Sheathed electric heaters in heat transfer oil furnaces or asphalt tanks sometimes experience tube wall burn-through or insulation degradation shortly after being put into operation. Investigation reveals that most cases are related to the startup/shutdown sequence and the state of the medium. For example, stopping the circulation pump first during shutdown causes heat accumulation and local overheating; or directly applying full voltage when heating solid media results in excessive surface load on the elements.
To address the above problems, the medium characteristics and working temperature must be clearly defined during selection. The SRY7 sheathed electric heater uses No. 10 steel metal tubes and is suitable for media such as heat transfer oil and asphalt. Its working voltage is 380V and power is 2KW. The voltage can be staged for startup according to the melting point of the medium: first melt at low voltage, then switch to rated voltage. For the SRY4 type (maximum working temperature 100°C) and SRY2/3 types (maximum 300°C), different working conditions must be matched, and the working pressure of SRY2 and SRY4 types is less than 2 kg/cm².
Design and selection personnel should set up interlocks in the system: during startup, first turn on the circulation pump, confirm medium flow, then connect the heating power supply; during shutdown, first cut off the heating power supply, wait until the medium temperature drops to a safe range before stopping the pump. For fusible metals or solid media, voltage regulation or staged power supply circuits must be configured to avoid local overheating of the heating elements. Regularly measuring insulation resistance during daily maintenance can detect hidden dangers of sheath damage in advance.
