[Laszlo Sziva]

Hello All,

I have some issues with the ASME B31.1 PWHT requirements.

Issue:
Table 132 contains the PWHT requirements based on material P-Nos (position) and Gr. Nos (grade).
The P-No is clearly defined for each material in Mandatory Appendix A. For instance A335 P22 material’s P-No. is 5A.

The Gr. No. interpretation is unclear to me.
Staying with the same example. Appendix A – A335 pipe material for P-No 5A contains two grades starting with 2 : P21 and P22. I would assume, that the two different grades are interpreted as two grade numbers.

Here comes the twist. Back to table 132.
Table 132, P-No. 5A only mentions the requirement for Gr.No. 1. How should one understand this? Does Gr.No 1 refer to the first grade, P21?

What makes the picture more blurred is the example of material A335 P91. This material has a P-No. 5B and the only one grade of material A335 starting with 9 is P91 only. If I check again Table 132 for P-No. 5B, Gr. Nos. 1,2 are mentioned.

I attached two screenshots with the relevant sections.

If someone familiar with ASME B31.1, please help me.

Thanks.
Regards,
LSZ

Attachments:

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Discussion

[Laszlo Sziva]

Finally I have found out, that the P-No and Group No definition is given in ASME BPVC Section IX, section QW-420.
Table QW/QB-422 lists all base materials with P-No and Group No. This helps to understand PWHT requirements.

QW-420 BASE METAL GROUPINGS
[i]P‐Numbers are assigned to base metals for the purpose
of reducing the number of welding and brazing procedure
qualifications required.
P‐Numbers are alphanumeric designations: accordingly,
each P‐Number shall be considered a separate P‐Number
(e.g., base metals assigned P‐No. 5A are considered a separate
P‐Number from those assigned P‐No. 5B or P‐No. 5C).
In addition, ferrous base metals have been assigned
Group Numbers creating subsets of P‐Numbers that are
used when WPSs are required to be qualified by impact
testing by other Sections or Codes. These assignments
are based essentially on comparable base metal characteristics,
such as composition, weldability, brazeability, and
mechanical properties, where this can logically be done.
These assignments do not imply that base metals may
be indiscriminately substituted for a base metal that was
used in the qualification test without consideration of
compatibility from the standpoint of metallurgical properties,
postweld heat treatment, design, mechanical properties,
and service requirements.[/i]

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