PWHT (SS Cladding 316)

[waliq]

Hello,

I recently reviewed a vessel of material SA 516 70, cladded with SA 240 316. The thickness is 14mm and is in lethal service. The vessel requires PWHT as per UW-2 due to being lethal.
If I refer to table UHA -32-3, it says that the PWHT for P No.8 austenitic stainless steel is neither required nor prohibited
However, I also came across some content that refers to the sensitization issue of stainless steel when subjected to PWHT temperatures. The recommended thing to do in case of SS is solution annealing.

But, in this case, the base metal is CS, which requires PWHT. Moreover, code also does not prohibit 316 grade from being post weld heat treated. But, I am worried about the sensitization issue.

Any recommendations?

 

[DVWE]

Use a dual certified 316/316L material.

The "L" designates Low Carbon and will greatly reduce the risk of sensitization.

The devil is in the details; she also wears prada.

 

316 or 316L? That has a massive impact on the solution.
There is also a big difference between weld cladding and other types such as roll bonding, where the substrate and the cladding are not metallurgically mixed.

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

 

I know this is probably a done deal, but at this thickness I think your designer would do well to consider solid 316 construction.
Fabrication with clad steel is fraught with pitfalls, particularly in the back cladding of weld seams; it is often done badly.
Cost-wise you may come out ahead.
Is this a reactor vessel for polyethylene or similar?

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

 

[EdStainless]

If this is roll or explosive clad then it is likely that they can/would use very low C 316L (like 0.015%C).
This material will survive PWHT with minimal sensitization.
But you have to be very careful with your welds. Even a little C picked up from dilution of the steel base material will make these very susceptible to sensitization.

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P.E. Metallurgy, Plymouth Tube

 

[r6155]

waliq
I could never design like your example. wrong design for lethal service.
I agree with ironic metallurgist: solid 316 construction.

Regards
r6155

 

[waliq]

@iron metallurgist: Yes, I agree it should be a solid 316L construction. And the clad is of 316L not 316. Moreover, it is a gas dehydration inlet separator and the service is lethal and sour.
But, since the vendor is giving guarantee of the vessel, I feel like he has the require expertise to carry out the job without affecting the properties of cladded material.

@edstainless: Can you give some more details on the types of cladding methods? Which method if used is susceptible to sensitization of cladding and which is safe to use. Because the code does not put any restriction, I really need some solid grounds to talk to the vendor

 

[SJones]

https://www.eng-tips.com/search.cfm?q=PWHT+of+stainless+steel+cladding&action=search

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

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

 

[EdStainless]

Monolithic clad is done by either explosive bonding or roll clad.
Weld overlay does not produce the same level of corrosion resistance.
Ask how they are cladding and what the NDT on the bod is.
The NDT is likely UT, but you want to know what critical defect size they are looking for and how much of the surface they are looking at.
The welds of the clad material can be very problematic. They have to done very carefully and they are the weak spot of the structure.

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P.E. Metallurgy, Plymouth Tube

 

[waliq]

As per API 582,clause B.1.10, (edition 2001), I understand that PWHT is not required if the clad/overlay thickness is 5 mm even if the base metal required PWHT. However, if the thickness is less than 5 mm then you need to perform PWHT. Is my understanding of the clause correct since its a kindaa confusing statement written there. I hope I am comprehending that statement correctly.

 

[DVWE]

waliq,

That clause is talking about welding attachments (clips, angles, etc.) directly to the weld overlay.

The devil is in the details; she also wears prada.

 

[r6155]

See API RP 582 (2016)
B.1.11 When PWHT of the base metal is required, PWHT does not have to be performed for welding attachments to
the overlay/clad when the actual overlay/clad thickness is 3/16 in. (4.8 mm) or greater. When the overlay/clad is less
than 3/16 in. (4.8 mm) thick, a specially qualified WPS shall be provided to verify that the attachment weld does not
affect the base material.

NOTE This requirement may be waived for P-No. 1 materials when PWHT is a requirement due to material thickness and not
for process reasons.

Regards
r6155

 

[weldstan]

Hundreds if not thousands of carbon and low alloy vessels have been clad or weld overlayed with 316(L) or other stainless steel alloys and required PWHT due to base material requirements. Some of those vessels did require repairs to cladding due to corrosion and I have been involved in aa number of repairs thereto. I think that the questioner may be over concerned especially when he states that the cladding is 316L. I have seen numerous such vessels in service, as has been described, with long service lives.

One must assure that the Manufacturer is competent and experienced in clad vessel construction and that the Buyer have appropriate specifications, in addition to that of Code, governing manufacture and inspection.