Corrosion or produce during the welding?

[cespi82]

Hi everyone!

I hope everybody is doing fine.

This is a Gas Lift Line (dry gas, or at least it is described as dry gas) that was remove from service for installing Wear Pads in some locations. After the welding of one of the weld pad we conducted hydrotest and we found the pipe leaking in one of the wear pads installed. The leak was exactly in the weld seam. We cut the pipe off and opened it and we saw three areas with a significant metal loss.

At a first sight, it could look like localized corrosion straight away but now looking at the failure carefully, the metal loss areas are exactly in weld route. any other area of the pipe is showing signals of corrosion other than normal rust.

The tube thickness is 1/4" and the pad installed is 3/4". could this localized metal loss due to the welding process (may be burn through), instead of corrosion. It seems to me very weird and such casuality that the welder hit exactly the only and isolated localized corrosion areas in at least 2 meters pipe.

your thoughts are much appreciated.

Kind regards,

Cesar

 

[metengr]

It looks as though local melt through occurred versus local corrosion.

 

[cespi82]

Thanks metengr... It is an strange case. If at least the damage areas would have been located in another area rather than perfectly aligned with the welding route, I could fearless say that we are dealing with corrosion... Based on the service (dry gas), do you visualize any failure analysis we could perform to identify if it is actually corrosion or just melt through?

Kind regards,

 

[metengr]

Yes. Destructive metallurgical examination would confirm what we discussed above or other. This would require locating a suspect area and obtaining a cross section to prepare for metallographic examination. If you absolutely need this information, I would suggest engaging a local metallurgical or materials lab and explain to them what exactly you need - metallographic examination to confirm if melt through or corrosion occurred.