Dezincification of brass water meters in a long-term study: effects of anions, alkalinity, and residual chlorine

Abstract

The dezincification of brass water meters in a water distribution system is affected by tap water characteristics. However, the effects of mixed water quality on corrosion and scale formation on the behaviour of brass water meters have remained unclear. This study investigated the long-term impact of tap water characteristics on the brass dezincification of commercial water meters, using a household-simulated circulating pipeline system. The effect of water anions, alkalinity, and residual chlorine on dezincification and corrosion of such brass water meters were quantitatively and electrochemically examined for over a period of 376 days. The results show that water meters suffer the most severe dezincification when the tap water has a high level of anions (SO₄²⁻: 120 mg L⁻¹ and Cl⁻: 60 mg L⁻¹) and low alkalinity (120 mg L⁻¹ as CaCO₃). Under such conditions, a considerable amount of zinc is leached, amounting to 146–153 mg L⁻¹ over 376 days, accompanied by high corrosion rates of 42.2–45.8 μm per year. Exposure to water with high anionic concentrations and low alkalinity also results in a positive shift of 15 to 50 mV in the corrosion potential of chips of scaled brass, leading to heavy scale formation. The majority of Zn (∼50%) in the scale was demonstrated by ICP-OES and SEM/EDS. The data obtained from XPS suggest that scales of ZnCO₃/Zn(OH)₂ formed as a result of the long-term dezincification of brass. By contrast, minor dezincification was observed when the water meters were exposed to water of low anionic concentrations (SO₄²⁻: 60 mg L⁻¹ and Cl⁻: 6 mg L⁻¹), low alkalinity (120 mg L⁻¹ as CaCO₃), and low residual chlorine (0.2 mg L⁻¹ as Cl₂), even after 376 days. Under these conditions, the accumulative amount of zinc leaching and the corrosion rate were only 105 mg L⁻¹ and 13.2 μm per year, which are significantly lower than those obtained in the high anion concentration and low alkalinity situations. This study provides a further insight into how tap water characteristics impact the long-term brass dezincification of water meters, which benefits water utilities to forecast scale formation under specific tap water conditions.