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plunger
10-13-2011, 02:29 PM
I bought a cheap scratch arc tig welder and am finding it quite a steep learning curve.As a plumber almost all my welding and soldering is soft solder and lp gas at low temp.I very seldom have to silver solder and am bad at it.
I was asked if I could repair a copper geyser (water heater for those who talk funny) and it is a 450 liter tank and is leaking around the cold inlet (pinhole) Normally I would use my oxy acetalene and copper rod.As I am not good at this brazing technique I thought I would try and see if I could tig weld copper. I used a 2 inch pipe as a test piece and welded a 3/4 copper pipe into it like a tee.
I was absolutly suprized that it worked. I thought I would blow holes through the pipe like what happens when I try to weld stainless.
I am now confused as to know what technique I should use. Is this an alternative to oxy welding or should I stay away from it?I am kind of suspicious as to how well it worked and dont want to make a fool of myself on site

macona
10-13-2011, 02:50 PM
You need a pretty decent sized machine to tig copper. Takes a lot of heat to get things going. If you have a smaller tig machine watch your duty cycle. You can easily overheat the transformer or rectifier.

Otherwise tigging copper is no problem.

Rustybolt
10-13-2011, 04:00 PM
Just make sure the fumes blow away from your face. Have a fan at you back. The fumes are toxic and can make you sick.

boslab
10-13-2011, 05:13 PM
i can tell you from expirience, tiging copper is an art, its weld pool is like piss, use helium not argon or it will melt away, big amps sorry, beyond most sets!
mark

Dr. Rob
10-13-2011, 05:30 PM
Yes, it welds quite nicely.

Generally though, out there on a job site behind enemy lines is usually not a good time to start experimenting with new techniques.... especially fixing pinholes in an old? thin? corroded? water tank.

Oxyace and copper-phospherous rod sounds like a surer thing. Or if you like, a patch and soft solder. Whatever you do best.

.

lazlo
10-13-2011, 08:10 PM
Copper does TIG very nicely. Thermal control is a major PITA -- remember when you transitioned from TIG-welding steel to aluminum? Copper's a lot worse :)

Seriously, takes a lot of foot to get the puddle to form, and then it's a race to get across the piece, and then it's art to let off the pedal without blowing a hole.

By the way, I never knew that the copper fumes were toxic?? I was just using solid-core electrical wire for filler?

macona
10-13-2011, 08:27 PM
I think he is referring to the fumes from brazing.

There should be no fumes from tig welding copper. At worst you would get some copper oxide powder if there is not enough gas coverage.

What might be a good solution is to use a silicon bronze filler rod and tig braze the tank. I dont know if the bronze is food grade, cant imagine it wouldnt be.

vpt
10-13-2011, 08:34 PM
I was curious and gave it a try not to long ago and found that yes you can tig copper. I didn't think it was to hard at all. Pure argon, 2% thoriated and welded a 1" joint all the way around without a problem. Beat on it with a hammer and stuff and it seems to hold up good.

wierdscience
10-13-2011, 08:54 PM
You can cheat a little and preheat with a torch,same thing on Aluminum.

But for pinholes in Copper,Silver solder is the best ticket.