Please click on questions below to jump to the appropriate section.
    What are composite radiant tubes?
    How can composite tubes save money for heat treaters?
    How much do they cost?
    How do composite materials differ from conventional tube materials?
    What advanced configurations and applications are available?

What are composite radiant tubes (CRTs)?

    The composite radiant tubes (CRTs) discussed here are based on silicon and silicon carbide.  They can be used in most atmosphere heat treating furnaces in place of conventional metal alloy and mullite radiant tubes.  INEX has developed a patented, low-cost production technique and tested the advanced radiant-tube technology to improve the performance of indirectly heated furnaces.
    During the first decade of their use nearly 9,600 straight, single-pass tubes have been installed with nearly all of them still in use.  Typical composite tube life is estimated to be at least double that of conventional metal alloy or mullite tubes in similar furnace conditions.
                                    

How can composite tubes save money for heat treaters?

    The primary advantage of composite radiant tubes (CRTs) is reduced furnace downtime and maintenance due to extended tube life, especially in high-temperature furnaces.  Each time a furnace is shut down to replace metal alloy or mullite tubes, the cost of idle furnace time can amount to thousands of dollars in lost revenues. 
    Productivity improvement is another significant advantage.   Composite tubes can be fired much hotter than other tubes, providing shorter furnace recovery and overall cycle times when burner systems are optimized to deliver the required heat input.  Additional savings can be generated by electric-to-gas conversions and process improvements. 
    For more information on how INEX composite radiant tubes (CRTs) can save you money, please refer to our Payback Calculator.                                      

How much do they cost?

   Composite radiant tubes (CRTs) cost about the same or a little more than conventional metal tubes.  However, increased tube life and reduced furnace downtime can result in large cost savings over time.  Your cost savings can be estimated using the simple Payback Calculator. 
                                     

How do composite materials differ from conventional tube materials?

    Properly installed, composite radiant tubes (CRTs) resist failure due to creep, thermal shock, carburization (embrittlement), melt-through, and oxidation.   However, all composite tubes are vulnerable to breakage if dropped or struck by heavy objects.  Tube breakage during installation and operation can be avoided through training of shop personnel.

Material	Thermal Shock	Service Life	Temperature	Mechanical Strength
Composite	Excellent	Excellent	<2450° F.	Good
Mullite	Poor	Fair	<2500° F.	Poor
Metal Alloy	Excellent	Fair	<2000° F.	Excellent

What advanced configurations and applications are available?

    Composite radiant tubes (CRTs) can be used in all types of batch and continuous heat treating furnaces in commercial and captive heat treating shops.   Besides straight, single-pass tubes, single-ended recuperative tube/burner systems are also available.  For U-tube applications, composite elbows are  becoming available (not in all sizes) to meet the needs of the significant number of heat treating furnaces with this tube configuration.
                                      

Fact Sheet courtesy of GRI®

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