Cold forming heat treatment requirement

[qualitypro]

Our supplier intends to fabricate a P11 dish head with dimensions of 3000 mm ID dia and 120mm thick using crown and petal design. The vessel is in ammonia service.The supplier plans to use four petals that will be manufactured by coldforming without any postforming heat treatment, weld them up and then do PWHT for the vessel as a whole. Is this an acceptable manufacturing design process for this thickness per Asme sec VIII div.2 and is postforming heat treatment required prior to taking up welding?

 

[SJmetallurgist]

If the petals forming process does not subject the material to a %fibre elongation more than that specified in UCS79, then indeed the above proposal should be accepted. However, you must see the user/licensors specs, in case they have specified something more conservative than this approach. Also look out for intermediate Stress relieving that may have to conduct during forming.

 

[Don56]

If this is a hemispherical head the FE=5.6%. If it is any other shaped head it is greater. Stress relieving is required for the fiber elongation per UG-79, UHT-79. PWHT is required per UHT-56.

 

[Don56]

My bad. I missed that this is Div. 2.

 

[qualitypro]

@ SJmellurgist , Don56..thanks for your responses. For this P11 thickness of 120 mm, roughly 5 inch does hotforming have an advantage over coldforming?? Having crown snd petal design is adding more welding, Can welding be minimized by just having one weld seam?

 

[Don56]

Being P11 material I assume this is QT material. If you hot form you will need to re-quench and temper the formed parts. Heating formed parts to the austenizing temperature will likely result in distortion.