ASME B31.1 Postweld Heat Treatment (PWHT)

[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.

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

Thanks.
Regards,
LSZ

 

[weldstan]

Group number and grade are not the same. They are not interchangeable. Grades are chemistry related. Group numbers reflect tensile properties within a grade.
P91 is P No. 15E.

 

[sziva]

Thanks Weldstan. The attachment clearly shows, that P91 is P No. 5B. Even if it would be 15E, as you stated. How does the grade number come into the picture in terms of PWHT?

 

[metengr]

If you are working to an older edition of B31.1, the P-No for Grade 91 material was 5B before it was re-classified as P-No 15E Group 1 material. Group and Grade are not synonymous for steels. For P_No 15E Group 1 material (like Grade 91 steel), specific PWHT would apply as indicated in a later edition of B31.1.

 

[weldstan]

In your question regarding P No. 5A, Grade 21 does not relate to Group No.
Group No. 1 indicates a minimum specified tensile strength of 60ksi.

 

[sziva]

Now it is clear. The P-No and Group definition is described in ASME BPVC Section IX, section QW-420. Thanks a lot!

 

[CarlosVega]

The P number is a clasification for material in BPVC in Section IX. Is a common mistake.