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AL-6XN super-austenitic stainless steel (UNS N08367)

• 6.3% molybdenum
• Over 25 years of proven seawater service
• Practical immunity to chloride stress cracking
• 50% stronger than stainless
• ASME coverage up to 800°F
• Easily welded
• Available in ALL product forms

AL-6XN^® alloy (UNS N08367) is a low carbon, high purity, nitrogen-bearing "super-austenitic" stainless alloy. The AL-6XN alloy was designed to be a seawater resistant material and has since been demonstrated to be resistant to a broad range of very corrosive environments. The high strength and corrosion resistance of the AL-6XN alloy make it a better choice than the conventional duplex stainless steels and a cost effective alternative to more expensive nickel-base alloys where excellent formability, weldability, strength and corrosion resistance are essential.

Performance Profile

The levels of chromium, molybdenum and nitrogen in AL-6XN all serve to provide resistance to acidic oxidizing chloride solutions previously achieved only by the nickel base alloys. High nickel (24%) and molybdenum (6.3%) contents make AL-6XN a solution to chloride ion stress corrosion cracking. Because of its nitrogen content, AL-6XN has greater tensile strength than common austenitic stainlesses, while retaining high ductility and impact strength. The ASME allowable stresses for AL-6XN are up to 75% higher than for 316L stainless, and more than twice those for the copper-nickel alloys.

Specifications

UNS N08367

ASME SB-688, ASME SA-240, ASME SB-675, ASME SA-312, ASME SB-676, ASME SA-249, ASME SB-691, ASME SA-479, ASME SB-462, ASME SA-182, ASME SB-564, ASME SB-366

ASTM B688, ASTM A240, ASTM B675, ASTM A312, ASTM B676, ASTM A249, ASTM B804, ASTM B691, ASTM A479, ASTM B462, ASTM A182, ASTM B564, ASTM B366, ASTM B472

NACE MR-0175

Inventory

AL-6XN Plate, AL-6XN Sheet, AL-6XN Bar, AL-6XN Pipe, AL-6XN Fittings, AL-6XN Concentric Reducers, AL-6XN Tees, AL-6XN Stub Ends, AL-6XN Forgings, AL-6XN Billet, AL-6XN Welding Products

Chemical Composition, %

Applications

FGD Scrubbers

Reverse Osmosis

Distillation Columns

Offshore Oil and Gas

Heat Exchangers

Corrosion Resistance

AL-6XN has excellent corrosion resistance in high chloride environments as well as many acids. Below is a quick summary of the critical pitting and crevice corrosion resistance compared to many other alloys. AL-6XN has improved properties over stainless steels and all duplex grades. The practical immunity to chloride stress corrosion cracking has pushed AL-6XN into many seawater applications including seawater reverse osmosis. The resistance to acid and chloride environments is proven by over 20 years of service in the flue gas desulfurization process at coal fired electric power plants.

* CCCT - 10% FeCl₃ 6H₂0, per ASTM G 48 Practice B, CPT - 1 M NaCl, per ASTM G 150, PRE_N = Cr + 3.3 Mo + 16N

Workability

The toughness and ductility of the AL-6XN alloy provide for relative ease of fabrication in the shop or in the field. The formability and weldability of the AL-6XN alloy are much better than that of high alloy ferritic or duplex stainless steels that demonstrate comparable resistance to corrosion.

Ease of Fabrication

The low carbon and high nitrogen contents in AL-6XN alloy minimize the precipitation of carbides and secondary phases that can occur during welding. Therefore as-welded assemblies can be placed in service, provided a suitable over-matched filler metal, such as alloy 625 is used. AL-6XN alloy can be welded in the field using procedures similar to those used with other austenitic stainless steels.

Rolled Alloys AL-6XN Fabrication Guide gives welding parameters, welding joint designs, machining, bending and forming data.