WRC297 vs FEA 1

[Ehiman1]

Hello,
I was checking stress values in nozzle - shell junction with WRC297 and finite elementh method analysis, but I can't understand why there are a lot of differences between these 2 methods.
With WRC 297 I have the bigger stress value at 170% of allowable; with FEA I have the bigger stress value at 60% of allowable.
I designed nozzle and vessel with Compress.
Have you evere had a problem like this one?
I don't understand why the values are so different, because I use the same loads, materials and sizes.

 

[r6155]

Use hand calculation.

Regards

 

[JStephen]

I was thinking I had seen comparisons before, with something more like 30% difference. Forget where, either the WRC 297 publication or maybe some of the vessel handbooks.
Things to check:
-whether both results also include effects of internal pressure in the vessel
-whether stresses compared are the same, IE, bending vs membrane
-whether loading is identical or not

 

[Trestala]

The philosophy/rationale/theory of WRC 107/297 are described in the document itself. It will have different results from FEA even with identical geometries, properties and loads.

 

[DriveMeNuts]

I did a parametric study of a few geometries some time ago and found that WRC 297 stresses are 30-100% higher than FEA when t/T > 1.0.
For thinner nozzles the difference is even greater.
WRC 297 is very conservative. This is why it is rarely used in industry.