What are the common types of dirt on the surface of electric heating tubes?

Common types of dirt on the surface of electric heating tubes include scale, oil scale, metal oxides, and carbon deposits. The following is a detailed introduction:
Scale
Composition: Mainly composed of carbonates, sulfates, phosphates, etc. formed by calcium and magnesium ions in water. In areas with hard water, the water contains a large amount of calcium and magnesium ions. When the electric heating tube is used to heat water, these ions will gradually precipitate and adhere to the surface of the heating tube during the heating process to form scale.
Appearance: Usually white or off-white, with a relatively hard texture, sometimes showing a block or layered structure.
Oil scale
Composition: Mainly a mixture of grease, dust, impurities, etc. If the electric heating tube is used in an environment with oily substances, such as in industrial production for heating lubricating oil, hydraulic oil, etc., or in an environment such as a kitchen, the oily substance may splash onto the surface of the heating tube and combine with impurities such as dust in the air to form oil scale.
Appearance: Generally yellow-brown or black, with a certain viscosity, it will feel greasy when touched.
Metal oxides
Composition: When the metal surface of the electric heating tube is exposed to the air, it will react with oxygen to produce metal oxides. In addition, if the heating tube works in a high temperature environment, the oxidation rate of the metal material will accelerate. Different metal materials will form different metal oxides, such as iron will form ferric oxide (rust), copper will form copper oxide, etc.
Appearance: The color varies depending on the type of metal, such as rust is usually reddish brown, and copper oxide is black. Metal oxide dirt is generally loose and easy to fall off.
Carbon deposits
Composition: Mainly carbonaceous deposits produced by incomplete combustion or high-temperature decomposition of organic matter. If there are organic matter around the electric heating tube, and the organic matter is pyrolyzed or incompletely burned during the heating process, carbon deposits will form on the surface of the heating tube. For example, in some equipment that heats organic solutions, or in gas heating equipment, the exhaust gas produced by combustion contains incompletely burned carbon particles, which will adhere to the surface of the heating tube.
Appearance: Usually black, brittle texture, easy to peel off.
In addition to the above common types of dirt, there may be other types of dirt depending on the use environment of the electric heating tube, such as crystallization of chemical substances, dust and dirt in the chemical production environment.