Establishment and Analysis of Congelation Fault Tree for Crude Oil Transportation Pipeline

Wax crystal in waxy crude oil precipitates gradually with temperature drop after shutdown. Congelation accident occurs and leads to heavy losses when the oil forms a intense structure. It is necessary to conduct identification of congelation risk, analyze various influencing factors of congelation accident and establish the fault tree of congelation risk for the pipeline operation safety. In accordance with the fact there are two immediate causes of influencing congelation failure. One is the pipeline flux can not be stable in limited time after restarting and the other is the restarting pressure is greater than the maximum allowed operation pressure of pipeline. Takeing the "congelation failure" as top event, and also combining with the influencing factors of pipeline failure, the fault tree was established in the paper. On the basis of the minimal cut sets principle, qualitative analysis of the fault tree was conducted. Therefore the main factors of pipeline failure are obtained, including low throughput in operation, low supporting pressure capacity of pipeline, wax deposition on pipe wall and overlong shutdown time. Finally, based on above mentioned elements, some improving measures can be provided to guide and support for better accident treatment, planned overhaul and scientific management.