Lead pipe and lead-tin solder scale formation and structure: A conceptual model

Lead-tin solder and lead service lines (LSLs) are important sources of lead, and after LSLs are removed, lead-tin solder will remain a major source of lead. A better understanding of the factors that control lead release from solder joints can help water utilities reduce lead. This paper reviews the reactions that take place at galvanic connections involving both lead-tin solder and lead pipe in contact with copper. A conceptual model based on these reactions was developed and is presented here to explain how such scale structure forms. The likely reactions that affect lead release for each of three cases, (1) no galvanic action, (2) lead anode and copper-brass cathode, and (3) lead cathode and copper-brass anode, are presented. The model also considers uniform corrosion that takes place on LSLs. This model should be useful when evaluating the impact of water quality changes on lead release from galvanic connections and LSLs.