Sealing NPT fittings

[Tofflemire]

Hi All,

I am in a debate at with a few people I work with on sealing NPT fittings. We us a couple of sizes 1/8" and 3/8" NPT fittings. We use Teflon tape on the threads and install, we then pressure test the assembly that this fitting is installed. My problem is if a fitting leaks, I just want the tester to pick up a wrench and tighten this fitting until the leak stops. The other side of the story is they just want to use Loctite to seal the threads. I feel that this is just a band-aid fix, which not really fixing the problem. Is there a torque value I should be calling out tighten these fittings too or just loctite the fittings.

TFAA

Tofflemire

 

[Cockroach]

Typically the MNPT seals on three (3) threads, sealing is a true mechanical joint between box and pin. From this point of view, whether you use teflon tape or LocTite, you are merely promoting probability of making the mechanical joint along the pitch diameter of threads. You may find that down the road, a leak develops.

Being heavily into the Oil & Gas industry, definitely tightening the plug is the way to go. In the field, absolutely nobody makes waste of time to refer to a torque spec, even if one is readily available. There are API specifications which do call out a limit, but these are rarely called.

It's like tightening the lug nuts on your spare tire after replacing a flat. Do you really worry about the manufacturer's recommended torsional specifications? Probably not. Therefore, get buddy to lean on the wrench to establish a better mechanical seal. Ocassionally, replace the pipe plug, it's the $CDN 0.23 fix, maybe it's bad or has already been wrenched beyond the recommended limit.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[Tofflemire]

Hi Cockroach,

Thanks for you info, I couldn't agree with you more on the tightening issue. I had to convince the production manager that he and his works were making a judgment call not to try and tighten the fittings for fear of damaging the threads. Once we over come this, they proceeded to tighten the leaking fittings and sealed all of them without loctite. Just as you and I knew these fitting would.


Thanks again,
Tofflemire