ASME VIII is not a design nor a construction handbook. It's a safety manual. It's primary purpose is not to teach you how to design or construct a pressure vessel. Its primary purpose is to tell you: "If you design and construct a pressure vessel according to the rules contained in the ASME VIII Code, the vessel won't explode".
So, if you carry out the PWHT following the procedure stated on the Code, your vessel won't bust. Don't bother about hydrogen. At the PWHT temperature and soaking time, hydrogen has long been expelled from the weld and HAZ.
Giovanni S. Crisi
Sao Paulo - Brazil
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