sealing NPT threads, is there research tape vs. sealer?
sealing NPT threads, is there research tape vs. sealer?
(OP)
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
Is anyone aware of actual test research between the various methods? Teflon tape, Loctite PST, Megaloc, Rectorseal, etc?
kevin j





RE: sealing NPT threads, is there research tape vs. sealer?
RE: sealing NPT threads, is there research tape vs. sealer?
The Ford/Chevy, Miller/Bud, whateere debates that go on forever and lead nowhere.
That's why I am looking for actual test data comparing something, instead of just 'we have always used this.....'
I expect somethere in the last decades Cat/GM/John Deere et.al. have researched this to death to make a corporate decision on what to use, but I have never seen any SAE or NFPS papers or presentations or articles in HP magazine. Seems awfully common and generic not to have been addressed many times. Even papers by those selling the sealant would help.
kcj
RE: sealing NPT threads, is there research tape vs. sealer?
RE: sealing NPT threads, is there research tape vs. sealer?
I chose one or the other depending. Stuff like Loctite PST for production line assembly. Tape on fittings that are oily as when doing repair. Tape requires care to not get it wrapped over the end of the fitting putting shreds into the system. Loctite PST can be messy if the person applies too much, especially on products delivered to customers.
I like being able to chose for my designs and after sale support. Both seem capable of creating a seal on pipe thread. I saw one guy use both together.
Ted
RE: sealing NPT threads, is there research tape vs. sealer?
RE: sealing NPT threads, is there research tape vs. sealer?
I know there are any number of other options for field assembly of NPT threads, but I picked the three that were used most often in this area.
I always wished I could have published the results internally before purchasing "helped", but once their decision was made it was final and publishing became counter productive.
David
RE: sealing NPT threads, is there research tape vs. sealer?
why need high paid engineers when we have purchasing to help out....
tks, kcj
RE: sealing NPT threads, is there research tape vs. sealer?
RE: sealing NPT threads, is there research tape vs. sealer?
Just like everybody else here, all I can give you is our own experience:
Tape alone is too dependent on the skill of the pipefitter in applying it, the quality of the threads and other factors. It's also susceptible to leakage after repeated thermal cycling because it has limited "memory". With machined threads, the right tape and a skilled fitter, tape alone can give high reliability joints. With Chinese 150# stainless fittings, Home Depot 0.25 s.g. garbage tape and pipe threads cut with dull tooling, it's a TERRIBLE sealant!
Anaerobic paste alone is far more idiot-resistant, provided you select the right paste for the service. People should STOP calling it "liquid teflon" or "teflon paste", because that's a terrible description for what an anaerobic paste is. These pastes have nowhere nearly the corrosion resistance or other properties of teflon- and most of them contain far more other stuff than they do teflon particles. It has other disadvantages including the mess factor- the affectionate name the fitters have for it is "bird sh*t".
We use heavy (at least 1.1 s.g.) tape with an anaerobic paste as a top dressing. We VERY seldom encounter leaks. The tape provides full coverage to the male threads which helps resist galling in stainless parts if the fitter gets a little too aggressive with the pipewrench. The paste does the rest and helps the joint resist vibration and thermal cycling.
RE: sealing NPT threads, is there research tape vs. sealer?
David
RE: sealing NPT threads, is there research tape vs. sealer?
Yes this discussion can go on forever. And the best rock and roll band was Yes.
RE: sealing NPT threads, is there research tape vs. sealer?
Did you ever get your orginal question answered? Or have you found out any more information that you can share. I am also looking for information on use of a combination of sealants for some NPT parts.
RE: sealing NPT threads, is there research tape vs. sealer?
I work for a company that has a policy against tape altogether due to the fact that there are several systems that would be impacted negatively if tape shreds ended up downstream.
Any and most of the above mentioned methods in this thread are operator dependent. A good operator can make a good joint that will seldom leak, and a bad operator can take the best sealant system and end up with a leaky joint as "Z" has pointed out above.
rmw
RE: sealing NPT threads, is there research tape vs. sealer?
I have not seen tape cause or contribute to corrosion.
RE: sealing NPT threads, is there research tape vs. sealer?
David
RE: sealing NPT threads, is there research tape vs. sealer?
Still looking for actual test data, but the responses have been pretty much in line with my personal experience.
I use good quality thick teflon tape when working from the toolbox (usually hydraulics), and Loctite PST when in one place for house construction (low pressure water and gas). I have not tried using both at once.
I don't have as much faith in the skills and meticulous nature of our shop assemblers, so have been specifying PST for shop assembly.
For new designs, I avoid NPT if at all possible. SAE oring boss, ORFS, split flange, JIC, or some sort of oring flanged joint if possible.
but would still like to know how the big boys made their decisions.....
tks to all. kcj
RE: sealing NPT threads, is there research tape vs. sealer?
Ted
RE: sealing NPT threads, is there research tape vs. sealer?
Most of the few remaining OEM NPT adaptors I have seen use preapplied anaerobic coatings. Maybe for performance reasons, or more likely assembly line and skill reasons.
tks to all for their comments. That represents many years of experiences and industries.
kcj
RE: sealing NPT threads, is there research tape vs. sealer?
I'm developing a very compact plumbing product that uses over 40 1" stainless fittings in a space of about 12" x 18". I used Weld-On White Seal to assemble the entire assembly. Upon testing I discovered a large, depressing, number of leaks. As this is a product in development, I treated it like data and forged ahead. I assembled it again thinking I was focusing better. Again, a bunch of leaks. I did it a third time, this time applying a little thread sealer onto the female threads. Leaks! I don't know at this point if it is the Weld-On sealer or the stainless. My experience with stainless is somewhat short.
Next, I tried standard thickness hardware store Teflon tape. I wrapped each thread very carefully 10 times, assembled everything and got leaks. Fewer leaks, but leaks. I disassembled and reassembled again but this time with 15 wraps. This time there were even fewer leaks, but still - leaks.
As a final repair to the last few leaks, I again wrapped the nipples with Teflon tape 15 times and applied some of the same problematic Weld-On White Seal onto the male and female threads. This solved the immediate problem, but provided no real data.
In the past I used Slic-Tite sealer which overall had a good success rate. However, I never tried it with stainless steel.
Hope this adds to the body of knowledge and experience.
Mark
RE: sealing NPT threads, is there research tape vs. sealer?
I again wrapped the nipples with Teflon tape 15 times. I thought about saying something, but my "swaib and de-boner" up-bringing would not allow me to comment. However, 15 times...how can you do this and not increase or change the thread design. We are only wrapping about 3-4 times...and true we have had leaks, but 15 times...is this a common practice in other industries. This might be the answer on what we are doing wrong. I remember reading somewhere and it might have been on this site or another, that with NPT threads wrap or fill until "it works". I would like to have some responces from others on the number of times each thread is wrapped. Thanks in advance...
RE: sealing NPT threads, is there research tape vs. sealer?
15 seems like a waste of tape. There is not enough space between the threads for all that tape.
Ted
RE: sealing NPT threads, is there research tape vs. sealer?
OTOH when taping an electrical wiring splice I may use several wraps - still not l5 wraps.
RE: sealing NPT threads, is there research tape vs. sealer?
off topic, but rather than make a relaible production assembly with so many possible joints to leak, can you eliminate many of those fittings and joints by manifolding, or machining into a block, or casting a plastic block, or using compression joints or multi function components or adaptors, etc etc.....
My career is hydraulics, and a cartridge valve/manifold block is the analogy that comes to mind. I realize low pressure, water, and consumer costs are constraints way different in your field.
RE: sealing NPT threads, is there research tape vs. sealer?
RE: sealing NPT threads, is there research tape vs. sealer?
It is very typical that those new to pipefitting have leak problems. NPT threads require high torque to tighten. Threads are often mis-formed of or dinged. High torque is required to get these thread imperfections elastically or plasticly deform the get the joint tight. The number of leaks you are experiencing indicates that you are not tightening the fittings enough.
RE: sealing NPT threads, is there research tape vs. sealer?
We have had better luck with Permatex Form-A-Gasket at hydraulic pressures below 3000 psi and compressed gasses under 2000 psi than any other material. Above these pressures pipe threads suck.
I do not recommend pipe threads for any fluid power application and will only use them if there is no other choice. I hope someday pressure gauge and transducer manufactures will start using o-ring connections as a standard.
Ed Danzer
www.danzcoinc.com
www.dehyds.com
RE: sealing NPT threads, is there research tape vs. sealer?
RE: sealing NPT threads, is there research tape vs. sealer?
Transducers seem to be equally avaialble either way. One pressure transducer manufacturer offers a 9/16-18 thread that is NOT an SAE o-ring port interchange and did not include, or allow, an oring for seal. The mfr claimed it was a 'special thread' just for us and they have never heard of any -06 oring boss port standard. After all the arguing we ended up tossing dozens of useless transducers.
TORQUE tought to get field people not to overtighten. We saw a lot of cracked centrifugal pump outlets andvalve bodies from overtightening. Eventual solution was to reinforce the pump casting, but that is another story.
This is a pdf from parker, posted on Brendan Casey's site, that attempts to define NPT tightening based on Turns from finger tight. It is a start, but since the numbers are typically 2 to 3 turns, that is a lot of variation. Also, 'finger tight' means a lot of variation.
Ultimately I think, mechanics feel and training by passing on the knowledge. Another reason to get rid of NPT if possible.
http://w
RE: sealing NPT threads, is there research tape vs. sealer?
What's the yield strength of an anaerobic pipe thread sealant?!
We have had our best luck with a combination of DENSE (s.g. > 1, preferably 1.3) teflon tape PLUS a top-dressing of anaerobic pipethread sealant. We use the ones from Henkel (Loctite brand) but there are numerous available. The teflon tape does the basic lubrication and large void sealing, with the sealant providing leak resistance against dimensional changes in the joint due to thermal cycling, vibration etc.
Excessive torque of NPT joints leads to galling which leads to a leaking joint which is difficult to disassemble and fix properly. NPT threads are NOT dry-seal threads, so there's limited benefit to be had from over-tightening. They REQUIRE a thread sealant to seal.
Industrial pressure transmitters (for the process industry) are available with I-flanges (2-bolt "footballs" with a glass-filled teflon o-ring). You can weld a "football" to a nipple connected to your process if you're that concerned about leakage at an NPT. Pressure gauges are available with integral Swagelok compression fitting connections too.
RE: sealing NPT threads, is there research tape vs. sealer?
Most anaerobic plastics are less than 5000 psi yield many are under 3000 psi yield. All anaerobic plastics seem to be brittle when cured making the material fail when the fittings swell from pressure.
Ed Danzer
www.danzcoinc.com
www.dehyds.com
RE: sealing NPT threads, is there research tape vs. sealer?
RE: sealing NPT threads, is there research tape vs. sealer?
I noticed much of this was prefaced with the advice, "Good clean-cut, uniform threads make tight strong joints, eliminate leaks, extend the life of the installation and result in complete satisfaction with the fabrication and the piping material.
Carelessly cut, wavy, shaved or rough threads result in a weakened piping system, localization of corrosion, high maintenance cost, and condemnation of the workman and the piping material." [At least I guess condemnation may not be as bad as damnation!!]
Even way back then there were many different types of materials threaded and thread assembled, and this reference made clear that how all this is suitably accomplished from thread cutting to assembly etc. varied with materials. How to accomplish all this right even with standardized threads and all sizes etc. is thus not necessarily as simple as it sounds.
At the end of the passage there was discussion of many thread sealants du jour that were also used at the time for various services, concluding with a mention of "wicking" (different than "wiping"!). I think wicking was basically as it sounds something like wrapping some sort of cord that probably looked not unlike a candle wick, and that may or may not have been soaked in some kind of dope, in the thread valleys and in essence that worked sort of like a gasket or packing when tightened up (while the author mentioned this was used in some parts of the country, I don't think he in general was necessarily too keen on this practice).
RE: sealing NPT threads, is there research tape vs. sealer?
I would imagine that "oakum" was also used- rope fibres in heavy grease, asphalt or pine tar- but none of it in my old system.
Nicely machined threads make the sealing job easier, but don't eliminate the need for the thread sealant.
EdDanzer: anaerobic pipethread sealants aren't solids- they're thick liquid pastes. The good ones NEVER solidify- that's how they can manage to provide sustained gap-sealing despite dimensional variations due to thermal cycling etc.
RE: sealing NPT threads, is there research tape vs. sealer?
I don't know how much warranty work you have wrote check for from pipe threads leaking but I personally have spent several thousand dollars of which could have been mine if the stupid thread sealants worked.
This quote is about Loctite "565 Thread Sealant is a single component, high viscosity, low strength acrylic thread sealing adhesive; it cures when confined in the absence of air between close fitting metal parts and resists shock and vibration." Acrylics tend to be a brittle material when cured.
Compositepro,
If you don't think materials will flow when the yield strength is exceeded should spend some time studying forging, and pressurized molding. The size of the gap will only slow the process not stop it.
Ed Danzer
www.danzcoinc.com
www.dehyds.com
RE: sealing NPT threads, is there research tape vs. sealer?
http://www
Ted
RE: sealing NPT threads, is there research tape vs. sealer?
As to the argument about yield strength in relation to thread sealant performance in an NPT joint, on this point I'm afraid you're just plain wrong. You can, and we do, use TFE tape in NPT joints for internal pressures well beyond the yield strength of solid teflon (internal pressures of 3,000 psi and even higher). I'll let other mechanical engineers explain the physics to you, since as a chemmie I should have no credibility on the subject!
We use a Loctite sealant as top-dressing to teflon tape as described above and very, very seldom have leaks either in initial testing or as warranty claims. We have success even with crap-tastic 150# threaded stainless or MI fittings from China, albeit those fittings being used only to their limit which is rather low pressure.
With suitable fittings we do use this system on high pressure gas and liquid services with good success, though we don't do industrial hydraulics. We of course minimize the use of threads in high pressure services, period, but are not afraid to use them when appropriate. We're not in a mass-market business- we build custom equipment, so our warranty claims record is probably of little use to you for comparison.
RE: sealing NPT threads, is there research tape vs. sealer?
RE: sealing NPT threads, is there research tape vs. sealer?
Short form of the previous is that thread clearances are very small compared to the length of engagment. Forces pushing sealant out are small compared to forces required to push the sealant out.
Use one to two full turns of a bead of sealant filling crest to root of the male thread placed one or two threads back from the end. That was our production procedure. Even I could get leak-free joints. We used Loctite PST.
Ted
RE: sealing NPT threads, is there research tape vs. sealer?
hydtool: Not only does 15 wraps seem like a waste of tape, but a waste of time and patience also. So far the 15 wrap prototype which has been in service for a month does not leak. It has not gone through any winter cold but has cycled from about 50 degrees to 95 degrees in the sun for two weeks before installation and two weeks after installation with 110# water pressure.
kcj: Yes! we really want to use fewer parts and our design has already changed again to reduce the number of fittings. We are also looking into a manifold system that we can use. We may have to manufacture our own, but at this point it seems like the only part of the construction that could be consolidated. I will research "cartridge valves and manifold blocks". Thank you for the suggestion.
Compositepro: 15 wraps does seem to be a lot, and yet, during our prototype process we need to try different things. 10 wraps produced more leaks. We are dealing with 304 and 316 stainless which seems very different than regular steel pipe. When we were in the "Weld-On White Seal" pipe dope phase we tried adequately tight, really tight, immediate service, and 24 hour baked in the sun service. We had leaks every time. I think in this case we ruled out the Weld-On product for stainless.
moltenmetal: In the past I have overtightened standard steel pipe fittings so much that I have cracked them. Stainless is way different in practice. It does not seem to yield as much and reaches tight "all of a sudden" (comparatively). With the prototype, we have used and reused stainless fittings over and over, and sometimes I felt that they were tightened ridiculously tight. I have not noticed any galling of the fittings. The nipples started out with a really nice looking sharp and mirror smooth thread, and they still have that look.
EdDanzer: Warranty work! Ouch. Years ago I went through a challenging time where many of my pipe joints leaked. And I am a careful organized systems type of person. I went to the local hardware store and asked one of the guys there what I could do. He told me that all the "real plumbers" use Slic-Tite. I started using that and never had leaks again. At least in standard steel pipe. Not science, but a start. When It came time to work with the stainless, this product was no longer easily availabel. Thus, my journey to find the TRUTH!
Thanks to everyone in this quest for some reliable data. Like I said, when we do some actual science, I will post our results.
Mark
RE: sealing NPT threads, is there research tape vs. sealer?
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
RE: sealing NPT threads, is there research tape vs. sealer?
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.
RE: sealing NPT threads, is there research tape vs. sealer?
Mark
RE: sealing NPT threads, is there research tape vs. sealer?
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
RE: sealing NPT threads, is there research tape vs. sealer?
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
www.danzcoinc.com
www.dehyds.com
RE: sealing NPT threads, is there research tape vs. sealer?
Mark