Marangoni effect issues on orbital welding

[XL83NL]

We have an issue with one of our orbital welding items, for which Im looking for out of the box ideas..
The issue deals with the Marangoni effect; the tube we weld is A269-TP316, and the other item - also SS316 - was found to have a too high (i.e. out of spec) sulphur content. The weld pool was so asymmetrical, that there's no complete side wall fusion on the OD, possibly also on the ID. so the weld failed on VT.

It was then found by OES that sulphur levels were as high as 0.043%, much higher than 3.1 MTR. Obviously, the item is out of spec. Due to various reasons were still investigating if we can still use these items. Hand welding is not possible, due to very small dimensions and accessibility. Weve tried a multi run orbital weld, with no effect.

Are there any other ideas, for orbital welding, that could provide a remedy? Perhaps a slightly modified weld bevel (Y-shape?), or some flux or addition? I know Swagelok uses orbital weld flux, but have no idea of its purpose

 

[EdStainless]

I have seen welds in sanitary systems where they are tying tube (0.005-0.017 S) to material with <0.002 S.
The higher S material is more fluid when molten, so they do use different bevel angles, and they offset the weld to the low S side.
Send a sample to an outside lab and get additional S testing.
I don't know how someone welded tube with that high of S.

 

[XL83NL]

We’ve done the S testing per OES, so we know exactly what the chemical composition is, and hence what the difference is.
The tube is low on S and has a regular spec. We’re welding it to a flow cell machines from A240 plate.
We’re also familiar with applying an offset, but in our case that didn’t work (sufficiently).
A Y/bevel rather than I-bevel, could that be an option? Changing shielding and/or backing has to some mixture that has more penetration?

 

[kingnero]

Can you weld manually with filler?

 

[XL83NL]

The weld is difficult to access by hand, and we don't have skilled hand TIG-ers, only orbital (ISO 4063-142)

 

[kingnero]

You can use consumable inserts with orbital equipment...

 

[XL83NL]

Thanks, we’ll take that into consideration

 

[kingnero]

Did you make any progress here, were you able to solve the problem? Or did you have to scrap the aberrant tubes?

 

[XL83NL]

Did you make any progress here, were you able to solve the problem? Or did you have to scrap the aberrant tubes?

Thanks for the reminder. Yes, we made some progress, by finding out that the tube and the body were not machined from 1 part. Instead, the body was machines from plate, and the tubes where pushed in. The main body/part was OES examined, so its likely the tubes are a different material. What the exact chemical analysis is, and how that affects welding, isn't known yet.
We're still investigating the case and Ill post any relevant update as soon as I have it.