[mjsmachine]

I'm doing a weld build up on a part that had a tap broken off inside it. I cleaned the part very well. everything was going well then i started getting really bad porosity. i ground it out and started again, same thing, moved the arc to another part of the weld, porosity formed there as well. my tank is low at about 400 psi and i can hear the gas flowing. At this point i'm going to get my tank filled just to rule that out. has anyone else heard of this sort of thing? I'd hate to spend the money of a fresh tank if not needed right now.

[cj737]

Is the aluminum cast? If so, pretty common when welding it. Any info you can provide on the material, piece, usage and condition would help...

[LtBadd]

I've never had a problem with 400 still in the tank (T size 330cf), still that doesn't rule it out. Can you post photos of your project?

[Poland308]

500 is my minimum, generally. I’ve pushed tanks lower than that but I’ve also had times it did cause porosity.

[sbaker56]

I've found things get a little dodgy past the 400 mark as well. You'll slowly start questioning if your gas lens is getting dirty or if your technique is getting inconsistent up until you switch to a new bottle and suddenly everything is better.

[G-ManBart]

This is a topic I've been following on multiple forums and it seems there isn't any set answer on how low you can go safely. I actually wonder if a lot of that comes from differences in flow meters/regulators. Regardless, time and again people post that at some point porosity shows up, for no obvious reason, and their tank happens to be on the low side. They swap it out and the problem disappears. I've even seen page after page trying to figure out how a tank could be contaminated, but just at the bottom....with no resolution after pages of back and forth.

400 in on the high side from what I've seen folks claim, but not unheard of.

Most important...let us know what happens after you swap tanks!

[Poland308]

There’s an old thread here that delves into the science of why moisture contamination in a tank can be worse at lower pressure. But suffice to say all moisture contamination of gas tanks comes from gas suppliers not processing there returning tanks like they should. When dealing with compressed gas cylinders, that have contents that are susceptible to moisture, my knowledge is mostly of refrigeration and a few other gasses. It’s standard practice to pull a deep vacuum on a tank, to ensure there is no moisture or other gasses left, depending on the size of the tank, the size of the vacuum pump, and the level of contamination. this may require multiple times of pulling a vacuum, and breaking the vacuum with an inert uncontaminated gas between each pull down. Needless to say this is a time sucking process, and time is money. So some people chose to save the time and collect the money. Leaving the tank holder with a contaminated tank of who knows what.

[BillE.Dee]

I"m with you Josh. Did a lot of work on a/c for road tractors. Deep vacuum would cause the moisture to boil out of the . Also tried to get my money's worth out of argon tanks. Found that when the tank got to around 350-400 psi, I would start to get lousy welds. Tried to use that tank while welding thinner materials and lower flow rates and got the tank dang near empty. I'm supposing that a low flow rate would leave the moisture in the bottom of the tank. I don't think that the tank fillers vacuum the tank enough and really don't care about the end user...as much as the money.

[BugHunter]

Not doubting the moisture angle one bit, but...

My experience has been slightly different. I used to have all sorts of trouble (Mig or Tig) using less than 400-500psi tanks. Then I got a new welder that came with a new regulator. Shazam! Issues on that welder were gone. After some thought about the other regulator, went on WTT.com and got another quality regulator for the other tank/welder. Again, no more need to run the tank to the store with 25% of the gas left. I run mine on the TIG down past 100psi now. No telling if the gauge is dead-on-accurate at that low pressure, but that's my story and I'm stick'n with it.

[BillE.Dee]

AGAIN, better equipment and better thought...better results.

[kiwi2wheels]

It could be interesting to put one of those inline moisture filters in place when this problem occurs for a back to back comparison.

IIRC, Jody did a video on these sometime back.

[Poland308]

Even for my personal welding, by the time the tank is below 500 it won’t really have much arc time left in it. Even if you run it down to 100. We’re talking about 2 or 3 hrs of arc time. But only a few dollars worth of gas. Now if it’s not critical work I’ll run below 500. But if a tank is at 500 and I don’t know what’s coming next I just change it out.