ALLOY 20

ASTM A 265, B 366, B 463
B 464, B 471, B 472, B 473
B 474, B 475
UNS N08020
NACE MR0175

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. Thissuperalloy 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.

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.

In what forms is Alloy 20 Available?

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 
 

What are the 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, %

In what applications is Alloy 20 used?

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 Specifications

Mechanical Properties
Annealed Material

*Incoloy® is a registered trademark of Special Metals Corporation group of Companies.

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