Thread-seal interference 1

[Jevons]

Hi All,

I'm currently in the process of reading an API guide on testing casing and tubing designs (which I don't have much experience of).
I've come across the term "thread-seal interference". From researching this term I found some very vague information regarding this.

From what I can gather, I believe it has to do with the way in which the threads interact and how they form seals properly. Is this correct? I would appreciate it if someone could point me in the correct direction or provide additional info, particularly with regards to the following definitions:

thread high - seal low
thread low - seal high
thread high - seal high
thread low - seal high

Thanks,

Jevons

 

[MikeHalloran]

There's a family of threads designated NPTF.
They are also called 'dryseal'.
There's a nominal thread interference (other than the taper).

It's a cosmic joke.


Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

As MikeHalloran notes, there is a NPT standard for tapered "dryseal" pipe threads. But these thread joints still leak around the tip/roots like any other thread form will. In order to get them to seal fully, some sort of tape or compound must be used to fill the empty space at the tip/root gap.

 

[blacksmith37]

There are hundreds of threads used on API tubulars, there are a variety of torque shoulder, seals, thread clearances, etc. Because most are proprietary, API cannot address them.

 

[blacksmith37]

This question belongs in Pet. Production.
API does not use NPT; it uses 8 round (and 10 round, and buttress), looks a lot like NPT. It requires API dope to seal , used to be full of lead, zinc, etc, but so many children were eating it, they had to take out the lead (25yr ago). And I forgot, 20 yr ago API reverse engineered the PH6 , old proprietary thread, and adopted it. I expect Hydril is still suing API.