Heat Tracing Plastic Lined Pipe

Many products freeze or become viscous when exposed to ambient temperatures. Other polymerize, react, or become corrosive when exposed to ambient temperatures (e.g., condensation of a permeating vapor through a PTFE liner). Successful storage and transfer of such products, in most cases, requires that the piping and associated equipment be heat traced. Throughout the industry, steam, fluid, and electric heat tracing systems are widely used. All are intended for the same purpose of pipe heating, but each has its own design considerations and limitations. The potential problem with heat tracing plastic lined pipe is overheating of the plastic liner. In PTFE lined pipe, localized heating can cause increased permeation, resulting in a single lobe collapse of the liner. Each liner has a maximum service temperature; however, some aggressive chemicals can reduce the temperature limits of the plastic. The following outlines the maximum service temperatures for the liners, recommended heat tracing methods for each liner, design considerations for each heat tracing method, and relative strengths and limitations for each heating system.

Available Liners	Maximum Temperature °F(°C)	Recommended Heat Tracing
Polypropylene (PP)	225 (107)	--Steam** --Fluid --Electric
Polyvinylidene Fluoride (PVDF)	275 (135)	--Steam --Fluid --Electric
Polytetrafluoroethylene (PTFE)	450 (232)	--Steam --Fluid --Electric
Perfluoroalkoxyfluorocarbon (PFA)	450 (232)	--Steam --Fluid --Electric
**Since useful steam temperatures are above the recommended temperature for PP, a special designed isolated tracing system must be used to limit the tracer temperature to prevent overheating of the liner.

Note:

Maximum Liner Service Temperature can decrease because of the service application; check Chemical Resistance Section for recommended temperature of each liner for the application in question.

General Design Consideration for Plastic Lined Pipe Pipe Size Liner Type Maximum Liner Temperature Decrease of Liner Service Temperature Due to Service		Application (per Chemical Resistance Guide) Insulation Type Insulation Thickness Temperature to be Maintained Ambient Conditions High and Low Temperatures Wind Speed
Steam Tracing: Special Design Considerations Steam Pressure and Temperature Since useful steam temperatures are above the recommended temperature for PP, a specially designed isolated tracking system must be designed to limit the tracer temperature to prevent overheating of the liner.		Recommended steam tracing technique
Advantages Often available as surplus in plant operations Good for heat up and temperature maintenance Can be used in explosive risk areas Disadvantages Useful temperature range: 200°F-350°F Temperature control difficult High installation and day-to-day maintenance
Fluid Tracing: Special Design Considerations Inlet Fluid Media Temperature and Pressure Fluid Media: Density, Specific Heat Viscosity Maximum Allowable Fluid Pressure Drop and Outlet Temperature Advantages Good for close temperature control Very good for cooling application Less susceptible to low temperature problems during system shutdown		Recommended tracing configurations for joints, fittings and valves.
Disadvantages Tracing fluids typically have a low heat capacity Environmental concerns with possible leaks Many tracing fluids are very expensive and require occasional regeneration
Electric Tracing: Special Design Considerations Available Voltage Hazardous Area Limitations Do not use an electric heating cable with a T-Rating above the recommended liner temperature for the application in question. Advantages Readily available in any plant facility Very low heat output capabilities Very good temperature control capabilities		Electrical tracing methods and configurations
Disadvantages Restricted in flammable/hazardous areas If sized for temperature maintenance, electric heat tracing provides slow heat up to the maintenance temperature When heat tracing plastic line pipe, the maximum liner temperature and any decrease of this temperature due to the service application must be considered. Each heat tracing method has its own strengths and limitations and are all recommended for plastic lined pipe. However, when steam heat tracing Polypropylene (PP) a specially designed isolated tracing system must be used. Some material extracted from "Steam vs. Fluid vs. Electric Heat Tracing," Thermon, 1990.