PWHT required for SS clad carbon steel plate? 2

[pvrerate]

It has been proposed that 347 SS clad carbon steel plate be used for fabrication of a MEA regenerator vessel which is considered as also being in alkaline service. Hence, a metalurgist has specified that the competed vessel must receive PWHT. Is PWHT required or even desired for this column?

 

[Chumpes]

hello
if not required by construction code, carbon steel vessels with full internal SS cladding (i would prefer SS 316L for aqueous service compared to SS 347 that is more adapted to HT service) will be resistant to stress corrosion cracking (HIC, SSC, MEA-SCC, ...).
PWHT applies to carbon steel welds in contact with the corrosive environment.
regards

 

[pvrerate]

Initially the cladding was specified as 304L SS. With the requirement of PWWHT added, and considering the high temperature for PWHT, apparently this was the reason for specifying 347SS cladding. The puzzling question for me is still why the need for PWHT unless there is a concern about loss or compromise of the cladding. Any other replies would be appreciated.

 

[Dhurjati Sen]

Dear pvrerate,

Is the vessel / column fully cladded? Normally, Amine Regenerator Columns are not fully cladded. The bottom portion that contains lean amine are uncladded.

Regards.



DHURJATI SEN

https://www.nace.org/people/dhurjatisen

 

[moltenmetal]

All hot work associated with clad vessels and their components must be done extremely carefully, to avoid damage to the material resulting from differential thermal expansion between the cladding and the base metal and metallurgical contamination of the cladding by the base material.

If I had to guess, the stabilized grade 347 would provide more resistance to sensitization of the cladding metal due to carbon transfer from the base metal. However, you would still need to be extremely careful in how you did any PWHT to avoid over-stressing the cladding layer.

 

[EdStainless]

The cases that I have seen where people had to SR a clad unit they chose to use a very low C stainless instead of a stabilized grade. If you are under 0.015% C you will see virtually no sensitization.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

In my book, carbon less than 0.020 gives effective immunity to sensitization.
I try to avoid the stabilized grades wherever I can; I almost consider 321/347 to be an evolutionary dead end, although they have their niche applications.

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

 

[weldstan]

We used 304L for MEA regenerators; never 347.

 

[pvrerate]

Thanks so much to all of you for your replies. They have been most helpful. In this case the client has dictated that the entire vessel will be clad/overlaid. Perhaps the more overriding question (the answer to which may have been alluded to) is: Since the entire vessel will be clad/overlaid is PWHT required? Again thanks to all of you for taking the time to reply.

Mr. DHURJATI SEN please see above for the answer to your question.

 

[Chumpes]

if the entire vessel is internally clad with stainless steel, then i anticipate no risk of SCC for this regenerator in amine service, and PWHT would be not required for corrosion reason (PWHT migth still be required by mechanical design)
corrosive amine solution will not contact carbon steel and stainless steel corrodes too slow to produce enough charging with hydrogen, that will not lead to SSC, SCC or HIC.

 

[Dhurjati Sen]

Dear pvrerate,

Agree with Chumpes. No PWHT is required for such a fabulous MEA regenerator. Guess the trays and the tray support rings are all SS.

Regards.

DHURJATI SEN

https://www.nace.org/people/dhurjatisen