Pipe Threads - Why No Pressure Ratings?

The SAE, in specification J530, is very specific as to the physical characteristics of pipe fittings in general as well as pipe threads. They detail such criteria as wall thickness, thread taper angles, major and minor diameters, profiles, etc. The SAE does not offer any stated or implied pressure ratings, however. There are three primary reasons for this apparent omission.

1 ) The multitude of different pipe thread types. Trying to rate NPT, PTF, NPTF and the British versions, BSP and BSPP, would be an impossibility especially since each size of each type would have to carry a separate rating.

2 ) Mating parts - A pipe fitting can be assembled into a machined part, forging, casting or molded part. It could be brass, steel, stainless, zinc, aluminum, plastic or other. Each has different thread sealing characteristics even though it is "pipe thread."

3 ) Assembly methods - There is no SAE specification relative to assembly torque or number of turns of engagement necessary to assemble. Here again, the number of variables are enormous and also dependent on the strength and determination of the assembler as well as the presence of a variety of thread sealing compounds.

A pipe fitting, and its connection, has only one mission and that is to not leak. Consider sealing all threaded connections including the Dryseal type.

--David Hoffman