I have a Compression Union, which connects two pieces of pipes. One joint leaked, because nut loosed. I unscrewed the loosed nut, applied “pipe thread sealant”, then tightened the nut very tightly. The leak stopped about half an hour. Then leakage started again and water came out from the nut, although the leakage was much slower than before.

Any idea of how to fix this problem? Why the new leakage did not start immediately after I tightened the nut?

Thanks a lot.

Inspect the union very carefully for a hairline thread crack.

Pipe thread sealer should not be used on compression fittings. The sealing surface is not on the threads.

Thank you very much.

Will the Compression Ring crack if I tighten the Compression nut too tightly?

Can the crack of Compression ring cause the leakage?

Zjclucky - Yes if you tighten it to far, you can also be putting a small kink in the pipe is why you are not getting a good seal . You did not say ( WHAT KIND OF PIPE YOU ARE WORKING WITH?? ) .That would help us a lot to know, If its copper and is not real stright where you are putting the compression fitting then that could be the causeand you could have tightened the fitting so tight that it cracked the copper pipe . SO TELL US WHAT KIND OF PIPE YOU ARE WORKING WITH?? GOOD Luck & GOD BLESS .::: Hello Kiss

Thank you very much. Yes, it is copper pipe and not straight.

But if I had cracked the pipe, a lot of water should have rushed out right away. Actually now the leakage is very slow.

What really confused me is that after I tightened the nut following the first big leakage, the leakage STOPPED FOR ABOUT HALF AN HOUR before it started again, although the second leakage was much slower than before. Why the second slow leakage did not happen immediately after I tightened the nut?

But if I had cracked the pipe, a lot of water should have rushed out right away.

Not necessarily true. Had one suddenly gush water about a month later. It's called stress.
Water flow and temperature changes cause minute movements.

How big is the pipe?

Compression fitting - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Compression_fitting)

Compression Fittings (http://wolfstone.halloweenhost.com/Plumbing/concom_CompressionFittings.html)

Thank you very much.

1/2" inch copper pipe.

Actually, the "copper pipe" used in the home is really "copper tubing" and I purposely used your terms. It comes in K, L or M grades which is the wall thickness and intended use.

The outside diameter of pipe and tubing are very different. It's somewhat complex. It's Schedule rating determines the wall thickness. Schedule 40 is the most common.

It's very important to get compression right the first time. Square (both the end of the tubing and the intended final position), burr free, clean and fitted tightly in the fitting before tightening the nut. Don't overtighten.

Thank you very mcuh.

it is copper pipe and not straight. To form, a perfect fit the pipes should be in line with oneanother. If they are cocked the connection won't be completely together leaving a small gap. Line the two pieces up and try again. Good luck, Tom

Thanks a lot.

From Wikipedia, the free encyclopedia, I found the following:

"It is important to remember to not apply joint compound or teflon tape to a compression fitting's threads. The compression is the means of sealing the joint, not the sealing of the threads themselves. Pipe compound or teflon tape will frequently lead to a leak in the fitting by causing the fitting to loosen as a reaction to the compression."

Did the “pipe thread sealant”, which I put around the compression seat, caused the second leakage, which did not happen immediately after I tightened the nut? After I tightened the nut following the first big leakage, the leakage STOPPED FOR ABOUT HALF AN HOUR before it started again, although the second leakage was much slower than before.

Can the “pipe thread sealant” explain why the second leakage did not happen immediately after I tightened the nut?

Thank you very much.

Most people when they screw up, put the thread sealant or tape on the threads, you put it on the seat.

Some thread sealants do not harden and I suspect yours may have been one of them.

Pipe dope has fine particles of some material within a binder. When the water was turned on the pressure acted against the binder and forced it out. You were then left with the fine particles of the material. Now with small voids, water can leak out. It takes time and pressure to force the binder out.