Heat Tracing of Piping Systems
Heat Tracing is a generalized term relating to the application of radiant heat input to piping systems from tubing attached to the outside of the pipe.
When Heat tracing is used to ensure that the system functions from a process standpoint regardless of climate conditions it is known as Process Control Tracing
Again when Heat tracing is used to prevent freeze up due to climatic conditions only it is known as Winterization Tracing.
- Steam tracing supply lines shall be taken from the top of the supply header to assure dry quality steam.
- Identify the locations for steam tracing supply manifolds and condensate manifolds early in design to reserve space in plant layout. This applies to non-steam supply and return manifolds (hot oil, glycol, etc.).
- Allow for increase in insulation sizing to allow for tracers.
- This specification is to be used by Piping for heat tracing of all in-line instruments. Piping will also provide steam supply and condensate collection manifolds for all other instruments. The break between Piping Traced Instruments and Control Systems traced instruments will match the drawing break between the two departments.
Using various media such as steam, hot water, glycol, or hot oil heat tracing is installed to protect the
piping, equipment, and instruments against temperatures that would cause congealing or freezing of the process fluids, interfere with operation, or cause damage to the equipment.
- The daily average low temperature of the coldest month shall be used to select the low ambient design temperature that then determines the degree of winterizing protection required.
- No winterizing is required for water service except where a sustained temperature below minus 1 degree C is often recorded for 24 hours or longer.
- Compressors, blowers, and other mechanical equipment shall be specified for operation at low ambient design temperature.
Methods of Heat Conservation
- Where feasible, insulation shall be used for heat conservation.
- Heat tracing, plus insulation, is the alternative method for heat conservation.
- Heat transfer cement may be utilized when a process line requires a high heat input and common methods of heat tracing are inadequate.
- Steam jacketing is utilized in specific cases where steam tracing with heat transfer cement is inadequate.
- Electric tracing is utilized when precise temperature control is required or where steam tracing is not practical. Thermostat setting for electric tracing should not be higher than fluid operating temperature.
Methods for Winterization
- Winterizing by circulation shall be provided where a sufficient power source is available to keep the fluid circulating.
- Utility water and utility air lines in intermittent service shall be winterized by draining.
- Winterizing by steam tracing is the preferred method when winterizing by circulation and draining is impracticable.
- Winterizing by electric tracing is utilized when a precise temperature control is required or where steam tracing is not practical. Thermostat setting for electric tracing should not be higher than fluid operating temperature.
- Minimum tracing steam pressure shall be 1 Bar; maximum required is 10.3 Bar. At minimum pressure, condensate shall be routed to the plant sewer system. If condensate is collected, the minimum usable pressure shall be 1.7 Bar.
Tracer Size and Length
- Required tracer size shall be determined by piping heat loss and tracer steam pressure found in the Heat Loss Chart (Fig. 1)
- Minimum tracer size shall be 3/8 of an inch OD tubing; maximum size shall be 1 inch OD tubing. For economy, where Heat Loss Chart indicates the requirements for multiple tracers, a single tracer with heat transfer cement shall be considered.
- When using heat transfer cement, tracers of 3/8 of an inch and 1/2 of an inch OD tubing are recommended. If more tracer area is required, multiple tracers of 3/8 of an inch and 1/2 of an inch shall be used.
- Maximum tracer length shall be based on tracer size and steam pressure as follows:
o Steam pressure 1 Bar through 1.7 Bar
- 60m for 3/8 of an inch and 1/2 of an inch tracers
- 100m for 3/4 of an inch and 1 inch tracers
o Steam pressure 3.5 Bar through 13.8 Bar
- 60m for 3/8 of an inch and 1/2 of an inch tracers
- 120m for 3/4 of an inch and 1 inch tracers
o Tracer lengths for tracing with heat transfer cement shall be based on recommendation of manufacturer.
- For stainless steel lines, the tracer material shall be low carbon steel. Stainless steel instrument leads shall be traced with copper tubing.
- Each tracer shall have its own trap. Tracer traps shall discharge to sewer. If condensate must be collected, minimum usable pressure is 1.7 Bar.
- Compression type fittings shall be installed outside of the insulation OD.
- Socket type fittings may be installed inside of the insulation.
- The steam tracers shall be pressure tested before the insulation is applied. Under emergency conditions, the insulation may be applied but the fittings shall be left exposed until the testing is complete.
Tracer Pocket Depth
- Pocket depth is the distance the tracer rises in the direction of flow from a low point to a high point. The total pocket depth is the sum of all risers of the tracer.
- Maximum tracer total pocket depth shall be equal to 40 percent of tracing steam gage pressure expressed in meters.
Example: Tracing steam 10.3 bar 30 m x 0.40 = 12 m feet total pocket depth
- Steam tracing tubing materials shall be in accordance with material specifications.
- Tracers shall be OD tubing. Soft annealed copper tubing shall be used where the temperature of the product line or tracing steam does not exceed 204 °C. Above this temperature, dead soft annealed hydraulic quality, low carbon, seamless steel tubing shall be used where the temperature of the product line or tracing steam does not exceed 399 °C.
- For aluminum pipe lines, carbon steel tracer material shall not be used.
- For aluminum pipe lines and all lines above 399 °C the tracer material shall be stainless steel.
- For conditions where the tracer could overheat lines containing acid, caustic, amine, phenolic water, or other chemicals, insulation spacer blocks shall be installed between tracer and pipe.
Fig.1: Typical Heat Loss Chart