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How to stop leaks on pipe threads

pyroman's picture

Occasionally I have a problem where I'm on the loosing end of stopping a small drip leak on my threaded connections, be it copper or CPVC. I'm on that loosing end again right now.


I have a 1/2" CPVC female threaded connector into which I am threading a chrome 6" 1/2" pipe onto which will be a 1/4 turn shutoff valve. This is for a sink. I originally used teflon tape, 4 wraps at least. When I left there were no leaks. HO calls and says it's got a "pinhole" leak at the threaded joint where the chrome meets the CPVC fitting. I went back and undid the joint and used pipe dope instead which almost always works every time, just messier than teflon tape. Same problem, pinhole leak. I cranked more and the leak only slowed, like every 5 minutes a drip. I can't turn it anymore, it's already that tight.


Andy ideas/advice on how to stop it? I wrapped with teflon and then doped it, so I got two sealing methods. So far no leak that I could see, but....What works best for you all to ensure no leaks and if you get one what is your remedy?

I did measure twice and cut once, and still messed it up.

(post #96127, reply #1 of 111)

I had a brass ball stop valve that leaked like that at the threads. I don't know how many time I redid it.

Then I looked at it closely and the threads where weird. Look at it was machined a little unsized before they cut the threads.

And I had a galvanized plug that kept dripping. It look OK, but replaced it and did not have any more problems.

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #96127, reply #2 of 111)

Some times the product you purchase has been made from a threader which may be worn out. I know in the past our old ridged pipe threader at the hardware store will actually rip the threads rather than cut. so to make a long store short the Die used to make the threads was worn out it sound like to me. or just out of Tolerance.


Run over to the local Small Hardware store and purchase a replacement valve if it continues to leak.  


Good luck!


Tony


 

(post #96127, reply #8 of 111)

I agree with Joeseph--oftentimes home centers and such get pipe cheap because the company making it is cheap and uses worn out dies. Then you have leaks. Get new valve from a good hardware store. I've also heard you should only use one layer of Teflon tape, though in the past I used several and never had problems. (I was first going to say, you think you have problems, read the thread above yours! but didn't want to be a smart guy....)

(post #96127, reply #3 of 111)

Don't use a CPVC female threaded adapter - ever.

Cranking in a metal nipple puts a lot of stress on the plastic and your leak could be from a microscopic crack which may/will eventually split the adapter right off the nipple.

There is a combination CPVC/brass adapter. The brass being the part of the unit that takes the stress of the connection. If your situation is stubbed out of a wall, chances are that you've used an elbow to turn the piping out. Lose the CPVC elbow and substitute a drop ear elbow which has the combination female threaded brass/CPVC as well as the 2 ears you use to fasten the unit to the blocking.

(post #96127, reply #7 of 111)

Ralph- we agree 100%.  CPVC female NPT parts have insufficient strength for use with metallic male threaded components.  It's far too easy to overtighten and the result is usually a crack failure of the CPVC part.  This is often helped along by the use of pipe dope compounds which are NOT rated for use with plastic piping components and tend to cause them to split or soften and yield.   Only the CPVC fittings with a hoop of metal around them are strong enough for ordinary use with metallic male threads.


Before you use pipe dope, make SURE it's rated for use on plastic fittings!  It must say so on the can, otherwise don't trust the idiot behind the counter at the supply house. That said, a good pipe dope offers a far more reliable seal for a plastic female/metallic male thread combination than does teflon tape IMHO.

(post #96127, reply #10 of 111)

Molten,


The pipe dope I used says on the can can be used on PVC, and CPVC as well as metal fittings. So no prob there.

I did measure twice and cut once, and still messed it up.

(post #96127, reply #4 of 111)

How timely. Reorganized the bathroom over the weekend and had to deal with a couple of drippers from new galvanized fittings. I replaced a pedestal sink with a small vanity cabinet and top. In the vanity, I put a 2.5 gal (120V) point source water heater to offset the 35 ft of 1/2" line from the main water heater. The first problem was tying off the existing hot water line. I had a slow constant drip from 2 sets of nipples and end caps, both times at the junction of the new fittings. The second set was better so I just let it drip into a pan until whatever hole plugged up with crud. I had a similar problem with a water heater replacement two years ago. Slow drip for a couple of days and then it stopped. On the cold line, I put in a 1/2" cutoff followed by a T and then feeds to the cold tap and the cold side of the water heater. This couldn't be easily pressure tested until fully assembled, and of course it dripped where the short nipple from the valve met the T-fitting. But after 8 hours it has really slowed as the crud migrates into the pinhole. In my case I think it is poor quality Chinese import fittings. I have no problem with any of the brass junctions. From now on I'll be getting galvanized fittings from the local plumbing supply house.

On an aside, I really like the small water heater. Before it used to take a minute to get hot water. Often my wife would turn it on and walk away to do other stuff or attend to the wild child, so sometimes the tap ran unattended for 2-3 minutes. Now there is hot water about as fast as you can get your hand from the tap into the stream. I'm not sure if it will save money but it will cut down on lost time and aggravation as I stand in the hallway wondering why the sink is running full bore and no one is there. :(

(post #96127, reply #5 of 111)

Sometimes a female threaded part or fitting has a microscopic crack that does not show readily to the eye. But when a male part is wrenched on, the crack opens just enough for the fitting to leak, no matter how much teflon or pipe dope you've applied. Replacing plastic with metal would likely fix the problem.

 

(post #96127, reply #6 of 111)

This is another reason I don't like CPVC.  But sometime you have to use it so....


Run down to the car parts store and get a small can of High Tack gasket sealer.  Use that on the threads.  That is the only product I use without issue on CPVC threads.  And I agree with above never use the female fittings.  They leak and when you try to tighten will get small hair line cracks that will leak.


I also disagree with the use of galvanized.  If you have ever taken a galvanized pipe out of a house after 20 years or so you will see that it honeycombs shut and restricts the water flow.   It is not a good long term product for domestic water supplys.  If you need to connect to a water heater use a dielectic nimple.  They have a plastic coating on the inside of the nipple.


You can also use brass nipples where needed although a little pricey they will not corode.  Also use pipe dope on any metal threads, not tape.  I have had a much better success rate with dope vs tape on any metal threads.  DanT

(post #96127, reply #9 of 111)

"I also disagree with the use of galvanized. If you have ever taken a galvanized pipe out of a house after 20 years or so you will see that it honeycombs shut and restricts the water flow. It is not a good long term product for domestic water supplys. If you need to connect to a water heater use a dielectic nimple. They have a plastic coating on the inside of the nipple."

Last year I finished the basement for a friend including replacing the "bath" that was there. The exsiting basement bath has a "campground shower" (concrete blocks over a floor drain) and a toilet with no partions.

And in the process replaced most of the hodge podge of galavanized and copper.

The house was built in the 50's.

I was SHOCKED when I saw the inside of the galvanized. It has fine white coating on it. Otherwise as good as the day it was made. No buildup, no restrictions.

That is my first experience working with galvanized. But I have heard so many stories about how old pipe like that is clogged up that it really surprised me. Not that I am suggesting that they don't have problems with buildup.

And we have hard water here. I don't think that it is real hard, but I and cleaned crud off of valves and aireators enough to know that it is hard.

The only place that there was a problem was one place where the copper was connected to the galvanized without a dielectric. Look perfect from the outside. But when I tried to replace the connection with a dieltric I could not make it stop leaking. Then when I tried to replace the galvanized elbow it colapsed in my hand. And the pipe was was full of a muck.

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #96127, reply #11 of 111)

"The house was built in the 50's.

I was SHOCKED when I saw the inside of the galvanized. It has fine white coating on it. Otherwise as good as the day it was made. No buildup, no restrictions.

That is my first experience working with galvanized. But I have heard so many stories about how old pipe like that is clogged up that it really surprised me. Not that I am suggesting that they don't have problems with buildup.

And we have hard water here. I don't think that it is real hard, but I and cleaned crud off of valves and aireators enough to know that it is hard."


I've seen that too.  Galvanized in perfect condition from the 50s.  I think it totally depends upon the water.  In your case, the hard water may be an advantage.  Hard water often is alkaline, and (being hard) not hungry for ions.  Soft water is often acidic and hungry.

(post #96127, reply #13 of 111)

"The house was built in the 50's.

I was SHOCKED when I saw the inside of the galvanized. It has fine white coating on it. Otherwise as good as the day it was made. No buildup, no restrictions.


This also may be to the lack of flow on this branch of the supply line.  My experience is that the high use fixtures/tees/lines are the ones that corrode, especially on the hot water side.  There must be a secondary correlation between flow and hardness.


Dean

(post #96127, reply #14 of 111)

In this particular case it was the mainline feed everything except one outside hose bib.

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #96127, reply #15 of 111)

Sometimes you get lucky, but be careful to generalize that result to other situations that aren't exactly the same.  The devil's in the details.


Copper to galvanized is an ~ 1.5 volt battery working to corrode the galvanized part.  In most (water) plumbing situations that's very bad news and results in rapid failure of the galvanized part.  


I've learned that some trustworthy practical people out there have had good luck with brass nipples instead of dielectric unions between the two services.  They're cheaper and less likely to leak, so they may be worth a try when you need to bridge copper to galvanized.  I've also learned that in closed systems without a constant supply of fresh oxygen in the water (like my ancient thermosyphon radiator hot water heater system, or a commercial cooling water loop loaded with corrosion inhibitors), junctions between copper and black steel or galvanized pipe can last for a very long time.

(post #96127, reply #18 of 111)

My house was 100% galvanized. The first project was to replace the service line and the first 20 ft in the house with 1" type L copper. I saw no evidence of another pipe ever having come through the front basement wall, so I wonder if this was the original water service to the house. If so, it outlasted two generations of wiring. That line obviously saw the most use and was the one which had started to weep a bit in one section. Weeping is a non-distinct leak where the now porous pipe forms water drops over an area but not from a distinct point. Not sure if the pipe is weaker here because there are more ions passing over which degrade the metal, whether there is a higher pressure head which forces water through the pipe walls, or whether the higher flow causes more of the pipe's inside to get eroded over time. Regardless, that section of pipe failed first. If we choose to do a major kitchen and bath renovation, then we will get into the ceiling and walls to replace those pipes with copper. Until then it is a combination of prayer and denial that holds the system together. My experience with repiping the main water heater a couple of years ago told me that it is best to ignore these pipes unless one plans to do a complete job, i.e. start the project at the beginning of a month long vacation.

(post #96127, reply #12 of 111)

They make special 'expansion' fittings specifically for transition from CPVC to metal.  Particularly important for hot water lines.

(post #96127, reply #16 of 111)

Lots of good advice from others. Pipe dope and teflon are probably not going to stop a leak... they're more for lubricating the threads as you tighten them, and the threads are supposed to mechanically seal themselves. Can you get inside the wall and replace the threaded elbow, or does the fix need to be with the existing elbow? If you can get in there, convert to a brass elbow. If not, what about a threaded stub of CPVC and some glue in the threaded joint?

(post #96127, reply #19 of 111)

NPT threads should never be considered to be capable of dry sealing.  They always need a thread sealant.  Otherwise, the best way to think of an NPT joint is as a long, thin spiral pathway connecting the stuff inside the pipe with the world outside the pipe.  Fill that gap or it will leak- maybe not now, but sometime soon.  With some thread sealants, tightening the joint beyond a certain point actually makes things worse, not better.  NPT threads have gotten a bad rap industrially because people haven't understood this fundamental point: they're a very useful, flexible and reliable connection when used for the right services, fitted up by a well-trained pipe fitter with the right thread sealant for the job.


Good thread sealants do lubricate the components as they're drawn together to prevent the parts from "galling" (cold welding in places, on their way to being seized).  A good thread sealant must also be somewhat flexible to handle minor changes in the size of the gap it's filling due to thermal expansion/contraction or vibration on the piping.  Teflon tape does the first job better than paste (especially if the fitter doesn't know his own strength with the pipe wrench), whereas a good anaerobic paste thread sealant does the other job far better.  So in our industrial plumbing we generally use both- paste on top of full-density teflon tape.  On low pressure, low temperature, low hazard services like household plumbing, that's overkill- one or the other is fine as long as it's used properly.


I wouldn't recommend using PVC cement as a pipe thread sealant.  It cures hard, rather than remaining soft and pliable to do its job properly as the parts expand and contract.  And if you use it with two PVC or CPVC parts, you end up with a badly-designed glue joint- better to use a proper glue socket designed for the job.  Might work in a pinch, but I wouldn't want it in my own ceiling.

(post #96127, reply #20 of 111)

the cure for threaded joints leaking on submarines is simple - its called welding.

This does add cost and more time to take apart tho.

(post #96127, reply #17 of 111)

I never use teflon, I just use PVC glue.  You do have to twist it on fast!

(post #96127, reply #21 of 111)

don't crank it down full tight before the first water test ....


found out young that most of my leaks were because I over tightened things before we ever got started.


now I have to remind myself ... U can always tighten it more later ...


 


especially with compression fittings ... but I've screwed up regular threaded stuff too.


 


Jeff


Buck Construction, llc   Pittsburgh,PA


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