Overview
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, cooper and titanium. The molybdenum addition improves its resistance to pitting corrosion in aqueous corrosion application while copper content bestows resistance to sulfuric acid. Titanium is added for stabilization. The Alloy 825 has excellent resistance to both reducing and oxidizing acids, to stress-corrosion cracking, and to localized attack such as pitting and crevice corrosion. It is especially resistant to sulfuric and phosphoric acids. Incoloy 825 alloy is mainly used for chemical processing, petrochemical piping, pollution-control equipment, oil and gas well piping, nuclear fuel reprocessing, acid production, and pickling equipment.
Corrosion Resistance
The outstanding property of Incoloy 825 is its corrosion resistance. In reducing & oxidising conditions, Incoloy 825 resists general corrosion, pitting & crevice corrosion, intergranular corrosion and stress corrosion cracking. It is particularly useful in sulphuric & phosphoric acids, sulphur containing flue gases, sour gas and oil wells and sea water.
Fabrication
Incoloy 825 can be readily hot or cold worked. Hot working should be in the range 870 – 1180°C, finishing at 870 – 980°C. For maximum corrosion resistance hot worked parts should be stabilise annealed before use. The alloy is easier to cold form than stainless steels.
Heat Treatment
Incoloy 825 is stabilise annealed at 940°C. The softest structure is obtained at 980°C. Sections heavier than sheet, strip and wire should be quenched to avoid sensitisation.
Chemical Composition of Incoloy Alloy 825
Element | % | Element | % |
Nickel | 38.0 – 46.0 | Carbon | 0.05 max |
Chromium | 19.5 – 23.5 | Manganese | 1.0 max |
Molybdenum | 2.5 – 3.5 | Sulfur | 0.03 max |
Copper | 1.5 – 3.0 | Silicon | 0.5 max |
Titanium | 0.6 – 1.2 | Aluminium | 0.2 max |
Iron | 22.0 min (~33%) |
Tensile Properties of Incoloy Alloy 825
Form | Condition | 0.2% Proof Stress | Tensile Strength | Elong |
Tube | Annealed | 440 | 770 | 35 |
Tube | Cold drawn | 880 | 1000 | 15 |
Bar | Annealed | 325 | 690 | 45 |
Plate | Annealed | 340 | 660 | 45 |
Sheet | Annealed | 420 | 760 | 39 |
ASTM Product Specifications
B163 | Seamless Nickel and Nickel Alloy Condenser and Heat-Exchanger Tubes |
B423 | Nickel-Iron-Chromium-Molybdenum-Copper Alloy (UNS N08825 and N08221)* Seamless Pipe and Tube |
B424 | Ni-Fe-Cr-Mo-Cu Alloy (UNS N08825 and UNS N08221)* Plate, Sheet, and Strip |
B425 | Ni-Fe-Cr-Mo-Cu Alloy (UNS N08825) |
B704 | Welded UNS N06625 and UNS N08825 Alloy Tubes |
B705 | Nickel-Alloy (UNS N06625 and N08825) Welded Pipe |
B751 | General Requirements for Nickel and Nickel Alloy Welded Tube |
Equivalent Grade Designations
Country | Body | Designation |
USA | UNS | N08825 |
France | AFNOR | NC 21 FeDU |
GB | BS | NA 16 |
Germany | DIN | NiCr21Mo |
Germany | Werkstoff | Nr 2.4858 |
Applications of Incoloy 825
1. Sulphuric acid piping and vessels
2. Phosphoric acid evaporators
3. Pickling tank heaters, pickling tanks and equipment
4. Chemical process equipment
5. Propellor shafts
6. Tank trucks
7. Calorifiers
8. Electrostatic precipitator electrodes
9. Hot vessels for food, water and seawater,
10. Ammonium sulphate vessels
11. Expansion bellows
12. Marine exhaust systems
13. Power station ash hoppers
