P.W.H.T. requirements:
Welds in carbon steels having a carbon content in excess of 0.32% (ladle analysis) or a carbon equivalent (C + 1 /4 Mn) in excess of 0.65% (ladle analysis) shall be stress relieved as prescribed in the ASME BPV Code, Section VIII. Stress relieving may also be advisable for welds in steel having lower carbon content or carbon equivalent when adverse conditions cool the weld too rapidly.
Welds in all carbon steels shall be stress relieved when the nominal wall thickness exceeds 1 1/4 in.
(a) Stress relieving shall be performed at a temperature of 1,100 F or greater for carbon steels, and 1,200 F or greater for ferritic alloy steels. The exact temperature range shall be stated in the procedure specification.
(b) When stress relieving takes place in a joint between dissimilar metals having different stress relieving requirements, the material requiring the higher stress relieving temperature shall govern.
(c) The parts heated shall be brought slowly to the required temperature and held at that temperature for a period of time proportioned on the basis of at least 1 hr/in. of pipe wall thickness, but in no case less than 1/2 hr, and shall be allowed to cool slowly and uniformly.