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Alloy 20 (UNS N08020) Plate, Sheet and Strip
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Alloy 20, also known as Carpenter 20, is a nickel-iron-chromium austenitic alloy developed for sulphuric acid service. The copper addition, combined with molybdenum, gives it a resistance to reducing acids that plain nickel-chromium alloys do not match, while chromium retains oxidation resistance. This page covers the flat product form to ASME SB-463.
Specification Coverage
ASME SB-463 covers UNS N08020 plate, sheet and strip in the stabilised-annealed condition. General requirements and permissible variations follow ASME B906 through Annex A1 of SB-463; where a conflict arises, SB-463 takes precedence. Matching forms:
- SB-444 / SB-473 — seamless pipe and tube, and bar and wire
- SB-464 — welded pipe
- SB-366 — wrought fittings; N08020 is listed in Table 2
- SB-462 — forged flanges and forged fittings, which list N08020
- SA-182 — forged pipe flanges, which also list N08020
Grade Comparison
| Grade | UNS | Ni | Cr | Mo | Cu | Nb+Ta | Key Characteristic |
|---|---|---|---|---|---|---|---|
| Alloy 20 | N08020 | 32.00-38.00 | 19.00-21.00 | 2.00-3.00 | 3.00-4.00 | 8 × C – 1.00 | Cu-bearing, sulphuric acid |
| Alloy 825 | N08825 | 38.0-46.0 | 19.5-23.5 | 2.5-3.5 | 1.5-3.0 | — | Similar acid duty, higher Ni |
| Alloy 30 | N06030 | Ni-Fe-Cr-Mo-Cu | — | — | Cu-bearing | — | More copper, stronger reducing acid |
Alloy 825 carries more nickel (38-46% against 32-38%) and less copper (1.5-3.0% against 3.0-4.0%) than Alloy 20, so Alloy 20 suits strong reducing sulphuric acid, while Alloy 825 suits combined acid and chloride exposure.
Chemical Composition (ASME SB-463 Table 1)
| Element | UNS N08020 (%) | Limit Type |
|---|---|---|
| Carbon | 0.07 max | max |
| Manganese | 2.00 max | max |
| Phosphorus | 0.045 max | max |
| Sulfur | 0.035 max | max |
| Silicon | 1.00 max | max |
| Nickel | 32.00-38.00 | range |
| Chromium | 19.00-21.00 | range |
| Molybdenum | 2.00-3.00 | range |
| Copper | 3.00-4.00 | range |
| Columbium (Nb) + tantalum | 8 × carbon – 1.00 | range |
| Iron | remainder | by difference |
The columbium-plus-tantalum requirement is tied to carbon content at 8 times carbon with a 1.00% ceiling. This stabilising addition ties up carbon as niobium carbide and prevents intergranular corrosion in the weld heat affected zone.
Mechanical Properties (ASME SB-463 Table 2)
| Property | Requirement |
|---|---|
| Tensile strength, min | 80 ksi (551 MPa) |
| Yield strength (0.2% offset), min | 35 ksi (241 MPa) |
| Elongation in 2 in. (50.8 mm), min | 30.0% |
| Hardness, max | 217 Brinell or 95 Rockwell B |
Yield strength is determined by the offset method at 0.2% limiting permanent set per Test Methods B906. Elongation for material under 0.015 in. (0.38 mm) thick is 20% minimum in 1 in. (25.4 mm). Either Brinell or Rockwell B hardness is allowed.
Heat Treatment and Corrosion Testing
SB-463 paragraph 5.1 requires the stabilised-annealed condition, with a recommended annealing temperature of 1800 to 1850°F (982 to 1010°C). Supplementary requirement S1 provides for corrosion testing: one intergranular corrosion test per lot, on a sensitised specimen, per ASTM A262 Practices. When specified, the applicable practice (B or E) must also be named; if Practice B is specified the specimen must pass at under 0.002 in. per month.
Product Forms and Size Range
Plate, sheet and strip are supplied rolled, with thickness, width and weight tolerances governed by ASME B906 through Annex A1 of SB-463. Alloy 20 plate is used for acid storage tanks, agitator shells and absorption towers, as lining material or vessel shell.
Applications
- Sulphuric acid storage tanks, tank linings and absorption columns
- Dye and pigment manufacturing equipment
- Copper and brass pickling tanks and baskets
- Pharmaceutical and fine chemical vessels
- Resin and polymerisation equipment
- Food equipment where acid cleaning is severe
Certification and Inspection
Material is supplied with a mill test certificate per EN 10204 3.1 unless otherwise specified. Available inspection items include:
- Full chemical analysis and product (check) analysis on request
- Tensile testing with test reports, and hardness testing
- Intergranular corrosion testing to ASTM A262 Practice B or E where specified
- Positive material identification (PMI) verification
- Non-destructive examination including ultrasonic and eddy current testing
- Third-party inspection by an internationally recognised agency
Ordering Information
Please include the following when requesting a quotation:
- Alloy: UNS N08020 (Alloy 20 / Carpenter 20)
- Product form: plate, sheet or strip
- Thickness and width, and length if cut-to-length is required
- Quantity and delivery schedule
- Certification: MTC per EN 10204 3.1, and whether ASTM A262 intergranular corrosion testing is required
- Inspection and testing requirements
- Shipping terms and destination port
Tell us the grade, dimensions and the acid service involved, and we will confirm the material, availability and an FOB quotation.
Related specifications and products. Alloy 20 is also supplied as fittings and flanges and as bar and wire. See our nickel alloy plate and sheet range Alloy 20 fitting and flange range Alloy 20 bar and wire for the dimensional and material basis behind this page.
