Mechanism of corrosion, scaling and failure of valves in drinking water distribution systems

Valve corrosion in drinking water distribution systems (DWDS) compromises system safety by causing operational failures, water quality deterioration, and leakage. Through disassembly of failed valves, SEM/XRD analysis, simulation experiments with pipe section reactors, and electrochemical monitoring, this study elucidates the corrosion processes and failure mechanisms of gate valves in DWDS. Results indicate that ductile iron, owing to its high corrosion tendency, generates iron‑oxide scales predominantly composed of goethite (α‑FeOOH) and magnetite (Fe₃O₄). Scale composition and morphology vary markedly with location: stable α‑FeOOH prevails in the upper part of valve under stable conditions, whereas dense, disordered scales rich in Fe₃O₄, zinc hydroxycarbonate, and silicates form in the confined, anoxic gap between the gate disc and the rail groove. While galvanic corrosion is suppressed under stagnant conditions due to carbonate deposition and mass transfer limitation, self‑corrosion leads to higher corrosion current for long term. Valve failure primarily results from scale obstructing gate movement in the guide groove and corrosion‑induced weakening of the stem. To mitigate these issues, periodic gate operation is recommended to disrupt anoxic environments, accompanied by high‑flow flushing to remove accumulated scale and lubrication of the stem to reduce wear.