All About Tempco's Tubular heating Elements

December 8, 2020

Tempco Tubular Heaters

Common Applications

Animal incubators for prenatal care
Combination radiant/convection heaters
Comfort radiant heaters
Epoxy curing
Food service equipment
Forced air heating
Fusing laminated sheets

Hopper and silo heaters
Hot runner molds
Immersion in liquids
Kettle and tank heaters
Ovens - process, curing or food
Paint and enamel baking equipment
Plastic sheet bending equipment

Spas and hot tubs
Steam tables
Sterilizers and Autoclaves
Stretch wrapping equipment
Textile and chemical dryers
Thermal forming machines
Welded, brazed or clamped to tanks or pipes

Construction Characteristics

Tubular Cut-Away and Dimensions
The cutaway view shows the tubular heater’s basic construction.

A computer-designed helical coil of 80% Nickel 20% Chromium alloy resistance wire is fusion welded to the nickel-coated steel terminal cold pin.
This coil assembly is precisely stretched and centered in the element metal sheath
The sheath is then filled with Grade “A” Magnesium Oxide powder (MgO).
The filled tube is then compacted by a roll reduction mill into a solid mass, permanently stabilizing the coil in the center of the tube while providing excellent heat transfer and dielectric strength between the coil and the sheath.

Tempco Tubular Heating Element Filling Machines
Tubular Heating Elements being filled with MgO insluating powder

Watt Density

Element Watt Density is the wattage dissipated per square inch of the element sheath surface and is critical to the proper heating of the application and to the life expectancy of the heater. The Watt Density is calculated with the following formula:

Element Wattage Watt Density (w/in²) =	Element Wattage
	π × Element Dia. × Element Heated Length

For a particular application element watt density will govern element sheath and internal resistance wire temperature. Factors to consider when choosing a suitable watt density are:

Many materials are heat sensitive and can decompose or be damaged if the element is running too hot.
Air and other gases that are poor conductors of heat require watt densities matched to the velocity of the gas flow to prevent element overheating.
When heating hard water or cleaning solutions, mineral deposits can build up on the element sheath, acting as a heat insulator and raising the internal element temperature. If these deposits cannot be periodically removed, use a lower watt density element to increase heater life expectancy.
When tubular heaters are used in UL recognized oil immersion heating applications the heated oil temperature cannot exceed 257°F (125°C). Steel sheath elements are limited to 60 watts/in2. Tubular heaters with steel or stainless steel bulkhead fittings used in UL oil heating applications are not pressure rated. Contact Tempco for other application specific UL file information.
Page 16-12 in the Engineering Data Section of this catalog lists the maximum recommended heater watt density for many materials.

For additional information and help please contact Tempco.

Resistance Tolerance

Tubular heating elements have an Industry Standard Resistance Tolerance of +10%, −5% which translates to a Wattage Tolerance of +5%, −10%. Consult Tempco if tighter tolerances are required for your application.

When heating any substance it is critical to match the heater watt density, operating temperature and sheath material to the specific medium being heated. Failure to do so will result in premature heater failure and/or unsafe conditions.

Forming Tubular Elements

The MgO insulation used in tubular heating elements is compacted by reducing the element diameter in a roll reducing mill.
The elements are then annealed in a controlled atmosphere furnace to relieve the metal stressing (work hardening) that takes place during the rolling to size reduction of the sheath.
Annealing brings the metal back to a soft state, allowing the element to be bent into virtually any configuration.
However, since forming also work hardens the metal, some precautions must be observed in order to prevent the sheath from breaking during bending or developing stress cracking marks.

Tempco Tubular Heating Element Rolling Machines
Roll Reducing Mill compacts the MgO powder

Agency Approvals

Tempco Tubular Heating Elements are certified as Recognized Components by Underwriters Laboratories (File Number E90771) under CCN UBJY2/8 to meet UL Standard UL1030.
Tempco’s equivalent CSA File Number is 043099.
Tubular elements with bulkhead fittings have also been certified for oil heating (File Number MP4154) under CCN MDST2/8 to meet UL Standard 574.
If you require UL, CSA, or other NRTL agency approvals, please specify when ordering.