Heat treatment (Stress relief) for DSS material - SA 240 UNS S31803

[vinothsvk]

Hi All,

I have confusion on Heat treatment(stress relief) due to straining. My PV-ELITE report shows fiber elongation is 7%. vessel material is SA 240 UNS S31803. DSS material required Heat treatment(stress relief) or not? If YES means, which section i want to consider. Please advise to me.

 

[metengr]

Do you have a reference to ASME Section VIII, Div 1?

 

With all due respect, should you be designing a PV with material you evidently know little about? Don't rely on the software to do all the thinking.
(Duplex SS is never stress relieved.)

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[pradipgoswami]

The only recommended heat treatment for Duplex SS is solution annealing (1080 Deg C and more). There're many issues with soln anneal, distortion, formation of Secondary Austenite(which may harm pitting resistance) and formation of intermetallic(Sigma and Chi) phases if the process is not properly controlled. The last one totally destroys DSS.

Typically ASME code recommends PFHT(Post Forming HT) , if outer fibre elongation is more that 5%.

With 2% extra deformation, I would think asking for solution annealing would be way too much.

31803,Duplex have good % EL, which may accommodate additional 2% strain.

I would think check of hardness in the excess deformed area followed by a volumetric NDE (subject to code/ project requirements)would be the way to go.

Thanks.

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
ca.linkedin.com/pub/pradip-goswami/5/985/299

 

[metengr]

With only 7% fiber elongation, a post forming thermal treatment is unnecessary for this duplex stainless steel based on ASME Section VIII, Div 1 requirements. Typically, for UHA materials, you need upwards of 15% forming strains and that only applies to the traditional austenitic stainless steel and certain nickel base alloys.