Abstract
ABSTRACTIn this paper, we present an electromagnetic surface technique for the integrity inspection of buried pipelines groups. The inspection includes the determination of the pipeline plan location and depth, assessment of insulation‐coating quality and cathodic protection conditions. This technique is based on the approximation of a metallic pipeline by a heterogeneous transmission line. In the transmission line model, the degree of coating damage (disbanded or cracked insulation) corresponds to the leakage resistance that is defined by the coating resistance and environmental resistivity. Using the transmission line model, we simulated the voltage and current distributions along a pipeline created by the cathodic protection system or an external generator in a low‐frequency range. The calculations were performed for both a single pipeline and interconnected pipelines with different insulation‐coating quality (model of a common cathodic protection system). We describe the field operations, which consist of measurements of the magnetic field created by the current flowing into a pipeline, voltages on the cathodic protection control posts and soil resistivity. To find the pipeline position, depth and current we apply the interactive inversion of the magnetic‐field data obtained along the profiles orthogonally oriented to the pipeline‐group route. The interpretation of the field data includes: calculating the leakage current (the current difference on the measuring interval) for each pipeline, determining the leakage resistance (the voltage to the leakage‐current ratio) and assessing the insulation‐coating resistance taking into account the surrounding soil resistivity. We present practical examples of the integrity inspection of interconnected pipelines group in Mexico. The successful results achieved allow us to recommend this electromagnetic technique for quantitative inspection of the technical conditions of interconnected pipelines.
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