Electromagnetic Surface Method for the Pipeline Periodical Inspection Based on the Heterogeneous Transmission Line Model

Abstract

The superficial electromagnetic methods are widely applied for non-destructive control of pipeline technical condition. For this purpose we have developed the theory and field technology for the pipeline inspection that allows: 1) determining the pipeline trajectory (plane position and depth), 2) delimitation of pipeline intervals with an insulation coating damage, and 3) estimating the condition of a cathodic protection system. The proposed method is based on the approximation of a metallic pipeline by a heterogeneous transmission line with variable distributed parameters: resistance and inductance along a tube (tube wall thickness) and leakage conductance. The field operations consist in measurements of magnetic field above a pipeline and voltage only on the control posts. The interpretation process includes the iterative inversion of the magnetic component in order to determine the pipeline depth and current distribution along pipeline. The current difference corresponds to leakage current and allow estimate the leakage resistance. We illustrate the practical application of this method using the obtained results for pipeline inspections in Mexico. Based on the voltage and current simulations for the infralow-frequency band (0–1kHz) we have evaluated the feasibility of the time lapse measurements of the magnetic field in some fixed points for the early prediction of an insulation damaging process.