Welding an Air Tank

I'm no metallurgist, but I would not do it. It's weak/thin already if it's leaking. I would drill out the rusty spot in the tank and epoxy a sheet metal screw/lag bolt in the resulting hole.

I weld holes in air tanks fairly often and to do it right you should use a good sized torch and heat up the metal around the hole. if its to thin you will easily burn through the bad spots. They also will be the first places that heat up the fastest. If you have a bunch of thin spots and are not a good experienced pressure tank welder don't attempt to repair it!

A bad weld can split and actually through dangerous rust flakes out of the tank with very high velocity plus what ever dirt and debris that is in the way of the air blast gets moved at violent velocities as well.

If its a cheap low grade tank from one of those $ 500 7.5 Hp 80 gallon air compressors its likely junk. The whole bottom is rusting through. The one hole is just the beginning.

IF its a commercial tank and you are a knowledgeable and experienced welder than it may be possible and worth patching. But still if attempted fill it full of water and pressure test it to above its maximum rated pressure.

I personally test tanks to 250% of ther maximum rated pressure with cold water but I stand around a corner while I pump them up any way. Many wont recommend this but it will give you a fair margin of comfort knowing that the tank can still hold that pressure if it passes.

If you don't have a means of pumping water to that high of pressure use a pressure washer to pump up the tank to above its rated pressure. But make sure you have the pressure gauge in place and a relief valve thats set for the maximum rated tank pressure in place. A bad weld or weak spot will not make a big explosion with water inside. At worst its typically just a snap and a momentary squirt.

Still use caution and be aware of the potential dangers.

In most countries it would be illegal to do this repair without proper weld procedure and inpsection of weld and vessel by certified/qualified IIA (Independant Inspection Authority) or governement certification body.

Lot of energy stored in that thing if it decides to go pop it could kill many.

Do not do it especialy if you cannot examine the condition of the inside. One hole could be the start of many.

IT COULD BE DANGEROUS.

Pressure of 120 psi is sufficient enough to injure somebody if that patch is brusted. (Which is likelly to happene). I have seen and experinced air bullet exploding due to welded joint like a bomb.(it was at comparatively very high pressure but even 120 psi is not less than a bomb.)

What caused the hole? How big is the hole? If it was a piece of machinery wearing a hole in it, then epoxy a patch on. Don't risk welding it.

If it was rust eating a hole through, then discard the tank, preferably after cutting it into quarters. This is just so nobody else gets the idea that they can salvage what has already become a piece of junk.

In the USA a firm with an R stamp is the only certified way to weld air tanks. In a commercial establishment you could be fined and the tank condemned if caught.

I looked at one welded the wrong way and it came apart went through the roof and landed in the parking lot.

Surely after a repair, a pressure test to 200% working pressure, using water only, must be made?

Periodic tests of this type needed for re-certification surely......

Meatlogger

The guys who make tanks weld a boss with pipe threads on tanks just about anywhere they choose. These are new tanks of course and in the final form have the ASME pressure vessel certification plate for 200 psig service attached.

As we become more of a Nanny state common sense isn't very common. I don't recommend any action for you or your situation that may get me sued, blued or tattooed.

For my situation I would know something about the age and condition of this tank to help decide if it would be OK to use for 120 psig compressed air or cut in two for a cattle trough.

I would: 1. Take a the tank to a place that is safe to work on it.

2. Fill it with water.

3. Rather than weld on a chunk I would use an official pressure port and guidelines for the hole size to place it in and weld away.

4. Attach a 600 psig gauge.

5. Route a high pressure hose with more liquid from a safe place to tank.

6. Hook an Enerpac or similar pump to the hose and pump liquid to 480 psig.

This is a 4/1 pressure ratio for your expected use at 120 psig.

If the tank ruptures it will not explode but split and dump liquid and pressure quickly.

If the tank does not rupture but pressure drops off when you stop pumping the tank is "growing" and might make a good water trough.

If the tank holds pressure without and wet spots from pin hole leaks or poor fittings for an hour or more drain the water. Blow out with compressed air or gas. Coat the inside with good oil. (Put in a gallon and roll the tank around and all over.) Drain the oil. Give it a coat of paint. Install a Code relief valve set for 150. Attach a durable tag with the test date and put it to work.

If you have concerns about the thought police ask a local fire fighter, policeman or bartender to observe your procedure. They do not have to or approve or endorse your action, just sign as your credible witness' that you took reasonable and proper precaution.

Just because I resent the erosion of our free will doesn't mean it might be less expensive to spend $400-$500 for a new tank and plant flowers in the old one.

Be well