No, your interpretation is not correct. If you review 331.1.3(b), it states..... heat treatment shall be as required for the ferritic materials....

For Any Grade 91 material, a post weld heat treatment should be performed in accordance with Code requirements to assure adequate ductility and creep rupture strength.

Mr.metengr,

Thank you for your comment.

as your comment,Welding condition of P91 to 50Cr-50Ni support with filler metal, ERNiCr-3, does not meet the requirement of  para.331.1.3(b), but conforms to the para.331.1.3(c)
 
If PWHT is required accoring to the para.331.1.3(b)as you commented, it seemed to me that there be not necessarily to specify the para. 331.1.3(c)in this Stanard.

For PWHT for any weld joint in fully compliance with the requirement of the para.331.1(c)would not be exempted unless the requirements of the para.331.1.3(b)would be met.
 
Your further explanation would be helpful.

Wooill Ihm

ASME B31.3 allows that fillets welds for non pressure parts to pressure parts in P5 are not heattreated if non air hardening filler is used. So your intepretation is correct.
However I would not use this rule for welds to P91. Advice to do PWHT at 750 Deg. C

I have to respectively disagree with ijzer. My interpretation of paragraph 331.2.3 (b) in B31.3-2004 does not reference use of austenitic (aka non-hardening) filler materials to avoid PWHT of a ferritic base material.

The words used in this paragraph are ferritic and austenitic materials and components. PWHT is dictated by ferritic material. In most DMW applications, it is implied that an austenitic filler metal would be used to join a ferritic material to an austenitic stainless steel.

Regarding welding pressure parts to non-pressure parts, it has been stated to follow the requirements of the pressure boundary base metal regarding preheat and PWHT requirements. In this case, the T91 material requirements must be followed for welding.

I have mis-typing in my previous query.

Please read as follows:

para.331.1.3(b) to 331.1.3(b)(2) and
331.1.3(c) to 331.1.3(b)(3)

CODE interpretation is different between two gentlemen.

Any other opinion who has.

Thanks

woo-ill ihm

My interpretation is based on par. 331.1.3 (b) 1,2 and 3 .
These paragraphs clearly specify the exceptions on PWHT.

These paragraphs are in the section titled "Governing Thickness", which relates to what thickness governs PWHT. If you go back to the beginning of this section, called "Heat Treatment", Table 331.1.1 specifies the heat treatment requirements for applicable materials. For P5B material (T91), ALL thicknesses require PWHT and refer to Note 5. This is clear and concise regardless of governing thickness.

Note 5 relates to Appendix F which deals with Precautionary
Considerations.

So once again, my interpretation is that NO exemption can be applies to P5B base material.

Would be a nice topic for a code interpretation.