Incoloy Alloy 20
Incoloy Alloy 20 (UNS N08020, also known as Carpenter 20) is an iron-nickel-chromium-molybdenum-copper alloy (32–38% Ni, 19–21% Cr, 2.0–3.0% Mo, 3.0–4.0% Cu) specifically developed for maximum resistance to sulfuric acid across its full concentration range from dilute to concentrated. The combination of high nickel (for reducing-acid resistance), chromium (for oxidizing-acid resistance), molybdenum (for pitting resistance), and copper (for sulfuric acid passivation) produces a material that handles sulfuric acid service conditions that would rapidly corrode either standard austenitic stainless or lower-alloy nickel materials.
Alloy 20 is niobium-stabilized (Nb: 8× carbon minimum) to prevent sensitization in welded fabrications, making it suitable for corrosive service in the as-welded condition. This characteristic, combined with its lower cost relative to high-nickel alloys like Hastelloy C-276, makes Alloy 20 the standard specification material for sulfuric acid process equipment fabricated from welded plate and pipe.
Product Forms & Size Range of Incoloy Alloy 20
Alloy 20 bar and rod per ASTM B472 is available in diameters from 0.250 inch to 6.000 inches, solution annealed. Bar is used for machined valve bodies, pump impellers, flanges, and structural fasteners in sulfuric acid and mixed acid process systems. Forging quality stock is produced for large valve and pump body forgings.
Alloy 20 welded pipe per ASTM B464 is available in nominal pipe sizes from 0.5 inch to 12 inches for process piping systems handling sulfuric acid, phosphoric acid, and chloride-containing process streams. Pipe is furnished solution annealed and pickled to remove mill scale and ensure maximum corrosion resistance at weld seams.
Alloy 20 plate, sheet, and strip per ASTM B463 are available in thicknesses from 0.010 inch to 1.000 inch and widths up to 60 inches. Plate is the primary form for fabricated chemical process vessels, storage tanks, and heat exchanger shells in sulfuric acid service. All flat product is solution annealed.
HEAT TREATMENT OF INCOLOY ALLOY 20
Alloy 20 is solution annealed at 1725–1800°F (941–982°C) followed by rapid water or air quenching. Niobium stabilization prevents sensitization in the weld heat-affected zone, allowing the alloy to be used in the as-welded condition for most sulfuric acid service applications. Stress relief annealing at 1650°F (899°C) is recommended for heavily cold-worked parts or highly restrained weldments. The alloy is not precipitation hardenable.
Incoloy 825
Ni-Fe-Cr-Mo-Cu alloy with outstanding resistance to sulfuric and phosphoric acid as well as seawater — for the most demanding corrosion service.
Hastelloy N
Ni-Mo alloy with exceptional resistance to molten fluoride salts — used in advanced nuclear and chemical processing at extreme temperatures.
Certified Material for Critical Service
Incoloy Alloy 20 is supplied to ASTM B463 (plate, sheet, strip), ASTM B464 (welded pipe), and ASTM B472 (bar, rod, billet, and forgings). All forms are solution annealed with niobium stabilization. Certified mill test reports document composition including Nb/C ratio, mechanical properties, and heat treatment condition per applicable ASTM requirements.