Thread sealants on NPT and others?

[JRH02]

Cleanliness has been mentioned through the replies. But unless you are building with new parts for both the male and email NPT threads your not going to have the privilege of fully clean threads. Of course the female is the worst of the two (don't read into that more than intended, wink). I'd have zero problems with teflon tape if done correctly. Seriously, one wrap plus a bit for overlap is sufficient. And CLEAN and dry with no oil slick, including your hands. More is not better with teflon tape or ANY sealant for that matter. The male threads should be sharp with no knicks. There's not much to be said for the female. What are you gonna do anyway? Run a NPT tap (by hand) into the hole on a control valve? Or any other connection. I've never had a problem with hydraulic connections of any type: NPT, compression or double flared. Clean, dry, proper fitup. And you NEVER use anything except for a touch of 'never seez' on compression type fitting and that is threads only.

NPT threads are 100% threads by design. There isn't supposed to be anything less than 100% thread. That's why they can seal without sealant. But of course you want them to maybe come apart some time later if needed. So use whatever with cleanliness and as little as possible for a non-hardening sealant. If the joint doesn't leak immediately it shouldn't ever afterward.

YMMV

 

[WinterDeere]

Seriously, one wrap plus a bit for overlap is sufficient... More is not better with teflon tape or ANY sealant for that matter

Teflon tape comes in different thicknesses, but I've made many tens of thousands of taped threaded connections in my lifetime, and have found that 2 - 4 thicknesses of tape usually gives the best chance of success in finding your system leak-free when pressurized. If you have tape of width similar to the engagement length of the thread, this can be just 2 - 4 turns, but on larger fittings with longer engagements, it may be 2 - 3 turns per tape thickness, often meaning 6 - 10 total turns before you reach a nominal 3 thicknesses.

Counting on sharp threads, even with new fittings that have been jostling around in shipping or the parts truck, is an optimistic. As to cleanliness, we typically clean male threads with a soft wire wheel on a bench grinder, and do our best with a wire bottle brush or copper fitting brush on the females. Tape cleans off used fittings much easier than dried dope.

 

[SteveS42240]

I use Gasolia sealant on all the metal NPT pipe I put together. Occasionally I will use teflon tape on some air fittings in the shop, but if it's on the compressor, it gets Gasolia as well.

 

[sixdogs]

If you use Teflon Tape, use the Yellow tape intended for gas and fuels. The white and pink will break down when exposed to hydrocarbons, including hydraulic and motor oils.

The yellow tape doesn't break down?

 

[WranglerX]

Again.....

Thread seal tape - Wikipedia

en.wikipedia.org

Don't you wish PTFE tape came with application information like some "pipe dopes"

 

[WinterDeere]

If you use Teflon Tape, use the Yellow tape intended for gas and fuels. The white and pink will break down when exposed to hydrocarbons, including hydraulic and motor oils.

I am familiar with white PTFE tape breaking down when exposed to natural gas, but do you have a reliable source that states the same happens with exposure to hydraulic and motor oil?

The advice I’ve seen in the past to avoid PTFE tape in hydraulic systems has everything to do with the probability of ham-fisted plumbers not applying it correctly, and the impact of getting loose tape strands into the system, but nothing to do with the actual product susceptibility to the fluids at play.

 

[etpm]

I am familiar with white PTFE tape breaking down when exposed to natural gas, but do you have a reliable source that states the same happens with exposure to hydraulic and motor oil?

The advice I’ve seen in the past to avoid PTFE tape in hydraulic systems has everything to do with the probability of ham-fisted plumbers not applying it correctly, and the impact of getting loose tape strands into the system, but nothing to do with the actual product susceptibility to the fluids at play.

Here is a link to teflon, AKA PTFE, compatability: Teflon PTFE Chemical Compatibility Reference Chart
As far as I know teflon tape sold in the USA is pure teflon except for dyes, like the yellow and pink stuff, and tiny amounts of contaminants. These contaminants are why teflon tape made for pure oxygen use is especially pure.
I am dubious about claims that natural gas breaks down teflon tape. I do know that the white teflon tape sold in the USA is thinner than the yellow teflon tape sold for natural gas and propane use. But I don't think the white stuff breaks down from exposure to methane.
Eric

 

[Flogger]

I’ve always used Teflon tape on NPT pipe/fittings, and always will

I once had 3 technicians involved in troubleshooting a machine. In total we had 160 hours involved and finally stumbled onto a tiny piece of teflon tape blocking an orifice coming from a shift valve. I always have Locktite 495 on hand and if I catch someone using teflon tape I offer them an opportunity to better themselves! Pipe sealants can cause numerous problems also.

 

[Flogger]

I once had 3 technicians involved in troubleshooting a machine. In total we had 160 hours involved and finally stumbled onto a tiny piece of teflon tape blocking an orifice coming from a shift valve. I always have Locktite 495 on hand and if I catch someone using teflon tape I offer them an opportunity to better themselves! Pipe sealants can cause numerous problems also.

Excuse me. Locktite 545 is the hydraulic sealant. 495 is a flange sealant which is also an excellent product.

 

[jigs_n_fixtures]

I am familiar with white PTFE tape breaking down when exposed to natural gas, but do you have a reliable source that states the same happens with exposure to hydraulic and motor oil?

The advice I’ve seen in the past to avoid PTFE tape in hydraulic systems has everything to do with the probability of ham-fisted plumbers not applying it correctly, and the impact of getting loose tape strands into the system, but nothing to do with the actual product susceptibility to the fluids at play.

Per DuPont, the ASTM, and the various building codes:

White tape is single density and intended for water pipes of 3/8 of an inch or less. It can sometimes be found in a silver color to match the pipes.

Red tape is triple density, for pipes one-half inch to 2 inches in diameter. It is designed for pipes with larger joints, such as water distribution pipes. Note that the container is red, but the tape itself looks pink.

Yellow tape is double density and designed for gas and fuel lines.

Green tape is grease and oil free and designed for pipes carrying oxygen.

Please note that these tape colors refer to specifications in the United States only.

From me: All the tapes except the green, have oil/hydrocarbon-based carriers in which the Teflon is embedded (might not be the right word, I lost a lot of vocabulary when I was down with COVID), and the carriers are soluble in various solvents. So, I would only use the yellow tape for anything with oils or aromatic hydrocarbons. None of the tapes are listed for hydraulic fluids, but hydraulic fluids and motor oils burn pretty much the same and are close chemically. Thus, the yellow tape, if I were to use tape.