I had to go back and read what Peng says (in Pipe Stress Engineering) about staging these transient forces applied at each elbow.
On page 403: "Although the forces are all acting at different times, it is necessary to apply the forces all at the same time in a static analysis. The time-history analysis, on the other hand, can consider the actual force shapes and arriving times at different locations."
I do not know why he says it is necessary to apply all static forces at the same time. This would just put each segment between elbows in tension and there would be no displacement other than the very small (due to high axial stiffness - AE/L) axial extension.
I would want to see the loads applied individually as those loads would develop the loads that pull the pipe off its axis.
I lean towards Ltorrado's load cases. But my interest would not be limited to those SUS+OCC stress cases, I would also take a hard look for excessive pipe displacements and support loads in those "operating plus single-leg imbalance" load cases (L2 to L5 in the example).