My application involves non-metallic pipes and vessels. Do I treat non-metallic (plastic) pipe or vessel application the same as those for metallic pipes and vessels?

There are important considerations when designing heat tracing for non-metallic pipes and vessels.

It is very important to consider the maximum temperature rating of the pipe or vessel material.

The heater cable operating temperature (sheath temperature) must not exceed the maximum temperature rating of the pipe or vessel. In most cases, the maximum operating temperature is calculated during runaway conditions.

Runaway conditions are typically calculated at the highest possible ambient and temperature controller failed with contacts closed resulting in a continuously energized heater. Lower power cables will have lower operating temperatures and are therefore the best chose for non-metallic heating applications.

Designs must also take into consideration that heat from the tracer does not transfer as easily into a non-metallic material. Constant watt heaters will operate at higher temperatures on non-metallic surfaces. Self-regulating (SR) cables will also operate at higher temperatures resulting in a reduction in power output. Heat transfer aids can help reduce these effects.

For example, a good design practice is to cover the cable with a parallel pass of 2" wide aluminum tape. This will help reduce sheath temperatures on constant watt cables and increase power output on SR cables.