GRADE PROFILE
Alloy 825 — N08825
Alloy 825 combines 38 to 46% nickel with chromium, molybdenum, 1.5 to 3% copper and titanium. The molybdenum-copper pairing gives it resistance to sulphuric and phosphoric acid; the nickel gives it practical immunity to chloride stress corrosion cracking. It is listed in NACE MR0175 for sour wells.
- Nickel alloy
- PREN 28–35 †
- Cost index 275
When to choose it
In sulphuric and phosphoric acid, in pickling and acid regeneration, in chemical processing and pollution control, on sulphurous flue gases and desulphurisation. And in sour oil and gas wells, where its NACE MR0175 qualification makes it a normative as much as a technical choice.
It also appears in nuclear fuel reprocessing and radioactive waste management, and it holds seawater — though cheaper grades exist for that.
When not to choose it
Above roughly 540 °C. Microstructural changes significantly reduce ductility and toughness; the alloy is not normally selected where creep governs design.
As a substitute for 316L on the basis of PREN equivalence. The logic of 825 is nickel and the molybdenum-copper pairing, not chromium-molybdenum alone: comparing PREN figures leads to a false conclusion in both directions.
On heavy sections slowly cooled after hot working without a stabilising anneal, because of the sensitisation risk.
Composition
| Element | % |
|---|---|
| Ni | 38–46 |
| Fe | ≥ 22 |
| Cr | 19.5–23.5 |
| Mo | 2.5–3.5 |
| Cu | 1.5–3 |
| Ti | 0.6–1.2 |
| C | ≤ 0.05 |
| Mn | ≤ 1 |
| S | ≤ 0.03 |
| Si | ≤ 0.5 |
| Al | ≤ 0.2 |
Mechanical properties
| Standard | Form | Rm (MPa) | Rp0.2 (MPa) | A (%) | Hardness |
|---|---|---|---|---|---|
| — | TUBE, état recuit | 772 | 441 | 36 | — |
| — | tube écroui (cold drawn) | 1000 | 889 | 15 | — |
Designations and standards
| Reference | Designation |
|---|---|
| EN (numeric) | 2.4858 |
| EN (symbolic) | — |
| ASTM / AISI | Alloy 825 |
| UNS | N08825 |
| JIS | — |
| AFNOR | — |
Tube product standards :
- ASTM B163
- ASTM B423
- ASTM B704
- ASTM B705
- ASME SB163
- ASME SB423
- ASME SB704
- ASME SB705
- DIN 17751
- ISO 6207
Availability
Available in welded and seamless tube to ASTM B163, B423, B704 and B705. Structured dimensional data for this grade is not yet documented in our reference set: send us your sizes. EN 10204 3.1 material certificates supplied with the goods.
Related grades
- 904L (1.4539) — the stainless route to the same acid problem, cheaper, with less nickel.
- Alloy 625 (2.4856) — the step above where high temperature is added.
- C-276 (N10276) — the most severe reducing acids.
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Frequently asked questions
- 825 or 904L for sulphuric acid?
- 904L covers moderate dilutions at appreciably lower cost. 825, with 38 to 46% nickel against 24 to 26%, holds conditions where 904L gives up — higher concentration, higher temperature, chlorides present.
- What does "listed in NACE MR0175" mean?
- That the alloy is among those the standard admits for oilfield environments containing hydrogen sulphide, subject to metallurgical condition and hardness limits. It is a frequent specification requirement in upstream oil and gas.
- Why is its PREN flagged as indicative?
- Because on an alloy with such high nickel content, resistance comes from a set of mechanisms PREN does not describe. The value is calculable and published for comparison, but it should not be the basis of a choice.