Sealing large NPT Pipe fitting without removing it?

dmbaile2 · Apr 23, 2018

I have a 60 gal compressor tank that is leaking air from the 2" Bung hex fitting that serves as a bushing for the 1/2" NPT outlet. The leak is coming from the bung where it threads into the tank. The leak is audible and the rate, best I can tell is about 1 psi every ten minutes.

I have read that these bungs can be very difficult to remove and at the risk of damaging the tank, are there any alternative methods to stop the leak without removing it?

TDegenhart · Apr 23, 2018

Empty the tank, clean the threaded area as best you can. Draw a vacuum on the tank. Apply Loctite 290 or other wicking sealant around the threads. After to sealant has wicked in, release the vacuum and warm the threaded area until it is too warm to touch. The sealant should be kicked over and be solid. Resume operations.

Tom

wheels17 · Apr 23, 2018

A friend of mine was given a 4 inch screwed drain line to install when he was an apprentice. He had a big back up at the pipe threader, so he went over to the electricians pipe threader, not realizing it was straight rather than tapered threads. The whole assembly went together wrong and leaked like a sieve. The journeyman came by and had him assemble the pipe loosely with the proper offsets. Then they draprd rags saturated a Sal ammoniac solution around the pipe joints. This rusted the threads overnight and sealed up the pipes. Never leaked, up to the point 30 years later when they knocked the building down.

WHHJR · Apr 23, 2018

If it is steel (both components) back weld. If not remove, clean, and seal with Loctite 515 or 518. Use heat and Kroil to remove.

2¢

Scottl · Apr 23, 2018

TDegenhart said:
Empty the tank, clean the threaded area as best you can. Draw a vacuum on the tank. Apply Loctite 290 or other wicking sealant around the threads. After to sealant has wicked in, release the vacuum and warm the threaded area until it is too warm to touch. The sealant should be kicked over and be solid. Resume operations.

Tom

That's what I would have suggested and also add to use only a low vacuum, 5 inches of mercury or so, and have it rigged so you can interrupt vacuum as the Loctite flows in. Otherwise it may continue to get sucked in and leave room for a leak.

I had to use wicking Loctite on compressor plumbing where a very roughly threaded filter/moisture trap unit attached.

Bill D · Apr 23, 2018

On my compressor the bungs have an o-ring seal under the flange. Not sure if the threads are NPT or straight. I believe they are 2" pipe on a 60 gallon tank.
I had to buy a 1" impact gun and rig a 1/2" hose direct with no quick connects. 3/8" hose with quick connects did not have enough torque.
Mine have a square drive hole in the middle.
Bill d

dmbaile2 · Apr 23, 2018

Scottl said:
That's what I would have suggested and also add to use only a low vacuum, 5 inches of mercury or so, and have it rigged so you can interrupt vacuum as the Loctite flows in. Otherwise it may continue to get sucked in and leave room for a leak.

I had to use wicking Loctite on compressor plumbing where a very roughly threaded filter/moisture trap unit attached.

I like this idea. Would I be able to perform this work with the compressor pump and pressure switch connected to the tank?

Thank you for the suggestions.

TDegenhart · Apr 23, 2018

dmbaile2 said:
I like this idea. Would I be able to perform this work with the compressor pump and pressure switch connected to the tank?

Thank you for the suggestions.

Ya, just shut them off. But you will need some way to get a vacuum, as Scott mentioned, not hard. Perhaps you could borrow or rent a refrigeration vacuum pump. Once the material starts to wick in, open a dump valve and keep the area around the thread flooded. The heat will do in a few minutes what would normally take hours or days.

Tom

dmbaile2 · Apr 23, 2018

I have a pump in the form of an old modified compressor. I have never measured the vacuum it produces, I believe I have a vacuum gauge burred in the garage somewhere so we will see. I can easily shut it on and off and can devise a way to interrupt the vacuum with a valve or simply by disconnecting the hose. I also have an IR heater I can warm it with without the damage of a flame... I am liking this idea a lot.

dsergison · Apr 23, 2018

I don't think you need to buy a vacuum pump. you already own one. a shitty one, but fast and sufficient.

disconnect the outlet of your compressor.
connect it's inlet to your tank instead. likely your compressor has some sort of air filter housing. likely with 3/4 inch or so pipe fitting into the compressor head. Just run that to the tank instead. Run the compressor a very few number of cycles and let it create a little suction. You don't want to go crazy and collapse the tank, but a 60 gal air tank is pretty rigid and built for pressure with nice hemisphere ends etc... so it's not going to implode instantly. Use a Tee and put your thumb over the extra leg to get an idea if it has created any suction. You don't need a lot to wick in the very thin Green locktite.

sable · Apr 23, 2018

Doesn't this bung need to come out for inspection ?

dmbaile2 · Apr 23, 2018

That is a good question.. I don't know anything about the inspection of compressed tanks, would a bore-scope be used for this purpose? And if so, what use is a 2" fitting when a 1" or 3/4" would suffice? I believe the bung on my tank acts as a bushing to reduce the 2" NPT to 3/4" NPT (I believe I miss-spoke in the first post).

If a professional tank inspector would use a bore-scope for such work, I don't see any reason not to weld the bushing on. Though I will be trying the vacuum solution first.

sable · Apr 23, 2018

dmbaile2 said:
That is a good question.. I don't know anything about the inspection of compressed tanks, would a bore-scope be used for this purpose? And if so, what use is a 2" fitting when a 1" or 3/4" would suffice? I believe the bung on my tank acts as a bushing to reduce the 2" NPT to 3/4" NPT (I believe I miss-spoke in the first post).

If a professional tank inspector would use a bore-scope for such work, I don't see any reason not to weld the bushing on. Though I will be trying the vacuum solution first.

I have seen them done with a mirror on a stick and a torch so a decent size hole would be needed.

Gordon Heaton · Apr 23, 2018

Bill D said:
On my compressor the bungs have an o-ring seal under the flange. . .

Same with my last two compressors, both US made.

You'll waste more time rigging that vacuum and trying (then failing) to draw sufficient sealant than it will take you to cuss the bung out and do it right. Especially if it is an O-ring seal. The fact that they can be difficult to remove does not mean it's impossible.

edwin dirnbeck · Apr 23, 2018

Get a cheap electric die grinder and a 1/4 carbide straight burr. Make 2 slots 180 degrees apart ALMOST OUT TO THE THREADS.This will take about 20 minuts. THE BUNG PROBABLY HAS A MALE HEX SHAPE. Just put a big pipe wrench on it and it will collapse and come right out. I have done 2 of these. The useless swine that welded the bung in ,did it with the bushing installed and then tightened it further when it was hot. put the new bushing in,with lots of tefflon tape and be happy. Edwin Dirnbeck

Hodge · Apr 23, 2018

Gordon nailed it, they can be pesky but the right persuader will do the trick, ie: correct socket, big pipe wrench, correct square bit with appropriate fit. Used in conjunction with necessary leverage. I've removed several with no issue, just used correct tools. Once out, use liquid pipe sealer, it will seal correctly and come out easier in the future without postponing the problem. This method should be the quickest as well. Good luck

rons · Apr 23, 2018

dmbaile2 said:
I have read that these bungs can be very difficult to remove and at the risk of damaging the tank, are there any alternative methods to stop the leak without removing it?

The inlet/output port fittings are not hard to remove. The steel i" fittings I removed were not too hard to remove. I used liquid wrench and a LARGE crescent wrench with a 6 foot pipe.

The clean out ports are going to be more difficult, so I heard. The square head fitting is screwed into the fitting and then the whole thing is welded to the tank. This distorts the thread. So I've been told. But with the appropriate amount of leverage it can be done. Good luck.

BTW, the pipe installers I meet use both tape and paste on their installs.

Garwood · Apr 23, 2018

I recently made a large funnel from an 80 gallon USA made compressor tank from the 1990's. Before sending it off for blasting and powdercoat I removed the two 2" bungs. I had to heat the area around the bungs to a dull red and it still took everything my 300 pound ass had on the end of a 48" pipe wrench to break them free. I had to chain the tank to a forklift to put the force into it.

metalmagpie · Apr 23, 2018

me, I'd braze it

jrmach · Apr 23, 2018

can try "green Loctite"
but first I would try to take it out without ruining it
If it starts looking like you need to call "Bubba" over to finish taking it out,,,stop,,,clean,Braze

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