heat tracing

Polymer Insulated Heat Cables: Chemical Resistance?

Thermon polymer insulated heat tracers have an overjacket covering the braid. This overjacket is intended be a chemical corrosion barrier for the braid and also provide additional mechanical strength.

What are Parallel Resistance Heating Cables?

A heating cable that includes a continuous series of short, independent heating circuits. Localized damage can result in only partial loss of heating. Watt-per-unit length output is relatively unchanged by variations in circuit length up to several hundred feet. Known as “cut-to-length”, parallel cables are easy to size because circuit lengths (within limits) do not have to be considered.

What are Series Resistance Cables?

Series resistance cables are single or multiple metal alloy conductors with a voltage applied at the ends.

The power output is a function of the voltage applied and the overall resistance based on type of metal alloy and circuit length. If the length changes the power output of the cable changes, so these heating cables are not considered “cut-to-length”.

What is the definition of a pipeline?

In a process plant, a pipeline is a length of pipe having valves, pumps or other line equipment attached to transport and control the flow of process, service or utilities materials.

Typically, process piping transports fluids from process feed tanks to the plant’s process units then carries the processed material to storage tanks.

What is heat?

The heat energy detectable in matter is due to the motion of molecules. The molecules move rapidly in an object that is warm. When the object cools down, the molecules slow down. This is known as the Kinetic Theory of Heat.

How does heat flow?

Heat flows between two objects because of a difference in temperature between them. When two objects are brought together, the molecules of the warm object imparts motion to the molecules of the cooler object.

What is temperature?

In measuring heat, there are two properties to be considered: the “intensity” of the heat and the “quantity” of heat.

What is specific heat?

The specific heat of a substance is the number of kilojoules (kJ) necessary to raise 1 kilogram (kg) of the substance 1°C compared with the number of kJ required to raise 1 kg of water 1°C.

Note: 1 kJ is almost the same as 1 Btu (1.055 kJ = 1 Btu).

How is specific heat used in heat calculations?

When the temperature of a substance changes, the heat gained or lost is found by multiplying the mass, or weight of the substance by the change in temperature (ΔT) and by the specific heat (sp ht).

What do absolute pressure and gauge pressure mean?

If a gauge measure pressure above atmospheric, then the atmospheric pressure of 1.013 bar (metric) or 14.7 (Inch-Pound) must be added to the gauge reading to determine absolute pressure.

What is freeze protection?

Freeze protection is a heat tracing application. Usually refers to maintaining water line temperatures at slightly above freezing (Tp = 40°F - 50°F).

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.

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