Max Torque that a female NPT threaded body can withstand 1

[aander3120]

What is the max amount of torque that could be applied to 1 in male threaded NPT pipe when it is threaded into a 1 in female threaded body that is made from ASTM 126 cast iron. The dimensions of the threaded female body are shown below. Essentially I would like to know what is the max stress that female threaded body can withstand.

 

[XL83NL]

https://www.eng-tips.com/viewthread.cfm?qid=5045

https://www.eng-tips.com/viewthread.cfm?qid=164688

NPT is not controlled by torque, so it seems useless to know this. If you really want to know, make a test setup and find out experimentally. And with withstand, do you mean up to where the point of yield starts, or failure by breakage (sorta plastic collapse), or ... ?

 

[aander3120]

I have tested experimentally what the torque would be until failure of the female threaded body, but all the tests I have conducted so far the threads fail on the female inlet before the casing around the threads. I would like to know how much torque it would take to have the outside casing fail if the threads were theoretically stronger. Basically want to know how much stronger is the female body then its threads. I was hoping to find an equation that would tell me this so I would at least have some theoretical values to go off of.