During on-site operation, terminal heating and insulation discoloration inside the junction box of sheathed electric heaters are common phenomena. During maintenance, first disconnect the power, use a feeler gauge to check whether the terminal crimping is loose, and use a micro-ohmmeter to measure the contact resistance. If it is significantly higher than the factory value, re-crimp or replace the terminal. Avoid direct copper-aluminum connections to prevent electrochemical corrosion from increasing contact resistance.
During operation, attention should be paid to the matching of surface load and medium temperature. This type of heater has a rated voltage of 220V or 380V, a power range of 1–15kW, and a recommended surface load not exceeding 4W/cm². After the temperature of media such as thermal oil rises, viscosity changes and the heat transfer coefficient decreases. If the surface load is too high, the outer wall temperature of the sheath may exceed the allowable value of the medium, causing coking or oil deterioration.
Use a 500V megohmmeter every month to measure the cold insulation resistance of the heater; the reading should not be lower than 1MΩ. If it is lower than this value, check whether the junction box is damp or the sheath is damaged. In humid environments, moisture-proof heating tape may be added or sealing improved, but power must not be forcibly supplied.
During quarterly shutdowns, remove carbon deposits and oil scale from the sheath surface to avoid local overheating. At the same time, check the flange or threaded connections for leakage and whether fasteners are loose. When replacing, pay attention to the coaxiality between the heater and the pipeline to prevent the sheath from deforming under mechanical stress.
When starting, first turn on the circulation pump and confirm medium flow before energizing; when stopping, first cut off the heating power, and stop the pump only after the medium temperature drops to a safe range. Overtemperature interlock and low-flow protection should be provided to avoid dry burning. If frequent tripping occurs, first investigate whether overtemperature is caused by insufficient flow.
