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Coking or fouling is another problem that can lead to early heater failure. It often occurs in oil or other viscous products and increases as sheath temperatures increase. The degree of coking varies greatly, depending upon the maximum operating temperature of the oil being heated.
Do not get silicone lubricant on the heated section of the heater. It will prevent “wetting” of the sheath by the liquid and act as an insulator, which can cause the heater to fail.
Poor wiring connections account for many problems in the field. Regularly check to ensure that electrical connections are tight since process temperature, as well as the amperage going through the terminal area, creates heat in the terminal enclosure. As the process heats up and cools down, connections can be loosened, eventually leading to heater failure. A torque of 20 lbf-in (2.26 Nm). on each heater stud is recommended. In addition, the connections should be free of oxide, dust and dirt build-up. Make sure, too, that the interior of the terminal enclosure is clean and dry, and free of dirt, dust,
Thermal cycling might cause sealed joints, such as flange mounting bolts, to relax, resulting in leaks. Tighten threads and flange bolts.
Periodically check sensing probes (thermostat or thermocouple) to make sure they are operating properly and that the connections are all good. Also, remember to check proper grounding for safety.
Dennis Long is a product manager for Watlow with more than 28 years experience in the design and application of DEHEs. For more information, visit www.watlow.com.
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