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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.
Inconel 825
(UNS N08825)
A world-class technical reference for EPC contractors, process and oil & gas engineers, procurement heads, and TPI inspection agencies searching for “Inconel 825” — clarifying the correct trade name terminology for UNS N08825, and covering the alloy’s metallurgy, broad-spectrum acid resistance, sour service qualification, and the QC and documentation discipline required for critical chemical process and oil & gas production supply.
Alloy Metallurgy
& Selection Logic
“Inconel 825” is a widely used but technically incorrect market term — the alloy commonly searched for under this name is UNS N08825, correctly marketed under the trade name Incoloy® 825. This section clarifies the terminology before covering the alloy’s genuine engineering properties.
1.1 — Trade Name Clarification: “Inconel 825” vs. the Correct “Incoloy 825”
1.2 — What This Alloy Inconel 825 (UNS N08825) Is
UNS N08825 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. The molybdenum and copper additions are specifically engineered for aggressive aqueous acid and chloride-environment corrosion resistance — this is fundamentally a corrosion-resistant process alloy rather than a high-temperature structural superalloy, distinguishing its intended application from the genuine Inconel family (600/625/718), which are selected primarily for high- temperature strength, oxidation resistance, and aerospace/gas turbine structural applications.
1.3 — Key Engineering Properties
Broad-Spectrum Sulphuric Acid Resistance
The alloy’s most distinctive property — resistance to sulphuric acid across essentially the full range of concentrations and moderate elevated temperatures, a performance breadth achieved by few other single alloys, making it the standard, versatile choice for sulphuric acid production, handling, and pickling applications.
Chloride Pitting, Crevice, and SCC Resistance
The molybdenum and nickel content provide substantially improved resistance to chloride-induced pitting, crevice corrosion, and stress corrosion cracking compared to standard austenitic stainless steel, suitable for hot chloride-bearing environments where 304/316 stainless would be at meaningful risk.
Sour Service (NACE MR0175) Qualification
A widely used, well-documented material for sour (H₂S-containing) oil and gas production tubing, qualified under NACE MR0175/ISO 15156 — a standard corrosion-resistant alloy (CRA) specification for production tubing in sour well environments.
Titanium Stabilisation for Weldability
The controlled titanium addition prevents chromium carbide sensitisation during welding, allowing this alloy to be field-welded without mandatory post-weld solution annealing — a significant practical advantage for fabricated piping and equipment.
1.4 — If You Actually Need a True Inconel Alloy
If your application requires high-temperature strength, oxidation resistance above approximately 550–600°C, or gas turbine/aerospace- grade performance rather than aqueous acid/chloride corrosion resistance at low-to-moderate temperature, you may be looking for a genuine Inconel alloy rather than UNS N08825/Incoloy 825. RR Hydraulic can advise on and supply Inconel 600 (UNS N06600, general high-temperature corrosion and oxidation resistance), Inconel 625 (UNS N06625, exceptional combination of high-temperature strength and aqueous corrosion resistance including sour service), and Inconel 718 (UNS N07718, age-hardenable, the highest-strength common nickel superalloy for aerospace and high-stress applications) — contact our team to confirm the correct alloy for your specific service temperature, environment, and mechanical requirement before ordering.
Product Forms
& Composition Reference
UNS N08825 (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 UNS N08825 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 in this alloy.
ASTM B423 / ASME SB-423 — Seamless Pipe
Governs seamless 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
The specification family for tube product, including oil and gas production tubing applications, in seamless and welded forms respectively.
ASTM B564 — Forgings
Governs forged fittings and components — the specification for forged flanges, fittings, and valve bodies where forged (rather than bar-machined) construction is specified.
NACE MR0175 / ISO 15156
Provides the material qualification framework for sour service use of this alloy, including applicable hardness limits and heat treatment condition requirements.
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 Genuine Inconel Alloys and Other CRA Options
| Alloy | Trade Name Family | Nickel Content | Primary Selection Driver |
|---|---|---|---|
| N08825 | Incoloy (correct) | 38–46% | Broad-spectrum acid + chloride corrosion resistance at low-moderate temperature |
| N06600 | Inconel 600 (genuine) | ~72% | High-temperature oxidation/corrosion resistance |
| N06625 | Inconel 625 (genuine) | ~58% | Combined high-temperature strength + aqueous/sour corrosion resistance |
| N07718 | Inconel 718 (genuine) | ~53% | Age-hardenable maximum strength for aerospace/high-stress applications |
| N06022 (C-22) / N10276 (C-276) | Hastelloy (different family) | ~56–59% | Most aggressive reducing acids (HCl) and mixed acid environments |
Sulphuric Acid Performance
& Weld Practice
Correct heat treatment and welding practice are essential to realising this alloy’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
This alloy 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 applications; unlike a true age-hardenable Inconel alloy such as Inconel 718 (which relies on a precipitation-hardening heat treatment for its very high strength), this alloy is not further hardened or aged, since its intended engineering value is corrosion resistance rather than maximum achievable mechanical strength.
3.2 — Sulphuric Acid Corrosion Performance
This alloy’s sulphuric acid resistance is frequently illustrated using isocorrosion diagrams (Copson-type curves) plotting acid concentration against temperature. It 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 is the specific engineering value proposition making it the standard, versatile choice for sulphuric acid production, pickling, and general acid- handling process equipment.
3.3 — Weld Practice
Titanium Stabilisation Benefit
Titanium stabilisation allows this alloy 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.
Matching Filler Metal Selection
Welding consumables matched to the base alloy (ERNiFeCr-1 / ENiCrMo-3 type filler metals, depending on process) are used to maintain corrosion resistance and mechanical property matching in the weld deposit.
Cleanliness and Contamination Control
Strict cleanliness control (removing oils, grease, marking materials, and avoiding contact with carbon steel tools or grinding debris) before and during welding is essential to avoid weld defects and localized corrosion susceptibility.
Industry Applications
& Documentation
RR Hydraulic maintains full traceability from certified nickel alloy heat to finished, tested, and packed 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
Corrosion-resistant alloy (CRA) production tubing and downhole equipment for sour gas and oil wells, per NACE MR0175/ISO 15156 material qualification — a proven sour service track record and adequate mechanical strength make this alloy a standard specification wherever 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
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 across process equipment exposed to varying acid concentration and temperature.
Flue Gas Desulphurisation (FGD) and Pollution Control
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.
4.4 — Export Packaging Specification
- Tube and pipe ends capped and bore-protected to prevent contamination and moisture ingress during transit
- 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
- 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.