PWHT of CS and LAS cladded with Austenitic or Super Duplex SS material.

[DK44]

For Vessels designed to ASME Sec VIII Div 1, constructed of following MOC (for Shells and Heads), is it acceptable to perform PWHT when Base metal is required to be PWHT as per Code or as per service requirement in view of PWHT temperature being in the sensitization range of clad materials.
MOC:
a) Base metal CS or LAS + Clad Metal Austenitic SS
b) Base metal CS or LAS + Clad metal Super Duplex SS (Ex:2205)
c) Clad plates may be Roll Bonded or Explosion bonded.
d) Girth flange Gasket faces and bores as well as C/Seams and L/Seams exposed to corrosive fluids are Weld deposited equal to cladding thickness and with rest of the weld to suit base metal.

1. I understand that UCL-34 of Code does not prohibit the PWHT based on base metal as per UCS-56, but cautions on indiscriminate use in the sensitization range. The intention of this caution is not fully known.
2. I observed that, though the PWHT temperature is in the sensitization temperature range, the time of exposure of clad metal during PWHT is very much less than sensitization to occur as per TTS curves of above clad materials.
3. Hence PWHT is not detrimental to Clad metal.
4. However, a corrosion test (on a test piece) to A262-E may be performed on Clad metal after PWHT as safe practice to ensure that the corrosion properties are not effected.

Request guidance on the above form experts.

 

[EdStainless]

Fix your terminology, the DSS and SDSS will not sensitize (form carbides and Cr depleted zones) ti will for intermetallic compounds.
While the end result is similar the mechanism is quite different.
And while you might see the impact in a G48 pitting test there are tests for specific detection of the intermetallics, A923 being the most common.

You are on the right part, change clad metallurgy or make the vessel solid duplex.

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P.E. Metallurgy, Plymouth Tube

 

[weldstan]

Hundreds if not thousands of austenitic stainless steel clad vessels subject to PWHT have been in corrosion services for decades. And with low carbon grades pass G48. Having no idea of your service conditions, maybe one of the austenitic or super austenitic alloys would prove acceptable as cladding.

 

[DK44]

Dear weldstan.
Thank you for your remarks. Solid SDSS (not requiring PWHT) may be appropriate in these circumstances.

 

1. All in all, it appears that PWHT to ASME Sec VIII Div 1 UCS-56 of Vessels of CS/LAS + DSS or SDSS clad, appears to be risky.It is not risky, it is guaranteed to destroy the corrosion resistance (and impact toughness) of DSS and SDSS.

I have seen plenty of clad vessels, and plenty of duplex vessels. I have not seen a vessel clad w/ duplex.

I read of a large P&P digester constructed of carbon steel clad with 2205.



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

 

[weldstan]

DK44, Yes solid SDSS may be applicable but will it be the most cost efficient? Cladding with a better even more expensive alloy may be a more economical choice.

 

[EdStainless]

Often cladding is done with very thin layers of Ni alloys. This is the most efficient method for many applications.
Duplex cladding is common in cases where PWHT can be avoided.

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P.E. Metallurgy, Plymouth Tube

 

[SnTMan]

I read of a large P&P digester constructed of carbon steel clad with 2205.

Duplex cladding is common in cases where PWHT can be avoided.

Agreed, absent PWHT it would appear to present no problems.

Regards,

Mike



The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[DK44]

Thanks for all for providing your professional view points on the subject.