Contamination problem with the Tig

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I did a pressure test on a gas tank tonight and was repairing a few pin holes. all was going well until I got to the last one. I have ground the contamination out twice. I am pulling my hair out Now the pin hole has got a little bigger. If I grind it back out again and setup a back purge will I be able to solve this problem? Should I just pull out the O/A rig and just take care of that way? I would have to buy another regulator setup to back purge which isn't a big deal because I have been needing to do this for a long time. I am rusty as hell on the O/A welding and a little worried about putting to much heat into it and causing warpage. Any help appreciated.Thanks
Reply:You dont need another regulator for a purge line, we just run a t off the existing regulator with an inline valve to control the flow.Have we all gone mad?
Reply:If the tank was still sealed, the air inside will try to escape out the last hole.  Its almost impossible to weld it unless you vent the tank.DavidReal world weldin.  When I grow up I want to be a tig weldor.
Reply:It's a new tank. I will bring ing argaon through the petcock and it will vent out through the gas cap area.
Reply:You didn't mention what material it's made of, thickness, size, shape, or application ( marine?). If it's truly "new" then what caused the pinholes? Welding on any fuel tank is risky stuff,  always use extreme caution and proper safety practices. Adequate venting is a must. You could also be getting contamination from the inside if it's in an area where trash in the tank might settle. Hard to offer up more without more info from your end. The only times I've purged with argon is to prevent an explosion, but it sounds like you're past that point. If it still doesn't go for you, I might be able to help once I know a little more. Good luck...maniakLast edited by maniak; 05-01-2009 at 10:06 AM.Reason: slow brain
Reply:If there really is a bad spot of contamination, would it help to drill out the pinhole, removing all the suspect material, and then weld up the slightly larger hole?Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:Of course,  you can always cheat and use SS filler and kiss the pinhole goodbye.Not that I endorse this sort of thing...
Reply:This is a sporster tank that I cut the bottom off and the tunnel out and replaced with all new plus added a recess area to hide a M/C. I can't seem to upload the pick so here's a link to the underside of my tank. http://www.bikerradiomagazine.com/fo...t=29&start=105I bought a "Y" fitting and attatched another line to purge the tank. Hit it with a sand blaster and It worked like a champ.Supe, it's funny you said to pick up a SS rod . I accidently did pick one up and welded with one for awhile but then switch back.