Congelation Risk Assessment And Maximum Allowable Time Of Shutdown Research For Heated Crude Oil Pipelines

The heated crude oil pipelines transport high pour point and high viscosity oil, which need higher energy consumption and generate a lot of safety problems during running. Congelation is the major safety problem, once it happens, it will cause great economic losses and serious society effect. In order to avoid congelation, the maximum allowable time of shutdown should be determined, and the shutdown time should be controlled in it. So this paper will make risk assessment of congelation and do research on maximum allowable time of shutdown for heated crude oil pipelines, and hope to guide pipelines to run safely.Congelation risk assessment include risk identification, risk probability calculation and consequence analysis. First, the shutdown incidents of northeast crude oil pipe network were collected, the reasons for shutdown and time distribution were summarized. According to the results and some congelation accidents, a fault tree of congelation risk of heated crude oil pipelines was built. By qualitative analysis of minimal cut sets of the fault tree, the main factors lead to congelation were found. In view of these factors, some improved measures were proposed. About analysis on the results of congelation accident, the calculation models of all items on economic losses during accident handling were built. Based on the theory of reliability, a method using to calculate failure probability of congelation caused by shutdown was made, and programmed with C program language. Take Huludao-Suizhong pipeline for example, the major factors on corroded pipeline that affect the failure probability of congelation caused by shutdown were analyzed.The maximum allowable time of shutdown of the heated crude oil pipeline is related to temperature drop during shutdown. So the ANSYS software was used to simulate the temperature drop affected by some factors, such as inlet temperature, season, diameter, insulation thickness, thermal conductivity of soil. Based on the failure probability, the maximum allowable restart pressure was limited by failure probability acceptance criteria, and a new method for determing maximum allowable time of shutdown was formed. By using the method, Huludao-Suizhong pipeline's maximum allowable time of shutdown in four seasons of one year were determined in current corrosion condition.