In article , Ned Simmons
says...

I get about .925 dia at the root of the thread at the gage
line of a 3/4 NPT fitting. ID is .824 . Yield on A53B pipe
is 35 ksi min. Ultimate tensile is 60 ksi min.

.138 in^2 x 35000 lb/in^2 = 4830 lb to yield
.138 in^2 x 60000 lb/in^2 = 8280 lb to ultimate tensile

I assume your 3X multiplier is a stress concentration
factor, which sounds reasonable to me, so there will be
some yielding at the root above 4830/3 = 1610 lb., and
failure will occur at 8280/3 = 2760 lb. There's likely a
pretty high uncertainty in the second number depending on
exactly what happens at the root as it yields.

I have not run those numbers but they look good to me.

One point is, my 3X is a stress concentration factor,
for sharp V threads that are die cut. I made that up
off the top of my head.

Another consideration is, the ultimate 2700 that you
suggest is for a purely *static* load. It might be
possible to get shock loads that produce what,
five or ten Gs?

Jim

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