It has been estimated that the current installed base of steam tracing worldwide is 360 million feet (110 million meters), with the installed base in North America at approximately 150 million feet (45.7 million meters). However, most published articles discuss steam tracing “with tubing” without defining whether the tubing is bare convection, isolated, internal or conduction tracing.

As has been the case for decades, different steam trace methods can provide different levels of heat: light, medium and high heat. Proper references to the various steam tracing methods and whether the application is winterization or high-temperature maintenance should help reduce confusion or misunderstandings. It also should increase confidence and reliability in this common method of heat tracing in refineries, chemical plants and other process plants around the world.

The primary purpose of this article is to review and compare common steam tracing methods. Although there are clearly advantages and limitations to each, it does not attempt to compare steam and electrical heat tracing methods.

High-Temperature Steam Tracing

Enlarge this picture A single tube-type conduction tracing system can replace three or more bare tracers, with a cost savings in labor as well as reductions in steam and condensate-handling equipment.

High-temperature application for materials such as asphalt, phthalic anhydride and sulfur generally suggests temperatures above 225°F (110°C) and often involves heating mediums such as steam or heat transfer fluids.

Basically, three methods are used for high-temperature heating in process plants where melt-out or reasonably fast heatup requirements must be met. The three methods include:

• Conduction tracing with tubing and heat transfer compounds.
  
• Clamp-on pipe heating jackets.
  
• Fully jacketed piping.

Fully jacketed piping provides the highest heat transfer rates and will melt a material faster than other methods. However, plants frequently use tubing with heat transfer compounds or clamp-on pipe heating jackets because the heatup and melt-out times are sufficient and these methods eliminate cross-contamination problems that occur frequently with fully jacketed piping.

With jacketed piping, cross-contamination risks are due to leaks that develop in the process pipe without any warning until steam is detected in the process. A typical problem would be where steam leaks into molten sulfur, causing a very undesirable reaction. Once the contamination is detected, there is still no easy means of detecting the leak location.

In addition to the risk for cross contamination, the installed cost of fully jacketed piping is high. The fabrication of such a system also requires special fittings, skilled welders and more trapping stations than either conduction tracing with tubing and heat transfer compounds, or clamp-on pipe heating jackets. Additionally, construction time and final testing for jacketed piping is quite long, and the installed system cannot easily be modified.

Conduction tracing with tubing and heat transfer compounds as well as clamp-on pipe heating jackets frequently are installed on industrial piping systems for high-temperature heating applications. However, conduction tracing with commercially available tubing can be reliable and cost effective, and it can reduce the installation time for a piping system by eliminating welding of piping, jacketing or modification of clamp-on jackets.

Modern Conduction Tracing Systems

Enlarge this picture Fully jacketed piping provides the highest heat transfer rates and will melt a material faster than other methods.

Prior to the advent of heat transfer compounds, the process industry had to rely on fully jacketed piping or multiple bare tubes to maintain high process temperatures on piping. Today, conduction tracing systems, including clamp-on steam-heating jackets, rely on heat transfer compounds to maximize heat transfer rates.

Heat transfer compounds became commercially available in 1954. Tracers installed with these compounds have been highly reliable in replacing many fully jacketed piping systems and multiple bare or convection tracing systems. The performance results are notable as are the reductions in installed costs by minimizing steam traps and overall distribution costs.

Today, the cost savings for conduction tracing over fully jacketed piping can be in the 50 to 90 percent range, depending upon the piping system complexity. By comparison to other methods, a single tube-type conduction tracing system can replace three or more bare tracers, with a cost savings in labor as well as reductions in steam and condensate-handling equipment. Table 1 compares bare convection tracing and conduction tracing.

The hand-toweled method of applying heat transfer compound continues to be a convenient way to cover tracing on valves, pumps or other types of equipment. However, today’s heat transfer compound is likely to be a preshaped extruded material that is snapped over the tube-type tracer and held in place by a galvanized steel or stainless steel channel. The heat transfer compound material melts and cures when steam is supplied to the tracer.

Debunking Tracing Myths

Enlarge this picture The metallic tracer tube is covered with composite materials that lower thermal conductance to reduce heat output and temperature.

Even though steam tracing has been used in the process industry for more than 100 years, there is still misinformation that attempts to make steam tracing appear to be inferior to other methods.

Myth 1. Tube-type tracing is not a good alternative to steam jackets because it does not result in uniform temperatures along the process pipe wall.

The Facts. If the myth statement relates to bare convection tracers, it is true. However, if it relates to tubing installed with heat transfer compounds, it is untrue. Modern methods of thermal analysis such as finite element analysis (FEA) and computational fluid dynamics (CFD) commonly are used by engineers and designers of steam tracing systems to closely predict temperatures around the circumference of a traced pipe wall as well as at pipe shoes and supports, risers and other areas of concern.

Myth 2. Heat transfer compounds crack or break off when used on valves, pumps and other equipment.

The Facts. Literally thousands of valves, pumps and other types of plant equipment have been successfully steam traced with good quality heat transfer compounds. When properly installed on tube tracing, these can last as long as the equipment on which it is installed. Properly selected heat transfer compounds can also resist mechanical shock well. If cracking or bond separation does occur, it generally is due to improper selection or poor quality heat transfer compounds, poor surface preparation or improper startup and curing procedures.

In conclusion, steam tracing can be designed to maintain a range of process temperatures, even from a common steam pressure/temperature. Some companies offer design software for steam tracing piping, tanks or instrument tubing while others offer design support or proven heat transfer calculations.

But, beyond reliability, the real issue with all heat tracing systems is ensuring the lowest total cost of ownership with minimal operating and maintenance expense. Calculating condensate loads and knowing the maximum vertical rise for every steam trace design is critical to optimizing circuit lengths to reduce the number of steam traps and arrange the lowest installed cost possible for each application.