electrical heat tracing

electrical heat tracing

Describe heat loss

Heat loss is the rate at which process equipment heat flows to a cooler ambient, stated in either watts or BTU/hour.

The purpose of heat tracing is to replace that heat lost through the thermal insulation in order to maintain a desired temperature difference (ΔT or Delta T). Therefore, the first step in heat tracing system design is to calculate the heat loss.

Explain the term watts per meter

For pipe heat tracing it is convenient to think of the heat loss and respective heat required in Watts per unit length. Most pipe heat loss calculations are done with a per meter basis. Then it is only a matter of selecting a heating cable with this watt per unit output or higher.

Can you splice two different watt cables together (i.e., 3 watt to a 6 watt)?

Two different parallel watt density cables may be spliced together. Being parallel, the power out put in the two spliced sections will be different as rated. Care must be taken to not exceed the maximum circuit length and circuit breaker rating. The simple solution in this case is to use the maximum circuit length of the higher wattage cable.

What is a "run-a-way" temperature?

When the controller fails and the heating cable remains energized the pipe will increase in temperature to an equilibrium temperature. This is called “run-a-away” temperature. For stabilized designs in hazardous areas, the condition is used to determine the maximum heating cable sheath temperature.

Do all thermal insulation have basically the same products?

While thermal insulations have thermal conductivities, or k-factors, that reduce the flow of heat, the k-factors vary depending on the specific thermal insulation type. They also have different maximum temperature ratings. These factors must be addressed in a heat tracing design.

A heat loss is based on a 25 mph wind. The specification is for a 50 mph wind. Is there a major increase in heat loss?

Typically not, because most of the reduction in heat loss is through the thermal insulation. The increase for this change in wind speed may be only 2-5%.

Can a pipe or vessel be heated up in a short period of time?

Typically not. Heat tracing is primarily used for temperature maintenance. Heat-ups in short periods of time (minutes to a few hours) will most likely require more heat than that needed to maintain the temperature at the desired temperature above ambient.

What does thermal equilibrium mean?

This is a common term as it relates to thermodynamics and heat transfer calculations.
It is a state of thermal dynamics where the stabilized temperature is a result of the heat input equal to the heat loss.

How do I choose the right cable for my heat tracing application?

We offer a wide range of heat tracing cables & offer design services for completed solutions.

Find more info. Contact our consulting engineers


 

Can you install the cable on top of a pipe?

Installing the cable on top or directly at the bottom of a pipe is not recommended as it could result in mechanical damage to the cable.

On top of the pipe the cable is susceptible to personnel walking on cable.

Can a cable be installed on a pipe that runs through or to/from a heated building to outside?

Yes. However, the method of temperature control must address the fact that the heat loss will be different for the two ambient conditions.

For line-sensing control the sensor should be located on the outside portion of the pipe.

What is the function of thermal insulation for heat traced pipes?

  • Provides protection of personnel against hot surfaces
  • Minimizes heat loss and allows the pipe temperature to increase above ambient temperature based on the amount of heat added by the heat tracer
  • Conserves Energy

Is thermal insulation really necessary for heat tracing systems?

Yes. The heat losses without thermal insulation are excessive and not practical to compensate for with heat tracing.

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