Corrosion Assessment of Crude Oil Storage Tanks

摘要

Oil leakage from crude storage tanks due to corrosion of tank bottom represents a risk in plant operation with potentially negative environmental and social effects. The construction material of crude oil storage tanks is typically carbon steel, and corrosion prevention is ensured in the tank design by the application of a number of combined corrosion control methods like coating, cathodic protection, fluid treatment with chemicals, corrosion allowance. In the operation phase, periodical inspections are planned and executed to check the actual status of the tanks. The paper illustrates an integrated approach for internal corrosion assessment of in-service oil storage tanks is based on a number of steps, namely: a review of the degradation mechanisms and calculation of the expected corrosion rates (uniform and localized); a detailed review of the cathodic protection design to assess its effectiveness to date that includes a verification with Finite Element Modelling (FEM), and the evaluation of the remaining design life. The risk of corrosion occurrence is expressed through a corrosion risk matrix customized for oil storage tank farms, which includes and weights all the relevant affecting parameters. This corrosion assessment procedure is further integrated by application of Fault Tree Analysis (FTA) to assess the risk of oil leakage. FTA is a top down, deductive failure analysis in which an undesired state of a system is analysed using Boolean logic to combine a series of lower-level events. The paper discusses the logic for the construction of a fault tree relevant to the event of failure due to corrosion of the bottom of an oil storage tank.