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.

 

[SJones]

b) 2205 is not super duplex

4. A corrosion test is the way to assess whether unacceptable damage has been incurred. However, A262 might not be the most appropriate test standard.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[EdStainless]

With and austenitic alloy the correct test is A262, and don't allow practice A. There are also electrochemical tests that will detect sensitization. How long it takes a low carbon 300 alloy to sensitize is very dependent on how it was previously annealed. If it was barely annealed then it might re-sensitize in seconds.
For the duplex you need to look to a spec like A923. A duplex will not tolerate any prolonged exposure above 600F without forming detrimental secondary phases.

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P.E. Metallurgy, Plymouth Tube

 

[DK44]

Hope my view points 2 and 3 are in order. Experts' opinion is requested.

 

[SJones]

See point 4 in my reply above.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[EdStainless]

NO, you cannot rely on those curves to describe the behavior of your specific material.
A full PWHT is highly likely to sensitize your stainless.
And testing actual samples is the only way to validate the process.

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P.E. Metallurgy, Plymouth Tube

 

[DK44]

Thank you Edstainless.
Can an IGC test be performed on DSS and SDSS clad materials (before cladding on to CS or LAS Materials) simulating PWHT.

 

[DK44]

In continuation to above...
If so to what standard the IGC test is to be performed.

 

[EdStainless]

In austenitics you use A262 E.
In duplex it would not be IGC that is a concern but the formation of intermetallics.
The duplex alloys will not tolerate heating above 600F.
Buy the time that you reach 1300F the damage is done in a couple of minutes.
Remember that the published curves are for optimally annealed material and often the criteria is 50% loss in impact toughness.
The corrosion resistance starts dropping well before that level of IM is reached.
There is no PWHT for duplex alloys unless you do a full solution anneal and quench.
How would you propose to simulate the extended heating and cooling times if you are not testing actual clad samples?
I suppose that you could clamp a sample to a steel block, but would that be representative enough?

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P.E. Metallurgy, Plymouth Tube

 

[DK44]

Thank you Edstainless.
1. In view of your comments, what is the remedy for a Clad Vessel with Shell and Heads constructed of
CS+UNS S32750(SDSS 2507), with base metal requiring PWHT as per UCS-56 of Code.
2. What tests for clad metal (before cladding or after cladding) are recommended in such case.

 

[r6155]

you can prepare a mock-up and test at your convenience.

Regards
r6155

 

[DK44]

Thank you r6155.
The question is what tests as queried at 2 above.

EdStainless:
1. Doing a solution annealing with quenching (Air cooling? Water cooling is not practical) of completed cladded vessel may be harmful to the vessel geometrical stability.
2. Please provide your comments at my queries 1 & 2 above.

 

[SJones]

@DK44

There are two types of test: Quality control tests and service simulation tests. The former are performed with test environments that, generally, bear no resemblance to the exposure conditions. These tests will serve to ascertain whether there has been any impairment of the material from its (supposedly) optimal supply condition. However, it will not be clear whether any impairment so found will actually result in unsatisfactory service performance. That will be determined with the latter type of testing. A classic example of service environment testing is that specified for H2S containing environments detailed in ISO 15156-3.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[DK44]

Thanks for the responses so far.
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.
2. May I know whether there are installations of Pressure Vessels with above Clad metals duly PWHT as per base metal requirement, working safely. If so what testing could have been done to ensure there is no damage done to clad metal in such PWHT.

 

[r6155]

IMO prepare a test coupon plate and weld equal to WPQT, then PWHT. Conduct tests according ASME IX plus ASTM A262 practice E. Please consult with welding / material engineer.

Regards
r6155

 

[EdStainless]

When clad materials such as 2507 which cannot be PWHT without damage to the corrosion resistance are used it is common to then select backing materials which can be fabricated into vessels without requiring PWHT.
This often requires the use of lower strength backing alloys and results in thicker vessels,
That is the trade off that is required.

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P.E. Metallurgy, Plymouth Tube

 

[DK44]

EdStainless.
Unfortunately, there are no Non-CS and NON-LAS materials that do not require PWHT in view of Thickness involved.
Does it mean we have to use Solid SDSS MOC?

 

[weldstan]

There may be better materials options than 2507. Have you checked your selection with a corrosion metallurgist?

Has the material been selected by the Owner and does he have experience with the alloy in the intended service when subject to PWHT? I would certainly discuss the issues brought up by Ed and Steve with the Owner.

 

[SnTMan]

I have seen plenty of clad vessels, and plenty of duplex vessels. I have not seen a vessel clad w/ duplex. Given the need to PWHT, hard to imagine a worse choice.

Regards,

Mike

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

 

[DK44]

Dear Weldstan and other respected experts.
Thank you for your views on the subject. I was also of the opinion, that CS/LAS + DSS or SDSS clad steel with UCS PWHT, the clad metal will quickly sensitize and if tested to NACE / ASTM G-36 & 48 for SSC / CSC / Pitting Corr test & Crevice corr test, it will fail. It is being debated accordingly for change in metallurgy.
Thanks to all once again.