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Other common names: Carpenter 20, 20Cb-3®, Incoloy® alloy 20
Alloy 20, also known as Carpenter 20, is a nickel-iron-chromium austenitic alloy that was developed for maximum resistance to acid attack, specifically sulfuric acid. This supperalloy has excellent resistance to general corrosion, pitting, and crevice corrosion in chemicals containing chlorides and sulfuric, phosphoric, and nitric acids. It also contains niobium for stabilization against sensitization and resultant intergranular corrosion. Carpenter 20 combines excellent corrosion resistance with elevated mechanical properties and relatively easy fabrication. Although originally designed for use in sulfuric acid related industries, Alloy 20 is now a popular choice for a wide variety of industries including the chemical, food, pharmaceutical, and plastics industries. In addition, this superalloy is used in heat exchangers, mixing tanks, metal cleaning and pickling equipment, and piping.
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There has long been a debate on whether Carpenter 20 is a stainless steel or a nickel alloy because the nickel content is right on the border of defining it as one way or the other. So, depending on who you talk to this alloy may be referred to as alloy 20 Stainless Steel or as a nickel alloy. Either way it is still great for corrosion resistance.
Alloy 20 (20Cb-3) is an austenitic stainless steel which was designed for maximum resistance to acid attacks and as such has excellent resistance to hot sulfuric acid. Alloy 20 is also resistant to intergranular corrosion in the as-welded condition. At 33% nickel, Alloy 20 has practical immunity to chloride stress corrosion cracking. Alloy 20 is used is a wide variety of applications from Sulfuric acid pickling tanks, racks and heating coil, Heat Exchangers, Process piping, Chemical and petroleum process equipment etc.
Available forms is Alloy 20
- Sheet
- Plate
- Bar
- Pipe & Tube (welded & seamless)
- Fittings (i.e. flanges, slip-ons, blinds, weld-necks, lapjoints, long welding necks, socket welds, elbows, tees, stub-ends, returns, caps, crosses, reducers, and pipe nipples)
- Wire
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Alloy 20 Specifications
| Bar |
ASTM B 473 |
| Plate |
ASME SB-463, ASME SB-464, ASTM B 463, ASTM B 464 |
| Sheet |
ASME SB-463, ASME SB-464, ASTM B 463, ASTM B 464 |
| Strip |
ASME SB-463, ASME SB-464, ASTM B 463, ASTM B 464 |
| Wire |
ASME SB-473 ASME SB-366, ASTM B 473, ASTM B 366 |
| Weld Wire |
AWS ER320LR |
| Other |
UNS N08020, Covered Electrodes AWS E320LR |
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Characteristics of Alloy 20
 Excellent general corrosion resistance to sulfuric acid- Excellent resistance to chloride stress corrosion cracking
- Excellent mechanical properties and fabricability
- Minimal carbide precipitation during welding
- Excels in resisting corrosion to hot sulfuric acids
Chemical Composition, %
| Ni |
Fe |
Cr |
Cu |
Mo |
Nb |
| 32.00-38.00 |
Balance |
19.0-21.0 |
3.0-4.0 |
2.0-3.0 |
8xC-1.0max |
| C |
Mn |
P |
S |
Si |
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| .07max |
2.0max |
.045max |
.035max |
1.0max |
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Applications of Alloy 20
Synthetic rubber manufacturing equipment- Processing of pharmaceuticals, plastics and organic and heavy chemicals
- Tanks, piping, heat exchangers, pumps, valves, and other process equipment
- Acid cleaning and pickling equipment
- Chemical process piping, reactor vessels
- Bubble caps
- Petrochemical process equipment
- Food and dye production
ASTM Specification
| Pipe Smls |
Pipe Welded |
Tube Smls |
Tube Welded |
Sheet/Plate |
Bar |
Forging |
Fitting |
| B729 |
B464 |
B729 |
B468 |
B463 |
B473 |
B462 |
B366 |
Mechanical Properties
Annealed Material
| 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% |
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Steel Pipes & Tubes
ALLOY 20 PRODUCTS