Concentration Cells and Pitting Corrosion of Copper Available to Purchase

Certain aspects of copper tube failure in drinking water systems are inconsistent with the “membrane cell theory” of copper pit propagation, which postulates that cathodic reactions occur immediately above the pit tubercle. To examine the basis for this theory, classic experiments of Lucey were revisited and alternative interpretations were apparent that are consistent with concentration cell effects. In fact, under chemical conditions thought to support Type 1 copper pitting, more than 90% of electron loss at the anode was accounted for by concentration cell effects rather than cathodic reactions occurring above the pit. In addition, the qualitative trends in currents arising from concentration cells are consistent with practical observations regarding the role of bulk solution pH in Type 1 pitting; that is, waters between pH 6.5 and pH 7.8 sustain currents that support pitting, but at pH < 6.5 or pH > 7.8, currents become self-limiting.