In article , Ned Simmons
says...

"Assuming a stout flange, my SWAG is that failure would
occur at the root of the threads near the fitting, where
the wall of the pipe is thin due to the threads."

No SWAG needed, this is the point of highest stress
concentration - threaded fasteners invariably fail
at the root of the thread, exactly even with the
surface of the female threaded part.

The only question would be, how badly would the stress
concentration reduce the apparent ultimate strength
of the material? For a sharp-V NPT thread, done
with a die head in black iron, my own SWAG would
be nearly a factor of three.

That is, to figure out the strength of the pipe
under tension, simply look at the cross section
area of the pipe, calculate based on the ultimate
psi strength for black iron, and then divide by
three. Ed's comments about the joint failing
by collapsing under hoop stress not withstanding.

My guess is the pipe will break before it collapses
inwards. Another SWAG.

Jim

Jim

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