Abstract
Firewater (FW) pipelines network maintenance and monitoring are of utmost importance since they are not easily accessible for inspection. Failure and corrosion of carbon steel FW pipes, particularly localized corrosion, can propagate leaks and bursts of pipelines, which leads to expensive repairs or replacement, or even uncontrolled situations during an emergency. Therefore, being aware of the pipeline conditions, predicting their failure mechanisms, their remaining life, planning to manage emergencies, and evaluating their conditions are essential. In this study, visual inspection, metallurgical examinations using optical microscopy in combination with scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), and corrosion test using a three-electrode system were employed to determine the cause of failure. Also, the water samples were subjected to various chemical and bacterial analyses. Corrosion and scale-forming potential, Physico-chemical properties, sulfate-reducing bacteria, Iron-reducingbacteria, and total bacterial count were investigated on water samples to evaluate the corrosion conditions of FW pipes. Furthermore, the remaining life prediction and monitoring of the pipelines have been studied based on laboratory simulation experiments and advanced non-destructive tests (NDT) by using Long Range Ultrasonic Testing (LRUT) and Phased Array Ultrasonic Testing (PAUT). The results indicate that the oxygen corrosion attack especially the accumulation of air bubbles (dissolved oxygen), forming tubercles, and aggressive anions (Cl- and SO42-) that are the root causes of the pipeline's failure. It can happen in general and localized forms such as localized pitting corrosion, tuberculation, top-of-the water line corrosion (TWLC), and cavitation damage. Also, by comparing NDT tests and laboratory experiments results, the remaining life results in state 2 are in good agreement. Thus, the laboratory simulation experiments are verified and can be used as a desirable indicator for the remaining life of FW pipelines and strategies for improved durability design and maintenance.
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