API 571 : Boiler Water Condensate Corrosion

Boiler water condensation corrosion occurs when dissolved gases, specifically oxygen and carbon dioxide, are present in the water. These gases can react with the metal surfaces of the boiler, causing corrosion. Therefore, it is true that boiler water condensation corrosion is the result of dissolved gases, oxygen, and carbon dioxide.

CO2 corrosion refers to the corrosion that occurs when carbon dioxide (CO2) dissolves in water and forms carbonic acid. In the context of Boiler Water Condensate Corrosion, CO2 corrosion tends to cause a smooth grooving of the pipe wall. This is because the carbonic acid formed by the reaction of CO2 with water is a weak acid and does not cause pitting or localized corrosion. Instead, it gradually wears away the pipe wall, resulting in a smooth groove. Therefore, the statement "CO2 corrosion tends to be a smooth grooving of the pipe wall in Boiler Water Condensate Corrosion" is true.

Corrosion in boiler feedwater and condensate return systems is usually the result of dissolved gases, oxygen and carbon dioxide. Carbon dioxide can react with water to form carbonic acid, which can corrode metal surfaces. This corrosion can lead to damage and failure of the system if not properly controlled.

Laboratory analysis of boiler feedwater is the most commonly used method to ensure that boiler feed water corrosion is not occurring. This involves regularly testing the water samples from the boiler feedwater for various parameters such as pH, dissolved oxygen, alkalinity, hardness, and chloride levels. By analyzing these parameters, any potential corrosion issues can be identified and appropriate measures can be taken to prevent or mitigate corrosion in the boiler feedwater system. This method allows for proactive monitoring and maintenance of the boiler feedwater, ensuring the longevity and efficiency of the boiler system.

Operating pressure is not a major factor associated with boiler water condensate corrosion. Corrosion in boiler water condensate is primarily caused by factors such as oxygen content, carbon dioxide content, process pH, and temperature. The operating pressure of the boiler does not directly contribute to corrosion, but it can indirectly affect corrosion rates by influencing other factors such as oxygen and carbon dioxide content.

The correct answer is "All of the above". This means that all of the mechanisms mentioned - CO2 Corrosion, Corrosion Fatigue, and Erosion/Erosion-corrosion - are related mechanisms of Boiler Water Condensate Corrosion. This suggests that all of these mechanisms can contribute to the corrosion of the condensate in a boiler water system.

Magnetite, Fe3O4

The correct answer is maintaining a protective corrosion layer of magnetite (Fe3O4). This is achieved by adding chemicals to the boiler feed water that promote the formation of magnetite on the inner surfaces of the boiler. Magnetite acts as a protective layer, preventing corrosion of the boiler material by creating a barrier between the metal and the water. This helps to prolong the lifespan of the boiler and ensures its efficient operation.

Corrosion from oxygen in boiler feed water typically results in isolated pitting. This occurs when localized areas of the metal surface are attacked, leading to the formation of small pits. Unlike uniform corrosion, which affects the entire surface evenly, isolated pitting is characterized by the formation of small, isolated holes. Oxygen in the feed water can cause the formation of a protective oxide layer on the metal surface, but if this layer is disrupted or damaged, pitting corrosion can occur in certain areas.

Oxygen scavengers are added to the process to prevent boiler feed water corrosion. Corrosion in boiler feed water systems is primarily caused by the presence of dissolved oxygen. Oxygen scavengers are chemicals that react with and remove oxygen from the water, thereby reducing the likelihood of corrosion. By removing oxygen, the scavengers help to protect the metal surfaces of the boiler from oxidation and degradation. This treatment is essential to maintain the integrity and longevity of the boiler system.