Does npt threads need Teflon tape?

Depends,, do you want it to seal high pressure air? get the tape! some will tell ya to get the yellow for natural gas or the expensive black,, there is a right direction and there is a wrong direction to wrap the tape, also 2 full wraps, not less, not more, the guy in this vid over does it with too many wraps





https://www.youtube.com/watch?v=j5jYLvNsK94





https://www.google.com/search?q=yellow+tape+for+gas&oq=yellow+tape+for+gas&aqs=chrome..69i57.j0j4&sourceid=chrome&ie=UTF-8

Edit: sorry Raden, I was typing and linking as you posted faster than I ,, I agree, the yellow is better,, my comment was not to put you down
the threads 'do' crush together and thats what makes the seal, true, but as said above the tape is a lubricant to allow it to be twisted tighter .. ive had a rough time getting an absolute seal using tape, in other words a seal that will hold air without losing any with pressure left on as in an external reg application etc .. what works is loctite 545 and no tape, but it needs to be applied liberally and allowed to cure for a week 10 days to hold hpa .. but tape is fine on a fill setup where alittle seepage is inconsequential ..
Word of warning- if these NPT fittings aren&#;t PARKER or a quality fitting like PARKER fittings, but ones made overseas, you can easily split them by over tightening. I say over tightening but it wouldn&#;t have been over tightening with a Parker fitting. Talking from experience. I barely had two full turns in and I put a hairline split that was undetected till I went to use it and had a leak. 
Coming from a plumbing background (LU230, San Diego, CA), if you're connecting pipe/fittings for a low-pressure air system (or water), then yes, use the yellow Teflon tape that is made for natural gas piping. Natural gas piping is normally malleable fittings with steel pipe using the NPT threads, which are tapered as mentioned. They don't really crush together, they simply form a seal via the taper. This might be for .5" > sizes.

If you're using pipe/fittings for high-pressure air, there could be an issue using the yellow Teflon, which maybe sufficient. The reasoning is that MOST Teflon tapes are manufactured with an oil based product So to be on the safe side, I use a product called Formula 8 (a paste), which is made specifically for Medical Oxygen piping in hospitals and is safe to use for any threads due to being inert. There is also a specific Medical Gas Teflon tape that I use that is not an oil base product, so is as safe as the paste. I only use these on high pressure connections.

My 2¢ anyway.

mike

Ok thanks guys. I thought npt thread didn't need Teflon tape cause they are tapered. thought only bsp and m10x1 needs it. Will get some Teflon tape too.

M10 and BSP fittings don&#;t get Teflon tape. They are usually sealed by a plastic tiny square cut doughnut ring seal like what came inside your lightning parts bag, or metal rubber seals called Dowty seals



@ Union brother Revoman- great advice to post up on an open forum. I&#;m out of LU 104 Bay Area/Sacramento. Be good, buddy 
NO...NPT threads do NOT NEED Teflon tape !

I normally use oil (engine oil !) on ALL of my NPT threads. Be them brass, aluminum, steel or stainless steel. I've NEVER used Teflon tape on ANY of my NPT threaded joints. I've worked on cars, motorcycles, boats since I was around 14 or 15. I'm 71 right now !

Funny thing, even most plumbers don't even use that crap. They use Teflon paste. Unless you are perfect at applying it, it gets into everything. I can't tell you how many people that I've helped with their engine oiling problems and their fuel system problems...only to find...Teflon tape where it should NOT be.

If you feel that you can't make this connection correctly with out help, use Teflon..."PASTE". MUCH better at lubricating, MUCH better at sealing.

Your toys, your money, Use whatever you see fit, if you'd like to stop by my house for a demonstration, I can show you why the tape is crap.

Mike
"NO&#;NPT threads do NOT NEED Teflon tape !"

While this may be a good idea for oil, it's not for gasoline, or clean systems that cannot have any oil. Teflon tape is a very valid means of creating a solid, leak-proof connection. As I also stated, I use paste for high-pressure air lines where oil is bad juju, but will also use the RIGHT Teflon tape when needed.

It is completely dependent upon the material being conveyed. A blanket statement is not justified. To each their own.

Bigragu....I KNEW that you would appreciate the affiliation!

mike

As a general rule, fittings with tapered pipe threads (NPT) should not be assembled to a specific torque because the torque required for a reliable joint varies with thread quality, port and fitting materials, sealant used, and other factors. (Source: Parker Hannifin Catalog Port End Assembly, page T7)

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Leakage path through NPT threads occurs between the very peaks of one thread and the very valley of the opposing thread. No matter how tight you make NPT threads, a leakage path still exists. It is the function of the sealant to block the path between the male and female thread.

This is most helpful!

Most screwed piping is tightened until it feels "right" and the fitting is pointing in the desired direction. What the experienced mechanic is often "feeling" is how the fitting is getting tight. Screw it into until it starts to seat. Then up the force a little by yanking. If each yank gives less movement, you probably have a sound joint. If the movement stops suddenly, you have probably bottomed out. The experienced plumber knows when to stop before he damages the fitting or boss. Caution is advised, tapered pipe fittings into an aluminum boss as excessive torque can crack the boss. This is especially true when using Teflon tape because the low friction of Teflon makes it easy to over-tighten.

According to this reference, the pipe should be in the fitting 9/16" for 3/4 NPT threads.

This one states 0.400 inches for hand tight and 0. for maximum. WRT the above 9/16 is 0. inches, so some minor disagreement there.

This one agrees (within rounding error) with the second (0.400 and 0.546), and also provides a helpful guide for number of turns (4.5 to hand tight, 3 with wrench beyond that)

I also recall, but am not finding a reference for a rule of thumb that there should be 3 threads exposed past the fitting (the picture in the last link is particularly good at showing why, I think, but does not mention the RoT) This sprinkler document does provide something on that line, indicating a range of 3.4-3.9 threads for 1/4 to 1-1/4 pipe sizes, and up to 5.1 on some larger sizes.

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And yes, despite any misleading information you may find on the internet, whether it's pipe dope or tape, it is a required "SEALANT" for the helical leak path at the thread roots. Lubrication is all well and good, but that not why it's used. I've personally moved from old-stye dope to teflon tape to new-style teflon dope. YMMV.

PTFE tape DOES seal. NPT threads have a spiral leak path even when fully tight. This is because they engage on the thread flanks, but the roots and crests don't touch each other.

With iron and steel piping, as a general rule, if it doesn't break when you tighten it, it won't ever.

Fittings most often run undersized compared to the standard; in fact, in about half of samples, they are out of tolerance. So it takes fewer turns to reach full tightness.

I assume that you are referring to National Pipe Thread fittings. Unfortunately there is no real one answer to the question of how tight should I tighten them as there is may differences between materials and the quality of the threads. This really becomes a "tighten until it just feels right" type of answer and that comes with experience. In general terms you want to aim for 2 to 3 full turns after hand tight. If it still feels loose, complete another full turn. A lot of plumbers will use both teflon tape and pipe dope. Depending on the thickness of the teflon tape you will want to use 3 to 6 wraps in the direction on the threads.

Actually, you could just have someone experienced tighten it to the minimum and then have you tighten it another turn or two, that should give you a pretty good idea. That's what I asked my buddy to do for me when I started. 1/2" to 1-1/2" are pretty easy to feel out. The bigger sizes have less of a gradient and that one more turn you think you have might not make it.

Remember, water is the only thing that's really high pressure. After the regulator on the tank gas is like 45psi or lower, like 1/2 to 5 psi in the house. And heating oil is like nill as well unless they have a pump on the tank but then it's still only like 15psi.

Luckily I have never cracked a regulator which is pretty easy to do if you're new, but I did crack an air chuck of my own putting it on a hose. Luckily I had two and it was cheap. I blame the hose maker because the hex bit for the wrench is slighty smaller than the crimp ring making real difficult to grip without screwing up the crimp seal which I have also done. Insert fittings and hose clamps are much better.

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