Assessment of an Unloading Line
The pressure surges due to the transient 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 forces were then applied to a CAESAR II piping model of the system. The dynamic solver within CAESAR II was used to calculate the stresses arising in the unloading line as a result of the pressure surges.
It was shown that by extending the closure time of the valves the magnitude of the pressure surges could be kept within the pressure rating of the pipe. It was also recommended that a two stage closure profile, within which the last part of valve closure is very slow, be implemented for one of the valves.
The dynamic piping analysis showed that excessive stresses would result in the piping system 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. 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.