Effect of PWHT on CS

[jamiegla1]

Does anyone know of the benefit of post weld heat treating a carbon steel vessel (the entire vessel) with regards to sulfide corrosion? If treated, will the vessel be more resistant? Would cladding with inconel 625 be better?
Thanks in advance,
Jamie

 

[metengr]

jamieg1;
What are your process conditions regarding exposure to sulfide? I can tell you that the two main benefits derived from PWHT of carbon steel are the reduction of residual stresses from welding, and the reduction of hardness in the base metal heat affected zone (HAZ).

If the corrosion process involves stress corrosion cracking or stress-assissted corrosion, PWHT would help to reduce suscetibility. Otherwise, PWHT would have no impact on general corrosion resistance of the vessel.

 

[jamiegla1]

The sulfide pitting is from Ammonium Bisulfide (aka hydrosulfide to some) and H2S. Conditions in the vessel are around 256F and <50psig. i believe its more a matter of the salt not staying in solution and erroding the metal.

 

[SJones]

Look at Clause 5.1.1.2 of API RP 571

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/