Troubleshooting TIG weld (porosity, unstable arc, etc.)

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I'm doing some rather basic TIG welding on some mild steel making frames for furniture pieces.  I'm having a problem that, so far, I've been unable to solve.  Setup is:Mild steelArgon at ~12 cfm (I've tried about 7-20 cfm)1/16" tungsten ground to a pointRegular 8 cup or 12 cup with gas lensHF startPedalChinese machine (DC only)Symptoms are: loud arc (somewhat crackly, sometimes like the noise of jet engine exhaust), unstable green arc, porosity in the welds (external, it makes bubbles while I'm welding, especially on outside corners), green sparks flying off the piece.The symptoms are variable.  Welding autogenously on a flat piece of steel, the symptoms are minimized.  Welding an inside corner produces a louder arc and more sparks.  Welding an outside corner is almost impossible, producing a very loud, unstable arc and creating bubbles that come to the surface in the pool.  Also, sometimes the arc starts clean and then weld starts throwing off sparks and then the process degrades further.  Other times, the arc starts crackly, but then cleans up and goes OK for a while.I'm sure that my technique is VERY imperfect, but these problems seem to be building in intensity and are appearing under the same conditions that, in the past, have produced decent welds.I've tried getting a new, larger cup with gas lens, I've cleaned and switched tungstens, I've changed grounding options, and I've played with gas flow rates.Please let me know if you have any ideas on the root cause or if you have any questions on the setup that I can answer.Thanks,-Rob
Reply:Pics....zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Direct Current Electrode Negative polarity?  I.E. the TIG torch is hooked to the negative terminal and the work clamp is connected to the positive terminal.confirm that you can feel gas flowing from the torch cup.  Some of what you describe sounds like you're welding without shielding gas.  Sparks flying, crackling noises, and a "jet engine" noise are symptoms of contaminated or no shielding gas.  You might have a leak at a fitting that is drawing atmosphere in to the shielding gas flow too.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:Zap, please see the picture at the bottom of this post.  This represents the worst of the problem, particularly the bubbling on outside corner points.DAB, I can confirm the DCEN setup.  Gas does flow from the torch, at least when I initially hit the pedal.  Given that the rig welds decently on flat pieces, I also believe that at least some gas flows out of the torch during welding.  The tungsten doesn't seem to be getting destroyed like when I've REALLY had no gas running before, but it does end up discolored (dark grey) after almost every pass.  Do you suggest putting soapy water on different parts of the gun to see if there's a leak?  The idea of sucking atmosphere into the flow seems like something I should check out.  I was wondering if the intermittent jet engine noise and the sparks indicate the presence of oxygen in the environment.  I was also thinking about swapping out my gas bottle (tiny bottle, I think 40 cubic feet).After reading some older posts, it seems that welding through the light mill scale (wire brushed prior to welding) might be part of the problem.  However, I've done this operation with better results in the past, so I'm having trouble understanding what else might have changed.Thanks very much for the help.-Rob
Reply:if gas flow is not an issue i would say that you are picking up contamination from the backside of the weld.
Reply:Originally Posted by TheRob44I'm doing some rather basic TIG welding on some mild steel making frames for furniture pieces.  I'm having a problem that, so far, I've been unable to solve.  Setup is:Mild steelArgon at ~12 cfm (I've tried about 7-20 cfm)1/16" tungsten ground to a pointRegular 8 cup or 12 cup with gas lensHF startPedalChinese machine (DC only)Symptoms are: loud arc (somewhat crackly, sometimes like the noise of jet engine exhaust), unstable green arc, porosity in the welds (external, it makes bubbles while I'm welding, especially on outside corners), green sparks flying off the piece.The symptoms are variable.  Welding autogenously on a flat piece of steel, the symptoms are minimized.  Welding an inside corner produces a louder arc and more sparks.  Welding an outside corner is almost impossible, producing a very loud, unstable arc and creating bubbles that come to the surface in the pool.  Also, sometimes the arc starts clean and then weld starts throwing off sparks and then the process degrades further.  Other times, the arc starts crackly, but then cleans up and goes OK for a while.I'm sure that my technique is VERY imperfect, but these problems seem to be building in intensity and are appearing under the same conditions that, in the past, have produced decent welds.I've tried getting a new, larger cup with gas lens, I've cleaned and switched tungstens, I've changed grounding options, and I've played with gas flow rates.Please let me know if you have any ideas on the root cause or if you have any questions on the setup that I can answer.Thanks,-Rob
Reply:It looks like it was doing OK until you tried to stop on that corner. Probably a torch angle issue. You could try starting at each corner and welding to the middle. Make sure you're not trying to weld dirty or oily steel. Could just be crummy metal.
Reply:Is that tubing?Very hard to tell.If so you need a blowhole somewhere where it won't be seen......zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Thanks for all of the input.  That is tube, 1" square tube with 0.065" wall.  The suggestion about picking up impurities from the back side of the weld makes a lot of sense, as the outside corners that are causing such an issue would be the joints with the largest gap, and might be prone to pulling in material from the inside of the tube.  What is the general solution for that problem?  Are you supposed to clean the inside of the pipe before doing welding of this sort?Filler is 1/16" ER70S6.  I'm also going to get a torch flow meter so I can get an idea if there's some gas flow problem going on.
Reply:Tube = Blowhole.Gasses build up and need a escape route and that's what is happening. ...zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Yeah,That's why you see inconspicuous, yet purposeful holes in bicycle frame tubing and other stuff with closed ends. It's not just to allow moisture to escape. Originally Posted by zapsterTube = Blowhole.Gasses build up and need a escape route and that's what is happening....zap!
Reply:Ok, to follow up on this question, the problem has been fixed.  After getting a new ground, inspecting the torch for o-ring and collet problems, changing tungstens, changing base metal, and looking for gas leaks, the answer was, as unlikely as it seems, "bad" gas.  I don't know exactly was mixed in there but, as soon as I swapped the bottle out for a new one, everything returned to normal and I'm back to being only as mediocre a weldor as I was before the thing started spitting and sputtering.Thanks to everyone for their input and help getting this figured out.-Rob