PWHT on Piping

[albaweld]

Under B31:3 2006 edition, if I PWHT a welded joint but the whole pipe is set in an oven for the process, can I weld attachments (shoes) to the pipe afterwards without more PWHT?

 

[rneill]

I guess it depends on the intent behind the PWHT. Was the PWHT based on a code requirement pertaining to thickness of welds or was the PWHT a customer requirement based on service conditions.

If PWHT was based solely on code mandated requirements for weld thickness then you would judge the shoe attachment weld on it's own merits to see if it meet code criteria for PWHT. If the PWHT was based on customer requirements (e.g., sour service) then their specs may require that all welds to the pressure containing envelop receive PWHT as the PWHT may be targeted at reducing the likelihood of in service problems.

 

[albaweld]

Thanks for such a quick reply, this is based on thickness requirements in the code, but I do not see anything attending to attachments after PWHT in B31:3.

 

[rneill]

B31.3 specifies PWHT on a weld by weld basis. There is no requirement for whole spools to receive PWHT, only for individual welds to receive PWHT. Entire spools are often put in an oven as this is easier and more cost effective than doing individual PWHT on all of the welds.

For your attachment of pipe shoes, you would need to determine if B31.3 required these welds to have PWHT. If the code req'd these to have PWHT, then of course you would have to PWHT them. If the code does not require these to have PWHT then you do not have to PWHT. The fact the spool has previously been PWHT in an oven does not affect this decision.

PWHT of welds attaching pipe supporting elements (pipe shoes) is governed by Para 331.1.3(b) of ASME B31.3.

 

[albaweld]

Many thanks for your help...it's much clearer now..