Use of Coupled Electrode Arrays to Elucidate Copper Pitting as a Function of Potable Water Chemistry

Abstract

The electrochemical pitting behavior of UNS C11000 copper was investigated in synthetic potable water and several other HCO3- , SO42- and Cl- containing waters using microelectrodes and coupled multi-electrode arrays. Studies were systematically conducted (pH from 6 to 10, [Cl2] (as NaOCl) from 1-5 ppm, and with or without Al(OH)3 additions). Studies of the effect of water chemistry on electrochemical properties of copper were accomplished using the cyclic voltammetry and cathodic polarization methods. Critical potentials for copper pitting are observed to be brought about and decreased by certain water chemistry variables. High [SO42-]/[HCO3-] and [Cl-]/ [HCO3-] lower pitting potentials (EPit) while high [HCO3-] and pH raise EPit. ClO- increases cathodic reaction rates and thus raises OCPs towards EPit. Certain water chemistries (pH from 8 to 10, [Cl2] > 2 ppm and with Al(OH)3) are found to promote pitting conditions where strong, persistent anodes developed at certain sites and pitting factor was raised.