Weldoverlay Thickness towards vessel MAWP

[Meck91]

Folks,
- I have a pressure vessel with weld overlay ( overlay thickness is 1/4") & Base material thickness is 1/2".
Since weld overlay will diffuse with the base material, so, can i take advantage of weldoverlay thickness towards increasing vessel MAWP. If this is correct, It means MAWP will be calculated on basis of thickness = [(1/4") for weldoverlay + (1/2" - HAZ - C.A) for base material].
Where: C.A (Corrosion allowance)
HAZ ( Heat affected zone)
- Is this reasonable to take a value of 1/8" for heat affected zone or it varies with material metallurgy.

Any Thoughts?

Meck91

 

[metengr]

Meck91;
This smells like an alteration. Are you attempting to re-rate an existing vessel?

 

[vesselfab]

I have never, nor will i ever, taken credit for a corrosion resistant or heat resistant lining towards the pressure rating of a vessel.

I would think that you would have to have tensile pulls on your overlay procedure. Kinda hard since the overlay is not by itself on the coupon.

 

[jte]

Any reason to not use UCL-23(c)? Not that I've seen it used often, and I wouldn't necesserely go there for new construction, but for a post construction rerate...

jt

 

[SnTMan]

Better check with your AI....

 

[metengr]

Better check with your Jurisdiction! If you intend to take credit for the weld overlay, the strength of the overlay should be equal to or greater than the base metal strength otherwise you will be dealing with a strength reduction factor. Section I recently allowed weld overlay credit toward total thickness, with restrictions.

 

[jte]

Metengr-

So... as I said, what's wrong with UCL-23(c) and the guidance it gives regarding materials of differing strengths?

jt

 

[GRoberts]

If mechanical properties are required for weld overlay, the welding procedure can be qualified as overlay and in addition, qualified as weld buildup (using dissimilar metals), or even buttering, in accordance with Section IX. Of course it is probably too late for that on an existing vessel.

Why are you subtracting the HAZ from the thickness? I'm not a vessel designer, but haven't seen it done before. Is it a code requirement somewhere?

 

[metengr]

jt;
Nothing, I was only reinforcing what you mentioned using Section I for additional precedence. Do I think the Jurisdiction or insurer (if no Jurisdiction involvement) would allow a re-rate using this approach? I give it a 50-50 chance. It all depends on the the presentation of the calculations, vessel condition, in-service environment and how long the vessel has been in service.

 

[gr2vessels]

The AI would not have resons to reject a re-rating of this kind if rigorous calculations are supporting the proposed increase of the MAWP. I do believe the AI will request a controlled hydrotest, prior to final approval. I don't think it will cause a rejection without appropriate reasoning from AI. From the original post, there is nothing to suggest any problems, unless the poster presented only half the story... I found somehow strange to overlay 1/4" stainless on 1/2" carbon steel plate, but it's not impossible, so no further comment.

 

[elphou]

CRA thickness is never included in basic wall thickness requirement calculations

 

[jte]

elphou-

Please consider reading UCL-23(c) and then perhaps revisiting your statement above. Alternatively, please explain how your statement is not in direct contradition to Section VIII Div. 1.

Now that I think about it, Meck91 never stated that the code of construction is VIII-1. We all just sort of assumed that. Meck91 - can you confirm that you're dealing with a VIII-1 vessel?

jt

 

[roca]

jte
I think what elphou is saying that any client / end-user worth his salt will not allow the clad material to be used for strength – he didn’t mention any code requirement.
e.g.
Thickness of the stainless steel cladding or weld overlay shall not be included in the pressure
design, unless specifically approved by the Company in writing

 

[GenB]

Interesting, Have you checked NBIC?
At least you can use the T of the Corrosion allowance in the pressure rating/re-rating, if it was one in the original design.

 

[weldtek]

Those that say never may someday find the need to revise their position.
We recently received some welded, clad heads, incidentally, supplied by our customer, that were evidently, not welded with sufficient attention to detail. When looking at the bevelled end, it was obvious that the overlay portion of the weld extended well into the portion that was designed to be carbon steel. Ooops - insufficient design thickness.
Suffice it to say that this presented an interesting situation.

 

[jte]

roca-

I suspect you are coming at this strictly from a new construction perspective. As I mentioned in my previous post, I wouldn't support using the cladding or overlay material for new construction (so... am I worth my salt?). However, for post construction issues, I'm much more open minded to achieving a safe, workable solution without necesserely being hindered by new construction paradigms. Post construction issues can, as pointed out by weldtek, be much more "interesting," and I don't like to use the word "never" very frequently when it comes to code allowable approaches to vessel design.

jt

 

[roca]

Jte:
Yes I was talking about new build – the initial post does not specifically say that the vessel is being rerated, although you can read between the lines that it probably is.
With respect to re-rate like vesselfab I have never nor would I accept the use of the CRA material for pressure vessel strength unless fully convinced by the re-rate design and all applicable NDE / testing. In the end it will down to the end user / client / insurer / AI to accept as stated above.
There are other ways to overcome the issue like reducing the vessel DP and DT which of course has knock on effects to the allowable operating conditions and then possibly the plant process / final product.