Super Stainless Steel Alloy 20 (UNS N08020)
Alloy 20, often referred to as "Carpenter 20," is a columbium-stabilized austenitic material that blurs the line between stainless steel and nickel alloys. Specifically engineered for maximum resistance to acid attack, it contains a precise blend of nickel, chromium, and molybdenum, bolstered by a significant addition of Copper. This unique chemistry makes it exceptionally resistant to general corrosion, pitting, and crevice corrosion in environments containing chlorides and sulfuric acid.
At Aries Alloys, we supply Alloy 20 to industries where sulfuric acid concentrations are a constant challenge. It is the premier choice for replacing standard stainless steels that suffer from stress corrosion cracking or rapid thinning in acidic process streams.
Key Performance Benefits
- Sulfuric Acid Specialist: Designed to withstand boiling 20% to 40% sulfuric acid, as well as general resistance to phosphoric and nitric acids.
- Niobium Stabilization: The addition of Niobium (Columbium) prevents intergranular corrosion by ensuring that chromium carbide precipitation does not occur during welding.
- Immunity to SCC: The high nickel content (32-38%) provides excellent resistance to chloride-induced stress corrosion cracking.
- Pitting & Crevice Defense: Molybdenum and Chromium work in tandem to protect the surface in stagnant or chloride-rich environments.
- Ease of Fabrication: Despite its "Super Stainless" status, it can be easily welded and formed using standard industrial techniques, similar to 316L.
Technical Profile & Composition
The Role of Copper:
The inclusion of Copper (3-4%) is the defining characteristic of Alloy 20. Copper acts as a specialized inhibitor against the reducing nature of sulfuric acid, allowing the alloy to maintain a stable passive film where other metals would dissolve.
Mechanical & Physical Data:
- Density: 8.08 g/cm^3
- Tensile Strength: 80,000 psi (551 MPa)
- Non-Magnetic: Remains non-magnetic in all conditions.
- Thermal Expansion: Similar to standard austenitic steels, ensuring compatibility in mixed-metal systems.
Primary Industrial Use Cases
Aries Alloys is a strategic supplier of Alloy 20 for high-acid environments:
- Chemical Processing: Mixing tanks, heat exchangers, and process piping for the production of plastics, synthetic fibers, and explosives.
- Petrochemical Refineries: Equipment for alkylation units and acid-cleaning systems.
- Pharmaceutical Manufacturing: Reaction vessels used in the synthesis of organic and inorganic acids.
- Food & Dye Production: Equipment for handling spicy or acidic food products and aggressive coloring agents.
- Pickling Operations: Racks, baskets, and heating coils used in steel pickling lines involving sulfuric acid.
Product Availability at Aries Alloys
We stock and supply Super Stainless Steel Alloy 20 in accordance with ASTM B463, B729, and B473:
- Round & Hex Bars: Precision rods for machining acid-resistant pump shafts, bolts, and valve stems.
- Sheets & Plates: Durable flat products for the fabrication of acid tanks and pressure vessels.
- Seamless & Welded Pipes: High-integrity tubing for chemical transport and heat exchanger service.
- Forged Fittings: A full range of flanges, elbows, and tees designed for secure, leak-proof connectivity.