PWHT Requirements for P1 Materials

[Sharik]

Here is something which has bothered my mind for a long time:

An ASME Section VIII, Div. 1 pressure vessel with a shell made of SA-516 70 (P1 material), 1" thick does not require PWHT.

An ASME Section I steam drum with a shell made of SA-516 70, 1" thick does require PWHT. Same goes for ASME B31.3 piping made of SA-106 B (P1 material), 0.875" thick, PWHT is required.

Why the differences for identical or similar materials?

 

[metengr]

Sharik
The Section I code rules have changed for P-No 1 base material. In the 2009 Addendum, the requirement for PWHT has been made to align similar to B31.1 with preheat requirement and carbon equivalent calc.

The reason for the original differences had to do with Section I and their approach and tradition. Technically, there should be no differences.

 

[CodeRef]

Sharik,
Good question! In my opinion, from dealing with the many ASME Codes, I believe the basis for PWHT is solely based upon whether the pressure vessel is direct fired or unfired.
As a whole, and generally speaking, ASME Section I is for fired vessels and ASME Section VIII is for unfired vessels. Hence the "U" in the stamping to represent "Unfired"....and the "S" in boilers for "Steam"
perhaps it should have been "F" for "Fired", but the traditions within each of the Codes and Committees are strong.....

As an example, if you were to design to the provisions within ASME Section VIII-1 paragraph UW-2(d), which describes vessels with direct firing, PWHT becomes mandatory (based upon the conditions described)

As for B31.3, I think metengr handled that one....

FAQ731-376