sealing NPT threads, is there research tape vs. sealer? 11

[kcj]

The perennial discussion of teflon tape vs. anaerobic sealants for NPT threads goes on forever on boards. My opinion, your opinion, etc.

Is anyone aware of actual test research between the various methods? Teflon tape, Loctite PST, Megaloc, Rectorseal, etc?

kevin j

 

[Latexman]

Barring valid technical reasons for one product over another, I wonder if the pipefitter is allowed to use the product of his choice would there be less issues? This suggests psychological reasons, but with limited data, it may be a valid stradegy.

Over the years I have developed the same feeling with mechanical seals. It seems the best one to use is the one the maintenance guys want.

Good luck,
Latexman

 

[Compositepro]

NPT threads have been used very successfully for for a long time. If you are having such problems with leaks there is a reason that is specific to your case and not NPT thread in general.

Have you checked your thread geometries? NPT threads are designed to not have a sharp vee at the peak or root. This creates the spiral groove that must be sealed. A sharp vee that contacts a truncated vee in the thread root will create an interference that will prevent proper tightening. You will not have contact at the thread faces, resulting in a far larger gap to seal. Also, external pipe stresses will have to be carried through the sealant so the seal will not be reliable.

 

[InfinityTech]

Compositepro: Thank you for your input. I just checked the stainless fittings that we have been using. The female fittings seem to have familiar imperfect threads. However, the nipples have these very nice smooth threads and seem somewhat sharp at the peaks but not sharp (or torn) enough to cut me. I don't really know how to test for this. It sure makes sense, though, that if the peaks are sharper than the valleys it would be difficult to get the faces to seal. And, perhaps especially so for stainless.

Mark

 

[Cervantis]

InfinityTech said:

I don't really know how to test for this. It sure makes sense, though, that if the peaks are sharper than the valleys it would be difficult to get the faces to seal. And, perhaps especially so for stainless.

Mark,
you do have a calibrated and certified L-1 gage for both the ring (male) and plug (female) checks don't you? I must have missed something in the translation.

I do know that the B:1:20:1 standard allows for a gentle rap or tap to the part if it "hangs" up during the intitial L-1 gage check. The standard also allows for a total of 2 turns..1 plus or 1 minus, but these only qualify the pitch diameter, not the pitch. You would have to have additional gages for the pitch checks, and by the standard they are not "stated" but accepted use is the ANPT gages, but labeled as an NPT. These have a tighter tolerence check and will check the pitch.

john

 

[EdDanzer]

Back to the original question of is there any actual test research data.

I provided some data from our tests over many years only to be told I can’t see physical phenomena and do not know anything about physics or material science. I do have a patent on a high pressure hydraulic seal developed from my observational skills, understanding of physics and material science that saves customers money so I don’t think I’m an idiot.

How many companies want to spend many thousands of dollars to have an independent test lab do several hundred tests with a few hundred material combinations to provide public results?

If pipe threads were so good why do so many other connection designs exist, because there are applications where pipe thread, including NTPF are a poor choice for fluid connections.

I would like to thank those who have provided their methods that work for them. I have not tested Teflon tape with anaerobic pipe sealant but will be trying it on 5000+ psi nitrogen on Swagelok stainless steel fittings soon.

Ed Danzer

http://www.danzcoinc.com

http://www.dehyds.com

 

[InfinityTech]

I have to agree with EdDanzer's implication that pipe thread is lacking in certain respects. The most glaring limitation for us is that assemblies made with pipe thread have very little consistency in the assembled length. On the other hand, pipe thread comes in large sizes and has the ability to lock fittings into place. I wish there was some other quick (or not so quick) release fitting that had these criteria and, of course, good sealing.

Mark