Voids/pores in mig welds

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Hey guys,New here, been welding for a couple of years as a hobby. I build modern furniture often leaving the steel frame raw and sealing with wax. Anyway, I grind a lot of my welds smooth and have recently been getting the odd weld with pores or small voids. Sometimes happens when my gas is getting low but even with a full tank I get it sometimes.  And when I go back to reweld the area it still happens.Last night I did quite a bit of welding and it happened on only one weld in the bunch, not sure what is going on.Running a Millermatic 175 with argon mix and .030 wire on 14g steel tube. Recent lead and liner, roller, wire, tip, you name it I've replaced it in the last 6 months.Thoughts?  Wish I had a photo...Thanks
Reply:If it happens amongst good welds, it is probably contamination from the metal. Is it new oiled steel? If so you need to clean off the oil.Dynasty 200DXPassport plus w/ spoolmate 100victor 315c oxy/(act and prop)Miller digital elitemilwaukee power tools
Reply:Turk is correct since the voids are in the puddle not on the surface contamination is likely.  Some plate is coated but then it should happen more often, Fit up can also allow air from the back side, grinding can leave contamination and just plaine welder error is possible, quality of plate, recycled steel can have inherent voids and contaminants..
Reply:Yes, this is all new steel. I wipe the oil of as much as possible where I weld...perhaps I just missed some.Thanks for the tips.
Reply:The cut ends of the tubes need to be cleaned prior to fit up.Swabbing the tube inside removes residual oil from cuttingor the mill. Having trace oil waaay up inside a long tube get heated bythe welding then running down into the weld area is a deal breaker.On fussy jobs I wash/swab the tube innerswithout even thinking about it.Last edited by dave powelson; 11-02-2012 at 04:26 PM.Reason: additionBlackbird
Reply:Porosity. That's the technical jargon. Tons of culprits. You have to grind the porosity all the way out. If you go over it again it will still be there. Possibly make it worse. Some processes you can run hot enough and burn it outa there but in your situation l'm guessing that isn't practical. Sounds to me like a momentary lapse of gas coverage for whatever reason since it was only the one out of the bunch.  How do you leave it raw and seal it with wax? I have a few projects that l'm going to build and that's exactly what l want to do…just don't know the best option of clear coating it.Last edited by Dystopia; 11-03-2012 at 06:19 AM.
Reply:Never thought about cleaning the ends/insides of the tubes...I'll have to do that!Dystopia. I degrease using Simple Green and rags, sometimes some 0000 steel wool soaked in Simple Green. I find acetone changes the color of the steel. I then use Minwax natural furniture wax, give it 3-4 coats and you're done. Time consuming but gives a great finish that has held up very well for me. Easy to touch up as well if need be.I've not found any other finish I like, they are all too shiny. Tried some matte bruch on Poly and it was ok, but when I scratches you can see it.