P.W.H.T. requirements:
Welds shall be stress relieved when the effective weld throat exceeds 32 mm, unless it can be demonstrated by welding procedure qualification tests, using materials of the
same specification, type, and grade with an effective weld throat that is equal to or greater than the production weld, that stress relieving is not necessary.
Welds in carbon steels having an effective weld throat larger than 32 mm and not larger than 38 mm may be exempted from stress relieving if a minimum preheating temperature of 200°F (93°C) is used.
The welding procedure specification shall specify when stress relieving and/or heat treatment are required due to composition, thickness, welding process, restraint
of the weld joint, or service conditions.
The postweld stress relieving and heat treatment requirements in ASME B31.3 or Section VIII, Division 1 or 2 of the ASME Boiler and Pressure Vessel Code may be used as a guide for minimum stress relieving and heat treating requirements.