Grooving Corrosion and Premature Leakage Characteristics of Electric-Resistance-Welded Components of Secondary-Side Fire Protection Piping of Pre-Action Sprinkler Systems

This study investigates the grooving corrosion and premature leakage mechanisms along the bond line of electric-resistance-welded (ERW) carbon steel pipes employed in fire- protection piping systems. Specifically, leaked secondary-side branch pipes from pre-action sprinkler systems were examined via visual inspection, metallographic analyses, scanning electron microscopy with energy dispersive spectroscopy analyses, thermodynamic interpretation, and potentiodynamic polarization testing. Overall, the leakage sites coincided with the ERW bond line, and Cl was detected in the corrosion products, suggesting that Cl⁻ enrichment and O concentration differences under stagnant water conditions may have contributed to localized corrosion growth. Moreover, electrochemical analyses showed that the weld zone exhibited more active corrosion behavior and a higher corrosion rate than the base metal did, supporting the possibility of selective corrosion along the bond line. Furthermore, thermodynamic interpretation based on the Pourbaix diagram indicated that, in the presence of Cl⁻, passive film instability and delayed repassivation following pit initiation may promote the continued growth of localized corrosion. These results suggest that grooving corrosion in ERW fire-protection piping can be attributed to localized corrosion along the bond line, resulting from the combined effects of electrochemical vulnerability of the weld zone, Cl⁻ enrichment in stagnant water, O concentration differences, and passive film instability.