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ASME B31.3-2016 <br /> temperatures may be required by the WPS or by the procedures to avoid contamination by hydrogen- <br /> engineering design. producing sources. The surface of the base metal pre- <br /> 330.1.2 Unlisted Materials. Preheat requirements pared for welding shall be free of contaminants. <br /> for an unlisted material shall be specified in the WPS. (d) After cooling and before welding is resumed, <br /> visual examination of the weld shall be performed to <br /> 330.1.3 Preheat Temperature Verification assure that no cracks have formed. <br /> (a) Preheat temperature shall be checked by use of (e) Required preheat shall be applied before welding <br /> temperature indicating crayons,thermocouple pyrome- is resumed. <br /> ters,or other suitable means to ensure that the tempera- <br /> ture specified in the WPS is obtained prior to and 331 HEAT TREATMENT <br /> maintained during welding. <br /> (b) Thermocouples may be temporarily attached 331.1 General <br /> directly to pressure-containing parts using the low 331.1.1 Postweld Heat Treatment Requirements <br /> energy capacitor discharge method of welding in accor- (a) PWHT shall be in accordance with the material <br /> dance with para. 328.7. groupings (P-Nos. and Group Nos.) and ranges in <br /> 330.1.4 Preheat Zone. The preheat zone shall be Table 331.1.1 except as provided in Table 331.1.2 and <br /> at or above the specified minimum temperature in all Table 331.1.3. The P-Numbers and Group Numbers are <br /> directions from the point of welding for a distance of the defined in ASME BP V Code, Section IX, <br /> larger of 75 mm (3 in.) or 1.5 times the greater nominal Table QW/QB-422. (Note that the P-Nos. are also listed <br /> thickness. in Appendix A.) <br /> The base metal temperature for tack welds shall be (b) The PWHT to be used after production welding <br /> at or above the specified minimum temperature for a shall be specified in the WPS and shall be used in qualify- <br /> distance not less than 25 mm (1 in.) in all directions ing the welding procedure. <br /> from the point of welding. (c) The engineering design shall specify the examina- <br /> tion and/or other production quality control (not less <br /> 330.2 Specific Requirements than the requirements of this Code) to ensure that the <br /> 330.2.1 Different P-No. Materials. When welding final welds are of adequate quality. <br /> two different P-No. materials, the preheat temperature 331.1.2 Other Heat Treatments <br /> shall be the higher temperature for the material being (a) Heat treatment for bending and forming shall be <br /> welded as shown in Table 330.1.1. in accordance with para. 332.4. <br /> 330.2.2 Interruption of Welding. After welding (b) See Table 302.3.5 for special heat treatment require- <br /> ments for longitudinal or spiral (helical seam)welds in <br /> commences,the minimum preheat temperature shall be Elevated Temperature Fluid Service. <br /> maintained until any required PWHT is performed on <br /> P-Nos. 3,4, 5A, 513, 6, and 15E, except when all of the 331.1.3 Definition of Thicknesses Governing PWHT <br /> following conditions are satisfied: (a) The term control thickness as used in Table 331.1.1 <br /> (a) A minimum of at least 10 mm(3/8 in.)thickness of and Table 331.1.3 is the lesser of <br /> weld is deposited or 25%of the welding groove is filled, (1) the thickness of the weld <br /> whichever is less (the weld shall be sufficiently sup- (2) the thickness of the materials being joined at <br /> ported to prevent overstressing the weld if the weldment the weld or the thickness of the pressure-containing <br /> is to be moved or otherwise loaded).Caution is advised material if the weld is attaching a nonpressure- <br /> that the surface condition prior to cooling should be containing material to a pressure-containing material. <br /> smooth and free of sharp discontinuities. (b) Thickness of the weld, which is a factor in <br /> (b) For P-Nos. 3, 4, and 5A materials, the weld is determining the control thickness,is defined as follows: <br /> allowed to cool slowly to room temperature. (1) groove welds (girth and longitudinal) — the <br /> (c) For P-Nos. 513, 6, and 15E materials, the weld is thicker of the two abutting ends after weld preparation, <br /> subjected to an adequate intermediate heat treatment including I.D. machining <br /> with a controlled rate of cooling. The preheat tempera- (2) fillet welds — the throat thickness of the weld <br /> ture may be reduced to 95°C (200°F) (minimum) for (3) partial penetration welds — the depth of the <br /> the purpose of root examination without performing an weld groove <br /> intermediate heat treatment. Intermediate heat treat- (4) material repair welds—the depth of the cavity <br /> ment for P-No.5B or P-No.15E materials may be omitted to be repaired <br /> when using low-hydrogen electrodes and filler metals (5) branch welds — the dimension existing in the <br /> classified by the filler metal specification with an plane intersecting the longitudinal axes, calculated as <br /> optional supplemental diffusible-hydrogen designator indicated for each detail using the thickness through <br /> of H4 or lower and suitably controlled by maintenance the weld for the details shown in Fig. 328.5.41) and <br />