AISI 316 CLADD OVERLAY REPAIR 3

[GabrieleB]

Our valve supplier raised an NCR to avoid to replace a welding overlay on carbon steel LF2 material made with one pass of AISI 309 and second pass of AISI 316 (3 mm of cladding).
The welding process shows a big porosity (out of acceptance criteria), there are in the cladded surfaces many point of porosity and bubbles where seems to be that welding gases were entrapped (due most probably to an insufficient heat input being in the NCR reported a "cold welding bed phenomena").
The supplier suggests to repair the porosity filling with new materials point by point and re-machine locally.

In my opinion a lot of repairs one very close the the other can cause 2 main risk, sensibilization of the SS (with precipitation of carbides on the grain boundaries due to thermal cycles) and matrix residual-tensioning due to high dilatation coefficient of SS that in frequent thermal cycles can create such problem.

Therefore we suggest to remove the entire clad material and repeat the process, avoiding multiple local repairs, what do you think about?

Kind regards

 

[TugboatEng]

I would agree. To have so many defects means the process was defective. The trouble is that there may be porosity that you can't see and it won't get corrected during repair. A pore and the galvanic cell it produces will quickly lead to a hole.

 

[EdStainless]

It isn't uncommon for repair procedures to have limits on the size and spacing of repairs.
You can't have too many, they can't be over a specific size, and they can't be too close.
What numbers to use depends on the materials.
But a weld overlay with 'lots of pits' is a signal that the process was done wrong.
Make them re-do it all.

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P.E. Metallurgy, consulting work welcomed

 

[Dhurjati Sen]

Which part of the valve is being weld overlayed?
Check if the original specification mentions such a thing.

DHURJATI SEN
Kolkata, India

 

[GabrieleB]

Seat ring and stem sealing area surfaces are subjected to the overlay and to the mentioned issues. The Project specification requires it. See pictures below:

 

[weldstan]

Have them remove the OL and replace based on your photo.

 

[EdStainless]

If they say that they will just remove the 316 and leave the 309 you need to ask questions about how they will know the correct depth and what NDT they intend to use to verify that the 309 is sound.
At this point they are likely to say that they will take it back to the original dimension and start over.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed