Chemical erosion of electric heating tube

Chemical erosion of electric heating tube

A small amount of impurities in refractory materials and thermal insulation materials, such as FeO, P2O3, B2O3, Na2O, K2O, V205, etc., will interact with Al2O3 and Cr2O3 in the oxide film on the surface of the heating element at high temperatures to produce low melting point compounds and destroy the protection of the oxide film Function and corrode electric heating elements. The few impurities are the same as Al2O3 and Cr2O3, and the main low melting point compounds formed are shown in Table 4-13. It can be seen from the table that the most dangerous impurity oxides for heating elements are V205, P2O5 and B2O3. These impurity oxides erode the heating element when the temperature is low. Therefore, the content of refractory materials must be strictly controlled when selecting refractory materials to avoid corrosion.

In order to avoid corrosion, the following insulation materials and products are strictly prohibited from contacting electric heating elements at high temperatures: asbestos, slag wool, diatomaceous earth, vermiculite, perlite, pumice, water glass, foam concrete, glass fiber, etc.

When relative movement occurs between the surface of the heating element and the supporting refractory material, the protective oxide film on the surface of the element will be worn. The reason for the relative movement is that the electric heating alloy expands when heated and contracts when cooled. Although this phenomenon is not very related to refractory materials, if the design is reasonable and fixed properly, this effect will be reduced.

Electric fusion erosion is a short-circuit discharge between turns of an electric heating element, which causes damage to the surface of the element. This phenomenon occurs in high-temperature and intensive media. At this time, the unstable oxide Fe2O3 contained in the refractory material in contact with the electric heating element is reduced: Fe2O3+3CO==2Fe+3C02 metal iron is deposited on the contact surface, causing a short circuit between the electric heating element turns, causing local melting on the surface of the element. The local resistance of the heating element increases, which accelerates the failure process.

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