Shear strength of NPT threads

[kstaylor]

Does anyone know of a method to calculate the shear strength of tapered pipe threads (NPT type threads)? The load would be an axial tensile force on the pipe. Much thanks for responses.

 

[johnp]

Take pressure rating of pipe and pipe fitting. Apply this on the end as Force = Pressure x Pi (D^2)/2. This is the minimum force the fittings are designed to take in axial tension.

 

[ghillis]

JohnP is probably pretty conservative, since pressure limits are based on hoop stress in the pipe.

Assuming male and female joints are same material the answer would be based on the shear area equal to half the engagement length times the mean circumference (at pitch diameter)of the threads. Engagement should be conservatively estimated, since imperfect threads have limited capacity.