Flange electric heating tube (also called plug-in electric heater): U-shaped tubular electric heating element is adopted. According to the heating medium design specification, it is assembled on the flange cover according to the power configuration requirement, inserted into the material to be heated, and the heating element works. The large amount of heat that is emitted is transferred to the heated medium to raise the temperature of the medium to the desired process requirements. When the medium temperature reaches the set value required by the process, the control system adjusts the output power of the electric heater according to the temperature sensor signal, and performs temperature control on the resistive load of the heating element. The medium temperature is made uniform to meet the required requirements; when the heating element is over-temperature or low-level, the interlocking protection device of the heating element immediately cuts off the heating power source to avoid burning of the heating element and prolongs the service life.