A mid-ranged corrosion resistant alloy with good strength
- Good corrosion resistance to moderate acids & sea-water
- 50% stronger than stainless steel
- Usable temperature limit of 1000°F
- AL-6XN chemistry & specifications
- Hex head bolt features and benefits
Originally developed to combat sea water corrosion, AL6XN has expanded its role as being good mid-range corrosion resistant alloy. AL-6XN hex head bolts are a low carbon, high purity, nitrogen-bearing "super-austenitic" stainless alloy. With a higher nickel and molybdenum content than Duplex 2205 and Super Duplex 2507, it delivers better corrosion resistance while giving a more cost effective alternative to nickel super alloys like Inconel or Hastelloy in moderately corrosive conditions.
• Moderate general corrosion resistance
• Excellent chloride / salt water protection
• Good performance in phosphoric acid
• Moderate resistance to nitric acid
In chemical processes which utilize chlorides, such as paper mills and waste water, stress corrosion cracking (SCC) is a common culprit for 316L stainless failures. Duplex alloys will outlast environments that will cause SCC in 316 stainless, but for more severe low PH environments, hex head bolts made from higher nickel content alloys like AL6XN will generally work better. For the most extreme situations, alloys with >45% nickel content like Hastelloy are often considered.
Outstanding Resistance to Salt Water
Seawater is where AL-6XN hex head bolts outperform so many alloys providing protection to stress corrosion cracking, pitting and crevice corrosion in a broad range of marine applications. AL-6XN hex head bolts contain a minimum of 6% molybdenum content and it is this addition of molybdenum that provides the greatest protection against pitting and crevice corrosion.
Electrical Resistivity: 535 Ohm-circ mil/ft
Ultimate Tensile Strength: 108 ksi
0.2% Yield Strength: 53 ksi
Density: 0.291 lb/in 3
• High molybdenum content provides enhanced corrosion protection in chloride environments.
• Carbon helps to prevent sensitization during welding
• Chromium enhances pitting and crevice corrosion resistance
• The interstitial strengthening effect of nitrogen gives AL-6XN hex head bolts good high strength properties
• Desalination plants depend on AL-6XN hex head bolts for the salt water corrosion protection
• Pulp bleaching equipment and piping
• The power industry uses AL-6XN hex head bolts where salt water and chlorides are present such as steam surface condensers, supercritical, high pressure, feed water heaters, steam surface condensers, flue-gas desulfurization equipment and in nuclear power water piping
• Chemical Processing - processing tanks, vessels and pipes as well as plate and frame heat exchangers.
Resources: Al-6XN Torque Specs
It is important to differentiate between a AL-6XN hex head bolt and hex head cap screw. Often people assume they are the same, but they are actually very different fasteners in terms of how they are manufactured, as well as from an application perspective. Regardless of your choice, AL-6XN hex heads offer strong, stable joints because of their large head service.
The Hex Comparison
Hex Head Bolts
|Hex Head Cap Screw|
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AL-6XN Specifications: UNS N08367, ASTM A 240, ASTM B 688, ASME SA-240, ASME SB-688, ASTM B690, ASTM B691, ASTM A240, ASTM B688, ASME SA-240, ASME SB-688