Hi Abijith,
The WRC 107 method computes stresses on the upper and lower surfaces at the edge of the attachment. PV Elite uses the Lame equations and computes the surface stress on both the upper and lower surface of the shell. You should find these are accurate values. PR/T does not generally give an accurate result if the shell is thick compared to the radius. Also, note that the WRC 107 bulletin does not include the effect of pressure in the analysis.
Hopefully, this clarifies our approach.
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Scott MayeuxCADWorx & Analysis Solutions
Intergraph Process, Power, & Marine