When to Consider the Use of Thermal Maintenance on Valves and Piping Systems
By Henry Gaines, P.E. and Steve Rowe, P.E. of Controls Southeast, Inc.
Thermal tracing systems are applied to valve and piping systems to prevent freezing, eliminate hot spots and product adulteration to name a few.
The main purpose of "thermal maintenance" is to maintain consistent process temperature, not to raise the temperature. There are three main approaches to applying thermal maintenance; heat tracing, weld-on jackets and bolt-on jackets.
When to Consider a Process Heating System (Thermal Maintenance)
Process temperatures above 200 degrees F or low ambient temperature. The greater the difference between the process and ambient temperatures the more difficult it is to maintain process temperatures. Some materials have flowing temperatures well above 500 degrees F.
A sulfur stream must operate at between 252 and 260 degrees F. At low temperatures the elbows in a piping system can "freeze" and require shut down and maintenance.
A narrow temperature window. When the minimum and maximum allowable stream temperatures are close together, uniform thermal maintenance is a must. Several polymer processes require fluid temperatures of +/- 4 degrees. Other "narrow" fluids include; acrylic acid, dairy products and pharmaceuticals.
Frequent temperature cycling. Batch processing requires the temperature of empty process piping to be elevated rapidly to receive feedstocks.
Stream pressures above 300 psig. High pressure, whether in the process fluid or the heat-transfer fluid, must consider the mechanical strength of the system. High temperatures can over-pressurize steam and cause pipe to collapse.
Chemically aggressive fluids. For personnel safety and equipment protection, operations with certain classes of fluids demand absolute integrity of the thermal maintenance system.
Debottlenecking. Condensate in a system can cause bottlenecking of a process. Heating systems can overcome this.
Unacceptable risk of cross-contamination. A reliable steam jacketing system can assure process fluid integrity.
Piping density. Bolt-on systems are simple to use and eliminate "heat-sinking" of long runs of piping.
Proper heating and insulation can improve any temperature sensitive system.