Proposed methodology for coating defect and location in buried pipelines from frequency signal data applied in field conditions

Purpose: The purpose of this paper is to develop a real-time methodology to detect damages in coating and metallic structure in buried pipelines by using DC bias added to AC signal under field operation conditions, including cathodic protection. Design/methodology/approach: Impedance measurements were performed on buried pipeline for different field conditions, to develop a methodology to detect and locate damages by impedance distribution along the metallic structure. Findings: Field condition measurements were conducted as a pilot test on a buried steel pipeline segment with a diameter of 16 inches and length of 20 km. The frequency-based technology shows some differences but overall good behavior between impedance magnitudes vs localization of the interface changes at the soil-coating-steel interface at different frequencies using DC bias added to AC signal under field operation conditions, including cathodic protection. Research limitations/implications: The methodology is not applicable to highly resistive soil or high degradation coatings. Practical implications: In this work, we depict a methodology that describes real time monitoring technology for buried metallic structures using AC signal. This monitoring is capable to detect and locate real time damage occurrences on the pipe surface (coating break). Field measurements include different conditions, such as temperature, soil resistivity and soil physical structure and chemical composition. Social implications: In consideration of the satisfied application in the field of the methodology, it is believed that it can be used for the monitoring of damages in pipes in areas with high consequences and hence pipe integrity can be increased. Originality/value: This real-time methodology is based on the impedance distribution signal and the differential changes along the pipeline under operating conditions. The results showed good agreement with the proposed methodology, which is able to discriminate some situations inherent of field conditions by using different impedance measurements performed along ±10 km of buried steel pipeline and assuming the reference location as the cathodic protection set up.