Electrical Heat Tracing Can Minimize Piping Temperature Variation
Electrical heat tracing has become the standard for many applications since the invention of the self-regulating (SR) parallel
circuit heat tracer in the early 1970s. Initial applications for the SR heaters were in freeze protection, but with the advent of higher
temperature heaters, process temperature maintenance became a viable option. In the early 1970s approximately 2 percent of
heat tracing was electrical with the remainder steam or hot fluids. In 1990 about 30 percent had been converted to electrical.
There are a number of reasons for this migration, including energy costs, maintenance problems with steam and hot fluids,
environmental constraints on fluids and condensate steam and the need for accurate and repeatable temperature control.
Statistical process control has been increasingly used to increase product quality and yields. With the monitoring of more
variables, heat tracing has become a second order variable that is now monitored as a process control variable. The piping,
control, tankage, and instrumentation system is a complicated collection of components that have different heat capacities, heat
losses and different insulation systems applied to maintain process temperatures. Point temperature control, while giving an image
of reliability and precision, guaranteed a temperature only at one point. Valves, supports and open ended vents, as well as
instrument lines operated at different temperatures since the thermal heat loss characteristics were not the same as the main pipe
where the point sensor was located.
The larger the delta T (temperature difference between ambient and the maintain temperature of the system) the more variation
the system would experience. While this is usually not a problem for replacement of steam tracing systems, tighter statistical
process control parameters predicted better yields and product quality if the temperatures could be held in a tighter range.
Exploration of methods for controlling temperatures give a greater insight into the possibilities for tighter temperature control for
electrical heat tracing systems.