What Is Inconel 600 (UNS N06600)?
Inconel 600 is a nickel-chromium solid-solution alloy containing a minimum of 72% nickel, 14.0-17.0% chromium and 6.0-10.0% iron, with low carbon, manganese, silicon and copper. Because of its high nickel content, the alloy resists reducing conditions and a wide range of organic and inorganic compounds, while chromium provides resistance to oxidizing media. It is supplied as pipe, tube, plate, sheet, strip, bar and wire under ASTM/ASME specifications such as B167, B168, B163 and B564, and is identified internationally as UNS N06600 or W.Nr. 2.4816.
High-Temperature Performance in Tubular Air Heaters
Tubular air heaters operate under continuous heat flux, cyclic temperature swings and exposure to combustion gases, which makes material selection critical. Inconel 600 is chosen for this service because it retains useful strength and toughness at elevated temperatures while resisting the main degradation mechanisms: oxidation, scaling, carburization and thermal fatigue.
Oxidation resistance: Inconel 600 tubing resists scaling and oxidation at temperatures up to approximately 1093°C (2000°F), which is essential for air heater sheaths exposed to high process temperatures. Mechanical strength: the alloy maintains high strength and toughness at temperature, extending component life and heater efficiency. Corrosion resistance: it withstands dry gases such as chlorine and hydrogen chloride, and resists dry chlorine up to about 538°C (1000°F). Chloride stress corrosion cracking: the high nickel content makes the alloy virtually immune to chloride-induced stress corrosion cracking, a common failure mode for many other alloys. Nitriding and carburization resistance: Alloy 600 performs well in high-temperature nitriding atmospheres and offers excellent resistance to carburization, helping to prevent embrittlement of heater tubes.
Composition and Physical Data
Typical chemical composition per ASTM B168: nickel 72.0% minimum, chromium 14.0-17.0%, iron 6.0-10.0%, carbon 0.15% maximum, manganese 1.0% maximum, silicon 0.5% maximum, copper 0.5% maximum, sulfur 0.015% maximum and phosphorus 0.015% maximum. The alloy has a density of about 8.47 g/cm³ and a melting range of roughly 1354-1413°C. In the annealed condition it typically shows tensile strength in the range of 550-700 MPa with elongation of 30-40%, while the guaranteed minimum values are defined in the governing ASTM specification.
Fabrication and Welding Considerations
Inconel 600 exhibits cold-forming characteristics generally similar to chromium-nickel stainless steel, so tube bending, flaring and rolling can be performed with conventional equipment. The alloy is readily welded by gas tungsten arc welding (GTAW/TIG), gas metal arc welding (GMAW/MIG) and shielded metal arc welding (SMAW), using a matching nickel-based filler metal. Because the alloy resists grain-boundary precipitate formation in the weld heat-affected zone, it can be used in many chemical process applications in the as-welded condition without mandatory post-weld heat treatment. Cleanliness is important: any iron contamination from tooling or grinding should be removed before high-temperature service.
Typical Applications
Beyond tubular air heaters, Inconel 600 is used for furnace components, heat exchanger tubing, heat-treating baskets and fixtures, chemical processing equipment, caustic handling systems, and components in the nuclear and aerospace industries where high-temperature integrity and corrosion resistance are required.
Selection Guidance
Choose Inconel 600 when the service involves high temperatures combined with chloride, caustic or reducing-acid attack. For less aggressive service where cost matters, an iron-based heat-resistant alloy may be adequate; where higher creep strength above about 800°C is needed, consider Incoloy 800H/HT or Alloy 601, and confirm the design limits against the applicable ASME code allowable stresses.
FAQ
Q: What is the maximum service temperature of Inconel 600?
A: The alloy resists oxidation and scaling up to about 1093°C (2000°F) in continuous oxidizing service without significant mechanical load. For load-bearing applications at temperature, design limits are lower and must be checked against the governing code or standard.
Q: Is Inconel 600 resistant to chloride stress corrosion cracking?
A: Yes. The high nickel content (72% minimum) makes Alloy 600 virtually immune to chloride-induced stress corrosion cracking, which is why it is specified for heater sheaths and heat exchanger tubing in chloride-containing environments.
Q: What standards cover Inconel 600 tubing?
A: Seamless tube is commonly supplied to ASTM B163/ASME SB163, pipe to ASTM B167/ASME SB167, and plate, sheet and strip to ASTM B168/ASME SB168. Forgings are covered by ASTM B564.
Q: Can Inconel 600 be welded without post-weld heat treatment?
A: In most chemical process service, yes. The alloy resists grain-boundary precipitate formation in the weld heat-affected zone, so it can often be used in the as-welded condition, provided the filler metal matches the service requirements.
Q: What is the difference between Inconel 600 and Incoloy 800 for air heaters?
A: Inconel 600 has 72% minimum nickel and superior resistance to chlorides, reducing acids and caustic media. Incoloy 800 (UNS N08800) has about 30-35% nickel and higher iron, making it less expensive with good high-temperature oxidation resistance, but lower resistance in chloride-rich or strongly reducing service.
Q: Does Inconel 600 resist carburization?
A: The alloy offers excellent resistance to carburization and performs well in nitriding atmospheres, which helps prevent embrittlement in furnace and combustion gas service.
