Clad material Repairs

Question

Clad material Repairs

roca (Mechanical)

(OP)

19 May 03 21:42

We have a vessel designed and fabricated in accordance with ASME VIII Div.1
The vessel material is A516-Gr.70 + SS 316L cladding and the vessel has been PWHT.
It has now been found at site that there are some problems with the cladding before the vessel has even been in service.
The cladding in certain areas will need to be stripped to the base material and weld overlay applied in its place.
We are intending using minimum amperage parameters for the WPS with increased travel speed to minimise heat input to <0.77 - 0.81kj/mm.
My question is will PWHT nedd to be re-applied?

aybee (Mechanical) · Answer 1 · 2003-05-19 23:12:23

I would say yes with a local band of PWHT. If you set up the heating coils on the outside you can do the pre-heat and PWHT with the same set up. I have done this on a 3" thick 21/4cr lined vessel which had lining disbonding with cracking at the tray support rings. we set up insulation on outside to retain the heatinside to protect the welder with a small "window' in the inside insulation which allowed the welder to work without being cooked. We had 330C preheat which we reduced to around 280C. we had to repeat this one 3 levels of trays. the lining was 309 with 347 on top 3/8" thick
the problem with PWHT austenitics is that it can sensitise the lining and make it more prone to sigma phase embrittlement

sayee1 (Materials) · Answer 2 · 2003-05-20 05:28:32

I would question the need to do PWHT. See clause UCL 34 a para 2 and UCS 56 for P1 materials Note c(4). As per my interpretation which is subject to discussion, PWHT can be exempted for overlay provided preheat for a minimum of 200 degrees C is maintained during application of the first layer when thk of the pressure part exceeds 1 1/4 ". What is the thickness of the part to be overlaid?

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Sayee Prasad R
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stanweld (Materials) · Answer 3 · 2003-05-20 13:06:23

You did not state what the problems were. I assume it was clad disbonding of roll bonded or explosion bonded cladding.
ASME Section VIII, Div. 1 does not require PWHT for the weld overlay if a 200 F preheat is maintained for the first overlay pass when the carbon steel base material exceeds 1 1/4 inches. Your welding procedure must be qualified w/o PWHT, of course.
I would not recommend that you PWHT after O.L. It will reduce the corrosion resistance of the 316 O.L.

dig1 (Civil/Environmental) · Answer 4 · 2003-05-23 08:11:36

roca,

You write the vessel has not been put into service, but has the AI signed off on it yet; that is has it been U stamped.

If that is the case, you need to refer to NBIC and work with your AI. In any case, your AI needs to be involved.

Very often PWHT is not required for overlay as you are describing. Situations I'm refering to are overlaying carbon steel vessels with SS (typically 309 or 312) to provide a new corrosion resistant layer after the orignal CA has been spent.

Question, what carbon content did you limit the 316L to. We often specify 0.020 max or 0.015 max to reduce sensitization based on our metalurgist's recommendation.

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Clad material Repairs