Heat trace or heating cable is used to warm or heat underground structures, storage tanks, vessels, and instrumentation in order to maintain a specified temperature or eliminate the possibility of freezing. Heat trace or heating cable accomplish this task by adding the amount of heat energy to the process fluid that is lost from the process fluid. It is desirable to maintain a certain temperature since higher temperatures reduce viscosity, enhance combustion, and prevent freezing or crystallization of the fluid. Within the oil and gas industry, elevated temperatures are required to separate the crude oil or raw natural gas to the surface and freeze protection is required to allow refining and distribution of the fluid (Thermon South Africa (Pty.) Ltd. ). Heat trace or heating cable often utilizes resistance wire to provide a medium for voltage to pass through. Due to the resistance of the wire, the heat trace or heating cable becomes warmer and is able to use this heat to warm the underground structures that it surrounds. One material used in resistance wires is nickel-chromium (Peterjohn, Melillo, Bowles, & Steudler, 1993). Heat trace has been used since the early 1900s to ensure the proper flow of petroleum, tar, and wax through pipelines. Since then, certain products within the petroleum and chemical industries needed to be kept between specific temperatures to ensure their quality. Today, the most commonly used heat trace medium is steam (Thermon South Africa (Pty.) Ltd. ). 

References

Peterjohn, W. T., Melillo, J. M., Bowles, F. P., & Steudler, P. A. (1993). Soil Warming and Trace Gas Fluxes: Experimental Design and Preliminary Flux Results. Oecologia, 18-24.

Thermon South Africa (Pty.) Ltd. . (n.d.). Heat Tracing Technologies. Retrieved from Thermon South Africa (Pty.) Ltd. : file:///H:/Users/rrs020.BUCKNELL.000/Downloads/thermon-sa_heat-trace-technologies_energy-savings.pdf