Corrosion Detection on Buried Transmission Pipelines with Micro-Linear Polarization Resistance Sensors

This paper presents an experiment adapting linear polarization resistance-based corrosion sensors, originally developed for aerospace applications, to measure the corrosion rate of API 5L ERW grade-B steel natural gas line pipe using micro-sized linear polarization resistance (µLPR) sensors made from the same alloy and grade steel. Sensors were installed under a 15 mil coating of fusion-bonded epoxy, at various proximities to a 1/8 inch defect introduced at a weld joint and along the pipe seam. After sensor installation the pipe was buried in an controlled environment with soil amended to a pH of five. This environment was held at a temperature above 35 °C while soil moisture content was modulated between wet and dry cycles, each lasting 7 days. LPR and environmental measurements were sampled at 5 min intervals. Post processing was performed to convert the LPR measurements to a surface-loss. Comparisons made in the data showed API 5L ERW grade-B steel natural gas pipelines were highly susceptible to corrosion along the seam, with all sensors showing activity in this region early in the experiment. Sensors adjacent to a weld joint began to display evidence of corrosion more slowly. These results verify the ability of µLPR sensors to measure corrosion activity under protective coatings in underground environments.