ASME B 31.3 piping

[klln]

hello all,

please help me.I am going to complete one A106 pipe weld of 30 inch dia and 60mm thick.I have one more to complete.Can i make a delayed stress relieve on the first completed weld?the client insisting on doing the pwht as soon as the weld completed.i have only one heat treatment machine at site.what is the difference between stress realieve and pwht?should it be carried out soon after the weld completed?

thanks,
klln

 

[unclesyd]

Unless it had been changed in later editions of the Codes or the NBIC there was no time limits on the start of PWHT or Stress Relief for A106.

Just make sure it gets completed before the pipe is commissioned or as in your case as soon as possible to satisfy the client.

 

[muthupal]

PWHT is primarily to relieve the residual stresses developed during welding. In PWHT, the weld and adjacent region are heated to below transformation range, holding for predetermined period and then cooled, where as in stress relief (SR) the entire structure / assembly is heated in a furnace to below tranformation range, holding for predetermined period and then cooled. Selection of PWHT or SR depends on configuration of structure, extent of welding in the structure, facility available etc.,

ASME B31.3-2002, table 331.1.1 does not specify any time period for PWHT after welding for P1 material (A106), so PWHT can be carried out any time before pressure test. However the table calls for heatreatment of P62 (Zr alloy material)materials within 14days after welding.

PS: Please ensure that there is no specific requirement in your client specification on PWHT about timing of PWHT.

Muthu

 

[rkg]

The primary reason for your client asking for an immediate PWHT is perhaps the thickness involved. The code and metallurgical considerations do not necessiate an immediate PWHT. However, it may be a good idea to post-heat the weldment subsequent to welding for a period of one hour, at a temperature that is slightly more than the Preheat maintenance temperature, say 150 deg. C. This should also get easily accepted by your client. This suggestion is made to satisfy your client rather than metallurgical considerations since material is only CS.