Tubular Heaters
Tubular heaters (Tubular Heater / Sheathed Heating Element), also known as heating tubes or tubular heating elements, are resistive electric heating devices that convert electrical energy into thermal energy, and are the most common and widely used heating elements in both industrial and civil fields. Their core feature is that a spiral resistance heating wire is enclosed in a metal tube, with magnesium oxide powder as an insulating and thermally conductive filler, manufactured through a tube reduction process.
Based on the Joule heating effect (Q=I²Rt): current passes through the spiral resistance wire inside the tube to generate heat, and the heat is radially conducted through the high-purity crystalline magnesium oxide powder (MgO) insulating and thermally conductive layer to the outer wall of the metal sheath tube, and then transferred to the heated medium (air, liquid, or solid) through conduction, convection, or radiation. The tube reduction process compacts the magnesium oxide powder to a density of 3.3g/cm³ or more, ensuring the heating wire stays centered without touching the wall, providing uniform heating and an uncharged surface.
Tubular heaters have a multi-layer concentric structure, from inside to outside as follows:
Resistance heating wire: located at the center of the tube, evenly distributed in a spiral shape. Material is nickel-chromium alloy wire (Cr20Ni80, temperature resistance up to 1400℃) or iron-chromium-aluminum alloy wire (0Cr25Al5, temperature resistance up to 1200℃)
Insulating filler layer: high-purity crystalline magnesium oxide powder, with high temperature resistance (above 1000℃), high insulation (breakdown voltage ≥500V), and high thermal conductivity (thermal conductivity ≥3.5W/m·K), which after tube reduction and compaction ensures the heating wire stays centered and positioned
Metal sheath tube: serves as the outer shell, providing mechanical support, corrosion protection, and heat transfer. Materials include 304/316L/310S stainless steel, Incoloy 800/840, copper, aluminum, low-carbon steel, titanium alloy, etc., with tube diameters typically φ6～φ30mm
Lead rod/terminal: conductive component connecting the heating wire to the external power supply, made of stainless steel or free-cutting iron, with nickel-plated surface for oxidation resistance
Sealing material: both ends of the tube opening are sealed with silicone, ceramic adhesive, epoxy, or glass to prevent moisture intrusion from damaging insulation
Insulator: used to secure and insulate the lead rod
Straight single-end heating tube Single-end lead, plug-in installation Mold heating, oil tank heating
Straight double-end heating tube Leads at both ends, through-type installation Water tank, acid-base tank heating
U-shaped heating tube Bent into U shape, increasing heating area Water heaters, boilers
W-shaped heating tube Multiple bends, compact and efficient Large-capacity water tanks, industrial tanks
Spiral heating tube Wound into spiral shape Shower units, water dispensers, ovens
Special-shaped heating tube Customized into various shapes per customer requirements Special equipment, non-standard working conditions
Classified by structure and lead-out method
Type A (standard type with leads at both ends): the most general structural form
Type C (single-end parallel lead-out): two lead rods led out in parallel from the same end
Type D (single-end coaxial lead-out): two lead rods led out coaxially from the same end, suitable for space-constrained occasions
Embedded element: directly embedded into equipment structure
Classified by magnesium oxide powder temperature grade
Grade Applicable temperature
Low-temperature type Below 400℃
Medium-temperature type 400～600℃
High-temperature type 600～850℃
Executive standard JB/T 2379-2016 "Metal Tubular Heating Elements"
Working voltage Not exceeding 440V
Tube diameter range φ6～φ30mm
Surface power density 2～3.8W/cm² (liquid heating can be as low as 0.7～1.5W/cm²)
Working pressure Up to 0.8MPa (high-pressure custom up to 20MPa)
Maximum working temperature 850℃ (special design up to 1050℃)
Insulation resistance ≥1MΩ (at room temperature)
Dielectric strength 2KV/1min
Electrothermal conversion efficiency ≥98%
Explosion-proof grade Up to Ex d IIC T1～T6 Gb
Household appliances: water heaters, ovens, coffee makers, water dispensers, dishwashers, showers
Industrial heating: reactor jacket heating, storage tank insulation, oil tank/water tank/acid-base tank heating
Petroleum and chemical industry: heavy oil/lubricating oil/diesel preheating, chemical medium heating, explosion-proof occasion heating
Power industry: boiler feedwater heating, power plant raw water heating
Food processing: continuous fryers (160～190℃ oil temperature control), pasteurization, tunnel drying
Plastics processing: extruder barrel heating, mold heating (PE about 200℃, PEEK over 300℃)
Metal processing: aluminum profile extrusion die heating, low-melting-point alloy melting
HVAC: air heating furnaces, duct heating, pipeline freeze protection
Laboratory equipment: drying ovens, constant-temperature baths, test electric furnaces
Simple structure: concentric multi-layer packaging, mature manufacturing process
High thermal efficiency: electrothermal conversion efficiency can reach over 98%, with almost all heat transferred to the heated medium
High mechanical strength: sturdy structure after tube reduction and compaction, shock-resistant and pressure-resistant
Uniform heating: spiral uniform distribution of core wire, dense insulating layer, basically eliminating local overheating
Safe and reliable: uncharged surface, reliable insulation performance
Long service life: long lifespan under normal use conditions
Strong adaptability: can be processed into various shapes, adapting to different media and working conditions
Easy installation: supports flange, threaded, welding, and other installation methods
Dry burning strictly prohibited: the effective heating area must be fully immersed in liquid or metal solid; dry burning will quickly burn out the element
Timely descaling: scale or carbon deposits on the tube surface must be cleaned before use, otherwise heat dissipation is affected and lifespan is shortened
Low-voltage startup: when heating solid media such as asphalt and paraffin, voltage should be reduced first, then raised to rated voltage after melting
Moisture-proof storage: elements should be stored in a dry place; if long-term storage causes insulation resistance to fall below 1MΩ, they can be dried in a 200℃ oven for several hours or restored by low-voltage energization
Grounding protection: the shell must be effectively grounded, and working voltage must not exceed 1.1 times the rated value
Wiring protection: the wiring part should be placed outside the insulation layer, avoiding contact with corrosive, explosive media and moisture
When heating air: elements should be arranged in a staggered and uniform manner to ensure good heat dissipation conditions
JB/T 2379-2016: "Metal Tubular Heating Elements" (core product standard, implemented on June 1, 2016, replacing JB/T 2379-1993)
NB/T 10309-2019: "Anti-corrosion Metal Tubular Heating Elements" (implemented on May 1, 2020)
GB/T 23150-2024: "Tubular Heaters for Water Heaters" (implemented on April 1, 2025, replacing GB/T 23150-2008)
GB/T 8623-1988: "Metal Tubular Far-Infrared Radiation Heaters"
JB/T 4088 series: Daily-use tubular heating elements
🛒 Selection key points
Clarify the heating medium: water/oil/chemical medium/air; different media correspond to different surface power densities and sheath materials
Determine working temperature: select the corresponding magnesium oxide powder grade and sheath material according to the medium temperature
Calculate required power: calculate based on medium mass/volume, specific heat capacity, temperature rise range, and heating time
Choose shape and structure: choose straight/U-shaped/W-shaped/spiral/special-shaped according to installation space and heating method
Confirm voltage level: single-phase 220V or three-phase 380V
Corrosion protection requirements: choose 316L/titanium alloy/Incoloy sheath for corrosive media
Explosion-proof requirements: explosion-proof type must be selected for flammable and explosive environments, and the explosion-proof grade must be confirmed
Installation method: confirm flange specifications, thread size, or welding method
