What are the main components of scale and corrosion products respectively?

Scale is the solid substance that forms at the interface where the heated surfaces of thermal equipment systems come into contact with water. Strictly speaking, this scale is a product deposited due to impure water quality. Pure scale is rare; it is often mixed with corrosion products that deposit together on the heated surfaces, with metal oxides such as iron oxide being the most common. With increasing unit parameters and more stringent water quality requirements, the main component of scale is oxides. Normal scale should be white or gray in color, with a dense, hard, and brittle texture; however, the scale found on the water-cooling walls of larger boilers is often red-brown and softer, which indicates that it is a combination of scale and corrosion products. Salt deposition: In thermal equipment systems, the salts carried by steam adhere to the interior of the system and form scale when the temperature drops, the steam flow rate decreases, or the passages become blocked. This process is known as salt deposition. Salt deposits often accumulate on the speed control valves of turbines as well as on their blades. Pure scale should be white and soft, and soluble in water. However, pure salt scale is very rare; it is often mixed with insoluble silicides, especially in high-pressure boilers, where the steam generated is more likely to carry silicates. Silicate scale is a type of scale that is insoluble or hardly soluble in water, has a hard texture, and is difficult to remove; it often occurs together with salt scale. Salt scale commonly occurs in units equipped with drum boilers, especially those with medium-pressure boilers, as these types of boilers use phosphates for boiler water treatment. Corrosion products: The metal materials of thermal equipment are corroded due to various factors during operation, and the substances resulting from this corrosion are collectively referred to as corrosion products. Generally, they deposit together with scale; when their amount is large, they also settle in areas where the water flow is slow, coexisting with sludge. Slag is a solid substance that precipitates from the boiler water in a suspended state; it gradually deposits in areas of slow water flow during boiler operation, such as in the continuous blowdown pipes and the lower header blowdown pipes. Additionally, after the major overhaul of the unit, residual dirt due to inadequate cleaning also accumulated as sludge in the water. Slag and corrosive oxides often coexist; the failure to remove slag in a timely manner can lead to more severe localized corrosion beneath the scale.

Scale: After water is boiled, some of the water evaporates, and calcium sulfate (CaSO4; gypsum is calcium sulfate containing crystalline water), which is not easily soluble, precipitates out. It turns out that the dissolved calcium bicarbonate (Ca(HCO3)2) and magnesium bicarbonate (Mg(HCO3)2) decompose in boiling water, releasing carbon dioxide (CO2); they then turn into insoluble calcium carbonate (CaCO3) and magnesium hydroxide (Mg(OH)2), which also precipitate out. Sometimes MgCO3 is also formed. This is how scale is formed.

The main components of scale are Mg(OH)2 and CaCO3, while the main components of corrosion products are metal oxides, such as iron scale (iron oxide scale, phosphate iron scale, and silicate iron scale), aluminum scale (aluminum silicate scale), copper scale, etc.

Scale is the solid substance that forms at the interface where the heated surfaces of thermal equipment systems come into contact with water. Strictly speaking, this scale is a product deposited due to impure water quality. Pure scale is rare; it is often mixed with corrosion products that deposit together on the heated surfaces, with metal oxides such as iron oxide being the most common. With increasing unit parameters and more stringent water quality requirements, the main component of scale is oxides. Normal scale should be white or gray in color, with a dense, hard, and brittle texture; however, the scale found on the water-cooling walls of larger boilers is often red-brown and softer, which indicates that it is a combination of scale and corrosion products. Corrosion products: The metal materials of thermal equipment are corroded due to various factors during operation, and the substances resulting from this corrosion are collectively referred to as corrosion products. Generally, they deposit together with scale; when their amount is large, they also settle in areas where the water flow is slow, coexisting with sludge.

Scale is generally composed of calcium carbonate, magnesium carbonate, etc. There are many types of corrosion products, generally iron oxides such as iron oxide and ferric tetraoxide.

Scale is generally composed of calcium carbonate, magnesium carbonate, calcium sulfate, and so on. Corrosion products include rust, which is mainly a hydrate of iron(III) oxide, as well as hydrates of mixed oxides of ferrous and ferric ions; there is also copper rust, zinc white, and others