npt pressure ratings

[tbydalek]

I need a pressure rating for 1" npt with stainless steel fittings. Is there a standard for pressure ratings of npt threads and fittings. Alternatively how could this be calculated.

 

[reichertc]

Assuming you are using ASME B16.11 threaded fittings, the first step is to determine what wall thickness of pipe you are going to be using (making sure that you don't take credit for the thickness of pipe that gets removed in the threading process.

Next you look up Table 2 in ASME B16.11 which tells you the class of fitting that corresponds with the pipe wall you have calculated. 2000# fittings correspond with S80 (XS) pipe, 3000# fittings correspond with S160 pipe, and 6000# fittings correspond with XXS pipe. Pick the class that matches the pipe wall you have chosen, or round up to 2000# or 3000# if you are using STD weight pipe. This will make all your fittings stronger than the associated pipe.

(Alternatively, you could specify your fittings as the weakest link in the system, but I don't know why you would want to do that.)

If you are using B16.3 malleable iron fittings, you will need to get a copy of the standard and check out Table 1, which gives pressure/temperature ratings for these 150# and 300# fittings.

Hope that was clear as mud.

 

Hello All,

A reference for this topic:

Pipe Fittings and Piping Handbook, Louis G. Lamit, 1984 Prentice-Hall Inc, publisher, ISBN 0-13-676601-1.

Also, Phil Ellengerger of WFI is working on a fittings book for CASTI Publishing.

Best regards, John.