electrical 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 Self-Regulating Heating Cables?

Any heating cable providing a watt output which increases as temperatures fall and decreases as temperatures rise. Self-regulating heating cables use a carbon matrix-heating element with variable resistance.

What are Power Limiting Heating Cables?

Parallel resistance heating cables that will reduce their power output as temperatures rise but do not have the high in-rush currents associated with self-regulating heating cables.

These cables are capable of delivering high watt per foot heat outputs.

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 difference between Power-Limiting and Self-Regulating?

Both self-regulation and power-limiting cables exhibit a PTC (positive temperature coefficient) resistance characteristic and subsequently power output decreases with increasing temperature.

As self-regulating heating cables increase in temperature they eventually reach a “shut-off” temperature.

Do pipe supports and valves need any additional heat?

Yes. Pipe support (non-insulated) and valves represent a region of much higher heat loss. This local higher heat loss must be made up with additional heating cable.

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.

If it is Self-Regulating Cable, do you need to have a controller?

This depends on the temperature control requirements of the application. If tight, temperature control is required within a few degrees, a line sensing device is recommended.

For freeze protection applications , ambient sensing is commonly used with self-regulating heating cables. The self-regulating effect reduces the resulting equilibrium pipe temperature during operation.

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.

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.

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