bacteria including aerobic and low nutrient. Certain types of bacteria( thermophiles)have been found to survive significantly high temperatures Conclusion. An evaluation of the cathodic protection system showed the design to be adequate provided it was eliably powered. Cathodic protection is one means of controlling MIC, although interruption in the cathodic protection service will adversely affect its performance. The effectiveness of the cathodic protection on established microbial deposits is questionable Recommendations. The tank floor was ultrasonically tested, and portions of the floor replaced based on the remaining wall thickness. Doubling the wall thickness of the replacement floor plates was recommended Example 3: Preventive Maintenance for Buried Pipelines. Corrosion is a major contributor to the deterioration of buried infrastructure such as pipelines in the United States. Figure 4 shows the result of an unexpected corrosion failure of a 100-year-old riveted steel water transmission main. The snowplow and icing of the power lines in the photograph indicate that repairs had to be made under less than ideal weather conditions. The costs associated with the evaluation, modifications, and cathodic protection of a water system typically represent less than 10% of the total cost to replace the buried infrastructure. These savings can be obtained through the implementation of a comprehensive corrosion-control program 一爬 Fig 4 Corrosion failure of 100-year-old riveted steel water transmission main Courtesy ofs. Paul Corrtech. inc To ensure that the proper corrosion-control method(s)are employed and the full infrastructure service life is realized, local factors contributing to corrosion must be understood. Where history or analyses indicate that the environment is aggressive, corrosion-control methods need to be developed and initiated. To evaluate corrosion-exposure conditions for metallic piping networks, field conditions such as soil type, soil pH, stray current effects, and electrical continuity require quantification by field investigation
bacteria including aerobic and low nutrient. Certain types of bacteria (thermophiles) have been found to survive significantly high temperatures. Conclusion. An evaluation of the cathodic protection system showed the design to be adequate provided it was reliably powered. Cathodic protection is one means of controlling MIC, although interruption in the cathodic protection service will adversely affect its performance. The effectiveness of the cathodic protection on established microbial deposits is questionable. Recommendations. The tank floor was ultrasonically tested, and portions of the floor replaced based on the remaining wall thickness. Doubling the wall thickness of the replacement floor plates was recommended. Example 3: Preventive Maintenance for Buried Pipelines. Corrosion is a major contributor to the deterioration of buried infrastructure such as pipelines in the United States. Figure 4 shows the result of an unexpected corrosion failure of a 100-year-old riveted steel water transmission main. The snowplow and icing of the power lines in the photograph indicate that repairs had to be made under less than ideal weather conditions. The costs associated with the evaluation, modifications, and cathodic protection of a water system typically represent less than 10% of the total cost to replace the buried infrastructure. These savings can be obtained through the implementation of a comprehensive corrosion-control program. Fig. 4 Corrosion failure of 100-year-old riveted steel water transmission main. Courtesy of S. Paul, CorrTech, Inc. To ensure that the proper corrosion-control method(s) are employed and the full infrastructure service life is realized, local factors contributing to corrosion must be understood. Where history or analyses indicate that the environment is aggressive, corrosion-control methods need to be developed and initiated. To evaluate corrosion-exposure conditions for metallic piping networks, field conditions such as soil type, soil pH, stray current effects, and electrical continuity require quantification by field investigation
Based on preliminary survey results, excavations of the pipe system are made to inspect the pipe for corrosion At each location, the pipe is cleaned and evaluated for uniform and pitting corrosion. Of concern for pipelines are the deepest pits and penetrations. Statistical analysis of the system is performed. Typically, greater than 95% of the pipe is in good condition with sufficient original wall thickness. By defining the corrosion exposure and understanding the exposure, personnel can then make informed decisions about extending the life of the buried infrastructure or developing replacement options. By applying proven technologies such as cathodic protection, corrosion can be arrested and infrastructure can remain in service for 50-plus years without failures and downtime Example 4: Structural Epoxy Rehabilitation of Steel and Reinforced Concrete Structures. Hydrogen sulfide gas is very aggressive to reinforced concrete structures in wastewater treatment plants. Figure 5 provides views of severe corrosion of a wastewater tunnel structure. Note the failed lining repairs. Structures of concern are sludge storage tanks, chambers, and head works structures. Typically, up to 15 cm(6 in. )of concrete corrosion loss has been found on many structures, affecting both structural integrity and function Fig 5 Two views of severe corrosion of wastewater tunnel structure. Note the failed lining repairs. Courtesy ofs. Paul, CorrTech, Inc. The extent of deterioration and factors contributing to it need to be defined by inspection of pipe barrel interiors, manholes and risers, flow splitting chambers, sludge tanks, clarifiers, and tunnels associated with wastewater treatment systems. The purpose of this task is to document the location and extent of coating and concrete deterioration and corrosion of reinforcing steel Much of the existing infrastructure, both of steel and reinforced concrete construction, can be internally lined or externally coated to prevent deterioration. Linings can be used to control corrosion of the structure as well as provide structural integrity where leaks exist. Properly selected and applied high-performance epoxy can protect H2S headspace corrosion on wastewater treatment facilities and related structures. The spray-on or trowel-on high-performance structural epoxy is a proven system for these applications in the water/wastewater, Thefileisdownloadedfromwww.bzfxw.com
Based on preliminary survey results, excavations of the pipe system are made to inspect the pipe for corrosion. At each location, the pipe is cleaned and evaluated for uniform and pitting corrosion. Of concern for pipelines are the deepest pits and penetrations. Statistical analysis of the system is performed. Typically, greater than 95% of the pipe is in good condition with sufficient original wall thickness. By defining the corrosion exposure and understanding the exposure, personnel can then make informed decisions about extending the life of the buried infrastructure or developing replacement options. By applying proven technologies such as cathodic protection, corrosion can be arrested and infrastructure can remain in service for 50-plus years without failures and downtime. Example 4: Structural Epoxy Rehabilitation of Steel and Reinforced Concrete Structures. Hydrogen sulfide gas is very aggressive to reinforced concrete structures in wastewater treatment plants. Figure 5 provides views of severe corrosion of a wastewater tunnel structure. Note the failed lining repairs. Structures of concern are sludge storage tanks, chambers, and head works structures. Typically, up to 15 cm (6 in.) of concrete corrosion loss has been found on many structures, affecting both structural integrity and function. Fig. 5 Two views of severe corrosion of wastewater tunnel structure. Note the failed lining repairs. Courtesy of S. Paul, CorrTech, Inc. The extent of deterioration and factors contributing to it need to be defined by inspection of pipe barrel interiors, manholes and risers, flow splitting chambers, sludge tanks, clarifiers, and tunnels associated with wastewater treatment systems. The purpose of this task is to document the location and extent of coating and concrete deterioration and corrosion of reinforcing steel. Much of the existing infrastructure, both of steel and reinforced concrete construction, can be internally lined or externally coated to prevent deterioration. Linings can be used to control corrosion of the structure as well as provide structural integrity where leaks exist. Properly selected and applied high-performance epoxy can protect H2S headspace corrosion on wastewater treatment facilities and related structures. The spray-on or trowel-on high-performance structural epoxy is a proven system for these applications in the water/wastewater, The file is downloaded from www.bzfxw.com
power generation, and other industries. Figure 6 provides a view of a severely deteriorated sludge storage tank during repairs Fig. 6 Severely deteriorated sludge storage tank during repairs. A structural epoxy will be applied to the reinforced concrete Courtesy ofs. Paul, CorrTech, Inc. Analysis and Prevention of Corrosion-Related Failures S.R. Freeman, Millennium Metallurgy Ltd Prevention of Corrosion-Related Failures of Metals Following analysis of corrosion failures, corrective actions are recommended to prevent or delay recurrence of failures. The approaches to corrective and preventive actions include Change in the environment Change in the alloy or heat treatment Design change Use of galvanic protection(cathodic protection and anodic protection) Use of inhibitors Use of nonmetallic coatings and liners Application of metallic coatings Use of surface treatments, thermal spray, or other surface modifications Corrosion monitoring Preventive maintenance Change in the Environment. Environmental control can be a complicated task. A complete understanding of the environment is key to changing or treating it. a detailed analysis of the environment should be performed prior to the implementation of any modifications or treatments Safeguards must be put in place to avoid unintended consequences of altering the environment, such as the introduction of a contaminant. In some cases, an environment is subject to seasonal changes such as changes in water quality and temperature Controls must then be seasonally adjusted as well Controlling the ph to lower corrosion rates is a common practice in municipal and industrial water supplies The chemicals that may be introduced are limited for public health reasons
power generation, and other industries. Figure 6 provides a view of a severely deteriorated sludge storage tank during repairs. Fig. 6 Severely deteriorated sludge storage tank during repairs. A structural epoxy will be applied to the reinforced concrete. Courtesy of S. Paul, CorrTech, Inc. Analysis and Prevention of Corrosion-Related Failures S.R. Freeman, Millennium Metallurgy, Ltd. Prevention of Corrosion-Related Failures of Metals Following analysis of corrosion failures, corrective actions are recommended to prevent or delay recurrence of failures. The approaches to corrective and preventive actions include: · Change in the environment · Change in the alloy or heat treatment · Design change · Use of galvanic protection (cathodic protection and anodic protection) · Use of inhibitors · Use of nonmetallic coatings and liners · Application of metallic coatings · Use of surface treatments, thermal spray, or other surface modifications · Corrosion monitoring · Preventive maintenance Change in the Environment. Environmental control can be a complicated task. A complete understanding of the environment is key to changing or treating it. A detailed analysis of the environment should be performed prior to the implementation of any modifications or treatments. Safeguards must be put in place to avoid unintended consequences of altering the environment, such as the introduction of a contaminant. In some cases, an environment is subject to seasonal changes such as changes in water quality and temperature. Controls must then be seasonally adjusted as well. Controlling the pH to lower corrosion rates is a common practice in municipal and industrial water supplies. The chemicals that may be introduced are limited for public health reasons
Pourbaix diagrams are used to predict material behavior with the adjustment of the pH. Pourbaix diagrams show the conditions of potential and pH under which the metal either is nonreactive(immune) or can form oxides. The diagrams do not provide any information regarding corrosion rates, however. Pourbaix diagrams also provide information regarding the formation of barrier films; however, conclusions regarding their effectiveness in the presence of specific ions cannot be drawn. General information can be retrieved from the diagrams indicating the potential for a corrosive situation in a given environment at a specific ph and how to djust the ph to avoid corrosion Changing the environment can be performed in various ways without the use of additives. Ozone treatment is one method used in municipal water systems to treat for MIC. Stirring a tank of fluid may be all that is required to avoid pitting corrosion Change of Alloy and Heat Treatment. Alloy changes are often employed to combat corrosion problems particularly when the replacement material is cost effective. For example, a copper alloy prone to selective leaching can easily be replaced by an inhibited copper alloy that is not susceptible to this kind of corrosion While proper selection of the material prior to use is the ideal, a complete understanding of the operating electrochemical environment, stresses induced by the operation, inherent stresses in the material from fabrication, and cyclic operating temperatures may not be possible. A failure and subsequent analysis or research of case histories of failures in similar situations may be needed to provide the necessary material selection information. Reviewing corrosion data for a specific environment or performing corrosion testing is helpful in determining the best material for the application Design changes involving components, pro or systems may be necessary to alleviate corrosion. Poor designs can cause materials highly resistant to uniform corrosion attack to fail catastrophically to local attacl Conditions that may cause an acceleration of corrosion include stagnation and rapid fluid flow. Designs that minimize the possibility of crevice corrosion, erosion-corrosion, cavitation, and impingement are desired Figure 7 shows good and poor examples of how design affects local corrosion(Ref 5) Thefileisdownloadedfromwww.bzfxw.com
Pourbaix diagrams are used to predict material behavior with the adjustment of the pH. Pourbaix diagrams show the conditions of potential and pH under which the metal either is nonreactive (immune) or can form oxides. The diagrams do not provide any information regarding corrosion rates, however. Pourbaix diagrams also provide information regarding the formation of barrier films; however, conclusions regarding their effectiveness in the presence of specific ions cannot be drawn. General information can be retrieved from the diagrams indicating the potential for a corrosive situation in a given environment at a specific pH and how to adjust the pH to avoid corrosion. Changing the environment can be performed in various ways without the use of additives. Ozone treatment is one method used in municipal water systems to treat for MIC. Stirring a tank of fluid may be all that is required to avoid pitting corrosion. Change of Alloy and Heat Treatment. Alloy changes are often employed to combat corrosion problems, particularly when the replacement material is cost effective. For example, a copper alloy prone to selective leaching can easily be replaced by an inhibited copper alloy that is not susceptible to this kind of corrosion failure. While proper selection of the material prior to use is the ideal, a complete understanding of the operating electrochemical environment, stresses induced by the operation, inherent stresses in the material from fabrication, and cyclic operating temperatures may not be possible. A failure and subsequent analysis or research of case histories of failures in similar situations may be needed to provide the necessary material selection information. Reviewing corrosion data for a specific environment or performing corrosion testing is helpful in determining the best material for the application. Design changes involving components, processes, or systems may be necessary to alleviate corrosion. Poor designs can cause materials highly resistant to uniform corrosion attack to fail catastrophically to local attack. Conditions that may cause an acceleration of corrosion include stagnation and rapid fluid flow. Designs that minimize the possibility of crevice corrosion, erosion-corrosion, cavitation, and impingement are desired. Figure 7 shows good and poor examples of how design affects local corrosion (Ref 5). The file is downloaded from www.bzfxw.com
ee? exposed seam Vessel Retained Poor Poor Possible Heat exchange fluid Narrow gap Poor Fig. 7 Examples of how design and assembly can affect localized corrosion by creating crevices and traps where corrosive liquids can accumulate. (a) Storage containers or vessels should allow complete drainage; otherwise, corrosives can concentrate in the bottom of vessel, and debris may accumulate if the vessel is open to the atmosphere.(b Structural members should be designed to avoid retention of liquids; L-shaped sections should be used with the open side down, and exposed seams should be avoided.(c) Incorrect trimming or poor design of seals and gaskets can create crevice sites. (d) Drain valves should be designed with sloping bottoms to avoid pitting of the base of the valve.(e) Nonsloping tubing can leave pools of liquid at shutdown.(f Nonvertical assembly of the heat exchanger permits a dead space that may result in overheating if very hot gases are involved.(g)Nonaligned assembly distorts the fastener, which creates a crevice and may result in a loose fitting that can contribute to vibration, fretting and wear . (h) Structural supports should allow good drainage; use of a slope at the bottom of the member allows liquid to run off, rather than impinging directly on the concrete support. (i) Continuous welding is necessary for horizontal stiffeners to prevent the formation of traps and crevices. Gi Square sections formed from two L-shaped members require continuous welding to seal out the external environment. Source: Ref 5
Fig. 7 Examples of how design and assembly can affect localized corrosion by creating crevices and traps where corrosive liquids can accumulate. (a) Storage containers or vessels should allow complete drainage; otherwise, corrosives can concentrate in the bottom of vessel, and debris may accumulate if the vessel is open to the atmosphere. (b) Structural members should be designed to avoid retention of liquids; L-shaped sections should be used with the open side down, and exposed seams should be avoided. (c) Incorrect trimming or poor design of seals and gaskets can create crevice sites. (d) Drain valves should be designed with sloping bottoms to avoid pitting of the base of the valve. (e) Nonsloping tubing can leave pools of liquid at shutdown. (f) Nonvertical assembly of the heat exchanger permits a dead space that may result in overheating if very hot gases are involved. (g) Nonaligned assembly distorts the fastener, which creates a crevice and may result in a loose fitting that can contribute to vibration, fretting and wear. (h) Structural supports should allow good drainage; use of a slope at the bottom of the member allows liquid to run off, rather than impinging directly on the concrete support. (i) Continuous welding is necessary for horizontal stiffeners to prevent the formation of traps and crevices. (j) Square sections formed from two L-shaped members require continuous welding to seal out the external environment. Source: Ref 5