MIZAT ADVANCED NDTP.O. BOX 31712 AL-KHOBAR 31952 TEL. NO. +966 3 802 9708 FAX NO. +966 3 802 9709 E-mail: [email protected] Website: www.mizatalkhleej.com.sa Document Title: Document No.: Revision No.: Rev. No. 00 POST WELD HEAT TREATMENT PROCEDURE MAN-QP-PWHT-001 Rev. 00 Description of Change Initial Release Rev. Date Prepared by Approved by 24.02.2010 GCC ISG MIZAT AL KHALEEJ HOLDING MIZAT Advanced NDT Page | 1 .2 Qualification The PWHT technician shall be either a science/technical graduate or an electrical apprentice high school graduate with basic electrical knowledge to undertake the heat treatment at the site. “K” type thermocouples attached to the work piece shall be connected to the temperature controller using compensating cables. The unit is fitted with circuit breaker and panel mounted cam-lock output terminals. 4. 3. alloy steel to carbon steel and carbon steel to carbon steel material of piping fabricated in accordance with ASME B31Pressure Piping and ASME BPV Code. Output from the power source is taken through connectors and made available on the output sockets.1 Power source Power source shall be a 3 Phase 65 KVA double wound class “H” insulated dry type power transformer suitable for primary supply of 380/415/440 V and gives 3 Phase output voltage of either 60 V or 80 V AC between phase and neutral.2 Programmable Temperature Controller It is a proportional controller used for controlling the temperature during post weld heat treatment.3. REVISION NO. Power supplied in an ON-OFF mode but the set point is shifted electronically by a measure at how far the process temperature is above or below the set point. The magnitude of control signal is proportional to the deviation between work piece temperature and set point temperature. EQUIPMENT 4. REFERENCES ASME Sec. Programmer is provided with automatic cold junction compensation. 2006 Pipeline Transportation Systems for Liquid Hydrocarbons and Other Liquids ASME B31. 4.DOCUMENT TITLE: POST WELD HEAT TREATMENT PROCEDURE DOCUMENT NO. 2007 Gas Transmission and Distribution Piping Systems 3. SCOPE The procedure covers the general requirements of Post Weld Heat Treatment (PWHT) of weld joints between alloy steel to alloy steel.8. 2008 Process Piping ASME B31.4. It shall be the responsibility of the employed PWHT technician to ensure personnel safety and clearance within the facilities before performing the activity.1 Safety Personnel working in the heat treatment shall be trained in PWHT work. REVISION DATE MAN-QP-PWHT-001 00 Initial Release 1. 2. RESPONSIBILITIES 3. VIII Division I Rules for Construction of Pressure Vessels ASME B31. Thermocouples can be connected to the recorder and each channel will be printed in different colours. Time proportional action is used to control heating/cooling rates and “Dwell” action to maintain soaking temperature. Thermocouple wires shall be attached to the job using a thermocouple attachment unit. Thermocouple plug and sockets shall be used for connecting thermocouple wires to compensating cables and compensating cables to the instruments.75% for 275 – 1260 °C range as per ANSI MC-96-1-1975. 4. 12 Nos. Temperature recorder shall be calibrated every three (3) months and a proper valid sticker shall be displayed. REVISION DATE MAN-QP-PWHT-001 00 Initial Release The six (6) channel controller energizes the contractorised heating circuits of the power source. Thermocouple putty shall be used on hot junction to eliminate the chances of error due to radiant heat. Thermocouple wire shall be covered with high temperature glass fibre material which acts as an electrical and thermal insulation as well as protect the wire from atmospheric contamination. pair) shall be used for measuring temperature of post weld heat treatment. 4. The thermocouple to extension cable connection shall be clear off heating zone.4 Thermocouple Wire Type “K” (Chromel-Alumel) thermocouple wire (22 SWG. Chart speed shall be selected either on 25 mm/hr or 50 mm/hr and can be verified by using a stopwatch. 4.DOCUMENT TITLE: POST WELD HEAT TREATMENT PROCEDURE DOCUMENT NO. joint identification. Proper cleaning of the area where the thermocouple to be attached shall be done (with wire brush or file) to make sure that it is smooth and free from dirt. REVISION NO. Calibration frequency shall be extended up to 12 months with the approval of Client Inspection Department if the documented calibration checks for that particular recorder demonstrate acceptable accuracy for a suitable period. MIZAT AL KHALEEJ HOLDING MIZAT Advanced NDT Page | 2 . heat treatment specification and chart receipt number. Inputs shall be “K” type thermocouples connected using Copper-Constantan compensating cable of 30 mm length via programmable temperature controller. chart speed. temperature-time cycle. Standard limits of error shall be ± 2 °C for 0 – 275 °C and ± 0. etc. Care shall be taken to ensure that the thermocouple wires do not touch. Copper-Constantan compensating cables shall be used to connect thermocouple to instrument terminals. away from the hot junction. potentiometric type strip chart recorder with built in thermocouple reference junction compensation circuit. Chart shall be fully identified with date.5 Thermocouple Welding and Attachment “K” type thermocouple wire (Nickel-Chromium and Nickel-Aluminum pair) shall be fixed to the job using thermocouple attachment unit working on capacitance discharge principle. name of the operator.3 Temperature Recorder Post weld heat treatment shall be progressively recorded using a multipoint. grease. oil. 5 mm outside the insulated area.DOCUMENT TITLE: POST WELD HEAT TREATMENT PROCEDURE DOCUMENT NO. arrangement for power connections. 180 x 145 mm and 1220 x 45 mm. b) The acceptable temperature range of the junction between the compensating cable and the thermocouple lead is from 0 °C to 80 deg. location. REVISION NO. For Type K thermocouples. weather protection for equipment. 4. REVISION DATE MAN-QP-PWHT-001 00 Initial Release Nickel-Chromium and Nickel-Aluminum wires shall be fixed with a distance of separation 4 – 6 mm for accurate measurements. 4. dust and coatings to avoid damage and short-circuiting of accessories/equipment. accessibility. 255 x 205 mm.7 kW. white) to the Nickel-Aluminum conductor (magnetic) of “K” type thermocouple. List of joints to be stress relieved shall be made with weld identification. heat treatment cycle etc. schedule of PWHT etc. Copper-Constantan (Type T) compensating cables may be used with the following conditions.8 Insulation Ceramic fiber mats of thickness 25 mm and size 1800 x 600 mm or 900 x 600 mm with stainless steel wire mesh cover shall be used as thermal insulation. thickness. a) The junction between the Copper-Constantan compensating cable and the type K thermocouple lead shall be a minimum of 0. 5. MIZAT AL KHALEEJ HOLDING MIZAT Advanced NDT Page | 3 .6 Compensating Cables Copper-Constantan compensating cables shall be used to connect “K” type thermocouples to the programmable temperature controllers and temperature recorders. and to be submitted to client inspector at site.2 Surface Condition The welds to be heat treated shall be prepared free of greases. 4. Standard sizes are 205 x 250 mm. 305 x 165 mm. blue) shall be connected to the Nickel-Chromium conductor (non-magnetic) and Constantan lead (negative. Minimum two (2) layers of insulation shall be used. Continuity checks shall be done for each heating elements before connecting it in the circuit. 5.7 Flexible Ceramic Mat Materials Heating elements used for post weld heat treatment shall be flexible ceramic mat heater of 60 V. PRE-START UP CHECK 5. The Copper lead (positive. drawing number. °C. material. 2. lubricants.1 Site Verification MIZAT heat treatment engineer/supervisor shall visit the site 15 days before starting the job to assess the location of joints. Flexible ceramic mat heaters are flexible and can easily be wrapped around pipes. Density of ceramic fiber shall be 120 kg/m3. diameter. Preheating is not required for fixing the thermocouple wire by using this equipment. threaded holes. 5. All the valves on the line shall be kept closed during PWHT to avoid chimney effect. REVISION NO. POST WELD HEAT TREATMENT 6. threads by the application of coating such as deoxyaluminate or any other suitable coating materials. divided by the weld thickness in inches. All flexible ceramic mat heaters shall be checked for continuity before connecting in heating circuit. one (1) hour for P1 material and minimum two (2) hours for P4 material and also per inch of nominal wall thickness of the pipe.5 Procedure to Avoid Chimney Effects The ends of open pipes shall be closed off using ceramic fibre insulation mats in order to eliminate drafts or air circulation that could lower the temperature on the inside of the joint. Welding or heating after the final PWHT is not permitted if the PWHT is required for service. 6.6 Equipment Checking All equipment used for PWHT shall be checked to ensure integrity before starting the job. Calibration of temperature recorder shall be cross-checked using calibrated thermocouple potentiometer.4 Pipes with diameter of 305 mm (12 inches) or less shall have at least one thermocouple. Tarpaulin roof/side cover shall be used in case of heavy wind and rain. Pipes larger than 610 mm diameter shall have at least 4 MIZAT AL KHALEEJ HOLDING MIZAT Advanced NDT Page | 4 . 6. but no case shall be more than 222°C/hr. Post weld heat treatment shall follow all welding and repairs but shall be performed prior to hydrostatic test. At least two (2) equally spaced thermocouples shall be used for circumferential welds on pipe diameters above 305mm through 610 mm (24 inches).2 Soaking period shall be min. 6. REVISION DATE MAN-QP-PWHT-001 00 Initial Release 5. During heating and cooling. Control circuit of power sources shall be checked before connecting the heating load. 5. shall be of standard quality and it shall be selected free of defects. 5. unless the internal surface also insulated.4 Protection from Extreme Weather Proper protection to the job and equipment shall be done in case of extreme weather conditions. all the electrical connections shall be checked before switching on. Thermocouple attachment unit shall be checked for battery condition.3 Surface Protection During heat treatment it shall be necessary to protect from oxidation the mechanical surface line flange faces. Connection materials required for the heat treatment.DOCUMENT TITLE: POST WELD HEAT TREATMENT PROCEDURE DOCUMENT NO.3 Below 315°C. 6. there shall not be a greater variation in temperature than 120°C between any two points in the heating zone.1 The PWHT heating and cooling rates above 316°C shall not exceed 222°C/hr. natural cooling under insulation in still air. 9 Any reduction in post weld heat treatments or alternative temperatures. 9. extending to a minimum distances of 300 mm on either side of the weld. whichever is smaller.2 On a daily basis. job shall be perfectly earthed during PWHT.DOCUMENT TITLE: POST WELD HEAT TREATMENT PROCEDURE DOCUMENT NO. The immediate area of the job shall be roped off. Check all cable connections using proper plugs and sockets.7 A minimum of 2 layers (50 mm) ceramic fibre insulations shall be applied. 6. PRECUATIONS Prior to the start of PWHT.6 Where the butt joint constitutes two (2) separate material thicknesses. Care shall be taken when shifting the equipment from one place to another. shall be transported suitably packed in shock proof containers. DISASSEMBLY Power source shall be electrically isolated before dismantling the secondary power cabling system. the heating elements shall be arranged in two circumferential bands with independent control. 6. REVISION NO. General safety aspects of “Hot Work” shall be strictly followed. listed in the codes shall not be permitted. 8. MT/PT should be applied to those areas when requested by the Client. 7. DOCUMENTATION AND RECORDS 9. MIZAT AL KHALEEJ HOLDING MIZAT Advanced NDT Page | 5 . mentioned start time by the technician prior to start of PWHT. but not less than 25 mm on either side from the edge of the weld. Gaps between heating elements shall not exceed the wall thickness or 50mm. Electronic equipment like recorders. programmers etc. For safety reasons. (see Appendix I THERMOCOUPLE LOCATIONS) 6.5 Flexible mat heaters are arranged about the weld seam to accomplish a heating area extending at least 3 times the thickness of the material being welded. Protect the power cables and thermocouple cable from damage. below normal holding temperatures. After completion of PWHT. a list of joints heat treated in the previous day along with all the relevant details including Time – Temperature graphs (chart) shall be submitted to QC department for approval. 6. 9. which protects it from extreme weather conditions. ceramic fiber insulation shall be removed only after the temperature has cooled below 150 °C.8 In case of premature termination of heat treatment (due to power failure etc.) it shall be recorded and repeated from the point of termination. REVISION DATE MAN-QP-PWHT-001 00 Initial Release thermocouples equally spaced around the circumference. components shall be checked to ensure that all restraints are removed and the component is free to expand and contract. 6.1 Procure the approval of the PWHT cycle and assignment for the weld joint to be heat treated. All identification of joints must be noted in chart and signed. all thermocouples shall be removed and the attachment areas shall be ground smooth in to clean and sound metal. Heat treatment equipment shall be placed at site in covered space. Hardness limits applies to both weld metal and HAZ (heat affected zone). the maximum hardness for P1 materials is 225 BHN for sweet service and 200 BHN for sour service.3 Hardness testing of deposited weld metal should be taken at the center of the weld bead. HARDNESS TESTING 10. Hardness testing of HAZ at a point as near as practicable to the edge of the weld. Before any hardness measurements. If all three (3) retest are below the specified limits.2 The hardness testing shall be performed with portable Telebrineller field hardness tester only. then a minimum of three (3) indentations shall be made near the original high reading.4 The heat treatment cycle chart shall be treated as the proof and record for any heat treatment completion. the surface shall be made smooth by filing. REVISION DATE MAN-QP-PWHT-001 00 Initial Release 9. 9. If any of the retest readings are found to exceed the specified limits. 10. Performance to SAES-W-011 Section 14 and/or NACE RP 0472 shall be made for the purpose of hardness testing. then the joint is acceptable. 10.1 Hardness checking shall be performed to determine the satisfactory performance of Heat treatment process.4 If any readings exceed the specified limits by no more than10 BHN.DOCUMENT TITLE: POST WELD HEAT TREATMENT PROCEDURE DOCUMENT NO. 10.3 Inform the client for any deviation in the heat treatment cycle. then the weld shall be considered unacceptable. 10. REVISION NO. MIZAT AL KHALEEJ HOLDING MIZAT Advanced NDT Page | 6 . REVISION NO. REVISION DATE MAN-QP-PWHT-001 00 Initial Release Appendix I THERMOCOUPLE LOCATIONS Diameters.DOCUMENT TITLE: POST WELD HEAT TREATMENT PROCEDURE DOCUMENT NO. mm (inch) D ≤ 305 mm (12 inches) Thermocouple Locations D > 305 mm (12 inches) D > 610 mm (24 inches) MIZAT AL KHALEEJ HOLDING MIZAT Advanced NDT Page | 7 . REVISION NO. REVISION DATE MAN-QP-PWHT-001 00 Initial Release MAN-QF-PWHT-001 Appendix II PWHT Form MIZAT AL KHALEEJ HOLDING MIZAT Advanced NDT Page | 8 .DOCUMENT TITLE: POST WELD HEAT TREATMENT PROCEDURE DOCUMENT NO.