Hi all

I'm designing some discharge piping for vessel over-pressurisation bursting disks, that vent back to a blowdown vessel. There are a couple of vessels all linked to a single header. The vent pipework is pressurised with an inert gas, and has a second bursting disc attached to the blowdown vessel. So in effect it is a closed system.

I'm trying to work out the best way to assess the forces generated when the vessel bursting discs go pop. I understand that there will be a transient state where a pressure wave will travel along the pipework, during which there will be out of balance forces on elbow pairs.

I noticed in the Caesar II Applications guide that it states that impulse loads initially produce axial acoustic waves in the steel pipe wall that can induce locally very high, very short duration forces and stresses. These short duration loads are usually not a design problem in ductile steel piping systems unless crack propagation is a concern.

This suggests that I don't need to assess the stresses against code allowables (B31.3). However there must be a limit to this rationale? Presumably at some point the strains are going to exceed a safe limit?

Does anyone have any guidance on this? Any help would be gratefully received!

Richard