07392 Use of Coupled Electrode Arrays to Elucidate Copper Piping as a Function of Potable Water Chemistry

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Product Number: 51300-07392-SG

ISBN: 07392 2007 CP

Author: Hongbo Cong, Noah D. Budiansky, John R. Scully, and Harold T. Michels

Publication Date: 2007

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The electrochemical pitting behavior of UNS C11000 copper was investigated in synthetic potable water and several other HCO3 -, SO4 2- and Cl- containing waters using microelectrodes and coupled multi-electrode arrays. Studies were systematically conducted over a pH range from 6 to 10 and Cl2 (as NaOCl) additions from 1-5 ppm. Additional studies were conducted both with and without Al(OH)3 additions found previously to promote pitting in potable water systems. Studies of the effect of water chemistry on passivity, general corrosion, and pitting were accomplished using the cyclic voltammetry method. Cathodic polarization studies yielded information on the effects of water chemistry on ClO- and O2 reduction kinetics. Critical potentials for copper pitting are observed to be brought about and decreased by certain water chemistry variables. High [SO4 2-]/[HCO3 -] and [Cl-]/[HCO3 -] lower pitting potentials while high [HCO3 -] and high pH improve passivity and raise pitting potentials. ClO- increases cathodic reaction rates and thus raises open circuit potentials towards pitting potentials. Certain water chemistries are found to promote pitting conditions where strong, persistent anodes developed at certain sites and the pitting factor was raised. These include pH from 8-10, Cl2 levels above 2 ppm and presence of Al(OH)3. The possible roles of Al(OH)3 towards the promotion of pitting are discussed.