Connecting 1/2" NPTF

[Falco de Negro]

To add a bit more to my "no tape" policy, most times, with careful application of tape, the first assembly is just fine.
It is the subsequent disassembly and reassembly that pushes used tape ahead of the male part and into the oil-stream.

There should never be even one tiny bit of old tape present when reassembling a fitting. Use a wire brush to remove all traces and apply new.

 

[Falco de Negro]

And to really kick off the discussion teflon tape is not a sealant it is a thread lubricant.
A good thread lubricant will allow NPT threads to distort and seal with no damage,
so they can be broken apart and reassembled without leaks.

Absolute truth! It was hard for me to accept this fact when a knowledgeable expert first told me that tape is not a sealant. It is essentially an anti-seize measure so you can disassemble the fitting later. I just made it up in my mind when I was a kid that it was a sealant.

 

[LD1]

DL,
If you disassemble a teflon taped fitting, you need to be really careful to remove ALL the scraps of tape left in the female part before reassembling. Some of those scraps are really small and hidden in the female threads but get pushed out of the thread by the male being advanced into the fitting--the second time.

On a related subject:
Once I helped a friend in the maple syrup equipment manufacturing business set up for a trade show. I screwed a DRY 1/2" SS nipple into a DRY SS female device, HAND TIGHT (for demo purposes only) and it galled the threads so bad it ruined both pieces.

Same can be said for stainless nuts and bolts too.

Not necessarily hand tightening them, because there is clearance in the threads of a bolt and a nut. But I have had stainless nuts and bolts galled the threads when using power tools like an impact well before tightening the actual nut down. Different grades of stainless react different.....but anytime I am using a powertool on stainless it gets lube of some kind.

 

[npalen]

Same can be said for stainless nuts and bolts too.

Not necessarily hand tightening them, because there is interference in the threads of a bolt and a nut. But I have had stainless nuts and bolts galled the threads when using power tools like an impact well before tightening the actual nut down. Different grades of stainless react different.....but anytime I am using a powertool on stainless it gets lube of somekind.

there is interference in the threads of a bolt and a nut.

Did you mean to say "there is no interference"?

 

[PILOON]

What has worked well for me is a construction grade urethane caulking* that is very much the same as automotive windshield adhesive.
Very little is needed, just barely enough to fill a few threads.
It is nice and paste like and sets up fairly fast but still can be unscrewed if needed.
The idea being 'just enough' to fill the minor thread gaps.

*Flextra is one brand,

 

[LD1]

there is interference in the threads of a bolt and a nut.

Did you mean to say "there is no interference"?

yes. I fixed it

 

[LouNY]

Same can be said for stainless nuts and bolts too.

Not necessarily hand tightening them, because there is clearance in the threads of a bolt and a nut. But I have had stainless nuts and bolts galled the threads when using power tools like an impact well before tightening the actual nut down. Different grades of stainless react different.....but anytime I am using a powertool on stainless it gets lube of some kind.

The best lube for stainless threads that I found many years ago while working in the Instrumentation Field with the majority of the tubing and pipe being stainless was Chesterton Spray Nickel anti-sieze.
That was amazing stuff, just checking it out on stainless 316 npt fittings putting them in a vise and using a large pipe wrench you could over tighten a fitting untill all the threads were out of sight and take it back apart with no galling or missing threads.

 

[WranglerX]

DL,
If you disassemble a teflon taped fitting, you need to be really careful to remove ALL the scraps of tape left in the female part before reassembling. Some of those scraps are really small and hidden in the female threads but get pushed out of the thread by the male being advanced into the fitting--the second time.

On a related subject:
Once I helped a friend in the maple syrup equipment manufacturing business set up for a trade show. I screwed a DRY 1/2" SS nipple into a DRY SS female device, HAND TIGHT (for demo purposes only) and it galled the threads so bad it ruined both pieces.

SS is great for that.... Only use SS when necessary for food grade work, and only use food grade "dope" for lubricating threads....