Stress relief of 316 or 2205 in amine service ? 3

[Wilkie]

Is PWHT necessary (or recommended) when using equipment & piping fabricated from 316SS or alloy 2205 in amine service (CO2 absorption)? There is a possibility that a small amount of chlorides may accumulate in the system which has me leaning toward 2205, but I can't seem to find an answer to the question of whether the equipment should be stress relieved after fabrication (either alloy).

The relatively high temperatures used to anneal stainless alloys raises the issue of vessel flange distortion and similar problems. Obviously I don't want to stress relieve the equipment if it's not warranted.

Does anyone have suggestions or a recommended industry practice for this application ?

Thanks,
Steve

 

[SJones]

PWHT is neither necessary nor recommended - the selected alloys are not susceptible to amine related damage mechanisms as indicated by API RP 571.

A properly operated sweetening process should not warrant you having to go higher than 316L. See if these two articles are of any use to you:

http://www.gastreating.com/pdf/Hc Processing Apr-May 1993.pdf

Steve Jones
Materials & Corrosion Engineer

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

 

[EdStainless]

If you are really worried about the chlorides then go with 2205.
Don't heat treat. You risk doing more damage than you will prevent.

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Plymouth Tube

 

[Wilkie]

Gents,

Thank you for the prompt replies. I had a copy of the Hydrocarbon Processing article you mentioned, and it is an example of why I turned to this forum for help. The article provides good information on corrosion mechanisms and the benefits of stress relief, but doesn't specifically indicate that stress relief is not required for stainless steels.
Several other references I had were also a little vague on the subject, and is why I came to this forum to get an opinion from the experts in the field.

Thanks again for the help,
Steve

 

[kevlar49]

They are right, 316 and 2205 are not susceptible to amine SCC. In addition, these stainless steels have very low tendency to chloride SCC in amine because the alkaline nature of the amine solution is not favorable for cracking. It has been said that pH should be lower than 6 to have significant risk of cracking. Some studies have demonstrated 300-series stainless are resistant to Cl SCC in amine in as high as 1000 ppmw chlorides.

Hope this helps.