A Comprehensive Guide to Nickel-Based Superalloys: Incoloy 825 (UNS N08825/W.Nr. 2.4858)
What is Incoloy 825?
Designated as UNS N08825 or DIN W.Nr. 2.4858, Incoloy 825 (also known as "Alloy 825") is an iron-nickel-chromium alloy with additions of molybdenum, copper, and titanium. The addition of molybdenum improves its resistance to pitting corrosion in aqueous corrosive applications, while the copper content imparts its resistance to sulfuric acid. Titanium is added for stability. Alloy 825 has excellent resistance to localized attack by reducing and oxidizing acids, stress corrosion cracking, and pitting and crevice corrosion. It is particularly resistant to sulfuric and phosphoric acids. Incoloy 825 alloy is primarily used in chemical processing, petrochemical piping, pollution control equipment, oil and gas well piping, nuclear fuel reprocessing, and acid making and pickling equipment.
Characteristics of Incoloy 825 (UNS N08825/W.Nr. 2.4858):
(1) Good resistance to stress corrosion cracking.
(2) Good resistance to pitting and crevice corrosion.
(3) Good resistance to oxidation and non-oxidizing hot acid.
(4) Good mechanical properties at room temperature and high temperature below 550℃.
(5) Certified for pressure vessels with manufacturing temperature up to 450℃.
Role of each element in 825 alloy
Ni: The role of Ni is to improve the alloy's resistance to chloride stress corrosion cracking.
Role of chromium: Cr provides resistance to oxidizing environment.
Titanium: Adding 0.6%-1.2%Ti plays a stabilizing role.
Molybdenum: Adding 3% Mo can improve the ability to resist pitting in water corrosion applications.
Copper: Adding 1.5%-3.0% Cu makes the alloy resistant to sulfuric acid corrosion.
Application Field Nickel-based alloy incoloy 825 (UNS N08825/W.Nr. 2.4858)
Incoloy 825 alloy can be used in many corrosive environments, including the handling and storage of reducing acids such as sulfuric acid and phosphoric acid solutions. It can also be used in a variety of oxidizing environments, including nitric acid solutions, nitrites and oxidized salts. Incoloy 825 also has excellent seawater corrosion resistance.
(1) Chemical treatment:
Heat exchange tubes, pipe fittings, evaporators, flanges, pump pipes, valves, containers, expansion bellows, tankers, scrubbers, condensers, storage tanks and container linings; Processing and transportation of sulfuric acid, phosphoric acid, hydrochloric acid, nitric acid, nitrites and oxidized salts.
(2) Pulp and papermaking:
Wet scrubber linings in sodium sulfate and sodium bisulfite solution systems.
(3) Pickling treatment:
Acid tank heaters and hook clamps.
(4) Ore dressing: Plate heat exchangers in hydrometallurgy and copper refining.
(5) Pollution control: Feed bottoms and discs of electrostatic precipitators; Pipes and baffles, flue gas reheaters, waste heat circulation exchangers, chimney liners and other wet scrubber components; Residue incinerators, wet scrubbers; Marine inert gas scrubbers; Radioactive waste dryers.
