Porosity from a mostly Empty Argon Cylinder.

[Don52]

On a recent welding project I MIG welded a fillet flare weld shown on picture 1 and everything was OK. Then I flipped the part over to weld the flare groove butt weld shown on picture 2 and the weld was porous. I hadn't changed the flow rate of the 75% AR 25% CO2 shielding gas between the two welds. I was welding the back side of the same metal and I had ground off the mill scale before welding. I was using ER70S-6 wire, which can tolerate some contamination. I checked the tank pressure and it red 300 psi. I checked the flow rate and it was 15 SCFH, so I bumped it back up to 25 SCFH. I made another weld and it was still porous. It took me a while but eventually I figured it out. I changed the Argon/CO2 tank to a new one and the problem went away.

Here is my Assessment

It turns out that that the zero on the tank pressure gage was off, so most likely the tank was below the minimum 50 psi that is required for the ball type flow meter (called a rotometer) to read correctly. Rotometers measure volume flow not mass flow. so they are dependent on the pressure differential and the temperature. When the flow meter was reading lower then my initial setting it was most likely caused by the low inlet pressure as opposed to the setting on the needle valve on the flow meter changing. If a rotometer doesn't have the required inlet pressure of 50 psi you really can't trust the reading. What faked me out was the false tank pressure reading of 300 psi when there was most likely less then 50 psi. The fillet weld trapped more of the shielding gas compared to the more open butt weld. I have gone through many tanks of shielding gas for both MIG and TIG. For some reason I never experienced this phenomenon before.

I bring this to your attention for two reasons:

1. So you don't have to scratch your head and waste time like I did figuring it out.
2. To see if you have ever had the same experience.

[Tinker Joe 2]

Thanks for that information, that is valuable , Joe

[ryanjones2150]

I am convinced that sometimes porosity issues are some sort of trick voodoo hex. Of course, if you see some of the garbage we use to build things and some of the stuff we work on...such as the Bamchero...you would not be surprised.

For example, tig welding away on that 9" rearend on the drag car, working on the suspension hangers. Tig root and capping it with the mig, no problems...then all of a sudden, porosity from ****. Swap over to the HTP from the lincoln precision tig, still bad. Change argon, still bad. Maxstar 150sth, still bad. Mig it, still bad. Scratch start tig off the thunderbolt, same argon...no problems. That's some voodoo action there. Or Murphy.

Not sure if there is a link to any of it, or if inverters are more prone or sensitive to metallurgical hockuspockus, but I seem to have more pososity issues with my inverter tig machines than with the transformer type. Takes us back to the post a while back about "granulation" look to tig aluminum beads if you guys recall.

I really don't use a lot of brand new metal and I can't recall ever having porosity issues when I did use new metal, but I also wasn't looking for a parallel. If I am using new metal, its almost always using new metal and welding it to some old junk. But in regards to your issue up there Don, I also understand butt welds to be more prone to sucking in air or surface junk from the backside of a weld, so that is of no help either.

For tig welding, I have a tube of 309L on hand. Its not something I like to do because its $10 or so a pound, but when I start to get a boiling puddle of porosity goop, I dab a little 309 in there and the puddle smooths out instantly. Of course I want my welds to be sound, but I'm also not welding on the shace shuttle escape pod hatches or anything. Using that 309 probably gives my weldment a mishmash of metal compounds that nobody will ever understand, but its worked for me in the past. When I have a job that I'm mig welding and start having issues, a lot of the time I'll stab a fresh 7018 or 6010 in there just to get the job done and on to whatever the end game is.