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
- Lap joint flange 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 lap joint flanges 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, lap joint flanges 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 lap joint flanges outperform so many alloys providing protection to stress corrosion cracking, pitting and crevice corrosion in a broad range of marine applications. AL-6XN lap joint flanges 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 lap joint flanges good high strength properties
• Desalination plants depend on AL-6XN lap joint flanges for the salt water corrosion protection
• Pulp bleaching equipment and piping
• The power industry uses AL-6XN lap joint flanges 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.
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
Lap joint flanges are unique in that they are made of two pieces, the flange itself and the stub end.
- The backside, has a slight shoulder that is square cut at the center or pipe hole
- The front side has a flat face with a filleted (rounded) center hole to match the filleted back face of the stub end. Here the stub end will wrap tightly around the center hole of the flange.
- Shaped like a short piece of pipe with a weld bevel on one. This portion of the stub end is also called the sleeve.
- Narrow shoulder on the flange facing end called is the hub. The back face of the hub has a rounded transition (or inside fillet) that joins the hub to the sleeve
Because a lap joint flange has a two piece configuration, it offers a way to cut cost when piping systems requires
- For high cost alloys the only "wetted" part is the stub end. In this situation, it is only required for the stub-end to be made of the higher cost corrosion-resistant material, where the flange itself can be the produced from lower cost steel.
- Ease of Work
By using lap joint flanges, work can be simplified in situations that require frequent and rapid disassemble and assembly during the operation of a plant. The ability to spin that backing flange compensates for misalignment of the bolt holes during assembly.