Sulfur Daily Question 2019.1.16
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Factors affecting boiler corrosion and its control? Answer: ①Dissolved oxygen: Oxygen is a cathodic depolarizer and the main factor causing electrochemical corrosion of boiler metals. Under normal conditions, the higher the oxygen concentration, the more severe the corrosion of the metal. For boilers equipped with deaeration devices, it is necessary to ensure their proper operation. ②pH value: The pH value of water has a significant impact on the corrosion of metals. A pH level of the boiler water that is too low (<8) or too high (>13) will damage the protective layer on the metal surface, accelerate oxygen corrosion, and may lead to acid or alkali corrosion. A low pH value means a high concentration of H+, which not only destroys the protective film but is also a type of depolarizer; therefore, in acidic media, metals are prone to hydrogen-induced depolarization corrosion. Maintaining an appropriate pH level in the water in the pot (usually between 10 and 12) helps to form a protective film on the metal surface, thereby reducing corrosion. ③Composition of salts in water: The higher the salt content in water, the faster the corrosion rate, as a higher salt content leads to greater electrical conductivity of the water, and thus a higher current in the corrosion cell. However, different ions in salts have significantly varying effects on corrosion: for example, when PO43— and CO32— are present in the water used in cooking, insoluble iron phosphate and iron carbonate protective films can form on the metal surface, thereby enabling anodic passivation and slowing down corrosion. However, when water contains Cl—, Cl— can easily be adsorbed by the metal surface and displace oxygen atoms from the oxide film, forming soluble chlorides; this thereby destroys the metal’s oxide protective layer and accelerates the corrosion process of the metal. Therefore, maintaining a certain level of PO43— or CO32— in the boiler water not only prevents scaling but also contributes to corrosion prevention. When the boiler is shut down, if wet protection is used, it is necessary to avoid leaving behind boiler water with a high salt content, in order to prevent accelerated electrochemical corrosion.
1. Oxygen corrosion is a type of corrosion that occurs due to the presence of dissolved oxygen in water. Ferrous oxide is formed through electrochemical reactions, and it is further oxidized to form Fe3O4. 2. Acidic corrosion is corrosion caused by the depolarization of H+. 3. Alkaline corrosion is caused by the concentration of free sodium hydroxide beneath the scale. It mostly occurs beneath the deposits in areas of the water wall tubes where the heat intensity on the fire side is high. After the sediment and corrosion products are removed, grooves appear on the tube wall, which thins out; in severe cases, the wall may even be penetrated. Alkaline corrosion may also be found in economizer tubes, superheater tubes, and desuperheaters. 4. Hydrogen damage or hydrogen embrittlement corrosion: Hydrogen generated by acidic substances penetrates into the metal beneath the deposits, combines with carbon in the steel to form methane, creating pressure within the steel that leads to cracks at the grain boundaries and thus causes damage to the metal. This type of corrosion tends to occur on the fire-facing side of the water wall tubes, and is characterized by brittle fracture. 5. Alkali embrittlement or caustic embrittlement corrosion is a type of stress corrosion cracking that occurs in steel in sodium hydroxide solutions; it often occurs at the riveting holes of boiler drums and at the expansion joints of furnace tubes. Conditions for the occurrence include the opportunity for NaOH in the boiler water to concentrate and the presence of stress; stress is generated by vibrations and periodic swings, as well as changes in temperature and pressure.
1. Oxygen corrosion is a type of corrosion that occurs due to the presence of dissolved oxygen in water. Ferrous oxide is formed through electrochemical reactions, and it is further oxidized to form Fe3O4. 2. Acidic corrosion is corrosion caused by the depolarization of H+. 3. Alkaline corrosion is caused by the concentration of free sodium hydroxide beneath the scale. It mostly occurs beneath the deposits in areas of the water wall tubes where the heat intensity on the fire side is high. After the sediment and corrosion products are removed, grooves appear on the tube wall, which thins out; in severe cases, the wall may even be penetrated. Alkaline corrosion may also be found in economizer tubes, superheater tubes, and desuperheaters. 4. Hydrogen damage or hydrogen embrittlement corrosion: Hydrogen generated by acidic substances penetrates into the metal beneath the deposits, combines with carbon in the steel to form methane, creating pressure within the steel that leads to cracks at the grain boundaries and thus causes damage to the metal. This type of corrosion tends to occur on the fire-facing side of the water wall tubes, and is characterized by brittle fracture. 5. Alkali embrittlement or caustic embrittlement corrosion is a type of stress corrosion cracking that occurs in steel in sodium hydroxide solutions; it often occurs at the riveting holes of boiler drums and at the expansion joints of furnace tubes. Conditions for the occurrence include the opportunity for NaOH in the boiler water to concentrate and the presence of stress; stress is generated by vibrations and periodic swings, as well as changes in temperature and pressure.
①Dissolved oxygen: Oxygen is a cathodic depolarizer and the main factor causing electrochemical corrosion of boiler metals. Under normal conditions, the higher the oxygen concentration, the more severe the corrosion of the metal. For boilers equipped with deaeration devices, it is necessary to ensure their proper operation. ②pH value: The pH value of water has a significant impact on the corrosion of metals. A pH level of the boiler water that is too low (<8) or too high (>13) will damage the protective layer on the metal surface, accelerate oxygen corrosion, and may lead to acid or alkali corrosion. A low pH value means a high concentration of H ions; this not only destroys the protective film but also, as a depolarizing agent, it causes hydrogen-induced depolarization corrosion in acidic media. Maintaining an appropriate pH level in the water in the pot (usually between 10 and 12) helps to form a protective film on the metal surface, thereby reducing corrosion. ③Composition of salts in water: The higher the salt content in water, the faster the corrosion rate, as a higher salt content leads to greater electrical conductivity of the water, and thus a higher current in the corrosion cell. However, different ions in salts have significantly varying effects on corrosion: for example, when PO4 and CO2 are present in boiler water, insoluble films of iron phosphate and iron carbonate can form on the metal surface, thereby causing anodic passivation and slowing down corrosion. However, when C1 is present in water, it tends to adsorb onto the metal surface and displace the oxygen atoms in the oxide layer, forming soluble chlorides; this thereby destroys the metal’s oxide protective layer and accelerates the corrosion process of the metal. Therefore, maintaining a certain level of PO4 or CO3 in the boiler water not only prevents scaling but also contributes to corrosion prevention. When the boiler is shut down, if wet protection is used, it is necessary to avoid leaving behind boiler water with a high salt content, in order to prevent accelerated electrochemical corrosion.
①Dissolved oxygen: Oxygen is a cathodic depolarizer and the main factor causing electrochemical corrosion of boiler metals. Under normal conditions, the higher the oxygen concentration, the more severe the corrosion of the metal. For boilers equipped with deaeration devices, it is necessary to ensure their proper operation. ②pH value: The pH value of water has a significant impact on the corrosion of metals. A pH level of the boiler water that is too low (<8) or too high (>13) will damage the protective layer on the metal surface, accelerate oxygen corrosion, and may lead to acid or alkali corrosion. A low pH value means a high concentration of H ions; this not only destroys the protective film but also, as a depolarizing agent, it causes hydrogen-induced depolarization corrosion in acidic media. Maintaining an appropriate pH level in the water in the pot (usually between 10 and 12) helps to form a protective film on the metal surface, thereby reducing corrosion. ③Composition of salts in water: The higher the salt content in water, the faster the corrosion rate, as a higher salt content leads to greater electrical conductivity of the water, and thus a higher current in the corrosion cell. However, different ions in salts have significantly varying effects on corrosion: for example, when PO4 and CO2 are present in boiler water, insoluble films of iron phosphate and iron carbonate can form on the metal surface, thereby causing anodic passivation and slowing down corrosion. However, when C1 is present in water, it tends to adsorb onto the metal surface and displace the oxygen atoms in the oxide layer, forming soluble chlorides; this thereby destroys the metal’s oxide protective layer and accelerates the corrosion process of the metal. Therefore, maintaining a certain level of PO4 or CO3 in the boiler water not only prevents scaling but also contributes to corrosion prevention. When the boiler is shut down, if wet protection is used, it is necessary to avoid leaving behind boiler water with a high salt content, in order to prevent accelerated electrochemical corrosion.
①Dissolved oxygen: Oxygen is a cathodic depolarizer and the main factor causing electrochemical corrosion of boiler metals. Under normal conditions, the higher the oxygen concentration, the more severe the corrosion of the metal. For boilers equipped with deaeration devices, it is necessary to ensure their proper operation. ②pH value: The pH value of water has a significant impact on the corrosion of metals. A pH level of the boiler water that is too low (<8) or too high (>13) will damage the protective layer on the metal surface, accelerate oxygen corrosion, and may lead to acid or alkali corrosion. A low pH value means a high concentration of H+, which not only destroys the protective film but is also a type of depolarizer; therefore, in acidic media, metals are prone to hydrogen-induced depolarization corrosion. Maintaining an appropriate pH level in the water in the pot (usually between 10 and 12) helps to form a protective film on the metal surface, thereby reducing corrosion. ③Composition of salts in water: The higher the salt content in water, the faster the corrosion rate, as a higher salt content leads to greater electrical conductivity of the water, and thus a higher current in the corrosion cell. However, different ions in salts have significantly varying effects on corrosion: for example, when PO43— and CO32— are present in the water used in cooking, insoluble iron phosphate and iron carbonate protective films can form on the metal surface, thereby enabling anodic passivation and slowing down corrosion. However, when water contains Cl—, Cl— can easily be adsorbed by the metal surface and displace oxygen atoms from the oxide film, forming soluble chlorides; this thereby destroys the metal’s oxide protective layer and accelerates the corrosion process of the metal. Therefore, maintaining a certain level of PO43— or CO32— in the boiler water not only prevents scaling but also contributes to corrosion prevention. When the boiler is shut down, if wet protection is used, it is necessary to avoid leaving behind boiler water with a high salt content, in order to prevent accelerated electrochemical corrosion.
①Dissolved oxygen: Oxygen is a cathodic depolarizer and the main factor causing electrochemical corrosion of boiler metals. Under normal conditions, the higher the oxygen concentration, the more severe the corrosion of the metal. For boilers equipped with deaeration devices, it is necessary to ensure their proper operation. ②pH value: The pH value of water has a significant impact on the corrosion of metals. A pH level of the boiler water that is too low (<8) or too high (>13) will damage the protective layer on the metal surface, accelerate oxygen corrosion, and may lead to acid or alkali corrosion. A low pH value means a high concentration of H+, which not only destroys the protective film but is also a type of depolarizer; therefore, in acidic media, metals are prone to hydrogen-induced depolarization corrosion. Maintaining an appropriate pH level in the water in the pot (usually between 10 and 12) helps to form a protective film on the metal surface, thereby reducing corrosion. ③Composition of salts in water: The higher the salt content in water, the faster the corrosion rate, as a higher salt content leads to greater electrical conductivity of the water, and thus a higher current in the corrosion cell. However, different ions in salts have significantly varying effects on corrosion: for example, when PO43— and CO32— are present in the water used in cooking, insoluble iron phosphate and iron carbonate protective films can form on the metal surface, thereby enabling anodic passivation and slowing down corrosion. However, when water contains Cl—, Cl— can easily be adsorbed by the metal surface and displace oxygen atoms from the oxide film, forming soluble chlorides; this thereby destroys the metal’s oxide protective layer and accelerates the corrosion process of the metal. Therefore, maintaining a certain level of PO43— or CO32— in the boiler water not only prevents scaling but also contributes to corrosion prevention. When the boiler is shut down, if wet protection is used, it is necessary to avoid leaving behind boiler water with a high salt content, in order to prevent accelerated electrochemical corrosion.
Answer: ①Dissolved oxygen: Oxygen is a cathodic depolarizer and the main factor causing electrochemical corrosion of boiler metals.
Answer: ①Dissolved oxygen: Oxygen is a cathodic depolarizer and the main factor causing electrochemical corrosion of boiler metals. Under normal conditions, the higher the oxygen concentration, the more so for the metal
①Dissolved oxygen: Oxygen is a cathodic depolarizer and the main factor causing electrochemical corrosion of boiler metals. Under normal conditions, the higher the oxygen concentration, the more severe the corrosion of the metal. For boilers equipped with deaeration devices, it is necessary to ensure their proper operation. ②pH value: The pH value of water has a significant impact on the corrosion of metals. A pH level of the boiler water that is too low (<8) or too high (>13) will damage the protective layer on the metal surface, accelerate oxygen corrosion, and may lead to acid or alkali corrosion. A low pH value means a high concentration of H ions; this not only destroys the protective film but also, as a depolarizing agent, it causes hydrogen-induced depolarization corrosion in acidic media. Maintaining an appropriate pH level in the water in the pot (usually between 10 and 12) helps to form a protective film on the metal surface, thereby reducing corrosion. ③Composition of salts in water: The higher the salt content in water, the faster the corrosion rate, as a higher salt content leads to greater electrical conductivity of the water, and thus a higher current in the corrosion cell. However, different ions in salts have significantly varying effects on corrosion: for example, when PO4 and CO2 are present in boiler water, insoluble films of iron phosphate and iron carbonate can form on the metal surface, thereby causing anodic passivation and slowing down corrosion. However, when C1 is present in water, it tends to adsorb onto the metal surface and displace the oxygen atoms in the oxide layer, forming soluble chlorides; this thereby destroys the metal’s oxide protective layer and accelerates the corrosion process of the metal. Therefore, maintaining a certain level of PO4 or CO3 in the boiler water not only prevents scaling but also contributes to corrosion prevention. When the boiler is shut down, if wet protection is used, it is necessary to avoid leaving behind boiler water with a high salt content, in order to prevent accelerated electrochemical corrosion.
①Dissolved oxygen: Oxygen is a cathodic depolarizer and the main factor causing electrochemical corrosion of boiler metals. Under normal conditions, the higher the oxygen concentration, the more severe the corrosion of the metal. For boilers equipped with deaeration devices, it is necessary to ensure their proper operation. ②pH value: The pH value of water has a significant impact on the corrosion of metals. A pH level of the boiler water that is too low (<8) or too high (>13) will damage the protective layer on the metal surface, accelerate oxygen corrosion, and may lead to acid or alkali corrosion. A low pH value means a high concentration of H ions; this not only destroys the protective film but also, as a depolarizing agent, it causes hydrogen-induced depolarization corrosion in acidic media. Maintaining an appropriate pH level in the water in the pot (usually between 10 and 12) helps to form a protective film on the metal surface, thereby reducing corrosion. ③Composition of salts in water: The higher the salt content in water, the faster the corrosion rate, as a higher salt content leads to greater electrical conductivity of the water, and thus a higher current in the corrosion cell. However, different ions in salts have significantly varying effects on corrosion: for example, when PO4 and CO2 are present in boiler water, insoluble films of iron phosphate and iron carbonate can form on the metal surface, thereby causing anodic passivation and slowing down corrosion. However, when C1 is present in water, it tends to adsorb onto the metal surface and displace the oxygen atoms in the oxide layer, forming soluble chlorides; this thereby destroys the metal’s oxide protective layer and accelerates the corrosion process of the metal. Therefore, maintaining a certain level of PO4 or CO3 in the boiler water not only prevents scaling but also contributes to corrosion prevention. When the boiler is shut down, if wet protection is used, it is necessary to avoid leaving behind boiler water with a high salt content, in order to prevent accelerated electrochemical corrosion.