Pipe Knocked From Supports by Hydraulic Transient Event

Following what was considered a routine realignment of liquid product lines and tankage at a storage and transfer facility, an incident occurred that resulted in significant movement of a 20-inch pipeline, causing a large section of it to fall from its supports. The event also resulted in the failure of a gasket at a valve flange and loss of containment. The alignment activities and pump startup were investigated for the potential to generate a hydraulic transient capable of generating sufficient force to cause the movement. A transient hydraulic model of the fluid in the piping as it was aligned at the time of the event was generated to assist in determining the cause and to help prevent a similar occurrence in the future. Several scenarios were modeled and are discussed in this paper: 1) pump shutdown from steady flow, 2) pump start up with the discharge valve open, 3) pump startup with the discharge valve closed, and 4) pump start up with a vapor cavity present near a closed valve at the high point in the line. Pipe stress and finite element analysis were used to assess the displaced pipe and to determine if it could be placed back into service. The piping stress analysis indicated that the highest stress in the piping was below the yield stress of the material. Results from a detailed finite element analysis with material nonlinearity confirmed that there was no global plastic strain in the piping due to the event. This left a potential for local plastic strain due to the impact of the pipe against any hard surfaces, and this was addressed with visual examination. In the end, the pipe was lifted back onto the supports, lateral restraints were added at pipe support locations, and procedural changes were implemented to reduce the likelihood of future events.