MFL ILI based assessment method of pipeline field joint coating failure

In order to formulate the repair plan and repair the defects in time, an assessment method of pipeline field joint coating failure based on magnetic flux leakage in-line inspection (MFL ILI) was proposed in this paper. In this method, the ILI signals of field joint coating failure are divided into four types. And the characteristics of type 1 and type 4 signals are more obvious than those of type 2 and type 3. Then, axial defects and circumferential defects were assessed using RSTRENG 0.85dL method and Kastner method, respectively, and the corrosion growth was predicted based on the boundary value of corrosion growth rate. Finally, combined with signal types and corrosion defect assessment results, a grading assessment and response code for field joint coating failure was set up. It is indicated from the field application that this method is higher in identification and assessment coincidence rate and can meet the requirement on field application.