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Corrosion Control Proposal

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This document discusses corrosion in drinking water distribution systems and methods for corrosion control. It describes how corrosion occurs via electrochemical reactions between pipe material and water constituents. Common corrosion control strategies include pH adjustment and adding compounds like carbonates and phosphates to form a protective scale layer. Effective corrosion control requires maintaining water quality during distribution and high organic removal during treatment. The objective of this project is to study calcium carbonate behavior in distribution systems and how to alter water parameters to form a protective calcium carbonate film on pipes through computer modeling and simulation.

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1. INTRODUCTION Drinking water distribution systems are primary made of iron and steel pipes that are subject to corrosion. Corrosion of system pipes has economic, hydraulic and aesthetic impacts, including water leaks, corrosion product buildup, increased pumping costs and water quality deterioration (red water).Because distribution system pipes are in place for long periods of time corrosion control is critical to maintain microbial, water quality and pipe integrity. Effective corrosion control during water distribution along with high organic matter removal during water treatment will allow effective disinfection and limit bacterial growth within the distribution system. 2. THEORY Corrosion processes consist of a series of electrochemical reaction occurring at the metal surface in contact with water and its constituents. The metal (Fe) is converted to ferrous solid (e. g. FeO), which may then be converted to ferric solids (e. g. Fe2O3) after reaction with oxygen. Corrosivity of a particular water depends on its chemical properties (e. g. pH, alkalinity, dissolved oxygen, Total Dissolved Solids) and physical characteristics (temperature, flow, velocity), as well as the nature of the pipe material (Volk C. et al., 2000) Corrosion control strategies include pH adjustment or/and the addition of inorganic compounds (carbonate, silicate or phosphates) that will form a profilm or passivation layer on the inside of the pipe to prevent corrosion. According to Hancke and Wilhelm in order to form protective scale a water should have the following characteristics, 7<pH<8.5 total alkalinity [HCO3-] > 0.5 mmol/L, [Ca2+] > 0.5 mmol/L, acidity [CO2] > 3 mg/L or 0.06 mmol/L (Hancke K. and Wilhelm S., 1996) 2
Calcium carbonate (CaCO3) saturation indices are commonly used to evaluate scale- forming and scale dissolving tendencies of water. Assessing these tendencies is useful in corrosion control and preventing CaCO3 scaling in piping and equipment. It is widely assumed that CaCO3 will precipice from oversaturated waters and that it cannot be deposited from undersaturated waters. Calcium carbonate may precipitate from water in one or more of three forms; calcite, aragonite and vaterite. Which of these allotropes precipitates depends on the pressure, the temperature, the presence of forign ions and the rate at which precipitation takes place. The calcite polymorph of calcium carbonate is the most common scale-forming mineral (Hamrouni, B and Dhahbi, M., 2002). Conceptually, piping is protected when CaCO3 is precipitated on its surface. CaCO3 is believed to inhibit corrosion by clogging reactive areas and providing a matrix to retain corrosion products, thus further sealing the surfaces (Clesceri, L. S. et.al., 1998). Protective coatings are best formed from rapidly moving water because the protective ingredients (calcium, alkalinity) are more effectively transferred to the pipe walls under such condition. Good protective coatings were found to be formed from water moving at about 0.7 m/s. Little protection can be expected in areas of low velocity (e. g. dead ends) and in these areas other means if protection are required (Merrill D. T. and Sanks R. L., 1978) 3
Indices that indicate CaCO3 precipitating or dissolution tendencies define whether a water is oversaturated, saturated or undersaturated with respect to CaCO3. The most used indices are saturation Index (SI) (Also known as the Langelier Saturation Index (LSI)) the relative saturation (RS), also known as the driving force index (DFI) and the Rynzar index (RI). The LSI is by far the most commonly used. The RI and SI are related however, the SI is more reliable and commonly used because the RI is semi- empirical. LSI is determined from the equation LSI=pH-pHs Where pH= measured pH and pHs= pH of the water if it were in equilibrium with CaCO3 at the existing calcium ion [Ca2+] and bicarbonate ion [HCO3-] concentrations. LSI is purely an equilibrium index and deals only with the thermodynamic driving force of calcium carbonate scale formation and growth. It provides no indication of how much scale or calcium carbonate will actually precipitate to bring water to equilibrium. The amount of CaCO3 that may be precipitated or dissolved is known as the Calcium Carbonate Precipitation Potential (CCPP). The CCPP is defined as the quantity of CaCO3 that theoretically can be precipitated from oversaturated waters or dissolved by undersaturated water during equilibration. The CCPP is negative for undersaturated waters, zero for saturated waters and positive for oversaturated waters. 4
The CCPP is commonly calculated with computerized water chemistry models and Caldwell-Lawrence diagrams. Water should be brought to oversaturated condition just prior to its entering the system that is to be protected. If brought to the oversaturated condition earlier deposition could begin prematurely in tanks or basins where protection is not really required. 3. CURRENT PRACTICES The current practices in dealing with corrosion is by adding inhibitors which are a)costly and b) might result in water quality related issues as the formula of such chemicals are not known and might cause health effects on the long run 4. PROJECT OBJECTIVE This project is aimed at studying a) the CaCO3 behavior of water in the public network system, b) the possibility of altering some water parameters (within the drinking limits) to form a CaCO3 protective film on the pipe walls and c) the amount of CaCO3 needed to be deposited for the protective layer with the aid of computer modeling. 5. APPROACH Water will be analyzed and the parameters related to corrosion will be evaluated for possible deposition capacities of the water via direct calculation and computer software. Having arrived at a conclusion from the results simulation work based on the water analysis will be run to measure the optimum flow rate, CaCO 3 concentration 5
required to form a protective layer and possible scenarios for other chemical deposition (e. g. MgFe) 6. CONCLUSION My main goal in enrolling in a PhD program at SQU is to use my long professional experience in the field of water analysis as well as the knowledge obtained during my M. Sc study in the University of Edinburgh to conduct a high-level applied research in this interesting and strategic research area touching the daily life of many people. Reference: 1. Clesceri L. S., Greenberg A. E., Eaton A. D. (Ed).,1998. Standard Methods for the Examination of Water and Wastewater. 20th ed., Baltimore: United Book Press 2. Melidis, P. Sandoziodu, M. Mandusa, A. Ouzounis, K. Corrosion control by using indirect methods, Desalination, 213(2007) 152-158 3. Hamrouni B., Dhahabi M., Calco-carbonic equilibrium calculation, Desalination, 152 (2002) 167-174 4. K. Hancke and S. Wilhelm (Eds.), Wasserauf-bereitung, Chemie und Chemische Verfahren-stechnik, VDI, Springer-Verlag, 5 Aufl, 1996 5. Douglas T. Merrill and Robert L. Sanks, Corrosion Control b deposition films: Part 3, A practical Approach for plant operators, Journal American Waetr Works Association, 70(1) 12-18 6

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Corrosion Control Proposal

  • 1. 1. INTRODUCTION Drinking water distribution systems are primary made of iron and steel pipes that are subject to corrosion. Corrosion of system pipes has economic, hydraulic and aesthetic impacts, including water leaks, corrosion product buildup, increased pumping costs and water quality deterioration (red water).Because distribution system pipes are in place for long periods of time corrosion control is critical to maintain microbial, water quality and pipe integrity. Effective corrosion control during water distribution along with high organic matter removal during water treatment will allow effective disinfection and limit bacterial growth within the distribution system. 2. THEORY Corrosion processes consist of a series of electrochemical reaction occurring at the metal surface in contact with water and its constituents. The metal (Fe) is converted to ferrous solid (e. g. FeO), which may then be converted to ferric solids (e. g. Fe2O3) after reaction with oxygen. Corrosivity of a particular water depends on its chemical properties (e. g. pH, alkalinity, dissolved oxygen, Total Dissolved Solids) and physical characteristics (temperature, flow, velocity), as well as the nature of the pipe material (Volk C. et al., 2000) Corrosion control strategies include pH adjustment or/and the addition of inorganic compounds (carbonate, silicate or phosphates) that will form a profilm or passivation layer on the inside of the pipe to prevent corrosion. According to Hancke and Wilhelm in order to form protective scale a water should have the following characteristics, 7<pH<8.5 total alkalinity [HCO3-] > 0.5 mmol/L, [Ca2+] > 0.5 mmol/L, acidity [CO2] > 3 mg/L or 0.06 mmol/L (Hancke K. and Wilhelm S., 1996) 2
  • 2. Calcium carbonate (CaCO3) saturation indices are commonly used to evaluate scale- forming and scale dissolving tendencies of water. Assessing these tendencies is useful in corrosion control and preventing CaCO3 scaling in piping and equipment. It is widely assumed that CaCO3 will precipice from oversaturated waters and that it cannot be deposited from undersaturated waters. Calcium carbonate may precipitate from water in one or more of three forms; calcite, aragonite and vaterite. Which of these allotropes precipitates depends on the pressure, the temperature, the presence of forign ions and the rate at which precipitation takes place. The calcite polymorph of calcium carbonate is the most common scale-forming mineral (Hamrouni, B and Dhahbi, M., 2002). Conceptually, piping is protected when CaCO3 is precipitated on its surface. CaCO3 is believed to inhibit corrosion by clogging reactive areas and providing a matrix to retain corrosion products, thus further sealing the surfaces (Clesceri, L. S. et.al., 1998). Protective coatings are best formed from rapidly moving water because the protective ingredients (calcium, alkalinity) are more effectively transferred to the pipe walls under such condition. Good protective coatings were found to be formed from water moving at about 0.7 m/s. Little protection can be expected in areas of low velocity (e. g. dead ends) and in these areas other means if protection are required (Merrill D. T. and Sanks R. L., 1978) 3
  • 3. Indices that indicate CaCO3 precipitating or dissolution tendencies define whether a water is oversaturated, saturated or undersaturated with respect to CaCO3. The most used indices are saturation Index (SI) (Also known as the Langelier Saturation Index (LSI)) the relative saturation (RS), also known as the driving force index (DFI) and the Rynzar index (RI). The LSI is by far the most commonly used. The RI and SI are related however, the SI is more reliable and commonly used because the RI is semi- empirical. LSI is determined from the equation LSI=pH-pHs Where pH= measured pH and pHs= pH of the water if it were in equilibrium with CaCO3 at the existing calcium ion [Ca2+] and bicarbonate ion [HCO3-] concentrations. LSI is purely an equilibrium index and deals only with the thermodynamic driving force of calcium carbonate scale formation and growth. It provides no indication of how much scale or calcium carbonate will actually precipitate to bring water to equilibrium. The amount of CaCO3 that may be precipitated or dissolved is known as the Calcium Carbonate Precipitation Potential (CCPP). The CCPP is defined as the quantity of CaCO3 that theoretically can be precipitated from oversaturated waters or dissolved by undersaturated water during equilibration. The CCPP is negative for undersaturated waters, zero for saturated waters and positive for oversaturated waters. 4
  • 4. The CCPP is commonly calculated with computerized water chemistry models and Caldwell-Lawrence diagrams. Water should be brought to oversaturated condition just prior to its entering the system that is to be protected. If brought to the oversaturated condition earlier deposition could begin prematurely in tanks or basins where protection is not really required. 3. CURRENT PRACTICES The current practices in dealing with corrosion is by adding inhibitors which are a)costly and b) might result in water quality related issues as the formula of such chemicals are not known and might cause health effects on the long run 4. PROJECT OBJECTIVE This project is aimed at studying a) the CaCO3 behavior of water in the public network system, b) the possibility of altering some water parameters (within the drinking limits) to form a CaCO3 protective film on the pipe walls and c) the amount of CaCO3 needed to be deposited for the protective layer with the aid of computer modeling. 5. APPROACH Water will be analyzed and the parameters related to corrosion will be evaluated for possible deposition capacities of the water via direct calculation and computer software. Having arrived at a conclusion from the results simulation work based on the water analysis will be run to measure the optimum flow rate, CaCO 3 concentration 5
  • 5. required to form a protective layer and possible scenarios for other chemical deposition (e. g. MgFe) 6. CONCLUSION My main goal in enrolling in a PhD program at SQU is to use my long professional experience in the field of water analysis as well as the knowledge obtained during my M. Sc study in the University of Edinburgh to conduct a high-level applied research in this interesting and strategic research area touching the daily life of many people. Reference: 1. Clesceri L. S., Greenberg A. E., Eaton A. D. (Ed).,1998. Standard Methods for the Examination of Water and Wastewater. 20th ed., Baltimore: United Book Press 2. Melidis, P. Sandoziodu, M. Mandusa, A. Ouzounis, K. Corrosion control by using indirect methods, Desalination, 213(2007) 152-158 3. Hamrouni B., Dhahabi M., Calco-carbonic equilibrium calculation, Desalination, 152 (2002) 167-174 4. K. Hancke and S. Wilhelm (Eds.), Wasserauf-bereitung, Chemie und Chemische Verfahren-stechnik, VDI, Springer-Verlag, 5 Aufl, 1996 5. Douglas T. Merrill and Robert L. Sanks, Corrosion Control b deposition films: Part 3, A practical Approach for plant operators, Journal American Waetr Works Association, 70(1) 12-18 6