PWHT Exemptions on A335 P9 attachment welds 1

[akvtech]

My vendor wants to claim an exemption to PWHT of some attachment clips to A335 P9 (P5C piping). (8-10% Cr) He is saying B31.3, Para 331.1.3 tells you what thicknesses to use with Table 331.1.1 with the end of that Para ending with “…except as follows:” where Para (b) states “…for attachment of external non-pressure parts such as lugs or other pipe supporting elements…heat treatment is required…except as follows: Para (2) “not required for P-No. 3,4,5, or 10A materials when weld throat thickness is ½ in. or less, regardless of base metal thickness…” Since these are lugs and since the pipe material is P-No. 5 it appears that heat treatment is not required per ASME B31.3.
What is confusing the issue -for me- is Table 331.1.1 "Requirements for Heat Treatment" indicates that for P5C (base material in question) ALL thickness require heat Treatment. Does anyone have a definitive explanation for this?

 

[metengr]

For P-No 5C Piping, PWHT is required for any welding. Look at B31.3, 2008 Edition, for material having greater than 3% Cr, ALL applies for welding, meaning any thickness.

 

[akvtech]

Appreciate the feedback, however I am loosing on this one because our engineering dept agrees with the vendor that the exception is allowed...in part based on the attachment being P8 material and welded with 309. I still don't get that warm fuzzy because the code isn't specific enough in the exceptions para (by not spelling out P5 A, B and C) or the table for not putting a (see note #) next to All where it allows for the exemption. To me All means All.

 

[metengr]

The assumption made by using an austenitic filler metal is incorrect. You are welding directly to the P9 base material, regardless of filler metal, you have a locally hardened base metal heat affected zone that needs to be subjected to PWHT. It is as simple as that. The 9%Cr material is air hardening.

 

[jamesl]

I think "All" in Table 331.1.1 refers to weld of base metals. If you weld pipe to pipe or branches, you have to PWHT for P5C material no matter how thin the pipe is. The exceptions in 331.1.3(b) deal with small fillet welds in small size connections and external attachments.
The exception is not in conflict with Table 331.1.1.

I agree with your vendor. Your engineering dept's argument seems to be based on 331.1.3(b)(3), which is also OK.

 

[metengr]

You better be careful here because you have P-No 5A, 5B and 5C. There is no generic P-No 5 base material designation, and to use this as an exemption for PWHT is not correct.

 

[Kiwi2671]

Hello guys,
Does this help ?

1•39. 1-40 B31.3 Interpretations No. I
Interpretation: 1•39
Subject:
Date Issued:
File:
331.3.6. Thickness Effect on Heat Treatment Requirements
April 24, 1981
1517
Question (1): In ANSI/ASME B31.3, is postweld heat treatment required for an NPS 2 or smaller
socket or seal weld if the fitting is A 182•F5, the pipe is A 335•P5, a 350°F preheat is used, and the fillet
weld size is less than 1/2: in.?
Reply (I): No, if the provisions of 331.3.6(b) (2) are met.
Question (2): Same, except the fitting is A 182•F5a?
Reply (2): Postweld heat treatment is required by 331.3.6(b) (2). Exceptions to this requirement are
in 331.1.1 and 331.3.6(b) (3).
Question (3): In ANSI/ASME B31.3, is postweld heat treatment required for an NPS 2 or smaller
socket or seal weld if the fitting is A 182•F5 or A 182•F5a, the pipe is A 335•P5, and the weld is made with
metal that is not air hardening?
Reply (3): No, provided the requirements of 331.3.6(b) (3) are met.

Regards,
Kiwi