Q&A: Maintaining Pipe Temperature
Self-regulating heating cable plays a key role in many pipe temperature maintenance applications. Learn how to employ this technology effectively.
Whether maintaining pipe temperatures in a petrochemical plant on the Gulf of Mexico or a platform off the windswept Scottish coast, facility managers are all too familiar with the challenges such a task poses.
On the one hand, pipe containing product — for instance, fuel oil — that must be maintained in liquid form will require viscosity control, which demands higher temperatures. On the other hand, across the facility, a pipe that transports water requires a lower maintenance temperature to keep the fluid from freezing during cold weather while minimizing energy costs.
To complicate matters, many engineers also must contend with maintaining internal pipe temperatures on pipes that are subjected to extremely high temperatures generated by steam cleaning or other factors.
While a one-size-fits-all solution has yet to be developed, advances in conductive polymer technology mean that an optimum pipe-temperature maintenance solution for every need is readily available. Central to these solutions is co-extruded monolithic self-regulating heating cable. Today, this familiar technology provides even more power, durability, flexibility and efficiency.
Option for High Temperature Self-Regulating Heating Cable
A high temperature self-regulating heating cable offers an option for especially rigorous applications. The monolithic coextruded self-regulating heating cable can maintain a maximum temperature of 302°F (150°C). With a continuous exposure temperature rating of 392°F (200°C) and an intermittent exposure temperature (power on or off) rating of 482°F (250°C), it continues to perform reliably, even when exposed to these high temperatures.
With these enhanced capabilities, the system is flexible. It is suited for applications that require higher maintenance temperatures for process temperature maintenance. Its durable design means that it withstands exposure to punishing high temperatures produced by steam cleaning.
Q. What Is Self-Regulating Heating Cable?
A. Anyone well-versed with the methods for maintaining pipe temperature is well acquainted with industrial electric heat tracing — and the critical role that self-regulating heating cable plays in it.
Developed in the 1970s to provide a simple, reliable method of maintaining pipe temperature, the heat output of self-regulating heating cable varies in response to the surrounding temperature. Variations in the ambient temperature, or heat lost through the thermal insulation, are automatically compensated for along the entire length of the cable, which is installed directly onto the pipe.
Q. How Is It Constructed and How Does It Work?
A. Self-regulating heating cable has a heating element consisting of a carbon matrix conductive polymer. This mixture is co-extruded around the conductors. The matrix exhibits a positive temperature coefficient. The resistance of the matrix increases as the temperature rises, and the cable’s power output decreases as the temperature rises. Therefore, as the temperature rises, the cable power output approaches zero.
Most self-regulating heating cable is supplied in a continuous length, so it can be cut to the proper length for individual pipe. It is installed on a pipe at the 4 or 8 o’clock position, and it is flexible enough to be installed on flanges, valves and pumps. It can be overlapped and it will not overheat.
Q. Is Additional Equipment Required?
A. In addition to the cable, the other items typically required to complete a self-regulating heating system on pipe are:
- Power connections and end terminations.
- Temperature controller.
Thermal insulation and cladding to help keep the thermal insulation dry are two of the most often overlooked components of a complete system. Thermal insulation is arguably one of the most important parts of a complete system.
Q. What Types of Industries Use Self-Regulating Heating Cable?
A. Because managing heat is a top priority across many industries, self-regulating heating cables are used by thousands of industrial companies around the world.
Oil and Gas. Many processing phases in the oil-and-gas industry — gathering, production, processing, storage and distribution — require controlling pipe temperature. So, it is no surprise that the global oil-and-gas industry is one of the biggest — if not the largest — users of self-regulating heating cable.
For example, the upstream sector carries out onshore and offshore exploration and drilling, and uses platforms, drilling rigs and floating production storage and offload (FPSO) units. The applications rely heavily upon pipe where proper temperatures must be maintained, and elevated temperatures are often necessary.
As the process progresses, the downstream sector requires temperature maintenance to refine, store and distribute these products. For example, gas storage tanks, pipe, valves and transfer lines must be maintained at the proper temperature.
Petrochemical and Chemical. To produce chemical products, chemical and petrochemical plants also require process maintenance heating to maintain temperatures in piping to keep certain products in liquid form. For example, caustics must be kept at about 80°F (26°C) so they remain in a liquid state.
Power Generation. Every plant that generates power — whether nuclear, solar, combined cycle or coal-fired — has a number of pipe-heating needs that must be met. For example, self-regulating heating cable is used to make certain that steam lines are winterized. Heat tracing also helps ensure that equipment used to control the plant operates reliably, so power is generated without interruption.
Q. What Types of Applications Does It Serve?
A. With the range of maintenance and exposure temperature capabilities that individual self-regulating heating cables offer, the types of applications are wide-ranging.
Freeze Protection. One of the primary applications of self-regulating heat tracing is to provide freeze protection for metallic and nonmetallic pipes, vessels, tanks and equipment during cold weather months. For example, should a pipe freeze that connects a terminal to a petrochemical refinery, it could cause a shutdown, resulting in a costly delay.
This application is characterized by heat delivery to offset heat loss through thermal insulation. It typically requires that pipe be kept to a temperature just above freezing — typically at 40°F (4.4°C).
This is especially meaningful for the oil-and-gas industry, where 25 percent of current oil-and-gas resources are situated in extremely cold regions. As a result, ships and platforms require varying levels of freeze protection for piping that also could be subjected to steam cleaning. It is extremely important to guard against freezing of piping, valves, fittings and instrument tubing used to hold protection water, potable water, sea and fresh cooling water, drill-water and bilge-water discharge.
Process Temperature Maintenance. To maintain the temperature of product in a process pipe — within a narrow range for processing, or for other purposes — self-regulating heating cable is effective. It makes it possible for the process piping to, for example, transport the fluid from a process feed tank to the plant’s process unit, and then carry the processed material to storage tanks. It also prevents condensation and hydrates from forming on gas pipelines.
Viscosity Control. A standard method of controlling the viscosity of process fluids is to use self-regulating heat cable to maintain the pipe or tank at the preferred temperature. As a result, the product is maintained in liquid form, facilitating transport.
High Temperature Self-Regulating Heating Cable Maintains Optimum Temperatures in Houston
A petrochemical plant in Houston wanted to heat trace a process piping network in order to sustain oils, acids and caustics in liquid form to ensure that they would flow easily. The plant manager contacted a manufacturer of heat tracing cable for assistance.
The piping network consisted of a number of lines and valve assemblies in different sizes. To complicate matters, temperature requirements varied from section to section, depending on the nature of the product and location.
Higher Temperature Maintenance
Following careful analysis of the piping network and environmental conditions posed by the plant’s location on the Texas Gulf Coast, the team from the heat tracing supplier developed a customized heat trace field design. In addition to heat trace monitors and controllers, the team specified 9.32 miles (15,000 meters) of new high temperature self-regulating heating cable be installed to ensure that all requisite temperatures would be maintained.
To date, the system is performing as planned. The enhanced ratings of the new cable are providing the petrochemical plant with higher maintenance temperatures at a reduced cost. The heat tracing design delivers the “gold standard” ratio of one meter of piping to one meter of cable.
The heat tracing cable delivers essential and reliable temperature maintenance service to the petrochemical plant. Cost effective to purchase and maintain, the heat tracing solution is contributing to the plant’s ability to operate without disruption.