You should refer to ASME Section 2 part D %E2%80“ Nonmandatory Appendix %E2%80%9CA%E2%80%9D paragraph A-350. Good Luck Scott

ASME code calls for PWHT for materials of a certain thickness%E2%80™ or alloyed material that would be susceptible to forming a martensitic micro structure (high hardness microstructure). 316L is an austenitic stainless steel that doesn't go through phase changes when welded or heated (stays austenitic because of the high austenizing elements - Nickel); meaning it will not form a hard micro structure in the HAZ even if quenched. Austenitic stainless steel can be aged hardened or strain aged hardened by cold working or if at high temperatures for a long period. Generally if you want to weld on material that has been aged hardened you want to solution anneal the material prior because the stresses in the material are high enough that welding is almost impossible %E2%80“ cracking will occur. As I mentioned in a previous response, there is a debate on PWHT austenitic SS for service environment to reduce the chances of SCC. PWHT would be done in the range were the SS material will become sensitized (you will loose corrosion resistance) but stresses would be reduced. To stay with the ASME code, you may want to look at ASME Section 2 part D %E2%80“ Nonmandatory Appendix %E2%80%9CA%E2%80%9D paragraph A-350. Are you determining if you are required to heat treat a component (vessel heads) or to heat treat welds?? Good luck Scott

U R right Scott UW-2 is for C.S. & low alloy steels.But my problem is%60nt Only PWHT. Stress relive for Head%60s also is a problem.