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Impedance Heating Systems

Indeeco can provide single-source responsibility for design, hardware and start-up assistance for an impedance heating system to heat gases or fluids flowing through your pipeline. The system can also be used over a wide range of temperatures to prevent freezing in cold weather, maintain fluidity of viscous materials, raise the temperature of heat sensitive materials, or maintain gas temperatures up to 1600o F.

Our capabilities go back 90 years. Founded in 1926, Hynes Electric Heating Company became a world leader with thousands of electric process and pipeline heating applications for temperature sensitive liquids and gases. Indeeco acquired Hynes in 1987. Today's team has strong, in-depth experience in electric process heating. We look forward to putting that experience to work for you in your next impedance heating application.

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Benefits of Impedance Heating

Low Voltage Operation

All systems operate at less than 30 Volts, many at 10 Volts or below. Indeeco systems meet or exceed the requirements of the National Electrical Code (Article 427), assuring safe operation.

Uniform Heating

Because the entire pipe effectively acts as the heating element, heat is generated uniformly throughout its entire length and circumference without hot spots.


The impedance method takes the complexity out of pipeline heating. A few basic components comprise the entire heating system. Installation is simple; it can be installed without disturbing most of the existing thermal insulation.

Wide Temperature Range

Indeeco has pioneered the use of impedance heating for applications ranging from below freezing to 1600o F. It is often the only viable option for high temperature pipeline heating.

Close Control

Thermocouple sensors placed along the pipeline provide precise, uniform temperature control. Optional SCR controls give the ability to achieve control within ± 1o F.

Low Cost

Installation costs are kept to a minimum by the inherent simplicity of the system. Likewise, maintenance is virtually eliminated; many systems operate unattended. Energy costs are low because the required energy is concentrated in the pipe and efficiently heats the fluid or gas traveling through it.

No Burnouts

When the pipe becomes the heating element, burnouts and failures associated with electrical resistance tapes and cables are eliminated.

Advantages Over Conventional Methods

No External Fluids

Pipeline heating with steam or high temperature fluids introduces a high degree of complexity and a potential hazard. Impedance heating accomplishes the same result in a simple, straightforward manner.

No Leaky Jackets

With impedance heating, you won't have leaky steam lines, cracked steam traps, pump failures or frozen return pipes.

No Hot Spots

Impedance heating eliminates the danger of overheating temperature-sensitive materials (asphalt, chocolate, heavy syrups) because hot spots associated with conventional pipe tracing are eliminated.

No Routine Maintenance

Routine maintenance is eliminated, along with the replacement parts and production shut downs associated with such maintenance.

How Impedance Heating Works

The basic concept of impedance heating is quite simple: Terminals are attached to each end of the pipe, and a low voltage current is passed through it. In other words, the pipe acts as its own heating element.

The explanation of how impedance heating works is a bit more complex. Traditionally, electric heat is generated by passing current through a wire that is purely resistive. This is how electrical resistance tape or cable tracing produces heat. With the impedance method, heat is generated by combining three different effects:

  1. The pipe acts as a resistor, much the same as a wire in the traditional method. The electrical resistance of the pipe depends upon its length, composition and wall thickness.

  2. When heating a straight length of pipe, it is necessary to attach a power cable to one end (see Figure 1). The cable is normally laid on the pipe's insulation jacket. The current flow in a typical impedance system is enough to set up a significant magnetic field around the cable. Since most pipes are made from magnetic materials, steel being the most common, the magnetic field interacts with the pipe, producing the second component of heat, skin effect/proximity effect.

  3. A 60 hertz power source produces a magnetic field that changes direction 60 times per second. The electrical inertia of the pipe relative to these changes produces a hysteresis effect, which is the third source of heat in the impedance method.

Taking all of these effects into account, Indeeco designs and furnishes a hardware package to generate the proper amount of heat for a given pipeline system. That package consists of the following:

  • Power Transformer: A transformer, fed from a commercial power source, produces the correct voltage to give adequate heat and safe operating conditions. Furnished in its own enclosure, the transformer has multiple taps to fine-tune the voltage output in the field. Output voltages range from 1 to 30 Volts.

  • Control Panel: Pipe temperature is controlled by a thermocouple sensor attached to the pipe. The standard control panel includes a process temperature controller, magnetic contactor and all necessary pilot lights, relays, fuses, etc. Optional solid-state proportional control, with fully modulated SCR, is also available for more precise temperature control.

  • Terminal Plates with Cable Lugs: Terminal plates are supplied for field attachment to the pipe and low voltage power cabling.

  • Flange Isolation Kits: In order to confine the electrical current to the section of pipe being heated, Indeeco can furnish isolation kits consisting of an isolator gasket for each end of the pipe and isolator bolts with proper washers to secure the gasket and mating flanges. Note that standard field-furnished flanges are used with the isolation kits. No special flange treatment is necessary

 When and Why to Use Impedance Heating

Impedance systems heat a wide variety of gases, liquids and viscous materials which are stored, pumped and processed in many different industries and applications. Impedance heating can be used in three basic ways:

  • Cold Start: Heat is applied to increase fluidity of static, viscous materials so they can be pumped. Typical materials include asphalt, molasses and heavy fuel oils.

  • Maintain Temperature or Pipe Tracing: Heat is applied to a liquid or gas flowing through a pipe to offset heat losses. Typical applications include freeze protection or maintaining the fluidity of viscous materials.

  • Temperature Rise: Heat is applied to a liquid or gas flowing through a pipe in order to raise its temperature between the inlet and outlet of the heated pipe. Typical applications include heating corrosive liquids or high temperature process air.