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Heating up history

Koen Verleyen, marketing manager at nVent, explores the rise of heat tracing cable technology.

Heat tracing technology has become an essential addition to many industries, used widely to protect pipes and surfaces from freezing, and to maintain fluids at the right temperature for processing or storage. The technology, which has been finessed over several decades, works by applying heat to a pipeline or vessel to replace heat loss through thermal insulation to the ambient environment. 

It’s a growing area; the electrical heat tracing market is expected to be worth US$3.26 billion by 2023. Today, the technology is commonly used in commercial and residential properties, to protect water lines, such as fire sprinklers and wastewater, from freezing. Its use also extends to roofs and walkways, to help maintain the process temperature of fluids, for example grease waste slips in factories and restaurants. The oil and gas industry, too, has come to rely on heat tracing technology to keep offshore vessels and platforms running safely and smoothly in freezing conditions. 

Steam: The very beginning

Before the use of cables, steam was used as a traditional heat tracing system as early as the 1900s, due to its high heat capacity and suitable heat transfer coefficient. It works by dissipating its latent heat to the process pipe, to compensate for the loss in heat, enabling it to maintain a constant temperature. These benefits mean steam is still frequently used today, often in power industries, where it is already a ‘free’ by-product of the core process. 

However, there are challenges to using steam. It can waste high amounts of energy, as more heat is provided to the system than is needed to maintain design conditions. It is also difficult to control the pipeline temperature and energy usage, which can lead to health and safety issues. Crucially, steam tracing systems can be costly to install and require regular maintenance to prevent leaks, corrosion or blocked steam traps. 

Innovation in electricity

The development of electric heat tracing began in the 1930s, as a result of innovative chemical and electrical experimentation. With a unique composition of copper wires, packed in a sheath alongside powdered materials, such as magnesium oxide, mineral insulated cables were a viable alternative to steam, ensuring low flammability, even when used in extreme temperatures and conditions. 

They were prone to fail at termination points in the presence of fire or moisture, and were unsuitable for use with heavy machinery as they could crack. Additionally, the magnesium oxide insulation was hygroscopic, causing the cables to draw in moisture and potentially cause electrical leakage. Early controllers were rudimentary and opportunistically adapted from other equipment. This carried some safety risks, as well as low accuracy levels. 

Raising the bar with resistance

The 1950s saw a more specialised mineral insulated resistance heating cable enter the market. Conductors were constructed from high-resistance alloy, which made them more specialised, and therefore, more effective than their previous counterparts. This was a huge step for industries, such as oil and gas, which needed a solution for applications with high exposure temperatures, or with a high-power output. This development also helped to meet the need for specific temperature conditions in bitumen production and liquid salt in concentrated solar power (CSP) plants, as well as preventing condensation in incinerators. 

Despite progress in this area, overheating and energy inefficiency continued to be a problem – particularly for many high-risk assets. Since they still contained magnesium oxide insulation, they needed to be designed carefully off-site to prevent electrical leakage. This made any on-site repairs or installations with last-minute changes challenging. Due to the intricate nature of the cables, they could also not be overlapped, leading to issues during complex piping installations.  

Experimenting with heaters

Continuing with innovation in the area, specialised heaters for long-line pipelines arrived in the 1960s. These worked by placing a current carrying conductor, energised at a high voltage inside a ferromagnetic tube, to allow a small current to be induced via magnetic inductance, causing resistive heating in the tube. This is known as ‘skin-effect’ heating and is limited to long runs of unbranched pipe work, between 1-15 miles (1.5-25 km). 

As such, these heaters needed careful planning for the design of the transformers and equipment to ensure the required level of heating. Demand was therefore still growing for an effective solution that would suit smaller circuits as well. 

Hitting a milestone

Through experimentation over the years, Raychem Corporation (now a part of nVent) developed the first conductive polymer self-regulating heat tracing cable in 1972. With polymer-based cables constructed from crosslinked polymers, a conductive path was created between conductors. In cold pipes, the core or fibre contracts microscopically, to open electrical paths and increase the current. In warms pipes, expansion disrupts electrical paths to lower the flow of current.

The introduction of self-regulating heating cables was a significant development, as power output could be more effectively regulated for the first time. Being able to control the temperature of pipework on a micro scale was crucial to overcome the overheating problem, in addition to lowering general energy costs. The wattage is also not affected by its length, enabling the self-regulating cables to be cut to length on-site — helping to save time and energy.  

Since this development, electric heat tracing technology has expanded to provide solutions for much broader applications, including roof de-icing, embedded snow melting, floor heating, window condensation prevention and marine applications. Globally, it has proved beneficial for use in harsh geographical conditions, such as the arctic and Middle East, as well as for specialised applications like sulphur transfer, crude oil transport, asphalt lines and oil well heating. 

Keeping it constant

Building on the success of self-regulating technology, constant wattage zone heaters have since been developed as a cost-effective alternative to mineral insulated cables. Their design is based on a constant wattage alloy, which is helically wound around an insulating core, shortening the deployed length of resistance wire. It is then wrapped around two insulated parallel bus wires, with alternating nodes at regular intervals, to create zones between 3-6 ft (1–2 m). 

This functionality allows cables to be cut to length to suit varied wattage applications in the field, enabling heaters to be overlapped once. Constant wattage heaters are also are well suited to higher temperatures and as such, hazardous conditions. 

Where next? 

As the world is becoming increasingly digitised, the demand for more intelligent, responsive systems will drive further innovation in the industry. Taking advantage of smart technology and the Internet of Things (IoT), the latest heat tracing systems will be much more intuitive and able to be integrated into a smart device management network, allowing for unprecedented levels of insight and control — even in large, complex systems. 

 

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