Pipe Heating Design

Thermal Equipment Sales Co., Inc. Self-Regulating Advantages: Cut to fit in the field. Possible lower operating cost. Possible lower installation cost. Wide variety of wattages Most tolerant to overlapping Low Cost Disadvantages: High start-up currents Difficult to precisely control temperature Not well suited for procsss control Low design temperatures Self-regulating cable         has two parallel conductors or bus wires extruded in a polymer core. The core's resistance changes porportionally with temperature. The key to understanding Self-regulating cable is the output adjusts proportionally to the cable sheath temperature not the temperature of the pipe heated. There is no direct feed back for the pipe temperature. Most self-regulating cables are designed to give their rated wattage at 50 degrees F. The wattage output will exceed the rated wattage when the cable temperature is below 50 degrees and the lower the cable temperature the larger this wattage i.e. amperage is. INRUSH!!   A high start up current is the result. Tight temperature control is also more difficult with self-regulating cable, because the wattage output is always changing seeking 50 degrees F on the cable not the pipe or fluid in the pipe. Self-regulating cable works quite well for freeze protection applications. Freeze protection and low temperature applications that do not require very tight control. The inrush can be considered on the design of wiring and breakers, and there are some other cost savings to consider. We always recommend a thermostat on every cable we sell. However, when there are several very short runs or several pipe size changes one ambient thermostat can save on a job. Visit our Math Page to: Calculate Heat Requirements for Maintaining Pipe Temp @ www.thermalinc.com/math/pipetrace.htm BACK TO TOP Return to our Home Page Call us at (901) 452-4516 or E-mail us at thermalinc@thermalinc.com Copyright 2000 Thermal Equipment Sales Co. Inc. Thermal Equipment Sales Co., Inc. Constant Wattage Advantages: Cut to fit in the field. Easily controlled Built in cold length at every power connection Wide variety of wattage outputs Low cost Design Temperatures up to 250 F Disadvantages: Requires pipe sensing thermostats Can NOT be overlaped Constant Wattage Cable is made up with two parallel conductors or wires. These wires have a heater wire wrapped around and connected in approximately 2-foot intervals in parallel. This design provides constant wattage output or a uniform output all along its length. The heater wires are designed such that if any section of cable should fail the rest of the heater would continue to operate without change. Constant wattage cable should NOT be overlaped. The effect of double the wattage where the cable crosses will cause high temp failures. The constant wattage output makes maintaining higher and more accurate process temperatures easier. This cable is well suited for freeze protection and many low temp process control applications. This cable can be cut in the field. When terminated the last 2-foot heater section becomes a cold sections "unheated". This provides an unheated section of cable to penetrate the insulation, enter the junction box and make up power connections. Constant Wattage Cable needs a thermostat on each pipe and each pipe size in order to maintain accurate temperature control. Visit our Math Page to: Calculate Heat Requirements for Maintaining Pipe Temp @ www.thermalinc.com/math/pipetrace.htm BACK TO TOP Return to our Home Page Call us at (901) 452-4516 or E-mail us at thermalinc@thermalinc.com Copyright 2000 Thermal Equipment Sales Co. Inc. Thermal Equipment Sales Co., Inc. Mineral Insulated Advantages: Maintains Temperatures         up 1000 degrees F Constant output controls easily Built in cold length at every connection Long Life Disadvantages: Can not be cut in the field Series Heater Wire Made to order Not very flexible         "difficult to install" Higher Cost Mineral Insulated Heater Cable is manufactured with heater wire / wires imbedded in magnesium Oxide insulation. Magnesium is a very good heat conductor and is also a good electrical insulator, which can take very high temperatures before this relationship breaks down. Therefore, the limit for Mineral Insulated heater cable is the temperature of the heater wire, 1000 to 1100 degrees F. MI cable is fairly rigid and can be difficult to install on pipe with many bends, valves and tees. Each cable comes with a factory made 7-foot cold lead and is specifically designed for each application. Mineral Insulated heat cable is designed with only 1 or 2 heater wires, because these wires are continuous any failure along the entire lenght of cable will completely shutdown the cable, NO Heat output. However, MI cable is extremly durable and these failures are rare. This cable is most ideally suited for high temperature applications, soap, tar, asphalt, and others where the temperature limits of Constant Wattage cable or Self-regulating cable are too low. Visit our Math Page to: Calculate Heat Requirements for Maintaining Pipe Temp @ www.thermalinc.com/math/pipetrace.htm Call us at (901) 452-4516 or E-mail us at thermalinc@thermalinc.com Copyright 2000 Thermal Equipment Sales Co. Inc. BACK TO TOP Return to our Home Page Thermal Equipment Sales Co., Inc. Impedance Heating Advantages: Accurately controlled Uniform Heating Temperatures up 1600 degrees F Long life Easy to Install Low retrofit cost No Burn-outs No real maintenance Disadvantages: High Cost Transformers are made to order Difficult to change length in the field Impedance Heating is a safe and proven system for electric pipeline heating. The pipe becomes the heater when low AC voltage is applied to it thru a special, custom designed transformer. The transformer provides a very low voltage, usally below 30 VAC and never over 80 VAC The pipe is your heater and therefore, there is no heater to burn out. These systems can be expensive due to the high cost of the custom transformer. Although this system may have the highest start-up cost, comparatively with the others discussed above it gives the longest life, least maintenance, and the best control of the pipe or process temperature. And because the insulation does not necessarily need to be removed the initial cost can actually be less on retrofit applications. Again, because the pipe is your heater, completely surrounding the material to be heated this system provides the most uniform heat of any system on the market. Visit our Math Page to: Calculate Heat Requirements for Maintaining Pipe Temp @ www.thermalinc.com/math/pipetrace.htm BACK TO TOP Return to our Home Page Call us at (901) 452-4516 or E-mail us at thermalinc@thermalinc.com Copyright 2000 Thermal Equipment Sales Co. Inc. E-mail us at thermalinc@thermalinc.com

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