Overview
AL6XN is a superaustenitic stainless steel with outstanding resistance to chloride pitting, crevice corrosion and stress corrosion cracking. It 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 demonstr ated to be resistant to a broad range of very corrosive environments. It is readily available from stock in a wide range of product forms, including thick plate that is suitable for multi-pass welding during field fabrication.
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 alter native to more expensive nickel-base alloys in applications where excellent formability, weldability, strength and corrosion resistance are essential. It is also a cost-effective alternative to less expensive alloys, such as Type 316, that do not have the strength or corrosion resistance required to minimize life cycle costs in certain applications.
The high nickel and molybdenum contents provide improved resistance to chloride stress-corrosion cracking. Copper (Cu) has been intentionally kept to a residual level for improved performance in seawater40. The high alloy composition of the AL-6XN alloy resists crevice corrosion and pitting in oxidizing chloride solutions to a degree previously achieved only by nickel-base alloys and titanium.
Specification
ASTM B462-18e1 Standard Specification for Forged or Rolled Nickel Alloy Pipe Flanges, Forged Fittings, and Valves and Parts for Corrosive High-Temperature Service
Chemical Composition
Ni | Cr | Mo | C | N | Mn | Si | P | S | Cu | Fe |
23.5-25.5 | 20.00-22.00 | 6.00-7.00 | 0.03 Max | 0.18-0.25 | 2.0 Max | 1.00 Max | .040 Max | 0.03 Max | 0.75 Max | Remainder |
Mechanical Properties
Temp. °F (°C) | Ult. Tensile Strength | .2% Yield Strength | Elongation in 2” | Charpy V-Notch Toughness |
-450 (-268) | 218,000 | 142,000 | 36 | 353* |
-320 (-196) | 196,000 | 107,000 | 49 | 85 |
-200 (-129) | - | - | - | 100 |
70 (21) | 108,000 | 53,000 | 47 | 140 |
200 (93) | 99,900 | 49,400 | 47 | - |
400 (204) | 903,000 | 40,400 | 46 | - |
600 (316) | 86,000 | 36,300 | 47 | - |
800 (427) | 87,000 | 36,000 | 48 | - |
Applications
1. Reverse osmosis desalination equipment and pumps
2. FGD Scrubbers
3. Chemical process tanks and pipelines
4. Seawater heat exchangers
5. Tall oil distillation columns and packing
6. Offshore oil and gas production equipment
7. Pulp bleaching plant washers, vats, press rolls and pipelines
Corrosion Resistance
The intrinsic corrosion resistance of the AL-6XN alloy in both acidic and alkaline environments provides protection against metallic contamination of process streams and prevents rapid degradation of components made of the alloy.
Cost Effectiveness
The AL-6XN alloy is often a viable alternative to nonmetallic materials that can provide high levels of corrosion resistance but are costly to install and maintain. AL-6XN alloy is significantly less costly than most nickel-base alloys.
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 demonstr ate comparable resistance to corrosion.
As-Welded Properties
The low carbon and high nitrogen contents in AL-6XN alloy minimize the precipitation of carbides and secondar y phases that can occur during welding. Therefore as-welded assemblies can be placed in service, provided that a suitable over-matched filler metal is used and the assembly has been properly cleaned. AL-6XN alloy can be welded in the field using procedures similar to those used with other austenitic stainless steels.
Wide Range of Product Forms
AL-6XN alloy is readily available in a wide range of product forms, such as tube, pipe, sheet, plate, bar, billet and forgings. Components such as pumps, valves, fittings, fasteners and castings are also available.
