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I have a brass nipple screwed into a brass elbow and the joint is leaking. After half a dozen tries at re-wrapping with teflon tape, I decided to see if I could just tighten the problem away. ~150 foot pounds of torque later, the leak had slowed but not stopped and I am out of leverage. I assume that I have damaged one or both of the components at this point. Is there a way to tell which, before I replace both?

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    I find today's quality control is not as good as years past I have found brass fittings to be slightly oversized or the nipple undersized. With 150 ft lbs of torque the elbow may now have a crack that is difficult to detect, if a few wraps of "teflon" tape won't seal I would replace the elbow, brass fittings in many cases don't need tape or dope because the brass is soft and will seal if properly manufactured.
    – Ed Beal
    Jul 12, 2018 at 15:03

3 Answers 3

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Try this; take the fitting back apart. Put 2-3 wraps of teflon tape (no more than 3). then coat the male threads with RTV silicone caulking. snug as normal and let set overnight. I would normally not use the teflon tape but the brass has been stretched and enlarged by the over tightening. When I as still working I would put whole jobs together using only RTV silicone and no pipe dope or teflon tape.

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  • This is the first I have ever heard of using RTV to seal pipe theads. Usually you want to turn on water immediately so waiting for RTV to cure would be a distinct negative. And how easily does it come apart later? Jul 13, 2018 at 21:42
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    I used this trick on pipe threads that you could not get sealed by any other means. After using numerous types of pipe dope, teflon tapes, and combinations of both, the RTV silicone was the fix of "last resort" and always worked. Where I lived in western Pa. I assembled thousands ofH.B.Smith screw nipple boilers sometimes using only RTV silicone, with never a leaking thread. No other dope was used. One of the contractors would only assemble these boilers that way. They came apart the same as using standard pipe dope.
    – d.george
    Jul 14, 2018 at 10:22
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    There are various RTV silicones. For a boiler did you use one of the high temperature rated ones or is this just the basic clear, colorless RTV silicone? What was the temperature/pressure category of these steam boilers you used the RTV on? Jul 14, 2018 at 10:39
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    The pipe threads I referenced in the boiler assembly were used for low pressure steam (15psi. max) or hot water heating, so the temperature of the threaded connections rarely exceeded 250 degrees f. The silicone used could be bought in tubes at Home Depot, Lowes, hardware stores or any auto parts store. The auto parts stores silicone was usually high temp rated but any silicone could be used. To view the boilers just "google" H B Smith series 3500, 4500 or 6500.
    – d.george
    Jul 15, 2018 at 11:59
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It is not certain that you have damaged the joint. Take it apart and reassemble with pipe joint compound. Some people use both Teflon tape and pipe joint compound. To do this I would apply a small amount of joint compound to the male threads, then wrap with tape.

It used to be one only applied pipe dope to the male threads, but I had a case recently where I had to redo a joint three times because of seeping. Finally I applied joint compound to the female threads too. I attribute these problems to design/manufacturing of the threads being different than in the past.

The next time I have to do one of these I intend to try "plumber's hemp" video which is used in Europe.

Five years ago I redid the clothes washer connections with Teflon tape and they seeped. Tightening did not stop the seep. I redid it with joint compound and it still seeped, but much less. I needed to get the washer in service so I wrapped a rag around the joint to absorb the seep and hoped it would stop. I looked after a few days and no seep.

A year ago I installed new outside valves. Our 1970 tract house has two outside taps on 1/2" copper tubing coming out of the ground with the taps originally sweated directly to the copper. In 1980 I redid them after they were damaged in a freeze, sweating on a 1/2" FIP adaptor.

This time I selected quarter turn 3/4" ball valves, labelled garden valves. I think ball valves are not really the best choice because they are really not metering valves, just on-off, but time will tell. This required two intermediate fittings to go from the 1/2" FIP fitting on the copper tube to the 3/4" male on the valve. I had to redo the joints several times to stop leaks, and I left it seeping. After a few days the seeping stopped.

In the store this Italian made "garden valve" was easy to turn even though it has only a small handle, round with a single projecting tab, but when installed and pressurized they were hard to turn . I could operate them by using both hands but my wife could not. I looked into replacement handles, but couldn't find any, then realized that an extension handle would work.

A 7 inch long extension handle of 1/2" hard copper with a splice connector soldered on the end worked. This slips over the tab on the handle. For the valve that my wife uses frequently I made a "wrench" to operate the valve without bending over. This is a 2 ft length of 1.5" dia PVC tubing with a notch in the end to engage the single tab on the valve handle.

EDIT

I would think that "hemp" is not specifically required. I would try heavy sewing thread. Put pipe "dope" on male threads, then wrap many turns with thread so that the thread does not get swept into the water stream. Be an interesting experiment.

More EDIT

I think US NPT threaded fittings used to be tighter than they are now. It seems to me that resistance would be encountered after one or two turns. But when I was selecting fittings at HD from their extensive set of brass NPT fittings they seemed looser than I remembered. I concluded quality has slipped when manufacturing went outside the US, but there is an alternative explanation.

It could be we are now getting European standard / world standard threaded fittings for plumbing and these might have always been looser and which required pipe dope and hemp or equivalent fiber. Fiber doesn't sound inert, it could be that microorganisms could grow there, but I have not heard of any such problems.

Still more edit There are US companies which advertise precision NPT threaded fittings which seal with Teflon tape alone, e.g., Hoke catalog

yet more editing Now this is real plumbing video of plumber threading steel pipe

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  • A ball valve can be used to adjust the flow by not fully opening or closing the flow is adjusted. I do find ball valves tend to crack easier than standard hose bibs.
    – Ed Beal
    Jul 12, 2018 at 14:57
  • Before I go ask this separately... tape+compound is suggested in many places online, but nobody ever distinguishes between tfe compounds and oil+mineral compounds. Should I worry about mixing one or both combinations?
    – Sparr
    Jul 12, 2018 at 16:53
  • @Ed Beal we use the ball garden valves in an intermediate position to meter flow, but the flow control is not as precise as the regular washer on a brass seal type. when you say ball valves tend to crack easier than standard hose bibs, do you mean "crack" as in split or fracture, or do you mean to open a small amount, i.e., open a crack, meaning open a small amount? Jul 12, 2018 at 19:33
  • I actually meant the brass splitting as I said and believe you support a ball valve can be used to adjust the flow ( I have at least 20 ball valves on my farm) some as big as 4" but many of the smaller ones have cracked so when going from on to off they now spray until in the opposite position.
    – Ed Beal
    Jul 12, 2018 at 21:16
  • Have you used these ball valves frequently in intermediate positions or do you mainly use them full on or full off? The failure mode I have heard about is deformation of the seal around the ball from being pressurized in an intermediate position. Jul 12, 2018 at 22:03
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Probably poor quality control in the manufacturing of one or more of your parts. Looking at all the remedies I see here posted, if you either want to put more "seal" on threads / and/ or start anew with new parts, whichever is cheaper, of which I'd say more sealant.

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