One of the most misunderstood and misused components of conductive steam tracing systems is heat transfer compound (HTC). HTC is a viscous mastic designed to fill small air gaps between the tracing element and the object to be heated. HTC is considerably more effective at transferring heat than static air, but it has relatively poor thermal conductivity compared to the other components in a steam tracing system. If used in very thin layers, however, HTC helps maximize the performance of heating systems. QMax Industries Inc., based in Charlotte, North Carolina, recently performed extensive testing and then wrote a paper that discusses and demonstrates why the performance and success of conductive steam tracing systems is highly dependent upon proper installation and use of HTC.
Around the world, sulfur and other chemical operations rely heavily on high-performance steam tracing and jacketing to heat piping, equipment and vessels. Failure to properly heat these systems can cause sulfur to freeze and ultimately shut down a processing plant or even an entire refinery. To ensure a steam tracing system will operate as designed, especially for critical processes like liquid sulfur and vapors with sulfur compounds, proper system installation is critical for long-term success.
To help understand how HTC thickness and installation quality impact tracing performance in critical operations like those involving sulfur, QMax focused on testing two high-performance steam tracing technologies: the Fluid Tracing System (FTS) and Carbon Steel Tracing (CST):
⢠FTS consists of four separate parts that are assembled during installation. A tube tracer contains the fluid heating medium. An FTS channel, extruded from aluminum to precisely fit the outer diameter of the process vessel, is installed over the tracer. The channel contains the tracer and HTC simultaneously and compresses them when stainless steel banding is used to secure the system to a pipe or vessel.
⢠CST systems consist of tracing elements that are individually fabricated from carbon steel boiler tube or similar material. The boiler tube is formed into a rectangular profile with one side contoured to fit the outside diameter of a process vessel. Caps are welded to the ends of the formed tube, creating a vessel capable of holding pressure. Usually female national pipe thread connections are welded on as the inlet/outlet of the trace element. Once fabricated, it is esseessentially a fourpart system consisting of tracers, HTC, stainless steel banding for fixturing and jumper hoses. The jumper hoses connect the outlet of one tracing element to the inlet of the next, allowing a fluid heating medium to flow through the system.
The systems were tested extensively with controlled HTC thicknesses for their effectiveness in melting elemental sulfur by tracing a sulfur-filled vessel in a QMax facility. The outcome of improperly installing HTC, regardless of the reason or steam tracing technology used, was consistent. As the HTC layer thickness between the tracing and pipe or vessel increased, the overall heat transfer rate from steam to process decreased. Increasing HTC thickness by only 1/16 of an inch from an optimal thickness of 1/32 of an inch increased the time required to melt elemental sulfur by as much as 70 percent.
Applying excess HTC between the tracing and pipe/vessel wall can have more damaging long-term effects than slowing down heat-up time. As the system cycles thermally, thick layers of HTC will dry, weaken and fall away, leaving open space between the tracer and equipment. Compound can also be eroded and displaced by excess moisture, creating undesirable air gaps. These complications transform the nature of the tracing system from conductive to convective, making it both ineffective and unpredictable.
The keys to guaranteeing steam tracing performance are:
⢠Training and educating installers on the characteristics of HTC, so its capabilities are well understood and will be properly implemented in the field.
⢠Using steam tracing systems that fit the surface of the traced equipment closely, allowing for excellent compression, containment and protection of thin HTC layers.
⢠Avoiding installing trace elements over weld beads and uneven pipe surfaces that create gaps, which must be filled with HTC. Follow the manufacturer's installation guidelines, and when in doubt, consult your steam tracing specialists for advice on installation methods.
To receive the full, illustrated version of this whitepaper or to learn more about steam tracing, call (704) 643-7299 or visit www.qmax industries.com.
