Free Chlorine Can\nInhibit Lead Solder Corrosion via\nElectrochemical Reversal

Galvanic corrosion of lead–tin solder in copper\nplumbing\ncan be a major contributor to water lead contamination. Here, we report\nthe electrochemical reversal of the copper-solder galvanic couple,\nin which the normally anodic solder becomes cathodic to copper via\na reaction with free chlorine. This reversal occurred after a few\nmonths of exposure to continuously circulating water with relatively\nlow pH and low alkalinity, causing dramatically decreased lead release\nand the formation of a Pb(IV) scale. Chloramine did not similarly\ninhibit solder corrosion over the 4–9 month test duration,\nresulting in up to 100 times more lead contamination of the water\nrelative to free chlorine. These findings have major implications\nfor corrosion control and public health and can help explain anomalously\nlow levels of lead contamination in some waters with free chlorine\nthat are normally considered corrosive to solder.