PWHT of CS and SS clad

Date 12-19-2001 08:04

In building a pressure vessel with PWHT requirement, concern was raised because the upper section of the vessel is cladded with 316L. It was suggested not to HT that section because of negative effects of HT on the SS (sensitization) but of course if the vessel is not HT'd than the whole vessel stucture is problematic. The vessel is from 516 Gr. 70 and is intended for Amine Service.
Does anyone have experience with this?
Any case studies?

By G.S.Crisi (****)

Date 12-20-2001 17:58

The need of PWHT or not is ruled by the Code under which the vessel was designed. Was it ASME VIII Section 1 or 2? Was it AD Merkblatter?Was it any other else? If the applicable code demands to HT the vessel, then it must be heat treated. 316 L is a low carbon stainless steel (C = 0,04 percent) which will undergo heat treatment without developing sensitization nor intergranular corrosion.
A vessel like that must have been calculated by a competent engineer or engineering company. It is his (or their) duty to give you a satisfactory advice on the matter.
Giovanni S. Crisi
Sao Paulo - Brazil

By George-kh (**)

Date 12-21-2001 16:37

Dear daon
As professor Giovanni S. Crisi said, 316L is not sensitive to PWHT very much. At 1200F and after 170 minute carbide precipitation occurs. It’s maximum carbide precipitation speed. At 1000F and after 10 hour carbide precipitation occurs.
You can PWHT your vessel at lower temperature for a longer time.

Best Regards