU On-Line Local Monitoring System. On-Line Local Monitoring Units (LMUs) perform automated, periodic monitoring using sensors permanently attached to the monitored machine. They provide much more frequent monitoring and therefore, earlier detection of problems. They interface with vibration analysis database management software. Measurements are taken automatically and transferred to host computer and database management software for analysis and trending. Because sensors are permanently attached to the machinery, LMU system measurements are taken much more frequently than portable SKF Reliability Systems - Fundamentals of Machine Condition 1-13 Basics of Condition Based Maintenance system measurements (on the order of minutes instead of weeks and months). This allows for earlier detection of machinery problems and additional trending data for scheduling repair efforts. Other advantages of permanently attached sensors are: • • • Consistent data collection Access to unsafe environments Access to hard-to-reach measurement locations • Sensors are permanently attached using eddy current probes, accelerometers, and temperature sensors. Many of these systems interface with vibration analysis database management software. On-Line Monitoring / Protection Systems Simultaneous measurements may be performed automatically and may be displayed and analyzed on the local monitoring equipment, or, with newer equipment, may be transferred to a host computer and database management software for analysis and trending. Because the monitoring equipment is wired permanently to the sensors, measurement time intervals can be short enough to be considered continuous. Chief among the advantages of on-line data acquisition and analysis equipment is its ability to continuously monitor machinery condition. Continuous monitoring provides for early detection of, and protective "action on critical machinery problems." Protective action taken by local protection equipment includes the tripping of alarms that warn machinery maintenance personnel of a problem, or the tripping of relays that automatically shut down machines approaching catastrophic failure. High Speed Data Acquisition On-Line Monitoring / Protection Systems. High Speed Data Acquisition System. On-Line Monitoring Systems provide earliest detection and protective action.Performs automated / simultaneous monitoring, many times up to more than 2000 channels Programmable, high speed data acquisition / monitoring systems provide continuous scanning, on-line machinery monitoring, long term steady state machinery data storage, run up / run down transient data capture, and very 1-14 SKF Reliability Systems - Fundamentals of Machine Condition Basics of Condition Based Maintenance powerful machinery analysis displays for numerous inputs simultaneously. Parallel / simultaneous data collection not only greatly enhances data collection / processing speed, but also automatically produces absolute phase information and provides a means to easily cross reference measurements. With permanently attached dynamic and static sensor input and programmable measurements, alarm set points, and rule base criteria, these systems: • Sense machinery change very early and automatically warn maintenance personnel of machinery problems. Automatically capture run up / run down transient data. Provide real time control room displays for visually monitoring steady state and transient conditions. Provide very powerful analysis displays for analysis of both long term and short-term steady state and transient data. Compare collected data to programmable rule base criteria and automatically indicate rule transgressions. management, and analysis of your machinery data. These database management programs for machinery maintenance store machinery data and make comparisons between current measurements, past measurements, and predefined limits (alarm set points). Measurements transferred to the vibration analysis software are rapidly screened for departures from normal conditions. Overall, FFT, and time domain spectra are produced to help identify, localize, and analyze these vibration changes. Reports are generated showing machines whose vibration and process levels transcend alarm set points. Current data is compared to baseline data for analysis and trended to show a machine's condition changes over a period of time. Trend plots provide early warning of machinery problems, and are used to schedule the best time for repair. Vibration analysis software is also used to configure and control the collection of machinery data, either from a portable data collector (i.e., setting up new routes), or from permanent on-line data acquisition and analysis equipment. • • • • Database Management Software Root Cause Analysis and Correction No vibration job is complete without a viable solution. Finding the source of the vibration is often an easy task compared to correcting the problem. With unbalance or misalignment, the solution is relatively straightforward. However, when dealing with resonance, flow induced vibration, certain electrically induced problems, and unusual bearing problems, the correction to eliminate or control the problem may require extensive effort and inspiration. Control is actually an important concept in vibration. No matter how well balanced, any rotor will still have a small amount of residual unbalance. No shaft alignment will be perfect. The correction is to reduce the unbalance or misalignment forces to the point that the vibration falls below acceptable limits. On the other hand, a pump or piping system vibration Database Management Software. Vibration analysis / database management software is available to aid in the collection, SKF Reliability Systems - Fundamentals of Machine Condition 1-15 Basics of Condition Based Maintenance due to recirculation can be virtually eliminated when the pump’s flow is corrected through process changes, piping design improvements, or impeller modifications. A failing rolling element bearing often produces distinctive vibration patterns. A recommendation to merely replace the bearing has not provided a correction to the underlying source or cause of the original bearing failure. Correction takes vibration from a “find and replace” mode to a true proactive process. A comprehensive proactive vibration program is therefore a combination of the elements described below: • • • • • • Detection of problem machinery or those with levels that may be damage causing Diagnosis of the probable fault or source Analysis of the machine to confirm the diagnosis Determination of corrective measures Generation of corrective and proactive work recommendations Verification of the correction 2. Factors to consider when selecting machinery for condition monitoring are ________________ . a. machinery history b. cost of an unexpected breakdown or failure c. personnel safety d. is the equip. manned or operating unattended? e. all of the above 3. The secret to effective condition monitoring is ______________ . a. selecting a large amount of measurements b. selecting a wide variety of measurements c. taking measurements on a continuous basis d. choosing measurements that most accurately define machinery condition 4. Critical machines prone to rapid deterioration from fault inception to failure require _________________ . a. continuous monitoring b. visual inspection c. periodic monitoring d. a large insurance policy A person that successfully performs these steps has graduated from a data collection technician to a vibration analyst. In addition, a company that follows these steps has moved from purely reactive maintenance into a proactive mode. Review Answer the questions below and review with a group discussion. 1. ______________ is considered the best operating parameter to judge dynamic conditions, such as balance, bearing stability, and stress applied to components. a. temperature b. oil analysis c. vibration d. none of the above 1-16 SKF Reliability Systems - Fundamentals of Machine Condition