NPT thread information

[doohicky]

Can anybody tell me, point me to a website, or publication that explains the mechanics of how a NPT thread is supposed to work, and possibly have some troubleshooting? I am familiar with ANSI B1.20.1, but need something that would explain the engagement that is supposed to occur. In a perfect world the flanks should should simultaneously engage, correct?

Thank you

Mike

 

[TBP]

IPT's Industrial Hydraulics Handbook has a section on pipe thread that's excellent. They publish about 10 of these little books on a variety of construction/industrial topics, and I highly recommend them for anyone involved in plant maintenance.

http://www.iptbooks.com

 

[thalon]

Have you lok in the "Machenry's Handbook" It has a whole section on pipe thread?

 

[doohicky]

Yes, I have an edition of the "bible", but I could not find any kind of mechanical explainations on the how's & why's a correct thread will perform when assembled into a mating part. I am more interested in any sort of troubleshooting that could be found with engagement.

Mike

 

[TBP]

The thread cut into the pipe should give 3 to 4 turns by hand into a fitting, with clean dry threads. (No tape or dope for this test.) Lots of people cut the threads too deep, and that's a bad thing. The last 3 threads cut are imperfect, so if you've got to wrench fittings on past those last threads, there's something wrong. (It could be the fitting - lots of junk out there any more, especially with 150# malleable.)

Don't wrench the joints up so fast that a lot of heat gets generated. This can happen with lazy fitters who jamb a wrench into power threaders to let the machine tighten the fittings onto the pipe.

Use the correct dope or tape for the service and size of pipe. For example, lots of Loctite products run out of gas at 300*F, making them unsuitable for most steam service. Many dopes from range of manufacturers are listed as being good for pipe up to 2".