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Copper Pitting and Brass Dezincification

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Copper Pitting and Brass Dezincification INSIGHTS INTO NON-UNIFORM COPPER AND BRASS CORROSION IN POTABLE WATER SYSTEMS Emily Allyn Sarver Dissertation submitted to the faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy In Civil and Environmental Engineering Dr. Marc Edwards, Committee Chair Dr. Sean Corcoran, Member Dr. Andrea Dietrich, Member Dr. Gerald Luttrell, Member Dr. Jeffrey Parks, Member November 1, 2010 Blacksburg, VA Keywords: copper pitting, brass dezincification, brass lead leaching, non-uniform corrosion, pipe-loop testing, corrosion inhibitors Copyright 2010, Emily A. Sarver INSIGHTS INTO NON-UNIFORM COPPER AND BRASS CORROSION IN POTABLE WATER SYSTEMS Emily Allyn Sarver ABSTRACT Non-uniform corrosion of copper and brass in potable water systems poses both economic and environmental problems associated with premature plumbing failures and release of metals. With respect to copper pitting corrosion, it was found that forensic testing (i.e., in pipe-loops) is the only investigative technique that can closely mimic conditions found in real water systems and produce unambiguous results; and, if used in combination with electrochemical techniques, it may also provide some mechanistic insights into the pitting process. Using pipe-loops, it was demonstrated that copper pitting in aggressive water qualities (i.e., chlorinated, high pH and low alkalinity) is deterministic and reproducible. Additionally, the effects of various chemical and physical factors on pitting were investigated. Overall, increased flow velocity and frequency, increased chlorine residual and decreased hardness were found to accelerate pitting; whereas increased phosphate and silica were found to decelerate pitting. Several mitigation strategies for copper pitting in aggressive water were further investigated, and experimental data were interpreted utilizing electrochemical theory to evaluate specific effects on the initiation and propagation phases of pitting. Surprisingly, it was found that decreased chlorine may delay pit initiation, however, even relatively low levels of chlorine may eventually initiate and propagate pits. Increased alkalinity appears to decelerate pit growth, but does not prevent pit initiation. NOM can delay pit initiation and propagation, although the potential for DBP formation in chlorinated waters makes inhibition by NOM an unfavorable alternative. At sufficient dosages, phosphate and silica corrosion inhibitors may completely stop pitting, consistent with the success of several field trials. At very low dosages, phosphate and silica may actually accelerate pinhole failures, so these inhibitors should not be under-dosed. While brass alloys exist that can limit dezincification problems, they are not always utilized in potable water applications due to high costs, and so dezincification is a re-emerging issue in some countries, including the US. Little research has been conducted in the past several decades regarding the effects of water chemistry, and almost no work has addressed the roles of physical factors associated with real plumbing systems. Thus, a comprehensive review of these topics was conducted. To better understand the effects of some factors associated with specific plumbing installations on dezincification and other brass corrosion types, a series of pipe-loop studies was carried out. It was confirmed that increased oxidant delivery rates to cathodic surfaces, either via increased oxidant concentration or increased flow velocity, can increase corrosion rates. Several key differences were observed with respect to corrosion of brass located in copper plumbing tube systems as opposed to plastic. When copper tubes contribute copper ions to water, brass corrosion becomes more selective for zinc; but if galvanic connections are made between the copper tubes and brass, selectivity for zinc is reduced while overall corrosion rates are accelerated. As opposed to copper tubing, plastic maintains oxidant (e.g., free chlorine) levels, and may thereby increase brass corrosion and build-up of corrosion by-products. Finally, it was found that increased temperature can significantly increase lead leaching from brass. Following recent outbreaks of brass dezincification failures, NSF/ANSI Standard 14 has been revised to require that all NSF 14-listed brass is dezincification resistant, as certified by satisfactory results from an accelerated test method (ISO 6509). Various brasses were tested using this method as well as a longer-term jar method utilizing real potable water. Results of the two tests were in good agreement with respect to dezincification, specifically; but some inconsistencies were observed with respect to uniform corrosion and lead leaching. DEDICATION For Pat and Steve… iv ACKNOWLEDGMENTS I would like to sincerely thank Dr. Marc Edwards. In addition to the research opportunities and technical insights he has given to me over the course of my doctoral work, Dr. Edwards has been a phenomenal mentor, and a constant source of honest advice and unwavering support. I would also like to thank my committee members, Dr. Andrea Dietrich, Dr. Jerry Luttrell, Dr. Sean Corcoran, and Dr. Jeff Parks, as well as Dr. Paolo Scardina, for offering their guidance and wisdom. I could not have completed this work without the help of Yaofu Zhang, Kara Dodson, Caitlin Grotke and Jaquelyn Dalrymple, and I am grateful for their efforts and friendships – and also for those of the other Edwards’ Research Group members. Additionally, I am very appreciative for the financial support of the National Science Foundation and the Charles E. Via Civil and Environmental Engineering Department of Virginia Tech. Finally, I am thankful for the love and encouragement of Kerem, Pat and Sarah. v TABLE OF CONTENTS TABLE OF CONTENTS.............................................................................................................. VI LIST OF TABLES........................................................................................................................ IX LIST OF FIGURES ....................................................................................................................... X PREFACE....................................................................................................................................XII Oraganization of Dissertation and Attributions ...............................................................xiii Complementary work....................................................................................................... xiv CHAPTER 1: COPPER PITTING IN CHLORINATED, HIGH PH POTABLE WATERS ........ 1 Abstract............................................................................................................................... 1 Introduction......................................................................................................................... 2 Materials and Methods........................................................................................................ 5 Part 1: A Decade of Pipe-loop Studies in Chlorinated, High pH Waters ..................... 5 Part 2: Examination of Various Investigative Techniques ........................................... 6 Part 3: Demonstration of Reproducibility and Deterministic Nature of Pitting ........... 6 Results and Discussion ..................................................................................................... 10 Part 1: A Decade of Pipe-loop Studies in Chlorinated, High pH Waters ................... 10 Part 2: Examination of Various Investigative Techniques ......................................... 14 Part 3: Demonstration of Reproducibility and Deterministic Nature of Pitting ......... 23 Conclusions....................................................................................................................... 29 Acknowledgments............................................................................................................. 29 References......................................................................................................................... 30 CHAPTER 2: MITIGATION OF COPPER CORROSION PITTING IN CHLORINATED HIGH PH, LOW ALKALINITY POTABLE WATERS ........................................................................ 34 Abstract............................................................................................................................. 34 Introduction....................................................................................................................... 35 Copper Pit Initiation and Propagation......................................................................... 36 Anodic and Cathodic Inhibitors.................................................................................. 37 Materials and Methods...................................................................................................... 39 Water Qualities and Inhibitor Dosages....................................................................... 40 Pipe-Loops .................................................................................................................. 41 Data and Analyses....................................................................................................... 42 Results............................................................................................................................... 45 Failure Times and Overall Pit Growth Rates.............................................................
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