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

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

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

It's kind of like asking who is the best rock band. The discussion can go on forever. I hope it doesn't.

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

2
(OP)
yup, and me too.
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?

What kind of test data will prove which rock band is best?

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

I have not seen any comparative test reports.

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?

I would like to see comparative tests that would be fair and well supported.  Tape works if it is wrapped enough times, but not to excess, and importantly in the correct direction.  Wrapping tape the wrong way will make the tape less effective.  We use a prebaked on sealant on our plugs, but now there is a debate on where and how much is applied on the plug.  Is there any standard information on where the sealant is applied on the thread.  Is there a starter thread that does not have the sealant or should it be applied and covered on all threads from top to bottom?
 

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

3
I did a comparative study 12 years ago (had three different crews each use tape on one location, tape and teflon paste on the next, and Coppercoat on the third, then repeat on 70 locations total--all locations had a similar number of fittings of similar size).  I was assembling the data when Purchasing weighed in with 200 cases of Coppercoat and wouldn't buy anything else.  The preliminary look showed that one crew had zero leaks with any of the sealants.  One crew had multiple leaks at every location with every sealant.  The third crew did marginally worse with the Coppercoat, but the tape vs. the tape and paste was indeterminate since both had zero leaks.  Made me think that the teflon paste was overkill as long as the crew was able to properly wrap teflon and any sealant applied with the proper torque would work approximately equally as well.

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?

(OP)
helpful, best 'data' so far. roughly in line with what I see, but still hoping for published tests.
why need high paid engineers when we have purchasing to help out....

tks, kcj

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

I see the question is more of what causes leaks and what can be done to identify the actual cause.  Education, informational sharing, and data exchange could save tons of dollars if this was addressed more.  Maybe it is, but I have not been able to find the information I needed.  This is the best place so far and the particpants that reply are brilliant.    

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

2
With a good sealant system, for the right services, threaded pipe can be a very reliable, flexible, inexpensive  and useful method.  Unfortunately, due to the lack of data and standards that we're discussing here, the method gets a VERY bad rap from a great many people.

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?

I called it "Teflon Paste" because it is white and says "Teflon Paste" on the can.  My mistake.

David

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

I use Teflon tape for my home projects.  Among the reasons for paste is that some people overlap the end of the nipple or fitting with the tape and the excess gets into the pipe or tube and blocks small pneumatic or analyzer components.  Done properly both are fine products.  I never use copper but have used "Never Seize" for hot joints.

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?

Kevin,

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?

In some applications the use of tape is forbidden; instrument air being one that comes to mind quickly.  Along that line, any piping where there will be small passages somewhere downstream that the tape can become clogged in.  Excessive paste be it Teflon or faux Teflon can do the same if slopped on to heavily.

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?

One consideration I have not seen mentioned here is that of corrosion resulting from improper use of paste sealants.  I have seen corrosion resulting from the use of cheap sealant and from sealant that was not appropriate for the application.  Both were on black steel pipe (fire sprinkler pipe) and caused extensive corrosion issues.  Pastes can also clog downstream orifices as well as tape (someone noted that before).

I have not seen tape cause or contribute to corrosion.

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

Some of the metalic based (e.g. Copperkote) pastes can create a galvanic cell, but the conditions have to be exactly right (pH is a big determiner) for it to happen.  I've only seen it once and that was in water service with a 6.5 pH.

David

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

(OP)
tks for info so far. I have been monitoring responses but not commenting.
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?

The big boys made decisions based on experience(tryng, failing, succeding), lacking any 'standards' which are really the general concensus of an industry based on the collective member experience.

Ted

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

(OP)
exactly. that is the experiance base I was hoping to be written up somewhere, but I think it is also a proprietory information, competetive advantage, etc.

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?

Just to add my rather chaotic experience:

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?

Infinity Tech said:

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?

I have found 3-4 wraps to be enough.  The first wrap starting one thread back from the end and to catch the starting tape end, then two to three more to cover about 1 1/2 tape widths up the thread.

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?

For something like a NPS 1/4 male tubing connector I may use just over one wrap.  Once I cover the starting point I begin to stretch and break the tape.  The final coverage is perhaps over 1.5 turns.  for a larger nipple I may cover more than the first 3/4" of the threads but not much more, again just to cover all threads necessary and stretch to break the tape with minimum overlap.

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?

(OP)
mark
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?

ISA 76 standards include modular components for analyzer sample conditioning systems.  These are intended to permit easy maintenance etc.  However, the initial cost of sample systems is capital cost and much higher for modular sample systems than stick-built tubing, valves and fittings.

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

15 wraps of tape is way too much and will likely cause leaks. The purpose of the tape is to fill the gaps that are a natural part of the thread geometry. When tightening the thread, tape will extrude from the face of the threads to the gaps at the root. If you use too much tape you prevent metal to metal contact at the thread faces which creates a strong and stable joint. Teflon has high thermal expansion and creeps.

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?

When sealing pipe threads the material considerations should be more application specific. For pressures less than 1000 psi Teflon tape or any Teflon containing material is fine as Teflon's yield strength is about 1000 psi. Anaerobic sealants are ok if the pressure is less than 5000 psi and there is not too much pressure generated deflections causing the material to break and crumble. The coating applied to many air fittings seems to give less than good results.

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?

"NPT threads require high torque to tighten."  I was under the impression that the ASME B 1:20:1 standards for NPT stated that turns (2) not torque was required.  We have found that going over board on our torque requirements were changing the internal structures of concentricity of the crests and flanks creating "spiral leaks" from the threads being crushed. Where can you find the exact torque requirements when there are so many different variables. If any one knows, please let me know.  This has been a discussion that has gone back and forth with no real verifiable facts or standards.       

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

(OP)
Gauges & transducers: some gauge mfr are starting to offer oring, but the -04 oring is pretty delicate compare to 1/4 npt. -06 is good. The selection is bleak.   
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://www.hydraulicsupermarket.com/download/taper_thread_torque.pdf

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

The yield strength of teflon has nothing to do with its use as a thread sealant in an NPT thread!

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?

The yield strength of a sealing material that fills a gap will determine when it will migrate out of the gap.

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?

The shear stress on the Teflon filling the long spiral gap in the thread will be much less than the fluid pressure.

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

When a book named "Methods of Joining Pipe" by J.E. York was published sixty years ago in 1949 (in which there is a pretty detailed 22 page chapter of technical issues related to various "Screwed Joints"), I believe such methods were already well-known and long-standing methods of piping connection.  This work explains that while the primary responsibility for the tightness of pipe joints is commonly assigned to the Contractor, it is desirable that the Engineer as well as the Contractor understand the "fundamental requirements" for making screwed joints which are "tight".
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?

rconner:  the joints in my 70-yr old home thermosiphon hot water radiator heating system were done with one of the standard "dopes" of the day:  plumber's putty, which is basically linseed oil mixed with ground limestone, chalk or plaster of paris.  Sets hard as a rock.  It took two of us, each with a 36" pipe wrench in one hand and a propane torch in the other, to break loose a 2" connection so we could make a change to the system.  The threads were in perfect condition.

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?

Moltennetal,
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?

EdDanzer:  take it from a chemmie that there's a world of difference between a "cured" anaerobic pipethread sealant paste and a chunk of Plexiglas, even though both of them contain acrylic polymers.  The Loctite sealants we use are still pastes when cured- I have never seen them set up hard.  As I mentioned, indeed this is one of their features.

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?

This is an amazing discussion that has developed over several months.  Only a fraction of science has yet been provided on the original question relating to emperical data available.  I wonder if there would be grant opportunities available to provide something like this for industrial use?  What I have gathered is that torque is important if it is the correct amount for the application and part used, which can have variables to skew things a bit.  And that tape, can have successes if the right tape and technique is used which can vary from application and part also. I also understand that combinations of tape and sealant have been effective for some but not all.  It seems that if there is a common thread (no pun intended) here, it is, that skill, product knowledge, product quality, and effective communication and training are the keys to making a NPT seal work.        

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

I just had to estimate how much force it would take to shear 5000 psi yield thread sealant.  It would have to fail in shear, shear at the thread surface.  The worst spiral gap between thread crest and root for 3/8npt would be if the crest and root did not contact when the joint is made up.  That cross-section area is about 1.767*10^-5 in^2.  The force on that area exposed to fluid pressure of 3000psi is .053lbf.  The force required to shear a 1 inch length of sealant is about 74.8lbf.  That tells me that if the sealant is properly applied and cured the joint will not leak.  In practice a tight pipe thread joint will not have that much gap between thread crest and root.  Theoretically the gap will close about .005 in. when the joint is tightened three turns after hand tight.  That will close the original gap of .003 in. to an interference fit.  In practice that does not happen because we have leaks without sealants.

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?

I agree with Cervantis that only very little science concerning the use of sealants. At some point we will do some science and testing with various products and methods and I will post the results, but that could be years off.

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?

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

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

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.  

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

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

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

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       

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

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
www.danzcoinc.com
www.dehyds.com

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

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

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