Corrosion prevention and control in water treatment and supply systems

ACKNOWLEDGMENTS 2 ACRONYMS . FREQUENTLY USED UNITS AND OTHER TERMS . . ... 3 . .... .4 1. PURPOSE . . 5 2. INTRODUCTION 6 3. DEFINITION OF CORROSION AND BASIC THEORY 8 Definition. . . . . . . . . . . . . . 8 Basic Theory 8 Electrochemical Corrosion of Metal Pipes 8 Corrosion of Metall ic Lead 10 Corrosion of Cement Materials. .. . 11 Characteristics of Water that Affect Corrosivity 12 Physical Characteristics. . . . . . . . . . . . . . . . . . . .. . 12 Velocity . . . . . . . . . . 12 Temperature. . . . . . . . . .. . 13 Chemical Characterist ics 13 pH . . . . . . . . . . . . . . . . . . 13 Alkalinity 15 DO " 15 Chlorine Residual 16 Total Dissolved Solids (TDS) 16 vii viii Contents and Subject Index Hard ness 16 Chloride and Sulfate 16 Hydrogen Sulfide (H 2 S) 17 Silicates and Phosphates 17 Natural Color and Organic Matter ' 17 Iron, Zinc, and Manganese 17 Biological Characteristics 17 4. MATERIALS USED IN DISTRIBUTION SYSTEMS 18 5. RECOGNIZING THE TYPES OF CORROSION 21 6. CORROSION MONITORING AND TREATMENT 34 Ind irect Methods 34 Customer Complaint Logs 34 Corrosion Indices. . . . . . . . .. . 35 Langelier Saturation Index 36 Aggressive Index (AI) 40 Other Corrosion Indices 41 Sampling and Chemical Analysis 44 Recommended Sampling Locations for Additional Corrosion Monitoring 45 Analysis of Corrosion By·Product Material 45 Sampling Technique 45 Recommended Analyses for Additional Corrosion Monitoring 45 Interpretation of Sampling and Analysis Data 46 Direct Methods 47 Scale or Pipe Surface Examination 47 Physical Inspection 48 X-Ray Diffraction. . . . . . . . . . . 48 Raman Spectoscopy 48 Rate Measurements 48 Coupon Weight-Loss Method 48 Loop System Weight-Loss Method 49 Electrochemical Rate Measurements 50 7. CORROSION CONTROL 51 Proper Selection of System Materials and Adequate System Design 51 Modification of Water Quality 53 pH Adjustment 53 Reduction of Oxygen 55 Use of Inhibitors 57 CaC03 Deposition 57 Inorganic Phosphates 57 Sodium Silicate 58 Monitoring Inhibitor Systems . . . . . . . . . . . . . . . . 58 Feed Pumps for Inhibitor Systems 60 Contents and Subject Index ix Chemical Feed Pumps . Cathodic Protection . Linings, Coatings, and Paints . Regulatory Concerns in the Selection of Products Used for Corrosion Control . .60 . .60 . .60 .62 8. CASE HISTORIES. . . . . . . . . . . . . . . . . . . . . .64 Pinellas County Water System. . . . . . . . . . . . .64 Background. . . . . . . . . . . . . . . . . . . . . . .64 Initial Investigation and Monitoring Program 65 Testing of Alternative Control Methods 66 Alternative 1: Adjustment of pH and CO2 •.........••.... 66 Alternative 2: Reduction of DO 66 Alternative 3: Sodium Zinc Phosphate (SZP) Pilot Test 66 Alternative 4: SZP Started on Plant 1. . . . . . 66 Alternative 5: Zinc Orthophosphate (ZOP) . . . 68 Alternative Studies . . . . . . . . . . . . . . . . . . . . . . . 69 Current Corrosion Control Methods . 69 Conclusions. . . . . . . . . . 69 Mandarin Utilities. . . . . . . . . . . . . . . . . . . . . . . 70 Background . . . . . . . . . . . . . . . . . . . 70 Corrosion Investigation and Monitoring of the Water Supply Procedure. . . . . . . . . . . . . . . . . . . . . .70 Recommended Control Methods . . . . . . . . .. . . . . . . . .71 Middlesex Water Company. . . . . . . . . . . . . . . . .. .72 Background. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72 Initial Investigation and Monitoring Program 73 Testing of Alternative Control Methods. . . . . . 73 Alternative 1: Inhibitor Treatment. . . . .. . 73 Alternative 2: Addition of Zinc Orthophosphate with and Without pH Adjustment. . . . . . . . . . . . . . . . . . . .75 Alternative 3: Testing of Zinc Orthophosphate Addition and pH Adjustment in the Distribution System 75 Small Hospital System. . . . . . . . . . . . . . . . . . . 75 Background . . . . . . . . . . . . . . . . . . . . . . . . .. 75 Initial Investigation and Monitoring Program .75 Boston Metropolitan Area Water System. . .. 77 Background . . . . . . . . . . . . . . . . . . . . 77 Initial Investigations and Monitoring. . . . 77 Testing of Alternative Control Methods. . 78 Alternative 1: Treatment with ZOP . . . . . . . . 79 Alternative 2: pH Adjustment with NaOH. . . . 79 Summary and Conclusions . . . . . . . . . . 82 Galvanized Pipe and the Effects of Copper. . .82 Background. . . . . . . . . . .82 Possible Remedies. . . . . . . . . . . . 83 Greenwood, South Carolina. . . . . . . . 83 Background. . . . . . . .. . 83 x Contents and SUbject Index Initial Investigation and Monitoring Program 84 Testing of Control Method 84 9. COSTS OF CORROSION CONTROL 86 Monitoring Costs 86 Sampling and Analysis 86 Weight- Loss Measurements 86 Control Costs 87 Equipment Costs 87 Lime Feed System Costs 87 Sodium Hydroxide Feed Systems 88 Silicate Feed Systems 88 Phosphate Feed Systems 88 Sodium Carbonate Feed System 89 Chemical Costs 89 GLOSSARY 90 ADDITIONAL SOURCE MATERIALS 96 PART II REVIEW OF MONITORING, DETECTION, PREVENTION AND CONTROL TECHNIQUES 1. INTRODUCTION 108 Background 108 Objectives 111 2. CORROSION AND WATER CHEMISTRY BACKGROUND 112 General Aspects of Corrosion and Leaching in Potable Water 112 Types of Corrosion 113 Corrosion Ind ices 114 General Corrosion Bibliography 120 Corrosion Indices Bibliography 120 3. MATERIALS USED IN THE WATER WORKS INDUSTRY 122 Pipes and Piping 122 Storage Tanks 127 References 129 4. CORROSION CHARACTERISTICS OF MATERIALS USED IN THE WATER WORKS INDUSTRY 130 Iron-Based Materials 130 Corrosion of Iron 130 Effect of Dissolved Oxygen 132 Effect of pH 134 Effect of Dissolved Salts 138 Contents and Subject Index xi Effect of Dissolved Carbon Dioxide 140 Effect of Calcium 142 Effect of Flow Rate and Temperature 145 Effects of Other Species in Solution 146 Comparison of Cast Iron and Mild Steel 147 Corrosion of Galvanized Iron 148 Effect of Water Quality Parameters 148 Stagnant Conditions 151 Hot Water Corrosion 153 Stainless Steels 155 Passivity 155 Type of Corrosion and Effect of Alloy Composition 156 Environmental Effects on Corrosion of Stainless Steels 156 Results in Potable Water 157 Corrosion of Copper in Potable Water Systems 157 General Considerations 159 Uniform Corrosion of Copper 160 Effect of O2 ......••............................. 160 Effects of pH 161 Effect of Free CO2 ....•..............•.•.....•.... 164 Effects of Temperature 165 Effects of Miscellaneous Parameters 165 Localized Corrosion of Copper 167 Causes of Pitting 167 Impingement Attack and Flow Rate Effects 169 Copper Alloys 169 Corrosion of Brasses 169 Corrosion of Bronzes 171 Other Copper Alloys 173 Corrosion of Lead in the Water Works Industry 173 Effect of Flow Rate and Volume of Water Flushed 176 Effects of Dissolved Oxygen 178 Effect of Hardness 179 Effects of pH 180 Effects of pH and Hardness 183 Effects of Alkalinity 185 Effects of Temperature 189 Effects of Chlorination 189 Effects of Carbon Dioxide 190 Lead Release from Solder Jo ints 191 Corrosion of Aluminum in the Water Works Industry 192 Effects of Velocity 194 Effects of Temperature 195 Water Quality Effects 195 Asbestos-Cement Pipe Performance in the Water Works Industry 205 Causes of Asbestos Fiber Release 208 Organic Release from Asbestos-Cement Pipe 217 Concrete Pipe 218 xi i Contents and Subject Index Plastic Pipe 220 Polyvinyl Chloride (PVC) 221 Polyethylene 221 Polybutylene 223 Acrylonitrile-Butadiene-Styrene (ABS) 223 Polypropylene 223 Deterioration and Release from Plastic Piping 223 References 228 5. CORROSION MONITORING AND DETECTION 237 Specimen Exposure Testing 238 Electrochemical Test Methods 242 Chemical Analyses for Corrosion Products 246 References 249 6. CORROSION PREVENTION AND CONTROL 251 Mechanically Applied Pipe Lining and Coatings 252 Hot Applied Coal Tar Enamel 252 Epoxy 253 Cement Mortar 254 Tank Linings and Coatings 255 Coal Tar Based Coatings 255 Vinyl 256 Epoxy 256 Other Mechanically Applied Tank Linings 256 Corrosion Inhibitors 258 CaC0 3 Precipitation 260 Sodium Silicate 263 Inorganic Phosphates 266 Miscellaneous Methods 269 Economics 270 Benefit/Cost Analysis 270 Trends and Costs of Mechanically Applied Linings and Coatings 273 Costs of Corrosion Control by Chemical Applications 275 Case Histories 283 Seattle 283 Carroll County, Maryland 286 Orange County, California 287 Additional Corrosion Control Practices 289 References 290 7. CONSIDERATIONS FOR CORROSION CONTROL REGULATIONS .. 295 References 306 8. RECOMMENDATIONS 309