Dear All,

I am performing a Dynamic Stress Analysis for a Carbon Steel 24" Gasoline Above Ground line.

Because of ESD valve closure, surge pressure is generated. I am applying the surge load in the most critical elbows of the model. Methodology followed for the Time History Analysis is as per COADE Mechanical Engineering News, June 1994.

The Static Analysis gives me a 75.7 % Code Stress Ratio at the very beginning of the model (Sustained Case).

Dynamic Stress Analysis, combined with the sustained case (because is the most critical Load case as per static analysis), gives me 51%. How can this be possible?? The combination method I am using is ABS, hence the Dynamic code stress ratio MUST be greater (or equal) than the static one, and NOT smaller!

If you have any idea, please share.

Thanks in advance.