Tubular Heater Design and Installation Guidelines

COMPONENT - Tubular Heaters

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Tubular Heater Design & Installation Guidelines

Design Considerations

Sheath Material

For resisting corrosion inherent in the process or environment and for withstanding the sheath temperature required. Standard sheath materials are INCOLOY ®, steel, copper and stainless steel (type 304). Other types of stainless steel, MONEL®, titanium and INCONEL are available.

Job Requirements

The calculation of total heat requirements for an application is outlined in Technical section. For assistance, contact your Local Chromalox field sales engineer who will be glad to contribute his judgement, experience and knowledge in solv ing your heating problem.

After the specific heater size and rating has been tentatively selected, the watt density must be checked against the curves in Technical section.

If the heater selected has a watt density higher than stipulated by the curve, consider these alternatives:

  • Use more heaters of a lower watt density to obtain the required kW capacity.
  • Reduce the kW capacity needed by reducing heat losses and/or allowing for a longer heat-up time.

Watt Densities

The watt density of the element, or watts per square inch of element heated area, should be low for heating asphalt, molasses and other thick substances with low heat transferability. It can be higher for heating air, metals, liquids and other heat-conducting materials. See curves in Technical section for determining allowable watt densities.

When high operating temperatures are needed, watt density must be limited in order not to exceed the maximum sheath tempera ture. Watt density is given in the specifications for each tubular heater.

In general, a viscous material with low thermal conductivity requires a low watt density. Higher watt densities can be used with thinner liquids and with materials of high thermal conductivity. Premature loss of the element due to excessive temperature may result if the material’s heat-take-away ability is low. Also, the material may be charred, carbonized or its chemical makeup altered by overheating.

Terminal Selection

Stocked tubulars are shipped with standard terminals, see Terminal Options in this section. Many other terminals and terminal end seals are available made to order.

CAUTION

Protect terminals from possible contamination from surrounding atmospheres such as oil fumes, chemical vapors from other processes, moisture, weather, etc. MgO insulation is hygroscopic.

Vacuums

Tubular heaters operate at higher temperatures in a vacuum because there is no air to take away the heat. Therefore, watt densities are recommended to be 20 to 30% lower. It is recommended terminals of the ele ment be kept outside of the vacuum.

Code Compliance

Chromalox manufac tures the highest quality heaters and controls and, where applicable, in compliance with such codes as the Canadian Standards Association (CSA), Underwriters Laboratories Inc. (UL) and Verification of Devices for Europe Testing and Certification Institute (VDE) and CE.

Installation Guidelines

Wiring

Must be in accordance with The National Electrical Code (NEC). It is important to use the correct wire gauge to carry the amperage required. A wire not large enough can overheat, become brittle and break. The ambient temperature must also be considered in choosing the correct type of wire and insu lation. Make sure wiring to terminals is tight. Keep terminals away from heat, if possible. (For higher temperatures, contact your Local Chromalox Sales office.)

Mounting Methods

Elements can be supplied with threaded fittings for mounting thru walls of tanks, ovens, etc. Compression threaded fittings are also available for easy field installation. Rings, clips, brackets and washers can also be attached to elements for mounting purposes.

Easy Bending

To put heat where it is needed, tubular elements can be bent to fit most requirements. See following pages for customer bending and factory bending details. Bending should be done around a smooth round object such as a piece of pipe. For mini mum bending radii, see Bending Guidelines.

Triangular Cross-Section

These unique cross-sectioned elements are specially designed for high element surface temperature applications, and wherever extreme rigidity is required.

Triangulation
Triangulation

A patented extra step by Chromalox to increase insulation density and maximize heat transfer and operating life. This method of compaction increases uniformity of resistance wire spacing to help eliminate hot and cold spots. It also increases the rigidity of the element, which is an advantage in some applications.

The terminal ends of these elements are re-rounded to facilitate the use of threaded fittings or other mounting methods.

The heart shaped cross-section is recom mended for certain heavy duty applications. It has added structural strength, achieved through die pressing, which resists deform ation or sagging when installed in the flow of high velocity air or thick oils and compounds, or in high surface temperature air heating.

Table 1: Sheath Material Dimensions for Tubular Heaters

Dimension (In.) Terminal Size
Sheath Material A B C D E F G
Copper 1 1 3/8 21/64 3-3/8 1-1/2 1±1/16 #10-32
Steel or INCOLOY ® 1 1 3/8 21/64 3-3/8 1-1/2 1±1/16 #10-32
Copper, Steel or INCOLOY ® 1 1 1/2 15/32 3-7/16 2-1/2 13/16±1/16 #8-32
1. See complete heater dimensions in table on product pages.

Tubular Heater Modifications

World Leader in the Manufacture of Electric Heating Elements

Chromalox offers the most complete line of tubular heaters avail able. Standard diameters are:

Tubular Heaters Standard Diameters

Round Cross Section

Highly adaptable where elements must be bent particularly if bending is performed in the field.

Triangular Cross Section

Patented process produces elements with the closest possible dimensional control.

Triangulated Cross Section

Flat pressed. Patented process provides large contact area for clamp-on applications. This means more efficient heat transfer, fewer elements since higher element ratings may be employed.

Voltage or Wattage

Heaters can be made for operation on any voltage and rated at any wattage suitable for the application within practical limits. For voltages higher than 480V, specify high voltage terminal construction. See Component section Tubular Heater (0.475 or 1/2" diameter only).

Special Wattage Distribution

Heaters can be made with higher wattages toward the end of the heated section to help offset losses in certain applications. Check with your Local Chromalox Sales office for additional information.

Tubing

Standard industrial grade wall thickness:

Repressed Bends

Tubulars can be bent to tighter radii at the factory. Bends are then repressed to ensure re-compaction of insulation for long life. Customer bending on larger radii does not require repressing. (See Factory Bending Guidelines in this section).

Sheath Length

Larger diameter heaters can be made in unspliced lengths up to 51 feet. This eliminates the need for a spliced joint which is always a possible weak point that might cause premature heater failure.

Table 2: Tubular Heater Sheath Length

Element Dia. (In.)
Max. Heater Length 
(Ft. ± 1%)
0.2 10
0.246 40
0.375 40
0.315 40
0.43 40
0.475 51
3/8 17±1/8"
1/2 17±1/8"

Note:Single-end elements have a maximum sheath length of 10 feet.

Terminal Construction

Many choices to suit your application. Tubular elements gener ally have a terminal for electrical connection at each end. Single end construction has both terminals at the same end.

UL and CSA

Chromalox tubular heaters can be furnished as UL Recognized and CSA Certified components with the addition of a terminal end seal. Terminal end seals can be added to stock elements and shipped in one week. (UL File E198480, Guide UBJY2, CSA File 40859). Use “end seal/moisture barrier” in place of end seal.

VDE and CE

Chromalox tubular heaters can be furnished as VDE Certified and CE certified. Contact your Local Chromalox Sales office.

Wide Choice of Sheath Materials

Available to meet a wide variety of applications. Standard sheath materials are: INCOLOY ® steel, type 304 and 316 stainless steel, copper, INCONEL® and MONEL®. In addition, titanium and other 300 series stainless steel sheaths are available upon request. For applications requiring other materials, contact your Local Chromalox Sales office.

Cold Section

Longer cold ends can be supplied, as required, up to 20 inches. For longer cold ends, contact your Local Chromalox Sales office.

Factory Bending

Tighter bends can be made at the factory. Tubular heaters can be formed to many dif ferent shapes to suit your application. This is done by specially designed bending tools and repressing dies for bending on many different radii.

Additional Features

Many additional fea tures are available for the difficult jobs which require custom designed elements employing Chromalox's vast engineering experience.

Threaded Fitting
Threaded Fitting

Table 3: Threaded Fittings

Element Dia. (In.) Fitting Material Mtg. Hole Dia. (In.) Max. Wall Thickness (In.) Thrd. Size Dimensions (In.)
F A B
0.246 Brass 13/32 7/32 3/8 - 24 15/32 7/8
0.315 Brass 15/32 5/16 7/16 - 28 13/16 7/8
3/8 Brass 17/32 5/16 1/2 - 28 13/16 7/8
1/2-0.475 Brass 21/32 5/16 5/8 - 24 13/16 1
0.246 Steel 13/32 7/32 3/8 - 24 15/32 7/8
0.315 Steel 15/32 5/16 7/16 - 28 13/16 7/8
3/8 Steel 17/32 5/16 1/2 - 28 13/16 7/8
1/2-0.475 Steel 21/32 5/16 5/8 - 24 13/16 1
0.246 Stainless Steel 13/32 7/32 3/8 - 24 15/32 7/8
0.315 Stainless Steel 15/32 5/16 7/16 - 28 13/16 7/8
3/8 Stainless Steel 17/32 5/16 1/2 - 28 13/16 7/8
1/2-0.475 Stainless Steel 21/32 5/16 5/8 - 24 13/16 1

Tubular Heater Factory Bending Guidelines

Note: OAL represents overall length.

Tubular Heater Factory Bending Guidelines 1

Tubular Heater Factory Bending Guidelines 2

Factory Minimum Bends for Tubular Heaters

Table 4: Factory Minimum Bends

Element Dia. Inside & Sheath Inside R1,2,3 A B1,2 C Inside D E
1/2" INCOLOY ® 5Steel & Copper : ∆
3/4
1/2 1,2,3
1-3/8
1-3/8
1
1 1,2
1-1/2
1-1/2
5
8
8
6
0.475" INCOLOY ®Steel & Copper
3/4
1/2
1-3/8
1-3/8
1
1-1/2
1-1/2
3
6
0.430" INCOLOY ®Steel & Copper
7/16
7/16
1-3/8 
1-3/8
1
1
1
1
3
8
6
3/8" INCOLOY ® 5Steel & Copper : ∆
9/16
3/8
1-3/16
1-3/16
1
1
1-1/2 
1-1/2
3-3/4
6
3
0.375" INCOLOY ®Steel & Copper
3/8 
3/8
1-3/16 
1-3/16
1
1
1
1
2-5/8
2-5/8
5
3
0.315" INCOLOY ®Steel & Copper
9/16
5/16
1-3/16
1-3/16
1
1
1-1/2 
1-1/2
2
2
5
3
0.260" INCOLOY ®Steel & Copper
1/4
1/4
1-1/8
1-1/8
1
1
1
1-7/8
1-7/8
5
3
0.245" INCOLOY ®Steel & Copper
3/8
1/4
1-1/16
1-1/16
1
1
1-3/16
1-3/16
1-1/2 
1-1/2
5
3
0.200" INCOLOY ® 1/4 1/4 1 3/4 1-1/4 5

To Order

Specify model, PCN, volts, watts, special features, if required, and quantity. Specify for Factory Formed Tubulars: A. Figure number. B. A, B 1,2, C, D, E, H, J, K, L 1,2and R 1,2,3dimension as required. C. N - number of turns, Dia. - Element Diameter- aid < - angle as required. D. Material for threaded fittings. E. Special terminal type. F. Position of crown (flat side) of element (TC, TI, TS only). G. Submit sketch with special details. Notes

  • These are general guidelines only. Special dimensions and configurations are possible. Contact your Local Chromalox Sales office.
  • A dimension can be less if no fittings are required.
  • C dimension may need to be greater if special fittings are used.
  • E dimension is a minimum when R dimension is less than customer minimum bending radius.
  • Heart Shaped cross-section only.

Tubular Heating Terminal Options

Standard, Alternate, and Moisture Resistant Terminals
Tubular Heating Terminal Options

Tubular Heating Customer Bending & Accessories

Brackets, Discs & Clips

Various types of brackets and clips can be fastened to the heaters to facilitate installation. The following are typical. For other brackets to meet your installation requirements, contact your Local Chromalox Sales office.

Tubular Heaters Brackets Discs and Clips

Compression Fittings

Field Installed Compression Fittings
Compression Fittings

For 0.475, 0.315 and 0.246" diameter elements . Available in both brass and steel, these fittings have been tested to 600 psi hydrostatic pres sures and may be used in tank walls for liquid immersion as well as in air ducts and a variety of other applications.

Compression fittings do not require brazing and can be field mounted in minutes. They may be positioned anywhere along the cold section of the heating element. Do not position over heated section. Cannot be installed over terminal Type #26 (Hermetic Seal), and some other terminals wider than sheath diameter.

Customer Bending

Simple element configurations can be made easily in the field from stocked tubulars listed in this catalog. If copper or stainless sheaths are selected, specify “To be fully annealed for bending.” Elements can be bent around any round, smooth surface of the right diameter.

Three precuations should be observed to prevent damage to the element:

  • Radius of the round object, around which the element is bent, should be no smaller than the minimum radius for the element, as shown in the table below.
  • Sharp edges of tools should not be permitted to gouge the element sheath while bending.
  • End of cold section of the element should not fall within the bend nor come within 1/4" of either side of the bend. To locate end of cold section, see dimensions for the element on its catalog page and determine as follows:

    Example

    To locate end of cold sectio n of TRI-1645 tubular element, refer t o the individual product page . Sheath length: 16 "Less heated length: 9-1/8 "Total cold length: 6-7/8 "Cold length of each en d (6-7/8" ÷ 2) = 3-7/16 "

Terminal end bending can be done with pipe section of slightly larger diameter than sheath. A minimum 1" straight section should be left at the end.
Note

To protect sheath, copper sheet can be bolted to vise jaws and end of pipe can be filed to remove sharp edge.

Before bending, it is best to lay out and dimen sion the configuration. Also, it is best to start bending from the center of the heater and work toward the terminal ends.

Customer Bending

Tubular Heater Custom Bending

Tubular Heater Design & Installation Guidelines

Design Considerations

Sheath Material —For resisting corrosion inherent in the process or environment and for withstanding the sheath temperature required

— Standard sheath materials are INCOLOY ® , steel, copper and stainless steel (type 304). Other types of stainless steel, MONEL ®, titanium and INCONEL are available.

Job Requirements — The calculation of total heat requirements for an application is outlined in Technical section. For assistance, contact your Local Chromalox field sales engineer who will be glad to contribute his judgement, experience and knowledge in solv ing your heating problem.

After the specific heater size and rating has been tentatively selected, the watt density must be checked against the curves in Techni cal section.

If the heater selected has a watt density higher than stipulated by the curve, consider these alternatives:

  1. Use more heaters of a lower watt density to obtain the required kW capacity.
  2. Reduce the kW capacity needed by reducing heat losses and/or allowing for a longer heat-up time.

Watt Densities — The watt density of the element, or watts per square inch of element heated area, should be low for heating asphalt, molasses and other thick substances with low heat transferability. It can be higher for heating air, metals, liquids and other heat-conducting materials. See curves in Technical section for determining allowable watt densities.

When high operating temperatures are needed, watt density must be limited in order not to exceed the maximum sheath tempera ture. Watt density is given in the specifications for each tubular heater.

In general, a viscous material with low thermal conductivity requires a low watt density. Higher watt densities can be used with thinner liquids and with materials of high thermal conductivity. Premature loss of the element due to excessive temperature may result if the material’s heat-take-away ability is low. Also, the material may be charred, carbonized or its chemical makeup altered by overheating.

Terminal Selection — Stocked tubulars are shipped with standard terminals, see Terminal Options in this section. Many other terminals and terminal end seals are available made to order.

CAUTION— Protect terminals from possible contamination from surrounding atmospheres such as oil fumes, chemical vapors from other processes, moisture, weather, etc. MgO insulation is hygroscopic.

Vacuums — Tubular heaters operate at higher temperatures in a vacuum because there is no air to take away the heat. Therefore, watt densities are recommended to be 20 to 30% lower. It is recommended terminals of the ele ment be kept outside of the vacuum.

Code Compliance — Chromalox manufactures the highest quality heaters and controls and, where applicable, in compliance with such codes as the Canadian Standards Association (CSA), Underwriters Laboratories Inc. (UL) and Verification of Devices for Europe Testing and Certification Institute (VDE) and CE.

Installation Guidelines

Wiring — Must be in accordance with The National Electrical Code (NEC). It is important to use the correct wire gauge to carry the amperage required. A wire not large enough can overheat, become brittle and break. The ambient temperature must also be considered in choosing the correct type of wire and insu lation. Make sure wiring to terminals is tight. Keep terminals away from heat, if possible. (For higher temperatures, contact your Local Chromalox Sales office.)

Mounting Methods — Elements can be supplied with threaded fittings for mounting thru walls of tanks, ovens, etc. Compression threaded fittings are also available for easy field installation. Rings, clips, brackets and washers can also be attached to elements for mounting purposes.

Easy Bending — To put heat where it is needed, tubular elements can be bent to fit most requirements. See following pages for customer bending and factory bending details. Bending should be done around a smooth round object such as a piece of pipe. For mini mum bending radii, see Bending Guidelines.

Triangular Cross-Section

These unique cross-sectioned elements are specially designed for high element surface temperature applications, and wherever extreme rigidity is required.

Triangulation — A patented extra step by Chromalox to increase insulation density and maximize heat transfer and operating life. This method of compaction increases uniformity of resistance wire spacing to help eliminate hot and cold spots. It also increases the rigidity of the element, which is an advantage in some applications.

The terminal ends of these elements are re-rounded to facilitate the use of threaded fittings or other mounting methods.

The heart shaped cross-section is recom mended for certain heavy duty applications. It has added structural strength, achieved through die pressing, which resists deform ation or sagging when installed in the flow of high velocity air or thick oils and compounds, or in high surface temperature air heating.

Triangulation

Tubular Heater Modifications

World Leader in the Manufacture of Electric Heating Elements — Chromalox offers the most complete line of tubular heaters avail able. Standard diameters are:

Tubular Heaters Standard Diameters

Round Cross Section — Highly adaptable where elements must be bent — particularly if bending is performed in the field.

Triangular Cross Section — Patented process produces elements with the closest possible dimensional control.

Triangulated Cross Section — Flat pressed. Patented process provides large contact area for clamp-on applications. This means more efficient heat transfer, fewer elements since higher element ratings may be employed.

Voltage or Wattage — Heaters can be made for operation on any voltage and rated at any wattage suitable for the application within practical limits. For voltages higher than 480V, specify high voltage terminal construction. See Component section Tubular Heater (0.475 or 1/2" diameter only).

Special Wattage Distribution — Heaters can be made with higher wattages toward the end of the heated section to help offset losses in certain applications. Check with your Local Chromalox Sales office for additional information.

Tubing — Standard industrial grade wall thickness:

Repressed Bends — Tubulars can be bent to tighter radii at the factory. Bends are then repressed to ensure re-compaction of insulation for long life. Customer bending on larger radii does not require repressing. (See Factory Bending Guidelines).

Sheath Length —Larger diameter heaters can be made in unspliced lengths up to 51 feet.

This eliminates the need for a spliced joint which is always a possible weak point that might cause premature heater failure.

Element Dia. (In.) Max. Heater Length
(Ft. ± 1%)
0.2 10
0.246 40
0.375 40
0.315 40
0.43 40
0.475 51
3/8 17±1/8"
1/2 17±1/8"
Note — Single-end elements have a maximum sheath length of 10 feet.

Terminal Construction — Many choices to suit your application. Tubular elements gener ally have a terminal for electrical connection at each end. Single end construction has both terminals at the same end.

UL and CSA — Chromalox tubular heaters can be furnished as UL Recognized and CSA Certified components with the addition of a terminal end seal. Terminal end seals can be added to stock elements and shipped in one week. (UL File E198480, Guide UBJY2, CSA File 40859). Use “end seal/moisture barrier” in place of end seal.

VDE and CE — Chromalox tubular heaters can be furnished as VDE Certified and CE certified. Contact your Local Chromalox Sales office.

Wide Choice of Sheath Materials — Available to meet a wide variety of applications. Stan dard sheath materials are: INCOLOY® , steel, type 304 and 316 stainless steel, copper, INCONEL® and MONEL®.

In addition, titanium and other 300 series stainless steel sheaths are available upon request. For applica tions requiring other materials, contact your Local Chromalox Sales office.

Cold Section — Longer cold ends can be supplied, as required, up to 20 inches. For longer cold ends, contact your Local Chromalox Sales office.

  Dimension (In.) Terminal Size
Sheath Material A B C D E F G
Copper 1 1 3/8 21/64 3-3/8 1-1/2 1±1/16 #10-32
Steel or INCOLOY® 1 1 3/8 21/64 3-3/8 1-1/2 1±1/16 #10-32
Copper, Steel or INCOLOY® 1 1 1/2 15/32 3-7/16 2-1/2 13/16±1/16 #8-32
1. See complete heater dimensions in table on product pages.

Factory Bending — Tighter bends can be made at the factory.

Tubular heaters can be formed to many dif ferent shapes to suit your application. This is done by specially designed bending tools and repressing dies for bending on many different radii.

Additional Features — Many additional fea tures are available for the difficult jobs which require custom designed elements employing Chromalox's vast engineering experience.

Threaded Fitting
Element Dia. (In.) Fitting Material Mtg. Hole Dia. (In.) Max.Wall Thickness (In.) Thrd. Size Dimensions (In.)
F
A
B
0.246 Brass 13/32 7/32 3/8 - 24 15/32 7/8
0.315 Brass 15/32 5/16 7/16 - 28 13/16 7/8
3/8 Brass 17/32 5/16 1/2 - 28 13/16 7/8
1/2-0.475 Brass 21/32 5/16 5/8 - 24 13/16 1
0.246 Steel 13/32 7/32 3/8 - 24 15/32 7/8
0.315 Steel 15/32 5/16 7/16 - 28 13/16 7/8
3/8 Steel 17/32 5/16 1/2 - 28 13/16 7/8
1/2-0.475 Steel 21/32 5/16 5/8 - 24 13/16 1
0.246 Stainless Steel 13/32 7/32 3/8 - 24 15/32 7/8
0.315 Stainless Steel 15/32 5/16 7/16 - 28 13/16 7/8
3/8 Stainless Steel 17/32 5/16 1/2 - 28 13/16 7/8
1/2-0.475 Stainless Steel 21/32 5/16 5/8 - 24 13/16 1

Compression Fittings

Field Installed Compression Fittings — For 0.475, 0.315 and 0.246" diameter elements. Available in both brass and steel, these fittings have been tested to 600 psi hydrostatic pres sures and may be used in tank walls for liquid immersion as well as in air ducts and a variety of other applications.

Compression fittings do not require brazing and can be field mounted in minutes. They may be positioned anywhere along the cold section of the heating element. Do not position over heated section. Cannot be installed over terminal Type #26 (Hermetic Seal), and some other terminals wider than sheath diameter.

Field Installed Compression Fittings
Compression Fittings

Customer Bending

Simple element configurations can be made easily in the field from stocked tubulars listed in this catalog. If copper or stainless sheaths are selected, specify “To be fully annealed for bending.” Elements can be bent around any round, smooth surface of the right diameter.

Three precuations should be observed to prevent damage to the element:

  1. Radius of the round object, around which the element is bent, should be no smaller than the minimum radius for the element, as shown in the table below.
  2. Sharp edges of tools should not be permitted to gouge the element sheath while bending.
  3. End of cold section of the element should not fall within the bend nor come within 1/4" of either side of the bend. To locate end of cold section, see dimensions for the element on its catalog page and determine as follows:

    Example — To locate end of cold sectio n of TRI-1645 tubular element, refer t o the individual product page . Sheath length: 16 "Less heated length: 9-1/8 "Total cold length: 6-7/8 "Cold length of each en d (6-7/8" ÷ 2) = 3-7/16 ", Terminal end bending can be done with pipe section of slightly larger diameter than sheath. A minimum 1" straight section should be left at the end.

    Note — To protect sheath, copper sheet can be bolted to vise jaws and end of pipe can be filed to remove sharp edge.

Before bending, it is best to lay out and dimen sion the configuration. Also, it is best to start bending from the center of the heater and work toward the terminal ends.

Tubular Heater Custom Bending

Download the Tubular Heater Design and Installation Guidelines