Welding and Metalworking - How to remove broken and corroded drain valve

I have an air compressor that the drain valve stopped working in because it got corroded. When I took a wrench to it to remove it, it broke off at the threads. So how can I go about removing it? I tried cutting slots in it with a dremmel and trying to turn it out with a screwdriver, but the metal is too soft. I think the drain valve is made of brass, it is like this one... Craftsman Drain Valve (http://www.sears.com/shc/s/p_10153_12605_00916369000P?vName=Tools&cName=AirCompressors&AirTools&sName=Air%20Compressor%20Accessories&psid=NEXTAG01&sid=IDx20070921x00003j)

http://img11.imageshack.us/img11/5267/1004091110.jpg

Spray the fitting with penetrating oil like Liquid Wrench or WD-40 and let it soak in and around the threads. Then I would try to cut inside the old brass valve until you amost get to the steel threads. I would use a hack saw blade held in my hand. No power tool. Do not cut the steel threads in the tank you need them in good condition to install a new valve. Once you have the brass cut; push, pick or pound on one corner of the brass next to your cut. Trying to tear and push the brass into the center. Once you have a tab of brass sticking up grab it with vice grips or pliers and try to tear and rip out the remaining brass.

Can you just drill the leftovers out and then drill and tap for the next NPT size up? Cos it's the steel threads that are rusted and will probably crumble away.

@markiz37, do you think from looking at the picture that going up a size in threads would be safe?

Have you tried an easy out? That would be my first choice and if that didn't work I'd use Pilot Dane's suggestion.

I didn't see the pic before..but you should measure everything to be safe. You need a 37/64 pilot for 3/8 npt tap, if you're going up from 1/4 npt. I would say you're safe if the total diameter of that welded port is 1 inch or more. If not, don't do it, not worth the risk.

Hopefully, you have the piece out by now. In the future, keep an eye out for left hand drill bits. We use them a lot for broken pipes and bolts. With a left hand bit, a lot of times the broken piece will unthread as you're drilling.

Definately try the LH drill suggestion (I have a set to 1/4"), the easy out, and you can find inexpensive "inner" pipe wrenches that grab better than an easy out. Have looked at these but do not recall if they go down to 1/4". Lastly, just keep drilling with larger bits until you clean out most of the waste, then go in with a 1/4" NPT tap to finish the job....no need to go to 3/8" if you work carefully. When you install your new drain, put in a (steel) street elbow (45 deg.) or a steel nipple and coupling to avoid the same problem again.

They make a bit that is tapered that you basically pound into the hole and use a tap wrench - which grabs the inside of the pipe and threads it's self into the broken piece - which usually helps to screw it out.

Most times, if you can machine flat the broken piece, you can drill to a smaller size and then use a tap and thread and put a bolt into the hole and the heat will allow the threads to loosen and the bolt can be welded to the brass and the fitting would come out.

Or if you had a mig or tig welder, you could just cut the bung off and weld on a new one. I have done it many times with a 70-18 welding rod in a couple of passes as long as you are careful not to blow a hole in the tank.

i would try an easy out first. most times this will work. if not, put a little heat on the nipple, then try the easy out again. if this doesnt work and it does need welded please be advised that this should be done by a professional. welding on a compressed air tank can be dangerous. if i were to weld this i would not cut the nipple off but would weld another nipple to the old nipple, there would be less chance of blow-thru.

An easy out should have easily removed the piece.
You need the right size driven well in but it should have worked.

Welding on the tank is not really a practical option.
For you and your family's safety you definitely need a ticketed pressure welder to do this but the cost of this compressor would make replacing it a better alternative.