NPT Thread advice 3

[davem416]

Does anyone know the specific steps to using an American National Taper Pipe Thread (NPT?) Specifics would be helpful. e.g. how many wraps of teflon tape would I need, etc.

Thanks,

Dave

 

[ecampos]

Check the Machinery's Handbook for info.
Wrap the teflon tape a couple of turns on the whole length of the thread. Take care to wrap the tape in the opposite direction of the thread. Example, you are going to turn the pipe fitting clockwise to install it, then wrap the teflon counter-clockwise to avoid the tape unwrapping.

Edson Campos
edsoncampos@earthlink.net

 

[drnengr]

To prevent getting strands of the teflon tape into your system, keep the wraps approx 2 threads back from the end of the pipe/fitting. Teflon strands can raise havoc in any system with small orifices or low clearance moving parts. Hydraulic servo syatems are one example that will not tolerate contamination by teflon. Consult your component suppliers about using Teflon tape.

 

[prex]

All you guys apparently don't know the teflon tape is already an old fashioned invention!
Sealing products are normally more effective, especially as they minimize the risk of contaminating the pipe.
prex
motori@xcalcsREMOVE.com

http://www.xcalcs.com

Online tools for structural design

 

[manian]

i understand that the NPT threads have generally been recognised as dry seal pipe threads which means, no additional sealant like Teflon tape is a must, but would assist in sealing if used. you could probably refer to the ASME/ANSI Standard B1.20.1.

Trust this is of some help to you.

regards

 

[jonralph]

Teflon tape should be wrapped in the same direction as the threads to avoid unwrapping. I was always taught 2 wraps on the front, 3 on the back. Obviously if you are using 1/4" NPT you can only get the initial 2 wraps on. There are a lot of alternative sealant pastes etc out there but tape still has its uses.

 

[TBP]

Wrap the tape in the same direction as the fitting screws on. Use the edge of the spool to "chase the theads", pushing the tape down into the thread. In addition to keeping the tape back a thread, use the GOOD heavy stuff - like "T-Tape", not the "cheap-o" thin white grade that gets used on domestic service. All Teflon tape is not created equal.

 

[waoolaa]

where can i find pictures for a buttress thead
thanx alot
bye

 

[boilerman]

I agree with 22 June reply wholeheartly, with the addition of adding liquid teflon on top of tape ( T-Tape ). I have been using this method for 35 years with 100 % successs, don't knock success, right

 

[yoel]

NPT thread needs no additional sealing like teflon! The tapper angel gives an excelent contact sealing when thread is wrenched to the end.

 

[TBP]

That's theory vs reality Yoel. You can't nearly always "wrench to the end" of the thread, because the fittings have to align with the rest of the assembly. If you're using 3000# forged steel fittings, when they hit the end, that's it, whether the fitting is properly aligned, or not. It's not going any further. Additionally, very few threads are "perfect". There's a large element of art as well as science in threaded pipe.

This is from IPT's "Industrial Fasteners Handbook"

"The prime purpose of tape or dope is lubrication to allow thread surfaces to deform and mate without seizing or galling. Pipe dope also helps plug openings resulting from improper thread manufacture and in some cases acts as a sealant to prevent leakage of gases and liquids."

If the threads aren't lubricated, there will be excessive heat generated when making up the fitting. Even with lubrication (and not tightening too quickly), you can put your hand on the fitting that's just been wrenched on, and feel the temperature increase.

If tape/dope isn't applied (and properly) to male pipe threads before assembly, you'll have a lot of leakers.

 

[diamondjim]

I think a lot of the discussion is valid depending
on the pressures and medium being used with the
fittings. Grease fittings generally have low pressure
being applied and do not need to be sealed that well.
To teflon or not to teflon, that is the question.
Forgive the humor.

 

[yoel]

In hydraulic systems joints we do not use Teflon with NPT.
In water joints we do. Probably hydraulic joints are more accurated.

 

[TBP]

You're most likely using a variation on NPT that is common in hydraulic systems - Dryseal ANSI Standard Taper Pipe Thread (NPTF). This thread is also known as the Standard Taper Pipe Thread for Fuels. Special dies, marked NPTF, must be used to cut this kind of thread. It's very hard to tell NPT from NPTF by just looking at it.

NPT may have a spiral leak path along the length of the thread, between the root on the internal thread, and the crest of the mating external thread. This requires a sealant be used.

NPTF will not require a sealant, however, assembly without a lubricant is prone to galling, especially with stainless steel or other nickel alloys. Thread sealant should be used not so much for leak prevention, as lubrication. System contamination can be an issue, so it sealant/lubricant should only be applied to male threads, and be kept back one or two threads from the end of the pipe.