Inconel Clad- Butt welds with Inconel filler

Date 05-01-2007 10:09 Edited 05-01-2007 10:17

Good Morning from the Mid East.

Just curious as to the technical, metallurgical explanation for welding an Inconel claded pipe to pipe butt weld (or for that matter any weld) with inconel root and then continuing with inconel right to the cap. It would be cheaper to fill it out with CS after a couple of inconel passes- especially on something big like 38" dia x 3" WT.I would like to know the possible consequences of a partial inconel weld followed by CS. I recon it has something to do with the dilution at the interface and that the carbides formed there might be detrimental to the mechanical properties. however if it is purely a sensitization issue we you have grainboundry carbides and a depleted passive range adjacent to the grainboundries therefore reducing corrosion resistance, then what is the issue?

Regards
Hanre

By MBSims

Date 05-02-2007 03:48

Shop welds or field welds? On shop welds, you should be able to bevel the ends down to the CS/Inconel clad interface, fitup with zero root opening, weld out the CS, then backgouge the Inconel clad from the inside back to the CS and weld the inside with Inconel. If accessible in the field, the same procedure could be used.

If you try to weld over Inconel with carbon steel weld, it will crack. Try it on a test coupon and see what you think after that.

By Eutectic (**)

Date 05-02-2007 04:25

MBSims,

Thanks for the reply, It is just a general hypothetical question applicable to any clad weld, I have heard that it would crack, but why?
your proposal sounds good, however if the backgoouging is carbon arc gouging this will almost certainly lead to some sort of carbon contamination and subsequent sensitization.
so to get back to the question, why does it crack?

By js55

Date 05-02-2007 15:00

It seems to me that you won't end up with a carbon steel weld metal if you run CS on top of nickel. You'll end up with a low alloy weld metal full of Cr, and Ni, and perhaps Mo, or Nb, diluted from the nickel, and depending upon the alloy of choice. This low alloy may form martensite (actually probably will) and require PWHT, whereas the nickel weld metal would not. This would tend to contribute to the possbility of cracking.

By jon20013 (*****)

Date 05-02-2007 15:19

I agree js55. Lot's and lots of cracking at that.