Identification of Small Corrosion Pits Based on Field Signature Method for Pipe Corrosion Monitoring

Field signature method (FSM) is an essentially potential-array method which arranges an array of measuring electrodes on external surface of pipeline and a constant current is injected into it. As there is a definite relationship between potential drop and wall thickness, FSM can monitor the degree of corrosion. FSM has been applied the field of oil and gas pipeline corrosion monitoring successfully because of its high-precision up to ±0.5%WT (wall thickness) in general corrosion monitoring and localized erosion monitoring. However, its precision in pit corrosion monitoring is relatively low (only ±15%WT). This paper introduces the principle of FSM, defines the small pit corrosion and points out the problem of unidentifiable small corrosion pits, and analyzes the cause and influence and presents a solution named major and assistant voltage method (MAVM). A large number of simulations demonstrate the feasibility of MAVM that is able to improve the precision of small pit corrosion monitoring greatly. It is significant for devolvement and perfection in FSM theory and practical applications.