Failure analysis of corroded underground pipeline

Abstract. Corrosion is a form of metal deterioration that cause damages in underground pipelines. In most cases, the causes of corrosion-based failure are not readily known. A rare case of the corrosion phenomenon is corrosion due to stray current. This paper presents the root cause analysis of an underground fire protection pipeline corrosion failure case associated with a sprinkler system that took place in the Arabian Gulf. Localized corrosion failure caused water leakage in the fire protection piping system. The leakage took place in a large industrial area around a four-kilometer building. Leakage in the fire suppression system was discovered during scheduled inspection when the jockey pump was observed to be continuously running due to low pressure in the main header as a result of the corrosion failure. Deeper investigation showed that leakage from the underground hydrant line was localized to only the main building's parking lot. Another observation was that previous failures had occurred at the same location and that the damaged pipe had been replaced by new one. However, past failure analyses did not identify the root cause. A third consecutive failure at the same location necessitated a new root cause analysis. Observations showed that the affected pipe sections had a thick epoxy coating on their outer surfaces. Precisely, failure analysis was conducted on four sections of the steel pipe. The consequent root cause analysis, metallurgical and soil investigation revealed that electromagnetic forces in close proximity to high AC and DC stresses were responsible for the damaged pipe sections. The corrosion was specifically due to the interference of various types of electrical cables, such as a high voltage cable and electrical ground discharge electrodes that generated stray current. This corrosion occurrence went unidentified over the last three years despite previous failure analysis. It was recommended that all damaged pipe sections adjacent to electrical conduits be covered with a double-layer insulating tape with high impedance and dielectric properties.