FEA ANALYSIS IN COMPRESS SOFTWARE 1

[thiru777]

In Compress, during the analysis of FEA for Self reinforced nozzle, the result FEA model shows as if nozzle is not attached to the shell, there is a huge gap between nozzle and shell. This raises the doubt whether compress actually check the nozzle to shell weld junction for Self reinforced nozzle.

Anyone kindly clarify!!!

thanks

Ananth

 

[marty007]

I'm not 100% certain, but I believe that Compress excludes this area because this is an area of local peak stresses per ASME VIII-2. This area would only need to be analysed if the vessel is in cyclic service and fatigue life needs to be analysed.

If you open up the options menu for the FEA analysis, you can choose to force this area to be analysed. (I haven't tried this as for fatigue analysis I have used other methods...).

Cheers,
Marty

 

[thiru777]

Thanks marty, i have tried forcing this area to be added from the options menu by checking on the "Compute stresses in weld" option and i could find the result being changed. The Analysis is being performed for the junction

Thanks for your help


Cheers,
Ananth

 

[pvrerate]

marty007 is correct. Compress utilizes Paulin Research Group's software to perform the FEA. Paulin, in their literature, does not recommend calculating stresses in fillet welds because of the inaccuracies involved. As marty007 has pointed out, only peak stresses are of interest for fillet welds and hence fatigue analyses. To perform a fatigue analysis, the FEA program determines the value of the alternating stress to be used in the fatigue analysis by using the highest secondary stress in the base metal adjacent to the weld area, dividing that value by 2 to get the magnitude of the alternating stress and then multiplying by a stress concentration factor. The value that Paulin recommends for the SCF is 1.35 based on their laboratory testing.