Causes of Duct Heater Failure

In a shut-off situation, such as when the duct heater's temperature control is controlled by the outlet temperature, the sensor signal may not provide an accurate signal, causing a continuous demand for heating. The heater will continue to heat up, and if the over-temperature sensor works, it can shut off the power. However, if the over-temperature sensor does not work, the heating element may burn out, or the container may crack or melt. Either of these situations can have unpredictable consequences in explosion-proof environments.

If the sensor is located close to one circuit of the electric heater and is not heating while other circuits are, the over-temperature sensor may not detect the correct temperature or may be hundreds of degrees late. When multiple electric heaters are used on the same skid, wires may be mistakenly connected and crossed. Many heat exchanger manufacturers have invested extensive research on tube cracking in shell-and-tube heat exchangers, but few papers have examined cracking in electric heater components. This is because it is believed that the heating element is filled with solid magnesium oxide powder, which can be ejected into the wiring cavity under high pressure, causing electrical leakage.

High-temperature magnesium oxide powder is a good thermal conductor and insulating material. However, magnesium oxide powder easily absorbs moisture, which causes a decrease in electrical insulation. The main reasons for moisture absorption are water vapor in the environment, long-term storage, or long wiring time with the cover opened. If the power is on and the circuit breaker is not turned off in time, the heating element may be broken down.