Air Compressor tank welding question

I picked up a Kellog two stage compressor the owner claimed had been freshly rebuilt..and after firing it up..I believe him. Quiet, good
compression and fast build up.
The issue I have..is the tank. Cosmetically..it looks very good. However..as best as I can figure..it was made in 1948. There is NO bottom drain plug..draining is accomplished by a pipe stinger coming out of the end bell and hanging down the inside of the tank to within a half inch or so of the bottom of the tank. I found this out by pulling one of the 3" plugs on the side of the tank..big! pipe wrench..6' snipe and some grunting.
Bottom of the tank has about 3/4" of sediment on it. A bit of poking with a stick moved enough stuff around to get a glimps of the inside of the bottom..and no big pits were noted. Ill get out the pressure washer this weekend and clean it out.
My question is...Im spooky about not having a drain plug on the bottom of the tank, and really think I should put one in. What I want to do..is drill a proper hole in the bottom of the tank, thread in a 1" fitting, then weld it in place. Tank data plate says tank walls are .235 thick..which is a smidge less than 1/4"..and if I cut into the tank..and find the bottom to be significantly less than that..Ill junk the tank, which the data plate says is rated 200lbs.
Does anyone have any caviats or hints and kinks to doing this? I plan on tapping the tank simply to hold the flange..threading it in..then MIG a bead around the fitting.. Or I could Tig..Ive got the capabilities of both.
Should I hydro the tank when Im done? Ill never run it above 100lbs..so I figure I can fill it with water, then pump up 150-175 and see if it springs a leak.
Any discussion on this would be apprciated
Gunner
"If I'm going to reach out to the the Democrats then I need a third hand.There's no way I'm letting go of my wallet or my gun while they're around."
"Democrat. In the dictionary it's right after demobilize and right before demode` (out of fashion). -Buddy Jordan 2001
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If the tank has already functioned like that snce 1948, I'd leave well enough alone.
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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
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Never weld a tank or kick a dog unless you have to.
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Well, I had to weld a tank, it was a portable air compressor w/5hp Briggs engine. The tank was leaking where the wheel brackets and the front stand brackets were welded to the tank.
I knew nothing about the fuss about welding on tanks, I just cleaned the area around the cracks some, welded the cracks and brackets. No pressure test, only a leak test. Remounted the engine and compressor and reinstalled the whole thing back into the pickup bed and used it for many years. Only thing that changed was the pickups and replacement engines and a compressor.
I suppose that tanks over 150 to 200 lb rating could be another story.
Dixon
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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.
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...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.
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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
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wrote in message

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
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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.
i
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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
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wrote:

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

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

I see. Thank you Lloyd, not I know a little more.
i
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rigger wrote:

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
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On Sun, 13 Aug 2006 22:05:53 -0500, KIMO <KIMO> wrote:

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.
i
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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
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On Fri, 18 Aug 2006 14:23:36 -0600, sylvan butler

I'd agree. Haven't seen you around in too long, Sylvan, have I been oblivious or have you been away?
Dave
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On Fri, 18 Aug 2006 14:23:36 -0600, sylvan butler

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

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...
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