I’m doing some research about SIF with D/t> 100. I’ve done a static structural analysis in ANSYS based in the correlation of SIF’s with stress indices using these considerations:
1. Tangents pipes of 3 times the outside diameter
2. i=(C 2*K2)/2
3. 90º Elbows and 45º Elbows
4. Material: Carbon Steel ASTM A234
I’m Concerned because I’ve obtained an error of 26% between FEA results and those obtained using the B31.3 equations. Did I do something wrong?
Because Tengku_Syahdilan said that he read that “an incorrect modeling of elbow or straight pipe with Large D/T can be lead an error result in order of 25%”
Besides I know the importance of the pressure in pipes with large D/t so I’m thinking analyze the models with internal pressure for study their behavior. Any recommendations for that?

I'll appreciate your help.THANKS