Impedance Heating

Product Overview: HX-881-Series, Impedance Heating System

An Impedance Heating System is a unique, safe and proven method for electric pipeline tracing and heating. The pipe actually becomes the heating element when low AC voltage is applied to it by a special, custom designed transformer.

Heatrex can provide single source responsibility for design, hardware and start-up assistance for an Impedance Heating System to heat gasses or fluids flowing through your pipeline. It 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 1600°F.

Benefits of Impedance Heating

  • Low Voltage Operation – All systems operate at less than 30 Volts, many at 10 Volts or below. Heatrex 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.
  • Simplicity – 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 – Heatrex has pioneered the use of impedance heating for applications ranging from below freezing to 1600°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 ± 1°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 shutdowns associated with such maintenance.

Talk to Heatrex representative here to get more information on Impedance Heating Solutions.


Component Heaters for Skid-Mounted Process Heating Systems

The Challenge

  • A global skid-process system manufacturer that works in the power gen, oil & gas, nuclear, and industrial sectors was challenged to design skid-mounted processing equipment for a major energy company. The energy company needed a modular system that would increase the efficiency of their turbines for a series of oil & gas applications. The modular system needed to heat and circulate lubrication oil used to lubricate the turbines. The quality of the heater was of utmost importance, as maintaining the oil at a precise temperature in the holding reservoir is paramount in ensuring the system consistently ran effectively. The customer needed a solution that perfectly balanced durability, ease of maintenance, and customization to specs.

Component Heaters for Skid-Mounted Process Heating Systems

The Solution

  • Heatrex’s reputation for quality has earned it a place on many preferred supplier lists, including being a GE approved Supplier.  In addition to producing premium quality products, Heatrex was awarded the contract to manufacture 16 immersion heaters due to its competitive price and short lead times. The Heatrex engineering team designed a flanged immersion heater that was ready to “plug in” to the modular system upon arrival, not only making installation smoother, but guaranteeing ease of maintenance.

Component Heaters for Skid-Mounted Process Heating Systems

The Benefits

  • Heatrex’s customized immersion heaters enabled the process system manufacturer to successfully deliver the optimal skid mounted process system for its customer. The skid manufacturing company was so impressed with these immersion heaters, they recognized Heatrex, in an ISO audit (International Organization for Standardization), as a supplier with unprecedented customer focus that consistently meets the sourcing requirements on quality and price, upholds the highest standards of delivery quality, and demonstrates the highest levels of flexibility and responsiveness.


Heatrex played an integral role in delivering the necessary quality, and continues to work closely with the manufacturer to exceed the energy company’s high expectations.

Customer Testimonial

“We have been very happy with the Heatrex heating elements, especially on lead times and pricing. The competitors can’t compare on those aspects.”

Global Process System Manufacturer



What is Delta T?

What is Delta T?

It can be frustrating to hear a reference to something and not understand what they are talking about.For this reason we want to explain what Delta T is in relation to the heating industry. While no one expects you to remember the Greek alphabet in its entirety, unless you were educated in Greece of course, the fourth letter of the Greek alphabet, delta, is used so widely in Western scientific circles that it has become somewhat recognizable. The real problem with the letter, denoted by a small triangular character, is that most people don’t even realize they are using it.


The Symbol

Known and widely used by mathematicians, engineers, physicists and all manner of other scientists as it is used to denote the change in any statically defined system. In fact, in scientific and engineering circles, the term “delta” is often used interchangeably with the word “change.” The ubiquitous term, “Delta T,” is just one such instance of this general inclination. In this instance, “delta” refers to the change while the letter “T” stand for temperature. As such, the phrase “Delta T” simply defines the change in temperature over a certain, defined period of time.

If this all seems like “Greek to you,” don’t worry, there are plenty of other people in the same boat. Just remember that when it comes to heating systems, delta T is simply the difference between the current temperature and desired one.

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Selecting an Appropriate Heat-Resistant Alloy

Temperature limit is the first factor when choosing a heat-resistant alloy for a certain application. However, there are many more factors to consider for your application to succeed and to keep employees safe. An article from by Marc Glasser will give some good insight on heat-resistant alloy.


The first and foremost variable to consider is the oxidation limit of a particular alloy. A continuous layer of chromium oxide on the surface of austenitic alloys is responsible for promoting oxidation resistance. Silicon and aluminum, at high enough levels in an alloy, will allow the formation of subscales of silica or alumina, which will further enhance oxidation resistance. Finally, the addition of rare-earth and other heavy metals will add another level of oxidation resistance by adding an oxide that will bond to the other oxides to create a tighter, thinner, more adherent oxide that is harder to break. A thinner oxide scale is less prone to crack and spall than a thicker oxide.

Exposure to Other Atmospheres

In the heat-treating world, materials of construction can be exposed to other atmospheres, including carburizing, nitriding (and combinations of these two), vacuum, hydrogen, inert gas and more. In vacuum, and to a large extent inert-gas atmosphere, oxidation resistance is less important because the purpose of these atmospheres is to create an oxygen-free atmosphere. It should also be understood that products of combustion contain both carbon and nitrogen at high temperatures, which can lead to nitriding and carburizing. In commercial heat treating, carburizing and carbonitriding are generally performed in the temperature range of 1600-1750°F (871-954°C), while nitriding and ferritic nitrocarburizing are generally performed at 985-1050°F (530-565°C).

Creep and Rupture Strength

Tensile strength can no longer be used as a design parameter above 1000°F (538°C). Instead, two very important factors in deciding on a heat-resistant alloy are the ability of the alloy to resist sagging and breakage with an applied load at temperature. These two parameters are known as high temperature creep and rupture resistance, respectively. Simply stated, creep is the phenomenon of metal stretching from its own weight or from an applied load at an elevated temperature.


High-chromium, low-nickel materials (stainless steels) change from ductile to brittle after anywhere from a few hundred to several thousand hours of service in the 1100-1600°F (593-871°C) range. This is due to the precipitation of a hard, brittle inter-metallic phase known as sigma phase. While sigma phase may not be harmful when the material is at temperature, it can completely embrittle the alloy at room temperature.

Thermal Cycling/Expansion

Thermal fatigue as it relates to heat-resistant alloys is cracking that occurs after repeated heating and cooling (quenching) of an alloy. Heat-resistant alloys have high coefficients of thermal expansion and low thermal conductivity. Simply stated, the metal surface heats and cools before the center does. During heating, the surface is expanding quicker than the center, which places strain on the center. Then during quenching, the surface is contracting faster than the center, placing more strain on the surface.

Please read more here.

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How to Size and Select Thermal Fluid Equipment

Proper selection ensures a safe thermal fluid system that will provide peak performance for many years.

fulton catch tank

A catch tank, used to safely collect discharge, is a critical component of a thermal fluid system.


A well-designed thermal fluid heating system can provide consistent, reliable and safe operation for decades. By selecting the right system with properly sized equipment, it can run at peak performance for its owner, optimizing output and production for a specific process. A properly designed thermal fluid heating system is composed of the following four main components plus at least one user:

  • A thermal fluid heater.
  • Circulating pump(s).
  • Expansion tank.
  • Catch tank.

Depending on the level of system complexity, one could also use additional system controls, control valves, secondary loops, heat exchangers or countless other system variations. But every system should include — at a minimum — the core pieces of equipment listed above. Here are a few tips to use as a baseline to help size and select each of these core pieces of equipment in a basic thermal fluid system.


An expansion tank, or combustion/thermal buffer/deaerator tank, can be selected based on determining the total system volume, maximum operating temperature required and the specific thermal fluid to be used. They are often skid-mounted as part of the thermal fluid system.

Sizing the Thermal Fluid Heater

The heater needs to be sized for the maximum BTU/hr requirements of the system during peak load. If the customer plans on expanding in the future, the future BTU/hr requirements also should be considered. In most cases, the customer knows what size heater is required. Otherwise, the heat required must be calculated by using the following equation:

Q = M x CP x ΔT


Q is the heat required.

M is the quantity of material being heated.

CP is the specific heat of material

ΔT is the difference between final temperature and initial temperature.

This calculation must include the product being heated as well as the vessel containing the product and any piping that carries the hot fluid to the product. Remember that the vessel must heat up in order to heat its contents. Heat losses also must be taken into consideration, and proper engineering practices must be followed to determine an appropriate safety factor.

fulton vertical coil

A thermal fluid heater such as the one in this vertical coil engineered system can provide peak performance for many year. A thermal fluid system operates in a closed-loop circulation system with minimal pressure.

Determining the Required Flow Rate

In many cases, the standard flow rate of the heater can be used as the system flow rate. This is always the simplest approach. For heaters with a fixed flow rate requirement, having a system flow rate requirement that is different than the heater flow rate presents some additional design challenges. In these situations, if the user requires a higher flow rate than can be passed through the heater, a heater bypass is required to carry additional flow around the heater. If the user requires less flow than is required for the heater, the heater must still see the required flow rate, so then a system bypass may be required to manage the additional flow around the user. Alternatively, a three-way control valve may be considered to divert the additional flow around the user.

When flow rates have to be calculated, it is important to revert back to the equation to determine how much flow is required to remove the appropriate amount of heat from the thermal fluid flow stream. However, for this calculation, we must rearrange the equation to solve for flow rate. It looks like this:

M = Q / (CP x ΔT)


Q is the heat being transferred to the user from the thermal fluid.

M is the required flow rate of the thermal fluid

CP is the specific heat of the thermal fluid

ΔT is allowable temperature drop for the thermal fluid across the inlet and outlet of the user.


Read more about sizing here.