Passivity and Pit Stability Behavior of Copper as a Function of Selected Water Chemistry Variables

Abstract

The electrochemical pitting behavior of UNS C11000 copper was investigated in a synthetic potable water found to cause pitting. Tests were also conducted in several other HCO3-, SO42- and Cl- containing-waters. Studies of the effect of water chemistry on passivity, uniform corrosion, and pitting were accomplished using the cyclic voltammetry method. Certain water chemistry concentrations promote pitting. High [SO42-]/[OH-],[SO42-]/[HCO3-] and [Cl-]/[HCO3-] ratios lower pitting potentials while an increase in alkalinity improves passivity and raises pitting potentials. HCO3-/CO32- can protect copper surfaces by forming carbonate containing minerals. However, carbonated species are less beneficial towards passivity compared to OH- with respect to passivation efficiency. Empirical equations that forecast pitting and repassivation potentials as a function of selected water chemistry variables were developed by linear regression analysis based on experimental pitting and repassivation potential trends with HCO3-, Cl- and SO42- content. The origins of the trends with water chemistry variables are discussed.