INPEC-PWHT-01 Post Weld Heat Treatment Procedure Revision: 1 Page 1 of 10 Date: 20/01/2014 QUALITY CONTROL PROCEDURE Industrial Projects Company (INPEC) POST WELD HEAT TREATMENT PROCEDURE Copy No. Controlled Uncontrolled 0.0 First issue 01/09/2012 Name REV. COMMENTS DATE Sign/date PREPARED BY Table of Content Name Sign/date APPROVED BY Name Sign/date ACCEPTED BY Post Weld Heat Treatment Procedure INPEC-PWHT-01 Revision: 1 Page 2 of 10 Date: 20/01/2014 1) Scope 2) Reference Code 3) General Requirements 4) Temperature Control 5) Thermocouples, Thermal Insulation and Recording Instruments 6) Preparation for Heat Treatment 7) Preheating, Interposes Temp. Monitoring and Out Gassing Heat Treatment 8) Post Weld Heat Treatment PWHT Parameters 9) Interrupted post weld heat treatments 10) Calibration 11) Reporting Post Weld Heat Treatment Procedure INPEC-PWHT-01 Revision: 1 Page 3 of 10 Date: 20/01/2014 1 Scope: 1 This procedure has the scope of giving instructions to the Company's personnel for the performance of Code heat treatment. 2 The local standards, legal regulations and other suitable precautions regarding health work and fire protection shall be observed, also if they are not mentioned herein. 2 Reference Code: - ASME Code Sec. I, in the applicable Edition and Addenda, ASME Code Sec VIII Div. 1, in the applicable Edition and Addenda, ASME Code Sec B 31.1, in the applicable Edition and Addenda, National Board Inspection Code "NBIC" for repairs or alterations of pressure retaining items. INPEC QC Manual. In case of any conflicts between client specification and code requirements, the code requirements shall govern. 3 General Requirements: 1 Preheating, Interpass temperature maintaining and intermediate heat treatment. Preheat for welding or thermal cutting, interpass temperature maintaining and Intermediate heat treatment (out gassing heat treatment,….etc ) may be done using a resistance system, linear burner, oxygen torch burner or other suitable system, which does not harm the base material or any weld metal already applied, and does not introduce into the welding area foreign material which is harmful to the weld. The Preheat temp. and interpass temp. and Intermediate heat treatment detail shall be limited by the code requirements and shall be indicated clearly in the welding procedure specification WPS. Temperature measurements shall be made near the weld (5 cm from the weld centerline max.) by suitable temperature indicating crayons or optical or electrical pyrometers. 2 Post Weld Heat Treatment (PWHT) Post Weld Heat Treatment Procedure INPEC-PWHT-01 Revision: 1 Page 4 of 10 Date: 20/01/2014 3.2.1 Furnace PWHT - Heat Treatment Furnace can be heated by gas fired burners. - Care must be taken to prevent direct impingement of the flame on the part. 3.2.2. Local final PWHT - Local PWHT may be conducted for items that cannot be placed in furnace. This shall be performed by an induction or resistance system, peculiar for- each wall thickness involved. - In case of particular geometrical uniformity, a number of thermocouples greater than indicated in par. 4.3.2 shall be used, in order to check the uniformity of the temperature gradients. 4 Temperature Control: 1 Number and location of thermocouples shall be according with Code requirements, standard practice or client’s requirements. 2 The distribution of thermocouples shall be sketched and attached with the PWHT Report (Exhibit No.38) 3 The following rules shall be applied unless otherwise advised by par. 4.1 4.3.1 Furnace PWHT - heat treatment temperatures shall be controlled with at least one thermocouple in every 3m with minimum of three thermocouples put on the parts to be treated in such a manner to detect the maximum foreseen temperature differences. -.additional two thermocouples shall be added for ASME P-No. 4, 5A and 5B. - additional two thermocouples in the internal surface of the pressure retaining items as applicable when it's thickness exceeds 25mm . 4.3.2 Local PWHT - for weld joints with NPS > 200mm : at least 3 thermocouples put nearest the joint. - for weld joints with NPS < 200mm : at least one thermocouple put nearest the joint. Post Weld Heat Treatment Procedure INPEC-PWHT-01 Page 5 of 10 Date: 20/01/2014 - thermocouples shall be in direct contact with the heat treated material to assure that the thermocouples show the exact temperature of the wall. 4 maximum allowable difference of thermocouple indications shall be 80 ºC during heating,100 ºC during cooling and 40 ºC during holding (soaking). 5 Thermocouples, Thermal Insulation and Recording Instruments: 1 Thermocouples a) all thermocouples shall be checked to ensure chromel-alumel type is used. b) Thermocouples, and thermocouple wires, shall be purchased to standard limits of error of not more than 0.75 percent in the range of 270ºC or 1200 ºC. This requirement shall be so stated in the purchase requisition. Thermocouple wire for capacitor discharge applications shall be covered with high temperature (1200ºC) insulation. c) thermocouple wire less than 1m in length shall not be used, and care shall be taken to ensure that the thermocouple conductor wires do not touch each other, or metallic components. d) thermocouples shall be attached at the extremities of the required heated bandwidth and in the weld metal area. Attachment shall be by the capacitor discharge method or by GTAW, if capacitor discharge method is used related WPS should be followed. e) Indicated temperatures for each thermocouple shall be indicated on a recorded chart with increments of 10 ºC as a number or color. f) Copper constantan compensating cable shall be used for extension of the thermocouple to the recording instrument. The copper lead (+ve) shall be connected to the Chromel conductor of the thermocouple (non-magnetic), and the constantan lead (-ve) shall be connected to the Alumel conductors (magnetic). 2 Thermal Insulation Revision: 1 Post Weld Heat Treatment Procedure INPEC-PWHT-01 Page 6 of 10 Date: 20/01/2014 a)Thermal insulation such as nonflammable paper, nonflammable blankets, mineral wool blocks, or ceramic fiber blankets shall be wrapped around the outside of the heated area. When using the quartz halogen lamp heating method, insulation is not required. Reflective foil may be used to supplement insulation. b)The inside of the area being post weld heat-treated should be sealed to prevent internal air currents from creating excessively high thermal gradients through the thickness of the piping. When possible, the pipe should be blocked on both ends. When it is impossible to block the pipe (e.g., direct connections between heat exchangers), the QCM shall waive this requirement. 3 Recording Instruments a) Multiple-point, temperature-indicating recorders shall be used. Recorders shall be calibrated in accordance with the manufacturer’s standard service instructions at least once every 12 months. b) For those cases in which four or more recording thermocouples are required, the PWHT may be accepted if not more than one recording channel is lost, provided that: - the holding temperature has been achieved and maintained for at least one-half hour before the channel was lost. - the heating equipment and the control system continue to function properly. - the PWHT chart is noted regarding the recording malfunction and proper heating function and signed by the PWHT supervisor, the welding engineer or the client representative. c) Chart speed preferably be (9 inch per hour). 6 Preparation for Heat Treatment: 1 The materials and welds shall be free of machining fluids or debris, inspection residues such as couplants liquid penetrants and magnetic particles examination fluids and particles and other contaminants which, when heated, may be detrimental to the base or weld material. 2 The components, or their parts, shall be supported, in such a way to avoid permanent deformations and maintaining their Revision: 1 Post Weld Heat Treatment Procedure INPEC-PWHT-01 Revision: 1 Page 7 of 10 Date: 20/01/2014 straightness, roundness, concentricity and geometrical shape. 7 Preheating, Interpass Temp. Monitoring and Out Gassing Heat Treatment: 1 Preheating a) Before welding weld or cutting operations the edge preparations shall be preheated according to the prescriptions of par. 3.1. b) The heat of welding may assist in maintaining preheat temperature after the start of welding. c) The extent of application of preheat and the maintaining shall be recorded if required. 2 Interpass temperature monitoring a) In welding P-No.5B materials (e.g. SA 213 T91 tubes), the interpass temperature shall be maintained and monitored below 300 ºC. b) After welding, before of every heat treatment (Whether it will be final or intermediate), the welding shall be cooled in still air down to a temperature of around 80 ºC. 3 Out gassing heat treatment a) After welding of P-No.5B materials (e.g. SA 213 T91 tubes) and prior to final PWHT an out gassing heat treatment shall be performed. b) The weldment shall be held at the minimum specified preheat temp. or higher for at least one hour). c) After out gassing, the weldments shall be cooled to below 100 ºC prior to starting the PWHT cycle. 8 Post Weld Heat Treatment PWHT Parameters: 1 Heating Rate a) The heating rate above 300 ºC shall not exceed 222 ºC /hr divided by the maximum metal thickness in inches, but in no case shall the rate exceed 222 ºC /hr. b) During the heating period, there shall not be a greater variation in temperature throughout the portion of the pressure retaining items being heated than 139 ºC within any 4.6m interval of length. c) Rates of heating and cooling need not be less than 56 ºC /hr. Post Weld Heat Treatment Procedure INPEC-PWHT-01 Revision: 1 Page 8 of 10 Date: 20/01/2014 2 Cooling Rate a) Cooling should be done with the insulation in place, except for the quartz lamp method and for those ferritic stainless steels that require rapid cooling to avoid embitterment. b) The cooling rate above 427 ºC shall not exceed 278 ºC /hr divided by the maximum metal thickness in inches, but in no case shall the rate exceed 278 ºC /hr Cooling c) From 427 ºC cooling may be done in still air for any metal thickness. d) For P-No. 6 materials, cooling may be done in still air from the PWHT temperature. e) For P-No. 7 Group Nos. 1 and 2 materials, the cooling rate above 650ºC shall be a maximum of 56 ºC /hr, after which the cooling rate shall be sufficiently rapid to prevent embrittlement. Shut off heat at 650 ºC and remove insulation, if any, as soon as possible. f) For the quartz lamp method, cooling from the post weld heat treating temperature shall be performed by properly down sloping the radiant heat input in still air so as not to exceed the maximum specified cooling rates. 3 Heat Band Width of Local Treatment a) For local heat treating of circumferential joints of pipe or tubing, the width on each side of the center line of circumferential joints in piping or tubing to be heated to the post weld heat treatment temperature shall be at least three times the greatest width of the finished weld. The portion outside the heating device shall be protected so that the temperature gradient is not harmful. b) Nozzles or other welded attachments shall be heat treated by heating a circumferential band around the entire vessel or header. The heated bank shall extend at least six times the wall thickness beyond the weld that connects the nozzle or other attachment. The portion outside the heating device shall be protected so that the temperature gradient is not harmful. 4 Heat Treatment Temperature and Time Cycle a) The holding temperatures and the related holding time are limited by Code requirements and shall be indicated clearly in the WPS. b) For dissimilar P-numbers, refer to the WPS and/or the applicable code. In general, the heat treatment requirements for the higher P-Number material should be used. Post Weld Heat Treatment Procedure INPEC-PWHT-01 Page 9 of 10 Date: 20/01/2014 c) For ASME P-No.5B (P91) materials, the PWHT holding temp. shall be within the range of 750:770 ºC. Holding time shall be based on 1(hr/in) with a 2hr minimum. 9 Interrupted post weld heat treatments: a) Interrupted post weld heat treatment is defined as decreasing below the minimum specified holding temperature or exceeding the maximum specified cooling rate and may be caused by loss of power, equipment malfunction, or operator error. b) For welds in which the post weld heat treatment temperature has dropped below the minimum holding temperature without exceeding the specified cooling rate, actions should be initiated to restart the heat treatment as soon as possible. c) The weldment shall be reheated at a rate not to exceed that specified in par. 7.1, and the holding temperature shall be reestablished. The additional required holding time shall be calculated by finding time remaining to complete the post weld heat treatment from the first holding period. The weld shall be held at temperature for this time period or for one-half hour, whichever is greater. d) For welds in which the maximum cooling rate was exceeded, the post weld heat treatment shall be redone for both the entire holding period and cool-down rate. e) Visual inspection (PT or MT for ASME P-No. 5A and 5B) of the heated surface shall be conducted after final post weld heat treatment. f) Interrupted post weld heat treatments shall be noted and explained on the charts and records. 10Calibration: 1 Heat Treatments equipments and instruments shall be calibrated in accordance with the manufacturer’s standard service instructions at least once every 12 months. 11Reporting : Revision: 1 Post Weld Heat Treatment Procedure - - INPEC-PWHT-01 Revision: 1 Page 10 of 10 Date: 20/01/2014 The PWHT Report (Exhibit No. 38) shall be used to document the PWHT parameters and the thermocouples location during the heating cycle. A unique No. for each recorded chart shall be established to provide a relevant connection to the reporting form. The chart and the related reporting form shall be reviewed and signed by the assigned QCM. All PWHT charts shall be made available for the AI.
