Alloy 20 (UNS N08020) is a nickel-iron-chromium austenitic alloy developed for maximum resistance to acid attack, particularly sulfuric acid. This super alloy has a high resistance to corrosion, crevice corrosion and pitting in chemicals containing phosphoric, sulfuric and nitric acids. It also contains niobium for stabilization against sensitization and resultant intergranular corrosion.
Alloy 20 (UNS N08020) is a combination of high corrosion resistance with mechanical properties and easy fabrication. Although designed originally to be used in sulfuric acid related industries, Alloy 20 (UNS N08020) is now a popular choice for a range of industries that include food, pharmaceutical and plastics industries. Furthermore, this super alloy is used in mixing tanks, heat exchangers, metal cleaning and pickling equipment, and piping.
Chemical Composition, %
The chemical composition of Alloy 20 is:
| Ni | Fe | Cr | Cu | Mo | Nb | C | Mn | P | S | Si |
|---|---|---|---|---|---|---|---|---|---|---|
| 32.00-38.00 | Balance | 19.0-21.0 | 3.0-4.0 | 2.0-3.0 | 8xC-1.0 max | .07 max | 2.0 max | .045 max | .035 max | 1.0 max |
Forms of Alloy 20
Forms of Alloy 20 (UNS N08020) are:
- Sheet
- Alloy 20 Stud Bolts
- flanges
- Pipe & Tube (welded & seamless)
- Fittings (i.e. flanges, slip-ons, blinds, weld-necks, lap joints, long welding necks, socket welds, elbows, tees, stub-ends, returns, caps, crosses, reducers, and pipe nipples)
- Wire.
Properties of Alloy 20
The properties of alloy 20 (UNS N08020) are:
- High general corrosion resistance to sulfuric acid.
- Good resistance to chloride stress corrosion cracking.
- Excellent mechanical properties and fabricability.
- Minimal carbide precipitation during welding.
- Excels in resisting corrosion to hot sulfuric acids.
Mechanical Properties (Annealed Material)
The mechanical properties of Alloy 20 (UNS N08020) are:
| Form | Tensile Min. | Yield Min. (.2% offset) | Elongation Min. | Reduction of Area Min. |
|---|---|---|---|---|
| Bar (hot or cold finished) | 80 ksi | 35 ksi | 30% | 50% |
| Sheet/Plate | 80 ksi | 35 ksi | 30% | – |
ASTM Specifications
The ASTM specifications of Alloy 20 (UNS N08020) are:
| Pipe Smls | Pipe Welded | Tube Smls | Tube Welded | Sheet/Plate | Bar | Forging | Fitting |
|---|---|---|---|---|---|---|---|
| B729 | B464 | B729 | B468 | B463 | B473 | B462 | B366 |
Applications
The applications of alloy 20 (UNS N08020) include:
- Synthetic rubber manufacturing equipment.
- Processing of pharmaceuticals, plastics and organic and heavy chemicals.
- Alloy 20 Cap fitting.
- Petrochemical process equipment.
- Food and dye production.
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