NPT Connections: Why Am I Cursed?

[rbattelle]

I have been cursed. 95% of the NPT connections I make leak. I've tried all these products:



-Teflon tape

-Rectorseal (T plus 2 and Number 5)

-Block

-Swak (by Swagelok)

-Loctite PST number 567



None of these - not a single one - has held more than about 10 psi. No matter the fluid: water, oil, diesel, gasoline.



And I've tried all the sealants in combination with teflon tape, too. That usually will get me to 20 psi before they start leaking.



My procedure is as follows:



1. Clean both parts using acetone until there is no oil or grease or whatever.



2. For teflon tape alone, wrap the male threads tightly with several layers of tape and assemble.



3. For chemical sealant alone, apply liberally to the male threads making sure the sealant is packed all the way into the root of the threads.



4. For the combination of teflon tape and a sealant, first I wrap with teflon then apply a coat of the chemical sealant.



5. Finally, thread the connection together and tighten.



I've tried TONS of torque on the fastener, and I've tried "just a little". No difference.



Normally, after doing this procedure anywhere from 3 to 8 times I finally get the thing to stop leaking at the threads. Then I move on to the next one.



WHAT AM I DOING WRONG? I'm the only person in the world that I know who has this incredible difficulty! I've had other people WATCH me do it, and tell me I'm doing it "right", and it still leaks.



Someone with more brains than me, please tell me what I'm doing wrong. Most of these thread sealants are rated to 10000 psi! I can't get them to reliably hold 20!



My latest project, a house plumbing job, I finally stopped the leaks (after 3 or 4 attempts on every connection) by going with a tight packing of plumbers putty in the male threads. This worked, whereas the 10000 psi Loctite #567 failed.



I've learned to dread every plumbing job because I know I'll spend many hours making and re-making connections until I get them to stop leaking. It's so frustrating!



Ryan



On edit: maybe I need to try this stuff next.

 

[Forrest Nearing]

guess I'm lucky, I deal with 10,000psi hydraulic pressure all the time, and I just put a couple passes of teflon tape on it and go. it'll usually hold hand tight just fine

 

[rbattelle]

guess I'm lucky, I deal with 10,000psi hydraulic pressure all the time, and I just put a couple passes of teflon tape on it and go. it'll usually hold hand tight just fine

Obviously, I'm cursed.



Ryan

 

[sstefanini]

If you can afford to use Swak on home projects you can afford some new fittings and nipples. The only times I've seen leaks on threads which are put together with tape and dope are when the fittings/nipples are used & abused, made in china, or the threads are cut too deeply. You'll figure this one out, this isn't turbine science.

 

[GHarman]

Ryan, I'm not sure what you are doing. What type of threader you are using or are the fittings pre-threaded? What size pipe? I am going to assume that you did not know this. So, forgive me if I am wrong. Hold the nipple in your left hand, threaded section that you are going to tape, pointing right. Start tape in front of you hold with thumb and wrap over the top from the end of the threads ( at the large diameter ) toward the end of the pipe ( Wrap from left to right ). This allows the tape to be tightened into the threads as the nipple is tightened into the female thread. about 4 wraps overlapped is all you need. Allow about 1/64" to 1/32" of tape overhanging the lead of the thread. When you apply pipe dope ( liquid thread sealant ), apply onto the male thread at the leading edge and back about 3 or 4 threads. Turning the male threads into the female threads will distribute the thread sealant up the NPT shank as it is tightened. About 6 - 7 threads engagement is all you need unless your die is an adjustable type that is incorrectly set? Dont use 1/4" wide tape on 3/4" pipe. Hope this helps. GregH

 

[Turbo Tim 1]

This stuff is great PLS2 I've used the Swak and a bunch of others but the PLS2 is great

 

[Dl5treez]

Too much sealant or tape is every bit as bad as not enough, least in my experience.



I use either plain old Teflon tape or Solution 30 thread sealant most of the time. Never really any major problems unless I use too much of it.

 

[BILLVO]

What type of fittings do you use? You should use only good quality brass or steel fittings. Do not even look twice at any black iron fittings these will be a guaranteed leaker at some point. Black iron should be outlawed. As stated above its usually chinese and poor quality and threads are cut deep too.

 

[GHarman]

Ryan, If you are stuck using cast iron fittings, inspect them closely. Sometimes they have flaws/sand holes that leak profusely. If you are buying fittings at "Home Deficit" or "Lowe 'down'" you can bet they are probably the low bid with equivilent quality. GregH

 

[rbattelle]

My fittings come from a variety of sources. Most of them are Swagelok (top quality, I think). The fittings for my latest water project all came from McMaster-Carr and are wrought copper. I've never purchased a threaded fitting from either Home Depot or Lowes (that I can recall, anyway).



GregH - that's the procedure I follow, with one notable exception. I don't apply either teflon tape or thread sealant to the first thread or 2. I thought you were supposed to leave those alone so that your sealant doesn't contaminate the fitting as you screw them together? Could that be what I'm missing? I hope it's that simple.



Ryan

 

[MLimpert]

Try Key Tite. A couple of wraps of teflon tape and dab of this stuff and you should be pleased with the results.



Heres a link I found:

http://www.plumbersurplus.com/Prod/505-Key-tite-Waterproof-Pipe-Joint-Compound-1-2-Pint/7506/Cat/272



A lot of the local plumbing shops in my area sell it over the counter.

 

[DJW]

Ryan, the only thing I can think of if you are having trouble making leak free joints, is if you are making your own threads, the dies need changing, the fittings are out of round, as many are if bought from variety stores, or by causing the parts to deform, in general it's the threads that make the seal, for the most part, except for special conditions joint compounds and tape is used just as a lubricant, for home pipe joints plain washing soap was used, (available in most homes and at hand) often if overtighting the joint will never seal. I have fitted water, oil, gas, air ,steam and hydralic, but without good threads no joint is sound.

 

[GHarman]

GregH - that's the procedure I follow, with one notable exception. I don't apply either teflon tape or thread sealant to the first thread or 2. I thought you were supposed to leave those alone so that your sealant doesn't contaminate the fitting as you screw them together? Could that be what I'm missing? I hope it's that simple.



Ryan

If you do that with stainless steel you will not get them apart. If you use the procedure that I mentioned I doubt you will ever have a leak. The application of thread sealant to the male fitting allows excess sealant to flow up the threads as it is screwed into the female fitting. Thread tape is a little tricky. To much overhang and you have strings hanging in your flow stream with the potential to clog up instrumentation in a critical application. To little overhang and you will gall your fittings with the exposed lead of the thread. GregH

 

[jwgary]

Are you actually dealing with NPT threads? I know it sounds like a dumb question, but it never hurts to check the obvious. Swagelock has some different types of thread forms and maybe you are trying to thread a tapered thread into straight. From everything you describe, it sounds like you are doing it correctly. You generally don't need to tighten any more than what "feels right" with the properly sized combination wrench on the fitting. I wish that people would stop refering to pipe dope and things like that as sealant. Sure, some are marketed that way, but as someone said above, plastic deformation of the threads is what creates the seal. The tape, dope, or whatever is just there so that the threads don't gall before you get it tight enough to create that seal. I generally try to stay away from tape since I have had plenty of hydraulic and pneumatic valves clogged with little bits of tape when you have to break a connection. Hope you can get it all figured out.

 

[sstefanini]

jwgary, I've been in on the sealant/lubricant argument since I started pipefitting 15 years ago. If tape and all the different types of dope don't aid in sealing then try oiling the joints you assemble next time and see how far lubrication alone will get you. You won't have a leak free installation.

 

[gilgle]

If tape and all the different types of dope don't aid in sealing then try oiling the joints you assemble next time and see how far lubrication alone will get you. You won't have a leak free installation.

I totally agree. 25 years of plumbing and I have never made a joint w/o using tape and/or dope, regardless if it is 1/8" or 4". I would fire one of my guys if I caught him putting a joint together w/o tape/dope. The very fact that you CAN'T guarantee a perfect thread everytime is why it is important to use it.

 

[nickleinonen]

i deal with quite a few pipe fittings at work. . and i rarely get leaks. . i use standard teflon tape often [nice to keep in pocket] but when i know i need it not to leak ever, i get out the plumbers pipe dope [we use masters teflon brand] i know the dope seals well [my test gauges will hold +100 psi for a month with no pressure drop when the air/water/oil gets bottled in behind the quick connect]



i have some lead based pipe dope too that works real well. . i will not use it on anything smaller than 3/4"npt. . anything smaller, and good chance is you will break the fitting if ever needed to be removed [at least with 3/4", you can get inside with a saw blade to cut the fitting out if it breaks]

 

[Dl5treez]

I call it pipe/thread sealant because that's what the tube says on it... ... guess they're wrong then.

 

[rbattelle]

Are you actually dealing with NPT threads? I know it sounds like a dumb question, but it never hurts to check the obvious.

Good point, but yes I am 100% certain of what I buy.



Ironically, NPTF threads also leak on me, even WITH doping!



I just don't get it. Maybe my definition of a leak is too strict? If I assemble a fitting and after being under pressure for 24 hours it develops a single droplet of water, I call that a leak. Is that reasonable?



Ryan

 

[sstefanini]

Yep, fluid/gas on the outside of said pipe is a leak. Then again are you sure it's not condensation?