welding after PWHT 1

[lostsailor]

Greetings all,
A vessel is being designed to ASME VIII-1 with a shell made of SA-387 Gr.11 Class 2 (P-4) and clad with SA-240-321 ( P-8). PWHT is required. Would it be permitted to weld a circumferential ring to the clad after PWHT?

After reviewing the requirements of UW-40, Table UCS-56 for P-4 materials, UCS-56, UCS-68, UCS-85, and UCL-84, I was not able to find any specific prohibitions although UCL-84 does indicate that the clad shall be subject to PWHT if required for the base metal.

All comments and thoughts welcome
Regards,
RLS

 

[metengr]

Yes. The code does not prohibit you from welding a ring to the cladding because cladding can be fusion welded to plate. However, in my reading of Table UCS-56, you will need to perform a local PWHT because my expectation is that you would consume the cladding and fuse to the Grade 11 base metal.

 

[lostsailor]

metengr,
Thanks for the reply. I should have mentioned that the clad thickness is 3/16". Do you still think consumption of the cladding and fusion to the base material is an issue? The ring, in all probability, will be GMAW double welded, full pen.
Thanks again,
RLS

 

[metengr]

Yes I do.

 

[arcer]

A couple of thoughts,
Perhaps the thickness of the ring is such that there may be a concern that a great deal of weld is necessary to complete the full pen joint, still, I'm not so sure that you would heat the base to the critical temperature range. We've qualified procedures for dissimilar joints between pwht'd and non pwht'd components with a butter layer 3/16" thick on the pwht'd side. I think the suitability of a given technique depends on several factors one of which would be heat input. You didn't mention the transfer mode for the GMAW process, but if it's shortarc I would think you may be ok. There may be a possibility that the heat from the weld could cause disbonding of the clad, and this should be considered.

 

[Rich2001]

Clad - what process was employed to apply the cladding?

Strip cladding,

http://www.twi.co.uk/j32k/protected/band_3/ksem001.html

Explosive cladding,

http://home.global.co.za/~opticore/

Wallpaper cladding,

http://www.nickelinstitute.org/inde...s=wallpaper&ci_id=6511&Submit.x=15&Submit.y=8

 

[metengr]

arcer;
Good point about buttering. However, I would expect that with a full penetration attachment weld, the cladding would be consumed in making the weld deposit and fusion would occur with the base metal. I agree, that further evaluation would need to be performed OR a temper bead method could be utilized for this method of attachment.

If this were a simple fillet weld, I would have no problem. Since this is a full penetration weld, my expectation is that this is a structural attachment and, as such, would require fusion with the vessel base metal.

 

[PAN]

I agree with metengr. In case of support ring, the fusion to base metal (shell) is necessary. Clad material should not be used for support the load.

 

[GenB]

It was never mentioned what's the ring for, if the ring is not to support loads it may be okay to weld to a 3/16th clad,
I see no problem with that.
GB

 

[adrianviorel]

Dear sailor,
Just some thoughts: PWHT is usually meant to eliminate HAZ and to insure a proper structure of the material. If cladding is made due to contained fluid's characteristics, I thing welding should be avoided after PWHT, simply because pwht links carbures in a solid solution and that gives a greater corrosion resistance. Refer to your client's specifications

 

[VeryPicky]

There is another option to qualify the welding of the ring. I have never done it with the explosion clading but with corrosion resistant weld overlay. The PQR can be qualified as both: corrosion resistant and stregth weld. A coupon has to be prepared as to permit both sets of tests: side bends, PT and chemical tests for corrosion resistant weld overlay and tensile and bend tests to qualify the strength. The issue is a bit coplex but manageable. In general it is better to weld the ring directly to the shell (if load bearing) but due to PWHT the alternative may be feasible.

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