PWHT repair of SS overlay on P5A material?

[metlsmith]

40 year old vessel is 6.5" thick SA387-D (2.25Cr) weld overlayed with 0.125" minimum 309Cb (first pass) + 347 SS. SS tray support ring is welded to the overlay (not to the base metal). Attachment fillet welds have toe cracks and transverse cracks in weld metal. If we decide to remove the existing ring, grind out any cracks in overlay, build overlay back up, and install a new ring:

1. Is PWHT of the shell required BY CODE even if there is sufficient thickness of sound overlay remaining to prevent forming a hard HAZ in the base metal?

2. If PWHT of shell is not required BY CODE, then do I have to qualify a special weld procedure (temper bead? overlay?) or can I simply use a P8 to P8 weld procedure to make the repair?

In either case, what are the applicable NBIC/ASME "chapters and verses" for this situation?

 

[metengr]

metlsmith;
The NBIC would be applicable if this is an in-service pressure retaining item, and it is located in the US or a location that regulates pressure vessels. Regarding weld repair, you can use Alternative Welding Method 5 in the NBIC to restore the original weld overlay w/o PWHT provided you follow the requirements in Method 5 (2004 Edition, 2006 Addendum of the NBIC).

Once you have qualified the temper bead method for the stainless overlay, you can weld directly to this overlay using a P8 to P8 WPS. Keep in mind you need to have a valid Certificate of Authorization from the National Board to weld, and you will need to have some form of NDT to verify defect removal and post weld repair NDT.

 

[stanweld]

Just a guess, but the vessel most likely was designed and manufactured per ASME VIII, Div. 2. I believe that you will have to have a P.E. review and seal the repair procedure if under NBIC. PWHT will not be required if your repair does not penetrate into the base material. Typically we have made these repairs to assure that at least 3/32" of clad remained after grinding. The actual thickness of overlay at the support ring locations is generally greater than 1/4".

 

[metengr]

As a guess, similar to Stanweld, I would suspect the cracks would penetrate deep enough that you would need to restore the cladding using Method 5.

 

[metlsmith]

Thanks to both of you for the quick responses.

We have made a mock-up plate and machined the overlay so that it tapers from about 3/16" thick at one end of the plate down to nothing at the other end of the plate. We then ran beads of SS down the length of the plate using varying size electrodes, heat input, etc. to determine how thin the remaining overlay can be without creating a hard HAZ in the base metal. We're in the process of doing the metallography/microhardness testing to define the limits for each weld procedure to avoid PWHT or temper beading.

My question is more about specifically where in NBIC or ASME Code does it say this can be done, or does this fall into the "generally accepted good engineering practice" category?

Thanks again for the expert advice.

 

[stanweld]

ASME VIII, Div. 2 defines PWHT requirements. NBIC provides Alternate methods to PWHT.

Cracks in these locations have been known to extend into the base metal. I hope, for your sake, they do not.

 

[metengr]

By the nature of your question it would seem to me that you do not fully understand requirments for in-service pressure vessel weld repairs. ASME Boiler and Pressure Vessel Code is for new vessel construction, and does not apply for in-service repairs.

Are you contemplating doing these repairs yourself? If so, please review my first post to your thread.