API 661 Airfin - PWHT needed for new header nozzle?

[DivideByZero]

Greetings fellow engineers,
I am supporting a project in which we will be adding a nozzle to an existing airfin heat exchanger designed to API 661.

API 661, para 9.2.1 states "All carbon steel..headers shall be subjected to post weld heat treatment".

I would like to understand the intent of the PWHT requirement, and to understand if once the new nozzles are added to the header box if the header box must be PWHT'd.

I suspect that the concern is high stress concentrations near the corners of the square header box geometry, and perhaps concern with brittle fracture (although the CET should be +10degF for this service). My feeling is that PWHT is not required for adding new nozzles, because residual stresses added during the welding process is minimal.

Please note that the airfin in question is constructed from carbon steel (SA516-70 - norm) and that the service does not require PWHT. Also, the maximum thickness of plate is 1-1/4", but the thickness of the area that the nozzles will be added is 3/4".

Any insight you can provide will be helpful. Thanks!

x/0

 

[gr2vessels]

You are right, there is no code requirement for PWHT of the added nozzle.
Cheers,
gr2vessels