Having some trouble with this one. I weld stainless for hi-Vac all the time without much issue. Now, i have Al tubing 1/2" OD x .120" wall thickness that snakes back-n-forth across a large shroud. 2 fittings were snapped off while tightening (form factor is called VCR), and then brought to me with " please help, this thing costs as much as a good used car to replace".
I have attached a pic of the old weld where it broke off, it is almost certainly a socket weld connection, fitting socketed over tube and then the joint lap-welded from outside (vacuum is from the outside, inside is for flowing some kind of cryogenic capable oil) . The fitting I'm trying to weld is "explosion welded" stainless to AL fitting, about $160. a piece.
First time around there was significant porosity in both welds, both times at the point where i stopped. Soapy water test reveled bubbles across a 1/4" circle sized area. I remove that metal with a clean new coarse file and re-weld. One fitting is now fine, passes Helium vacuum leak-check. The other is kicking my ass.
I get a tiny pin-hole , so small that the tubing will hold 50psi pressure under Argon for hours, but Helium check reveals a leak. Soapy water will show the tiniest of bubbles form. Some internet searches on vacuum sites reveals not much useful info
1)Use Helium instead of Argon purge for sections thicker than ¼” = not applicable
2)Clean weld and filler rod with abrasive like Scotch-brite before welding. This is to reduce thickness of oxicde layer (which gets thicker over time). I sanded the old tubing inside and out , but My filler rods are ancient, and while they look immaculate, could have thick oxide layer. The Oxide causes porosity. Will try this next
3)One thing I’m not sure of is which Alloy my filler actually is. All I know is that it’s “Rockmount Nassau Neptune TIG” and that it’s very expensive. I can't get an ER number for it though, not even from Rockmount.
If anyone knows the best filler please chime in, any other info appreciated
4) Welder is Miller Dynasty 350 with AC setting at 75% EN and 25% EP, 120 hz, 100 amps
pictures are of the old factory weld, my tube prep, and the fitting (which appears to have Copper in the join between AL and stainless)
I have attached a pic of the old weld where it broke off, it is almost certainly a socket weld connection, fitting socketed over tube and then the joint lap-welded from outside (vacuum is from the outside, inside is for flowing some kind of cryogenic capable oil) . The fitting I'm trying to weld is "explosion welded" stainless to AL fitting, about $160. a piece.
First time around there was significant porosity in both welds, both times at the point where i stopped. Soapy water test reveled bubbles across a 1/4" circle sized area. I remove that metal with a clean new coarse file and re-weld. One fitting is now fine, passes Helium vacuum leak-check. The other is kicking my ass.
I get a tiny pin-hole , so small that the tubing will hold 50psi pressure under Argon for hours, but Helium check reveals a leak. Soapy water will show the tiniest of bubbles form. Some internet searches on vacuum sites reveals not much useful info
1)Use Helium instead of Argon purge for sections thicker than ¼” = not applicable
2)Clean weld and filler rod with abrasive like Scotch-brite before welding. This is to reduce thickness of oxicde layer (which gets thicker over time). I sanded the old tubing inside and out , but My filler rods are ancient, and while they look immaculate, could have thick oxide layer. The Oxide causes porosity. Will try this next
3)One thing I’m not sure of is which Alloy my filler actually is. All I know is that it’s “Rockmount Nassau Neptune TIG” and that it’s very expensive. I can't get an ER number for it though, not even from Rockmount.
If anyone knows the best filler please chime in, any other info appreciated
4) Welder is Miller Dynasty 350 with AC setting at 75% EN and 25% EP, 120 hz, 100 amps
pictures are of the old factory weld, my tube prep, and the fitting (which appears to have Copper in the join between AL and stainless)