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.

The active/passive conditions for copper corrosion under nuclear waste repository environment

“…A number of studies in potable waters show that these anions (Cl − , SO 2− 4 , HCO − 3 /CO 2− 3 ) and the pH are dominant chemical influences on the pitting of Cu [6]. Increases in pH and [HCO − 3 /CO 2− 3 ] support the required passivation whereas Cl − and SO 2− 4 typically promote the breakdown of passivating oxides that can result in pit initiation.…”

“…This is commonly achieved by applying a potentiodynamic scan to the metal immersed in the solution of interest [7]. Many such measurements have been made in Cu systems by Cong et al [6], who determined the effects of Cl − , SO 2− 4 , HCO − 3 and OH − on E b and E rp and derived simple expressions for the relationships between the potentials and anion concentrations. These expressions were developed from measurements at room temperature, pH 8.3 and pH 9.5, and with anion concentrations in the range 10 −4 -0.1 mol L −1 , and the authors caution that the applicability of these expressions outside the range of measurements is uncertain.…”

Copper Corrosion and Biocorrosion Events in Premise Plumbing

“…Polarization scans may be used to understand the differences of copper corrosion at micro and macro scales [ 111 ]. Polarization scans can also suggest when copper is susceptible to pitting and what corrosion by-products are formed [ 112 ]. Recently, polarization scans have been used to study the persistence of corrosion inhibitors in copper pipes with tap water [ 113 ].…”

“…A prevention method is the addition of orthophosphate to the water which has been proved successful [ 19 ]. Another approach is to analyze the water quality parameters and predict if the water is susceptible to originate localized corrosion, by estimating the pitting potential of the pipe [ 112 ]. However, pitting corrosion on copper premise plumbing cannot be accurately predicted yet.…”

Nature of the near-field environment in a deep geological repository and the implications for the corrosion behaviour of the container

“…The anions of most interest for the localised corrosion of copper (as for other alloys and forms of corrosion) are Cl − , SO 2− 4 , and HCO 3 − (and pH) [24]. For the estimation of the timedependent pore-water concentration profiles, the following assumptions are made:…”