Troubleshooting & Maintenance
The following information is intended to assist in troubleshooting electric heat tracing systems. The primary objective is to provide an enhanced understanding of the elements of a successful heat tracing installation. Of these elements, one of the most important is the thermal insulation.
Before calling the heat tracing vendor, make a visual inspection of the installation; perhaps the thermal insulation is wet, damaged or missing. Also consider the possibility that repairs or maintenance of in-line or nearby equipment may have resulted in damage to the heat tracing equipment. These are common causes of tracing problems which are often overlooked. Other possible causes are listed below with their symptoms and remedies.
If an electric heat tracing circuit is suspected to be damaged, a dielectric insulation resistance (megger) test should be performed using a 2500 Vdc megohmmeter for polymer-insulated heating cables or 1000 Vdc for MI cable. Periodic testing with accurate records will establish a “normal” range of operation (refer to the Inspection Report Form on page 3). Dielectric insulation resistance readings which deviate from the normal range can quickly reveal a damaged circuit.
Please select from the symptoms below:
|I. No heat/no current||A. Loss of power (voltage)||A. Restore power to tracing circuit (check circuit breaker and electrical connections). Poorly made terminations can cause EPD-type breakers to trip unexpectedly|
|B. Controller setpoint too low||B. Adjust setpoint|
|C. High temperature limit switch activated||C. May require manual reset to reenable heat tracing circuit|
|D. “Open” series heating circuit||D. Repair or replace circuit 1|
|E. Controller failure||E. Repair sensor or controller 2|
|II. Low system temperature||A. Controller setpoint too low||A. Adjust setpoint|
|B. Temperature sensor located too close to heating cable or other heat source; may be accompanied by excessive cycling of control relays/ contacts||B. Relocate sensor|
|C. Insulation material and/or thickness different than designed||C. Replace insulation; increase insulation thickness (if dry); consider increasing voltage for higher cable output 3|
|D. Ambient temperature lower than designed||D. Install higher output heating cable; increase insulation thickness; raise voltage 3|
|E. Low voltage (check at power connection point)||E. Adjust voltage to meet design requirements 3|
|III. Low temperature in sections||A. Wet, damaged or missing insulation||A. Repair or replace insulation and jacket|
|B. Parallel heating cable; open element or damaged matrix||B. Repair or replace; splice kits are available from cable manufacturer|
|C. Heat sinks (valves, pumps, pipe supports, etc.)||C. Insulate heat sinks or increase amount of tracing on heat sinks|
|D. Significant changes in elevation along length of the heat-traced pipe||D. Consider dividing heating circuit into separate, independently controlled segments|
|IV. High system temperature||A. Controller “on” continuously||A. Adjust setpoint or replace sensor2|
|B. Controller failed with contacts closed||B. Replace sensor or controller2|
|C. Sensor located on uninsulated pipe or too close to heat sink||C. Relocate sensor to an area representative of conditions along entire pipe length|
|D. Backup heating circuit controller “on” continuously||D. Adjust setpoint or replace backup controller|
|V. Excessive cycling||A. Temperature sensor located too close to heating cable or other heat source; may be accompanied by low system temperature||A. Relocate sensor|
|B. Ambient temperature near controller setpoint||B. Temporarily alter controller setpoint|
|C. Connected voltage too high||C. Lower voltage|
|D. Heating cable output too high (overdesign)||D. Install lower output heating cable or lower voltage|
|E. Controller differential too narrow||E. Widen differential or replace controller to avoid premature contact failure|
|VI. Temperature variations from setpoint along pipeline||A. Unanticipated flow patterns or process operating temperatures||A. Redistribute heating circuits to accommodate existing flow patterns; confirm process conditions|
|B. Inconsistent cable installation along pipeline||B. Check method of cable installation, especially at heat sinks|
|C. Inconsistent cable performance||C. Compare calculated watts/foot [(volts x amps) ÷ length] for the measured pipe temperature with designed cable output for the same temperature; regional damage to parallel cable can cause partial failure|
Notes . . .
1. Flexible, plastic-jacketed heating cables may be field-spliced; MI cables usually require replacement.
2. Mechanical thermostat sensors cannot be repaired or replaced; RTD or thermocouple sensors can be replaced. Some controllers have replaceable contacts/relays or may require a manual reset if a “trip-off” condition on the heating circuit was detected.
3. The operation of most electric heat tracing cables is dramatically affected by changes in the supply voltage. Before making any changes, consult the cable manufacturer with information on the alternate voltages available. Otherwise, cable failure and/or an electrical safety hazard may result in some situations.