Marc Edwards, Paolo Scardina, Russell Taylor, and Nigel Goodman

OBJECTIVES:

The goal of this study was to rigorously evaluate the accuracy of several electrochemical monitoring techniques in predicting pitting propensity of copper tubing in potable water supplies.

BACKGROUND:

Copper pitting corrosion in residential plumbing is expensive to repair, stressful to utility customers, and the exact water quality and hydraulic factors that cause pitting remain difficult to discern. While many factors are proposed or suspected to cause copper pitting--including faulty grounding, improper grounding, manufacturing defects of the copper pipe, microbial corrosion, and improper plumbing installation--none of the factors have been proven to cause pitting corrosion in a laboratory under scientifically reproducible conditions. A number of different corrosion monitoring techniques have been used in an attempt to assess the likelihood that a given water quality could induce or allow copper pitting corrosion to occur in a particular water system.

HIGHLIGHTS:

Problems or inconsistencies were found with all of the electrochemical techniques that were tested in this study--E_Corr rise, electrochemical noise (ECN), and pit wires. Naturally-occurring water quality and hydraulic factors in the systems artificially affected the electrochemical data for all the methods tested. The team found that the monitoring results always depended on the specific test and site conditions, that the orientation and placement of the electrodes controlled the monitoring output, that turning the pump on or off created spikes in the electrochemical indicators, and that free chlorine or chloramines levels controlled the results.

APPROACH:

Four waters of known pitting propensity that have been studied extensively were used to test various electrochemical techniques. The research team used a continually-circulated pipe loop system of copper piping to test the electrochemical techniques with four test waters--a known pitting water, a biologically active water that is suspected to cause pitting, a non-pitting water, and a pitting water that also produces blue water events. The team also tested the electrochemical techniques under real conditions at participating water utilities.

RESULTS/FINDINGS:

Each of the electrochemical corrosion monitoring techniques was found to have inherent flaws or inconsistencies rendering them unreliable. For instance, some electrochemical data was artificially skewed by the concentration of chlorine, even in one water system where chlorine is necessary to stop blue water and micro-pitting in this system. Additionally, most of the methods were affected to some extent by fluid flow. This finding led to the discovery of another mechanism, known as flow electrification, which could increase or enhance the extent of pitting or corrosion activity via water flowing past the pipe surface; consequently, it was unclear whether spikes in electrochemical data were due to real pit activity, activation of the pump, or flow electrifications resulting from water movement. Other problems occurred when attempting to use these corrosion monitoring techniques onsite at participating utilities.

IMPACT:

It is clear that electrochemical techniques have fundamental limitations and cannot be used solely as a tool for indicating the pitting propensity of an unknown water system. In some cases, these methods could be used in conjunction with other methods or after there is extensive experiences with a given water system. The design and location within the system can clearly influence the net overall findings of a corrosion pilot study.

MULTIMEDIA:

A parallel phase of work occurred onsite at participating water utilities and each of these case studies are included in the accompanying CD-ROM.

PARTICIPANTS:

Water utilities from the United States and Australia participated in this project.