cut and etch problem

by Tom
(USA)

I have cut and etch both Mig and Tig welds. Mig welds, using 70S-6 wire with a robot, etching with 10% Nitric, the welds jump out at you. Tig welds, using 70S-2 wire and the frame has been painted,I can not get the welds to etch. I have even sand blasted the paint away thinking that the paint contaminated the weld area. After polish and letting cool to normal temp. they still will not etch. Had some luck with Coke overnight. Also tried 4% and 2% since the 10% turned the welds black. My thought why this is happening is that the TIG is to hot which is crystallizing the weld and not letting the etch work. I have seen welds break in the center of the weld and right outside of the HAZ. Your thoughts. Call if you like at xxxxxxxxxx to discuss.

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I will call...sounds like a case I consulted on a few years ago.

jody