determine axial strength of screwed joint

[gerrytt]

Need to determine axial strength of screwed joint. Main member 36" diameter pipe with 1" thick wall, 4" diameter sch 80 nipple with 8 no. threads per inch, only 1/2" screwed into main member (self threaded into main ), carbon steel. What maximum tension can this joint sustain?

My solution : the shear strength of 1/2" section of nipple,
.3 x 35,000 (psi, fy for pipe) x (PI x 4.25 x 1/2)(in2, cylindrical contact area) = 70,000 lbs
Off course divide by say 2 for safety, allowable 35,000 lbs

Your comments will be appreciated

 

[boo1]

I think I would apply a further reduction for the stress concentration factors, and lead angles of the threads.