Pressure surges caused by the determined upset scenarios were modelled using the transient one-dimensional fluid modelling package BOSfluids. The pressure profiles in the unloading line were used to determine the net (unbalanced) forces acting upon the piping.
The resultant forces were applied to a CAESAR II piping model of the system. With the dynamic solver within CAESAR II being used to calculate the stresses arising in the unloading line as a result of the pressure surges.
It was found that through extension of the valve closure time, the magnitude of the pressure surges could be kept within the pressure rating of the pipe. Another recommendation was the use of a two-stage closure profile, within which the latter portion of valve closure is very slow, be implemented for one of the valves.
The dynamic piping analysis showed that the piping system would experience excessive stresses due to the pressure surges. To ensure conformance with the EN13480 piping code it was necessary to add additional restraints to remove some of the degrees of freedom. Dynaflow Research Group (DRG) worked with the client to help ensure that these new supports were proposed in realisable locations.
The end result was an unloading line that conformed with the EN13480 for all of the transient upset scenarios.