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dkf7142 (Specifier/Regulator)
8 Dec 03 15:22
I'm having difficulty locating reference information for maximum operating pressure for NPT and BSP threads up to and including 2". Thanks for any help.
Helpful Member!  sethgus (Mechanical)
29 Dec 03 16:26
API 6A should include the NPT...I believe it is 10,000 psi to 1/2" NPT and 5,000 psi for up to 2"..check spec
Helpful Member!  JACeric (Mechanical)
30 Dec 03 10:45
Check ASME B31.1 or B31.3.  Formulas are available for various sizes.
Celebur (Mechanical)
12 Apr 04 19:23
Having essentially the same question, I appreciate the references given above.  This is what I found:


API 6A -- refers to "line pipe" thread rather than NPT.  The now-retracted 18th edition had a note on interchangeability for sizes up to 1 1/2" with a caution that the slight variation in thread form can increase wear and tendency for galling after several make-ups.

Table 4.1 in the 17th edition summarizes the pressure limits, but one needs to keep in mind the material requirements in Table 5.2 (which exceed those of ASME valves, for example).


ASME B31.1 and B31.3 are both piping specs (power and process respectively), and short of detailed stress analysis, neither standard addresses pressure ratings for female threaded connections.  B31.3 does mention (para 314.2.1c) that "female threaded components shall be at least equivalent in strength and toughness to threaded components listed in Table 326.1", which in turn references numerous other standards including B16.34a for valves.

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