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Certifications: EN 10204 3.1 / 3.2 material test certificates, NACE MR0175 / ISO 15156 compliance documentation, PMI verification, and complete export documentation packages.
Incoloy 825
(UNS N08825)
A world-class technical reference for EPC contractors, process and oil & gas engineers, procurement heads, and TPI inspection agencies specifying Incoloy 825 nickel-iron-chromium-molybdenum- copper alloy — covering alloy metallurgy, its distinctive broad- spectrum acid resistance, titanium stabilisation for weldability, sour service qualification, and the QC and documentation discipline required for critical chemical process and oil & gas production tubing supply.
Key Properties
& Selection Logic
Incoloy 825 (UNS N08825) is a nickel-iron-chromium alloy with added molybdenum, copper, and titanium — engineered specifically for broad-spectrum resistance to both reducing and oxidizing acids and for high resistance to chloride-induced pitting, crevice corrosion, and stress corrosion cracking, making it one of the most versatile corrosion-resistant alloys for aggressive aqueous chemical process and oil & gas production service.
1.1 — What Incoloy 825 (UNS N08825) Is and How It Differs from Incoloy 800
Incoloy 825 is a nickel-iron-chromium alloy with a nominal composition of approximately 38–46% nickel, 19.5–23.5% chromium, 2.5–3.5% molybdenum, 1.5–3.0% copper, and a controlled titanium addition (0.6–1.2%), with the balance comprising iron and minor elements. While Incoloy 825 shares the same base Ni-Fe-Cr family designation as Incoloy 800 (discussed in RR Hydraulic’s dedicated Incoloy 800 reference), the two alloys are engineered for fundamentally different service environments and are not interchangeable: Incoloy 800/800H/800HT is optimised for high- temperature oxidation, carburization, and elevated-temperature creep-rupture strength, while Incoloy 825’s added molybdenum and copper are specifically engineered for aggressive aqueous acid and chloride-environment corrosion resistance at low-to-moderate temperature — Incoloy 825 has comparatively modest high-temperature strength and is not specified for high-temperature furnace or reformer tube service where the 800 family is used.
1.2 — Key Engineering Properties
Broad-Spectrum Sulphuric Acid Resistance
Incoloy 825’s most distinctive and widely cited property — the alloy resists sulphuric acid across essentially the full range of concentrations and moderate elevated temperatures, a performance breadth that few other single alloys achieve (most corrosion-resistant alloys are optimised for either dilute or concentrated sulphuric acid, but not the full range). This makes Incoloy 825 the standard, versatile alloy choice for sulphuric acid production, handling, and pickling applications where the acid concentration may vary across the process.
Phosphoric Acid and General Mineral Acid Resistance
Good resistance to phosphoric acid and a broad range of other mineral and organic acids across varying concentrations and temperatures, extending the alloy’s versatility across the chemical process industry’s acid handling requirements beyond sulphuric acid alone.
Chloride Pitting, Crevice, and Stress Corrosion Cracking Resistance
The molybdenum and higher nickel content provide substantially improved resistance to chloride-induced pitting and crevice corrosion compared to standard austenitic stainless steel, and good resistance to chloride stress corrosion cracking even at elevated temperature — making the alloy suitable for hot chloride-bearing process environments where 304/316 stainless steel would be at meaningful SCC or pitting risk.
Sour Service (NACE MR0175) Qualification
Incoloy 825 is a widely used, well-documented material for sour (H₂S-containing) oil and gas production tubing and downhole equipment, qualified under NACE MR0175/ISO 15156 — the alloy’s combination of general corrosion resistance, sulfide stress cracking resistance, and adequate mechanical strength makes it a standard specification for corrosion-resistant alloy (CRA) production tubing in sour well environments where carbon steel’s corrosion rate would be unacceptable.
1.3 — The Role of Titanium Stabilisation
Incoloy 825’s controlled titanium addition (0.6–1.2%) serves the same fundamental metallurgical purpose as titanium stabilisation in stabilised austenitic stainless steel grades (321, 347, discussed conceptually in RR Hydraulic’s other material references) — titanium preferentially combines with carbon to form titanium carbides rather than allowing chromium carbides to precipitate at grain boundaries during welding or elevated-temperature exposure. This prevents sensitisation (localised chromium depletion at grain boundaries that would otherwise cause severe intergranular corrosion susceptibility in the heat-affected zone of welds), making Incoloy 825 a “stabilised” alloy that can be welded without the mandatory post-weld solution annealing that would otherwise be required to restore corrosion resistance in an unstabilised nickel alloy of similar base composition. This titanium stabilisation is a key practical advantage supporting Incoloy 825’s widespread use in field-welded piping and fabricated equipment applications.
Product Forms
& Composition Reference
Incoloy 825 is manufactured across tube, pipe, bar, and plate product forms, each governed by a specific ASTM/ASME standard. Full detail on related nickel alloys is available across our standards reference library.
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2.1 — Governing Standards
ASTM B424 / ASME SB-424 — Plate, Sheet, and Strip
Governs flat-rolled Incoloy 825 product — plate for pressure vessel fabrication, sheet and strip for general fabrication requiring the alloy’s corrosion performance.
ASTM B425 / ASME SB-425 — Rod and Bar
Governs rod and bar stock for machined components, forging billet, and fastener manufacture — the base material for Incoloy 825 bolting and machined fittings.
ASTM B423 / ASME SB-423 — Seamless Pipe
Governs seamless Incoloy 825 pipe for process piping applications — the primary specification for larger-diameter pipe in chemical process and oil & gas production piping systems.
ASTM B163 / B704 / B705 — Tube
B163 governs seamless tube for condenser and heat exchanger applications (shared specification with the Incoloy 800 family per RR Hydraulic’s dedicated reference); B704/B705 govern welded tube and welded tube with filler metal — the specification family for Incoloy 825 tubing, including oil and gas production tubing applications.
ASTM B564 — Forgings
Governs forged fittings and components in nickel alloys including Incoloy 825 — the specification for forged flanges, fittings, and valve bodies in this alloy where forged (rather than bar-machined) construction is specified for critical pressure-boundary components.
NACE MR0175 / ISO 15156
Provides the material qualification framework for sour service use of Incoloy 825, including any applicable hardness limits and heat treatment condition requirements — a mandatory reference for any Incoloy 825 supply into H₂S-containing oil and gas production service.
2.2 — Chemical Composition and Mechanical Properties
| Element / Property | Value / Range |
|---|---|
| Nickel | 38.0–46.0% |
| Chromium | 19.5–23.5% |
| Molybdenum | 2.5–3.5% |
| Copper | 1.5–3.0% |
| Titanium | 0.6–1.2% |
| Iron | Balance (~22–29%) |
| Tensile Strength | 550–620 MPa (typical, min. 585 MPa per spec) |
| Yield Strength | 240–290 MPa (typical, min. 240 MPa per spec) |
| Elongation | 30–45% |
2.3 — Comparison to Alternative Corrosion-Resistant Alloys
| Alloy | Key Alloying Additions | Best Suited For | Relative Cost |
|---|---|---|---|
| Incoloy 825 | Ni-Fe-Cr-Mo-Cu-Ti | Broad-spectrum sulphuric/phosphoric acid, chloride SCC/pitting, sour service | Moderate-high |
| Duplex 2205 (S31803) | Cr-Ni-Mo-N (duplex structure) | Chloride pitting/SCC at lower cost than nickel alloys; moderate acid resistance | Moderate |
| Hastelloy C-276 | Ni-Mo-Cr-W | Most aggressive reducing acids (HCl), wide range of oxidizing/reducing conditions | High |
| 316L Stainless Steel | Cr-Ni-Mo (austenitic) | General corrosion resistance, moderate chloride exposure — inadequate for aggressive acid or high-chloride SCC risk | Low |
Sulphuric Acid Performance
& Weld Practice
Correct heat treatment and welding practice are essential to realising Incoloy 825’s designed corrosion resistance — particularly its widely referenced broad-spectrum sulphuric acid performance, which depends on the alloy being in the correctly solution-annealed condition.
3.1 — Solution Annealing Heat Treatment
Incoloy 825 is supplied in the solution-annealed condition — heated to approximately 930–980°C and rapidly cooled (typically water quenched for tube and pipe) to dissolve carbides and other secondary phases into solid solution and retain the single-phase austenitic microstructure that provides the alloy’s designed corrosion resistance. This annealed condition is the standard, as-supplied condition for the vast majority of Incoloy 825 process and oil & gas applications — the alloy is generally not further hardened or aged, unlike some other nickel alloy families, since its intended engineering value is corrosion resistance and adequate (not maximum) strength rather than the highest achievable mechanical strength.
3.2 — Sulphuric Acid Corrosion Performance in Detail
Incoloy 825’s sulphuric acid resistance is frequently illustrated using isocorrosion diagrams (Copson-type curves) plotting acid concentration against temperature, with corrosion rate contour lines showing the boundary between acceptable (low corrosion rate) and unacceptable service conditions. Incoloy 825 demonstrates acceptable, low corrosion rates across an unusually broad combination of sulphuric acid concentration and temperature compared to most single-alloy alternatives — this breadth of performance, rather than the absolute best resistance at any single concentration/temperature point (which a more specialized, typically more expensive alloy might provide), is the specific engineering value proposition that makes Incoloy 825 the standard, versatile choice for sulphuric acid production, pickling, and general acid-handling process equipment where the acid concentration may vary or is not tightly controlled across the process.
3.3 — Weld Practice
Titanium Stabilisation Benefit
As discussed in Section 1.3, titanium stabilisation allows Incoloy 825 to be welded (typically GTAW/TIG for critical root passes, with GMAW or SMAW for fill passes on heavier sections) without mandatory post-weld solution annealing to restore corrosion resistance — a significant practical advantage for field-welded piping and fabricated equipment compared to unstabilised nickel alloys.
Matching Filler Metal Selection
Welding consumables matched to Incoloy 825 (ERNiFeCr-1 / ENiCrMo-3 type filler metals, depending on process) are used to maintain corrosion resistance and mechanical property matching in the weld deposit — using a mismatched or lower-alloy filler metal compromises the weld’s corrosion resistance even if the base metal itself is correctly specified.
Cleanliness and Contamination Control
As with other nickel alloys, strict cleanliness control (removing oils, grease, marking materials, and avoiding contact with carbon steel tools or grinding debris) before and during welding is essential — contamination, particularly sulphur- or low-melting-point-metal-bearing residues, can cause weld defects and localized corrosion susceptibility in the completed weld.
Industry Applications
& Documentation
RR Hydraulic maintains full traceability from certified nickel alloy heat to finished, tested, and packed Incoloy 825 component shipment. Chemical composition, mechanical, and NACE compliance verification are standard on all project-grade supply.
4.1 — Inspection & QC Protocol
4.2 — EN 10204 / Documentation Requirements
| Certificate | Content | EPC Requirement | When Mandatory |
|---|---|---|---|
| 2.1 / 2.2 | Declaration / non-specific | Not acceptable for critical process/sour service supply | Never for critical oil & gas or acid-handling equipment supply |
| 3.1 (EN 10204) | Heat-traceable chemical + mechanical test report | Mandatory — all EPC supply | All chemical process and oil & gas component supply |
| 3.2 (EN 10204) | 3.1 + TPI countersign | Critical / sour service / owner-specified critical items | Sour production tubing, high-consequence pressure equipment |
4.3 — Applications by Industry
Sour Oil and Gas Production Tubing
Incoloy 825 corrosion-resistant alloy (CRA) production tubing and downhole equipment for sour gas and oil wells, per NACE MR0175/ISO 15156 material qualification — the alloy’s proven sour service track record and adequate mechanical strength make it a standard specification for wells where carbon steel’s corrosion rate is unacceptable but the full cost of a higher-alloy or duplex solution is not warranted.
Sulphuric and Phosphoric Acid Process Equipment
Incoloy 825 tube, pipe, and vessel components for sulphuric acid production, concentration, and handling, and for phosphoric acid fertiliser production — leveraging the alloy’s specific broad-spectrum acid resistance advantage discussed in Section 3.2 across process equipment exposed to varying acid concentration and temperature.
Flue Gas Desulphurisation (FGD) and Pollution Control
Incoloy 825 components for FGD scrubber systems and other pollution control equipment exposed to hot, acidic, chloride-bearing flue gas condensate — a demanding combination of acid and chloride exposure at elevated temperature where the alloy’s combined acid and chloride resistance provides reliable long-term performance.
4.4 — Export Packaging Specification
- Tube and pipe ends capped and bore-protected to prevent contamination and moisture ingress during transit, particularly important given the alloy’s typical use in high-integrity process and oil & gas service
- Heat/lot number stamped or tagged on each item, cross-referenced to the accompanying material test certificate
- Components segregated from carbon steel and other dissimilar materials during packing to avoid surface contamination affecting the alloy’s corrosion performance, particularly critical for components destined for sour or chloride-critical service
- Documentation in a waterproof pocket: EN 10204 3.1/3.2 MTC, chemical composition report, mechanical properties report, PMI report, NACE MR0175 compliance declaration (where applicable), NDT reports, and packing list with form/size breakdown per item
- ISPM-15 timber or export cartons for international shipment, with country of origin and HS tariff code documentation matched to the nickel alloy product category
Submit your form, size, and quantity to RR Hydraulic for a complete, certified commercial offer.