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Frequently Asked Questions

What Are Composite Radiant Tubes?
Composite Radiant Tubes (CRTs) directly replace conventional metal alloy and mullite radiant tubes, and are composed of Silicon and Silicon Carbide.  INEX developed this patented, low-cost radiant tube technology specifically for indirectly-heated, atmosphere-controlled furnaces. Over the last three decades over 40,000 INEX radiant tubes have been installed throughout the world with most still in service. INEX tube life is at least double that of conventional metal alloy and mullite tubes under similar furnace conditions, usually 10 years and more.

How Do Composite Tubes Save Money for Heat-Treaters?
The obvious advantage of INEX Composite Radiant Tubes is extended life and reduction of furnace downtime and maintenance costs, especially in corrosive, high temperature environments such as Carburizing.  Every hour a furnace is shut down for replacement of metal alloy or mullite tubes, thousands of dollars of production and sales revenue are lost.

Another significant advantage is productivity improvement. INEX radiant tubes can be fired much hotter than metal alloy tubes, reducing furnace recovery and overall cycle times.

INEX tubes offer Unsurpassed Like, Twice the Heat & None of the CreepTM!

How Much Do They Cost?
Composite Radiant Tubes cost about the same or slightly more than metal alloy tubes.  However, increased tube life, higher temperature capability, and reduced furnace downtime result in substantial cost savings and rapid payback.

How Do Composite Radiant Tubes Differ from Conventional Materials?
Properly installed, Composite Radiant Tubes completely eliminate failures due to Creep (deformation, distortion &, rupture), Carburization (embrittlement & corrosion), Thermal Shock, Melt-Through, Weld Failure and Oxidation. However, all composite & ceramic tubes are vulnerable to mechanical fracture if dropped or struck by heavy objects.  Tube breakage during installation and operation is easily avoided with careful handling and proper training of shop personnel.

Material Thermal Shock Service Life Temperature Mechanical Strength
Composite Excellent Excellent <2450° F
(1340°C)
Good
Mullite Poor Fair <2500° F
(1370°C)
Poor
Metal Alloy Excellent Fair <2450° F
(1340°C)
Excellent

What Configurations and Applications are Available?
Composite Radiant Tubes are used in all types of batch and continuous heat-treating furnaces. In addition to our original Straight-Wall & Internally-Finned (straight-pass) tubes, Single-Ended Recuperative tubes (SER & EGR) and U-tubes are now available to meet the ever-increasing challenges of the heat-treating industry.