Installation Practices Key to Successful Heat Tracing
on Wed, 11/20/2019
An argument could be made that the most important element to implementing an effective heat-trace system is attention to detail during the installation. There are a multitude of factors at play when installing heat trace, and each must be carefully considered. Too often, heat trace is installed improperly or in an inconsistent manner, resulting in a system that is more prone to failure.
Every aspect of the system must be meticulously considered, including both the temperature requirements of the fluids being protected as well as the physical characteristics of the equipment being heat traced. There are published guidelines and diagrams available from each heat-trace manufacturer, and these need to be followed closely when available. For cases where standard procedures are not available, heat-trace installation becomes an art form, open to interpretation. For these cases, it is best to call upon experts with prior experience of installation best practices.
Thermal insulation is always required to make heat trace effective. Because the insulation covers the heat-trace routing and is difficult or impractical to remove, it is impossible to tell after the fact if a system will perform properly. For this reason, standards for installation and placement are critical.
It all begins in the planning stage. It is important to agree to a game plan before installation begins, and the more communication and advance training that can be done with the contractor, the better.
Equipment ConsiderationsSpecial attention must be given to the placement of heat trace on valves, pumps and various other instruments. Performance problems can occur in situations when there is a lack of coverage on a piece of equipment — or similarly, insufficient footage.
For example, for pipe elbows, there is considerably more material (thermal mass) on the outside of the elbow as opposed to the inside. This is particularly true as the pipe size increases. Effective heat tracing requires getting adequate wattage on each surface. In this case, the heat trace must always be routed on the outside of the elbow.
It often is helpful to view the system in terms of where there is standing fluid. For example, when a pressure gauge is installed in the line, heat trace should be applied in a very specific way. For a wetted gauge where the fluid sensor is inside the gauge behind the display, the heat trace should route around the entire outer circumference of the gauge head. In cases where there is an isolation diaphragm below the gauge, the fluid stops at the sensor, so heat trace should be placed to adequately protect the diaphragm.
Furthermore, valves typically have significantly more thermal mass than the adjoining pipe, and they deserve special attention during installation. If the material inside a valve body freezes, operation and process control can be affected negatively. In addition, some valve types have cavities where material collects outside of the process flow, and the expansion caused by freezing can lead to fluid leaks. When heat tracing valves, most manufacturers have developed a table that recommends specific heat-trace footage based on the valve type and pipe diameter. For example, one manufacturer’s table recommends installing 4’ of heat trace on an 8” globe valve. Utilizing these tables is a best practice for ensuring proper installation and a reliable system.
Elbows, pressure gauges and valves are just a few examples of the types of equipment that may be encountered during installation. There are many other unique devices such as filter vessels, air vents, pump heads and pressure transmitters. Each of these requires special attention and care when installing heat trace. They often have small-diameter fluid paths that are more prone to freezing than the main pipe. What is the best approach for addressing these types of challenges?
Unique ShapesThere are certainly a multitude of non-standard devices and shapes that can be encountered during a heat-trace system installation. This echoes back to the need for training, discussion and a comprehensive field walk and planning session on the front end.
If a unique shape or piece of equipment is identified that is not covered by manufacturer guidelines, it should be discussed with an expert to determine the best approach for applying heat trace. This exercise may even require thermal calculations based on desired maintain temperature, insulation characteristics, and the device shape and total mass. Addressing these unique situations provides an opportunity for developing standards for the current installation that can become a part of an organizational standard, useful for future expansions.
Poor Method of InstallationThere are several other examples of improper installation of heat trace beyond inadequate pipe and device coverage. This can include installing the wrong model or an excessive amount of heat trace, which in some cases can melt plastic pipe. Another is having the heat trace unattached or loosely attached to the pipe, leading to uneven contact or the potential for damage when the insulation is applied.
In addition, plastic is a poor thermal conductor. Aluminum tape should always be applied to plastic pipe before the heat trace, to aid in efficient heat transfer.
While the fundamental purpose of heat trace is to protect pipe and instrumentation systems from freezing or to maintain specific process temperatures, the overlying goal is to prevent impacts to normal facility operation. With poor attention to detail during installation, fluids can freeze and lead to abnormal outcomes or — worst case — a catastrophic pipe failure. The end result in that case is the need for emergency repair, increased maintenance costs and unplanned downtime, all of which can negatively affect the user’s bottom line and are generally preventable.
Article featured in Process Heating Magazine.
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