Code PWHT Requirements
Code PWHT Requirements
(OP)
Probably a silly question but: why if a pressure vessel is built to ASME Section VIII, Div. 1, out of SA-516 70, 25.4 mm thick, MAWP 3500 kPag @ 300C, PWHT would not be required (by Code).
If a steam drum is built to ASME Section I, out of SA-516 70, 25.4 mm thick, MAWP 3500 kPag @ 300C, PWHT is required (by Code).
Why is there a difference in PWHT requirements for the same material and same design conditions?
If a steam drum is built to ASME Section I, out of SA-516 70, 25.4 mm thick, MAWP 3500 kPag @ 300C, PWHT is required (by Code).
Why is there a difference in PWHT requirements for the same material and same design conditions?





RE: Code PWHT Requirements
Very good question. The simple answer is that the Section I SC is the keeper of their own domain (Code book section) and considering that Section I has been around before Section VIII, past precedence is the rule regarding PWHT. There is a move to relax the PWHT exemption requirments, and it will happen and be more aligned with Section VIII.
RE: Code PWHT Requirements
What is the technical basis of PWHT for CS materials? is it based entirely on residual stress due to weld shrinkage? Would there be any ASME VIII basis for a 2" thick shell of SA516-Grade 70 without PWHT is the design stresses were keep very low?
Joe Tank
RE: Code PWHT Requirements
vessels over 1.25 thick (unless preheated per code rules up to 1.5") shall be PWHT if P1
any vessel over 1.5" WILL be PWHT if P1
RE: Code PWHT Requirements
RE: Code PWHT Requirements
A long time ago the what we now call PWHT was called stress relief.
RE: Code PWHT Requirements
A long time ago for P1 materials, we now call PWHT was called stress relieving. There was never any mention of any other reasons for the thermal treatment.
Having said that there was a memo from Dupont written in the late 40's where one of their metallurgist was recommending that piping for certain waste streams and process piping be PWHT to help prevent cracking in highly stressed areas. This was still just a stress relief but carried an additional benefit of preventing stress cracking.
RE: Code PWHT Requirements
RE: Code PWHT Requirements
If I remember well also somewhere in the ASME VIII Div.1 is the PWHT required <8for any thickness,even lower than 1.1/2") if the vessel/equipment is STEAM GENERATOR...
may be UG......but I am not sure. please check.....
I would check by myself and then I will let you know.
Let me know if found.
rgrds
GENGI
RE: Code PWHT Requirements