Your transient event is this pressure wave that, once started by valve action, travels upstream to the source and then bounces back and forth on it's way back to equilibrium. (The is a similar event traveling downstream from the valve as well.)
Yes, the transient load continues until equilibrium is reached. This load will seen by each surface perpendicular to flow (e.g., every elbow). And there is reflection off these surfaces as well.
So, yes, you may have to run your time history simulation for a longer period to add these extra hits.
I suspect that you are using some sort of fluid transient hydraulics package to generate these loads for CAESAR II. You will have to first run that simulation longer to collect more time history for use in CAESAR II.
My guess, though, is that the first hit is most severe and later hammers are too late to sum directly with the response from the earlier hit.
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Dave Diehl