Air Compressor tank welding question

If the tank has already functioned like that snce 1948, I'd leave well enough alone.

Don't. Unless you're a certified pressure vessel welder, you take the chance of compromising the integrity of the tank.

A dip-tube type drain is completely effective if it's built and used correctly. The tube end should be cut to a slight angle (or castleated) so it cannot seal against any surface in the tank. It should be placed at the bottom-most part of the tank, in light contact with the surface. On a horizontal tank, this means at or near the seam of one of the end bells.

Then - on a horizontal - the entire affair should be shimmed just slightly out of level so that water runs to the low end. A 1/4" over the length of the tank is fine.

Lots of older tanks have the sort of drain you called a "stinger". A bottom drain is cheaper, which is why most manufacturers do it that way now. But it's also usually a lot less convenient to the operator than a drain mounted higher up.

LLoyd

...which won't reveal if you've inadvertently caused the start of a stress crack that you'll learn about when the thing tries to go into orbit. Compressed air storage failures really suck (or blow).

Suggestion 1: clean it out, make sure that the drain is set up to drain properly per LLoyd's reply, don't weld on the tank.

Suggestion 2: consider getting it really hydro-tested, which is a bit more complex than you filling it with water, but costs money, which is not a good thing, I know. Procedures vary slightly with tank type, but (speaking from scuba tanks, which I know more about the procedure for - is similar for high pressure gas tanks, and probably fairly similar with slightly different details for low pressure tanks) consist of putting the tank in a container of water, filling the tank with water, and applying a prescribed amount of overpressure, such as 4/3 the rated pressure. Failure includes tank rupture, but is not limited to tank rupture - the volume of the tank is monitored by checking the level of the exterior water in a rather finely calibrated manner, and if the tank does not substantially return to its original size when pressure is removed (ie, if it "takes a set" or permanently deforms too much) it is also failed.

Suggestion 3: if it looks grotty when cleaned out and Suggestion 2 is too costly, give it a 58th birthday bash and either take it to the scrapyard, or make a lovely barbecue grill from it.

I would not try to do a DIY hydrotest, and definitely would not try to weld on any fittings on the tank. You are in a pretty arid area with low humidity, right? Personally, I would continue to use it until it starts leaking, and then I would replace the tank. If you live in a low humidity area, you may die before the tank starts leaking. Given Gunner's scrounging abilities, I am sure that he can find a good tank in the meantime.

If he installs a intercooler between the pump and compressor, the amount of moisture in the tank would be minimal.

No, Iggy. An intercooler improves the pumping efficiency of the second stage, but any water in that air is ultimately going into the tank, intercooler or no. Where else would it go?

LLoyd

I would hope that most of it would be trapped if a water trap was installed after the intercooler...

Usually, unless the intercooler is much more robust (has a lot more radiating area) than most that come on commercial compressors, the air never gets cool enough to condense the moisture. A water trap counts on that condensation forming.

Now, I think I remember your saying you would use a refrigeration condenser coil you had as an intercooler. You might get the temperature low enough in that case. But the traditional two-stage pump type compressor has an intercooler that is a single pipe about a foot or two long... not enough for that purpose.

LLoyd

Yes, the HVAC person who replaced our A/C left the evaporator coil.

I see. Thank you Lloyd, not I know a little more.

When I had a ghastly oilless compressor, the bled-out water was showing rust color very soon after I bought it. Not a lot, but there was an orange color to it. I am now using a 30+ year old Quincy and the stuff bled out of the tank is a yellowish froth of oil, water and air, but no sign of rust yet! And, in St. Louis, in the summer, there can be quarts of water in there!

So, ordinary compressor oil does seem to be protecting the tank from corrosion.

Jon

Never weld a tank or kick a dog unless you have to.

I accquired a used Compressor tank. I was trying to find out about getting it tested. My compressor shop told me to call the city "boiler and pressure vessel" inspector. I did, and the guy said "i'm going to be in your area tomorrow, I could check it for you". He stopped by, and using a ultrasound device, measured the thickness of the tank at several locations. He then compared the readings to the spec on the tank. All for free. No complaints about the government here.

Bob

I should throw in, that when he saw my welder, he immediately asked if I was planning to weld the tank. He definately implied that it was a bad idea.

Bob

Another option, if you can live with quick & dirty, is to drill a #3 hole in the bottom and screw in a 1/4-28 threaded pipe and seal with epoxy. I've done this with very thin tanks because I can thread a valve stem to 1/4-28. The hole is so small that the actual force on the fitting is miniscule. At 100 psig the force would only be about 5#, epoxy can hold that. Of course the fitting is positioned so it would blow harmlessly down. Threads & epoxy avoid welding stress, looks crude but it works and I have used it many times. I have had occasional leaks trying to epoxy to rusted metal but never a blow-out, the 1/4-28 threads will hold more than the mere 5# force involved even in very thin metal.

Using PVC as compressed air piping is unsafe and illegal for employers, per PSHA regulations. Plus, larger tanks are subject to more stress per unit of thickness, for obvious reasons.

As already decided, that's a bad idea.

What I never saw mentioned, is what about remounting the tank so that an existing opening is down and put a drain valve under that?

For example, when converting an old propane tank for compressed air, simply mount it open end down. Put in a Tee, with a drain valve in the bottom and air in/outlet on the side.

OK, so you like the current orientation of the tank. :)

sdb

I'd agree. Haven't seen you around in too long, Sylvan, have I been oblivious or have you been away?

Dave

Well...that pesky motor/pump mounting assembly welded to the top of the tank sorta has something to do with it

Gunner

"I think this is because of your belief in biological Marxism. As a genetic communist you feel that noticing behavioural patterns relating to race would cause a conflict with your belief in biological Marxism." Big Pete, famous Usenet Racist

My humble opinion, this is NOT the time to weld up another spare tire mount - this one could easily kill someone if it lets go. And with your luck, you.

The stinger drain has worked fine for 60 years, the only thing I might suggest is to get the bottom end a little closer to the bottom of the tank so it'll suck out more of the crap.

If you can find someone who will do the work for cheap (tradeout for equipment service?) who has the proper welding certs, and the shop has a U stamp for boiler and pressure vessel repairs, go for it. They have the proper tools and fittings and know all the tricks. And more important, they know what they CAN'T do safely.

I have this strange feeling that the spuds need to be welded on from both the inside and the outside during tank construction, before they weld the two halves of the tank together. If for no other reason than the inside weld will seal the water out of the gap between the spud and the tank wall - that's how I'd do it...

Otherwise you'll get rust in the crack over time, and it could literally push the spud off the tank wall and rip the weld.

This is one of those times when a Lincoln Tombstone, a box of Farmer Rod and a "Git 'er Done!" attitude ain't gonna cut it. ;-)

How does that line go? Oh yeah: There are Old Welders, there are Bold Welders, but there aren't too many Old Bold Welders... ;-P

Yeah, they really don't work well upside down...

-->--

I already indicated that Ill leave it as is. Btw..the spare tire incident (blush) was the result of me being in too much of a hurry to use a proper machine, of which I do have several....shrug

Miller DiaArch 250 AC/DC (which had the leads 10' to short to reach...)

Airco 300amp Squarewave Tig (with WP18 Torch, Bernard cooler, "rod saver" stinger and tig/stick leads 15' too short to have reached the tire carrier)

Lincoln Tig 250/250, Magnum cooler, WP20 torch, and hoses 30' too short. (since sold)

Dan-Mig 200amp Mig, with a power cord 25' too short

Airco PhaseArc 350amp mig (didnt have the rotory converter running then)

Though..I could have used the Marguette 110vt buzzbox with 3/32 rod

When I built the replacement...I used the Miller, and a few sticks of Certanium 747 rod, that I have in the 400lbs or so of various kinds of stick that I keep on hand.

Bad judgement on my part. Pure and simple. Not the first time, wont be the last, but Ill not be making that sort of mistake again. It will be a new kind of fuckup, next time. Shrug

Gunner

"I think this is because of your belief in biological Marxism. As a genetic communist you feel that noticing behavioural patterns relating to race would cause a conflict with your belief in biological Marxism." Big Pete, famous Usenet Racist