Porosity in weld Tig root, 7018 cap

by Jay
(Canada)

Hey,

So i am welding 1 1/4 chrom with tig ER70Sb2L root, and 7018B2l cap and I am having problems with porosity in the weld. The porosity is showing up on the RT in failure levels. Just wondering if you might know where this would be coming from. I have many welders working on this job and the problem is not localized to one welder.

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It is really hard to isolate the problem from my end but here are some ideas...

high moisture in the argon (are you getting whiskers on the tip of the tungsten?)

welder using small cup with too much gas on root.

end of pipes not capped and breeze blowing thru pipe on root causing turbulence and loss of shielding.

too much cleaning of rods. ( a wipe with acetone is usually plenty...some oxidizers could be lost if the copper flashing is sanded off)

not cleaning inside of pipe enough.

using scotchbrite abrasives that leave a residue.

not wiping joint with acetone prior to welding.

thats all I can weigh in without being there...anyone else got anything?

Porosity and lack of fusion in Copper welds

We have a customer that wants us to TIG weld two dissimilar alloys. The first alloy is Bronze 4640 (Nickel, Aluminum, Bronze)and the second alloy is UNS C10100 (Copper). We will also be using the UNS C10100 as filler material. We have done trials with a Miller Maxstar 200SD welder, AC voltage, 100% argon, and 2% thoriated electrodes. We have experienced a large amount of porosity and lack of fusion between the two alloys. Can you offer any suggestions to help? I have heard that DC voltage may work better. How about throwing in some Helium?
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Are you sure you used AC current? a miller maxstar is a DC machine. maybe you meant miller dynasty 200sd.

in any case, dc current will penetrate more. and yes helium would help tremendously. Either uhp pure helium, or a mix of about 80 percent helium, and 20 argon.

also a preheat of around 200-300f would help with better fusion as well as less porosity