Showing posts with label Nelson Electric. Show all posts
Showing posts with label Nelson Electric. Show all posts

Monday, January 15, 2018

Basic Information for the Design and Selection of Heat Trace Products for Pipe and Vessel Heating

Heat Tracing
Heat Tracing Self-Regulating Cable
To specify components for an effectively designed, totally electric heat trace system, it is necessary to understand the basic principles involved. A heat trace system is designed to replace heat lost through the thermal insulation from equipment in the system. In some applications, heat tracing will also be able to provide enough heat to significantly change the process temperature. 

It is always recommended to use thermal insulation since heat loss from bare surfaces is very high and heat transfer between the heater and the pipe/vessel is highly variable. All insulation should be weatherproofed. Wet insulation is ineffectual and heater output is insufficient to dry it.

There are several distinctively different types of electric heaters - self regulating, constant wattage, mineral insulated and tank heating panels. Each type has its own characteristics, often making one more suitable for a certain application than the others.


Self Regulating Heater Cable
Self Regulating Heater Cable will adjust its own output in response to pipe temperature. Available in a variety of temperature and power ratings up to 230°C (450°F) and 65.6w/m (20w/ft.). Product features include:
  • Variable Output
    • Self-Regulating heaters will react to variations in temperature encountered at every point along its length. Colder sections receive more heat output, while warmer sections receive less. This provides greater energy efficiency and more uniform pipe temperatures.
  • Can Be Overlapped Without Damage
    • Because Self-Regulating heaters controls its own output, overlapped sections produce less heat, eliminating “hot spots” and possible burn-through common with other types of cable.
  • Fail Safe
    • Upon reaching the upper limits of its temperature range, Self-Regulating heaters diminishes its own heat output to an insignificant level. This guarantees that maximum temperatures (T ratings) cannot be exceeded no matter what product is used in any application.
  • Easy Installation
    • Because of its infinite parallel path circuitry, Self-Regulating heaters can be cut to any length in the field without affecting the heat output or creating “dead zones”.
Constant-Wattage Heater Cable
Constant Wattage Heat Tracing
Constant Wattage Heat Tracing Cable

Constant Wattage Heater Cable is a parallel resistance heater that produces the same watts-per-foot of heat along its entire length.
  • EasyInstallation
    • Constant-Wattage heaters can be cut to length and terminated in the field. 
  • Economical 
    • Provides good power densities and exposure temperatures with parallel circuit cable capabilities at economical prices. Exposure Temperatures to +204°C (+400°F). Ideal for maintaining many process temperature applications. 
Mineral Insulated Heater Cable
MI Cable
MI Cable

Mineral insulated Cable is a series conductor, high temperature heater cable with a special, thin metal sheath. Some of MI advantages are:
  • Corrosion-Resistant
    • Alloy 825 sheath provides excellent corrosion resistance and immunity from chloride stress corrosion - a common problem with stainless steel. 
  • Ideal for High Temperature Applications
    • Mineral Insulated heaters can withstand exposure temperatures up to 593°C (1100°F). Exposure temperatures can be increased to 750°C (1400°F) with special components. 
  • Ratings To 600V
    • Mineral Insulated heaters are available in a variety of voltages to match the available power supply. 
  • High Heat Output 
    • Mineral Insulated heaters have heat output ratings up to 10 times higher than most other cables, reducing the amount of cable required. 
  • Rugged Construction
    • A durable metal sheath provides greater mechanical protection.
  • Thin Wall Construction
    • A unique manufacturing process allows thin wall cable construction for easier field installation. 
Tank Heating Panels
Heating Panel
Heating Panel

  • Low Cost Installation
    • Flexible silicone construction allows panel to conform to tank wall. No bonding or heat transfer aids are required. 
  • High Temperature 
    • Tank Heating Panels maintain temperatures up to 79°C (175°F) and can withstand exposure to 204°C (400°F).

Thursday, August 13, 2015

Basics of Self-Regulating Heat Trace Cable

Heat Tracing Layout
Self-regulating Heat Tracing Layout
Self-regulating heater cable is a parallel circuit electric heater strip. An irradiation cross- linked conductive polymer core material is extruded over the multi-stranded, tin-plated, 18-gauge copper bus wires. The conductive core material increases or decreases its heat output in response to temperature changes. A thermoplastic elastomer dielectric jacket is then extruded over the conductive core. A copper braid is installed over this jacket providing a continuous ground path. A UV stabilized thermoplastic elastomer overjacket is provided to cover the braid for wet applications and exposure to the sun.

Principle of Operation:

The parallel bus wires apply voltage along the entire length of the heater cable. The conductive core provides an infinite number of parallel conductive paths permitting the cable to be cut to any length in the field with no dead or cold zones developing. The heater cable derives its self- regulating characteristic from the inherent properties of the conductive core material. As the core material temperature increases, the number of conductive paths in the core material decreases, automatically decreasing the heat output. As the temperature decreases, the number of conductive paths increases, causing the heat output to increase. This occurs at every point along the length of the cable, adjusting the power output to the varying conditions along the pipe. The self-regulating effect allows the cable to be overlapped without creating hot spots or burnout. As the cable self-regulates it heat output, it provides for the efficient use of electric power, producing heat only when and where it is needed, and also limiting the maximum surface temperature.

Application:

Self-regulating heater cable is ideal for use in maintaining fluid flow under low ambient conditions. Freeze protection and low watt density process temperature systems such as pipelines, fire protection, process water, dust suppression systems, hot water and structure anti-icing are typical applications for this product. For other than metal pipe heating, see appropriate application guide. The base product is supplied with a copper metal braid with a thermoplastic elastomer overjacket for wet applications, exposure to the sun, and where mechanical abuse is a problem. Cables are UL Listed and CSA Certified for use in non-hazardous locations and can be used on branch sprinkler systems.

For more information see the following Nelson Electric product sheet.