Internally clad vessel w/ PWHT 1

[chaulklate]

I have a vertical carbon steel vessel, 7/8" thick. Bottom portion is internally integrally clad with 317 SS. I interpret UCL-34(b) as all clad vessels are to be PWHT unless clad with 405 or 410S. Can anyone offer any rationale as to why I may be able to "not" stress relieve this vessel? My vendor is proposing to only PWHT the carbon portion (for sour service), but I think he should bake the entire thing. Any thoughts?

 

[metengr]

Why are you using UCL-34(b) in Part UCL of ASME Section VIII, Div 1? Is the cladding being used to take credit for the pressure boundary for design purposes or is the cladding simply a corrosion resistant weld overlay? The answer to this question will determine of part UCL applies or you default back to Part UCS.

 

[chaulklate]

The cladding is for corrosion protection only, no credit for pressure boundary. If it matters, the cladding is not weld overlay, it is rolled integral.

 

[metengr]

Ok, use Part UCS for PWHT requirements of the carbon steel base material not Part UCL.

 

[chaulklate]

Let me get this straight: are you saying that part UCL does not apply unless we are taking pressure credit for the cladding??

 

[metengr]

Yes sir.

 

[chaulklate]

How did you make that assessment? UCL-1 states the rules apply to clad vessels, not necessarily clad vessels where the cladding is being considered for pressure. What am I missing??

 

[weldtek]

Going back to your interpretation of UCL34(b), I think you have missed the correct meaning. Per that paragraph type 317L cladding would NOT require PWHT, unless per par (a) the base metal required it.

 

[lostsailor]

chaulklate,
I concur with metengr. The information you are looking for is not explicitly stated but implied in paragraphs UCL-11, 12, 20, and 22.
Regards,
RLS

 

[metengr]

weldtek;
Yes, regarding PWHT. The thickness to determine PWHT time is based on the total thickness of the base metal = metal A + cladding thickness. The PWHT requirement would indeed be dictated by Metal A, and not the corrosion resistant cladding because these metals are nonferrous or austenitic, and typically are exempt from PWHT.

 

[Ketul]

Chaulklate,

Per Table UCS-56 notes (2)(c)(5)-If minimum preheat temperature of 200°F maintained, I think PWHT is not required.

 

[weldtek]

Ketul,
This note applies when thickness > 1.25"

 

[weldtek]

metengr,
Correct me if I'm wrong, but, I don't think the entire UCL section can be disregarded because credit is not being taken for the cladding thickness, in the design of a clad vessel.
For example, paragraph UCL 34(b) indicates that there are situations where certain straight Cr overlays or claddding would require PWHT in any thickness. It has been my understanding that this requirement would apply even to vessels that were designed without taking credit for the overlay or cladding thickness.
It seems that UCL 23 outlines three scenarios for design, one where the lining is not used in design, another where some is used, and lastly, where full credit is taken.

 

[metengr]

weldtek;
It is my opinion that the confusion with this entire post is with the term integral cladding. Integral in Code space refers to being able to take credit for clad properties in addition to the substrate thickness for determining the minimum wall thickness of the vessel. The entire spirit of Part UCL is being able to take credit for cladding thickness. In some respects, the various Parts of Section VIII, Div 1 can overlap as you pointed out with a clause in Part UCL with Part UCS.

Since the original poster answered my question regarding the design use of the term integral clad – simply a corrosion resistant weld barrier (weld overlay or roll clad or whatever) with no credit being given or taken for the pressure boundary thickness, Part UCL really does not apply. In this case, part UCS would be used for design basis and the cladding (integral or not) would be considered as a corrosion resistant weld overlay.

 

[chaulklate]

Thanks everyone, I finally have closure on this, I appreciate everyone's input. I agree with my vendor to not PWHT the clad section.

I was confused by the term "chromium" stainless steel; I considered all stainless to be chromium. Someone pointed me in the direction of Section II, Part A, SA-240, it classifies particular grades of martensitic and ferritic stainless as 'chromium', and 317 is austenitic or 'chromium-nickel'. I am now better informed on stainless material classes.

Side note, I think the wording of UCL-34(b) to be ambiguous and confusing. Thanks again for all your input, I read every paragraph, tip and suggestion.

 

[lostsailor]

chaulklate,
Have you ever heard the alternate meaning of ASME?
Always
Sometimes
Maybe
Except
:0)

Regards,
RLS