Inconel 825: properties, composition, uses and standards
Inconel 825 is a nickel–iron–chromium alloy with molybdenum, copper and titanium, chosen for sulphuric and phosphoric acid service, chloride stress-corrosion cracking and sour gas. UNS N08825, W.Nr 2.4858, PREN ≈ 31, density 8.14 g/cm³.
What is Inconel 825?
Inconel 825 is a nickel–iron–chromium alloy with molybdenum, copper and titanium. Engineers choose it for sulphuric and phosphoric acid service, chloride stress-corrosion cracking and sour gas. It is also known as Incoloy 825, Alloy 825, UNS N08825, W.Nr 2.4858.
- UNS
- N08825
- W.Nr
- 2.4858
- EN
- NiCr21Mo
- BS
- NA 16
- JIS
- NCF 825
- Trade names
- Incoloy 825 · Nicrofer 4221
- Density
- 8.14 g/cm³
- Melting range
- 1370 – 1400 °C
- Magnetic
- Non-magnetic (annealed)
- PREN (approx.)
- ≈ 31
Chemical composition and what each element does
| Element | Weight % |
|---|---|
| Nickel | 38.0 – 46.0 |
| Iron | 22.0 min |
| Chromium | 19.5 – 23.5 |
| Molybdenum | 2.5 – 3.5 |
| Copper | 1.5 – 3.0 |
| Titanium | 0.6 – 1.2 |
| Carbon | 0.05 max |
| Manganese | 1.0 max |
| Silicon | 0.5 max |
| Aluminium | 0.2 max |
| Sulphur | 0.03 max |
Per ASTM B424 / B423 / B564 for UNS N08825.
Around 40% nickel takes the alloy well clear of the range where austenitic stainless steels crack in hot chlorides.
Molybdenum and copper give 825 its standing in sulphuric and phosphoric acid service, and help against pitting.
About 21% chromium handles nitric acid, nitrates and oxidising salts.
Titanium stabilises the alloy, so welded parts resist sensitisation in the heat-affected zone.
Mechanical properties
| Property | Value |
|---|---|
| Tensile strength | 586 MPa · 85 ksi |
| Yield strength 0.2% | 241 MPa · 35 ksi |
| Elongation | 30% |
Annealed, minimum values. Values for pipe, bar and forgings differ slightly — see the product standard.
Where Inconel 825 is used
- Sulphuric & phosphoric acid plants. Tank linings, agitators, heat-exchanger baffles in fertiliser and acid production. Industry →
- Oil & gas, sour service. Separator internals, downhole tubulars and clad overlays where H₂S and chlorides combine. Industry →
- Pickling & metal finishing. Tanks, hooks and baskets for mixed-acid pickling lines. Industry →
- Brackish & chloride-bearing water. Chloride stress-corrosion resistance for coolers and pump parts in brackish and chloride-bearing cooling water. Industry →
- Pollution control. Flue-gas scrubber components and ductwork. Industry →
- Heat exchangers. Tube sheets, baffles and tubes to ASTM B163. Industry →
Welding 825
The matching filler is ERNiFeCr-1 (AWS A5.14). ERNiCrMo-3 wire · ENiCrMo-3 electrode.
Keep heat input moderate and interpass temperature low, clean joints thoroughly, and pickle or passivate after welding where the service is corrosive.
Inconel 825 compared with similar grades
| Grade | PREN | Choose it for |
|---|---|---|
| Inconel 825 | ≈ 31 | Sulphuric and phosphoric acid service, chloride stress-corrosion cracking and sour gas |
| SS 316 / 316L | ≈ 24 | Chloride-bearing process fluids, marine air and pharmaceutical service |
| SS 904L | ≈ 35 | Dilute sulphuric acid, phosphoric acid and chloride-bearing cooling water |
| Inconel 625 | ≈ 51 | Seawater, high strength and high temperature in one alloy |
Inconel 825 standards by product
Buying Inconel 825: what to specify
- The product standard and the UNS or designation — for example ASTM B424 UNS N08825.
- Size, thickness or schedule, and quantity in pieces and kg or metres.
- Heat-treatment condition where the standard offers a choice.
- Certificate: EN 10204 3.1 as standard, 3.2 if a third party must witness.
- NACE MR0175 / ISO 15156 compliance if the service contains H₂S.