What Is a Seamless Incoloy 825 Tube?
Seamless Incoloy 825 Tube — UNS N08825 — is a nickel–iron–chromium alloy with molybdenum and copper additions (38.0–46.0% Ni, 19.5–23.5% Cr, 2.5–3.5% Mo, 1.5–3.0% Cu) produced to ASTM B163 from a solid billet with no weld seam.
The molybdenum supports pitting and crevice resistance, copper improves behavior in sulfuric and other reducing acids, and titanium stabilizes the alloy against intergranular attack after welding. With 38–46% nickel, 825 resists chloride stress-corrosion cracking and is qualified for sour service — a proven workhorse for acid plants, scrubbers and oilfield equipment. (Pipe sizes are covered by the companion specification ASTM B423.)
Size Range: OD 6–257 mm · WT 0.5–35 mm
Key Features and Advantages
Seamless UNS N08825 tube combines acid resistance, chloride SCC immunity and sour-service capability:
Outstanding Sulfuric and Phosphoric Acid Resistance: copper 1.5–3.0% plus molybdenum give exceptional performance in reducing acids across concentrations.
Pitting and Crevice Corrosion Resistance: 19.5–23.5% Cr with 2.5–3.5% Mo resists localized attack in chloride-bearing media.
Immune to Chloride Stress Corrosion Cracking: 38–46% nickel puts the alloy safely outside the SCC danger zone of austenitic stainless steels.
Intergranular Attack Resistance: titanium stabilization 0.6–1.2% maintains corrosion resistance in the sensitizing range and after welding.
Sour Oilfield Capability: widely applied under NACE MR0175/ISO 15156 in H2S-bearing production environments.
Product Specifications and Data
To provide a comprehensive overview of this high-performance material, here are the detailed technical specifications and performance data for UNS N08825 seamless tube.
Equivalent Grade
| UNS | Common grade name | EN material number | EN steel name | JIS grade | GB/T grade |
|---|---|---|---|---|---|
| N08825 | Incoloy 825 | 2.4858 | NiCr21Mo | NCF825 | NS1402 / NS142 (legacy) |
Grade correspondence does not make ASTM, ASME, EN, JIS and GB delivery requirements interchangeable. Confirm chemistry, heat treatment, mechanical properties, dimensions, testing and certification against the purchase specification. Approximate or unconfirmed correspondences retain their qualification. See the grade designation index.
Chemical Composition
the nickel–chromium–iron matrix with molybdenum and copper delivers the property mix.
| Grade | Ni | Cr | Fe | Cu | Mo | Ti | Al | Mn | C | Si | S | P |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UNS N08825 | 38.0–46.0 | 19.5–23.5 | 22.0 min | 1.5–3.0 | 2.5–3.5 | 0.6–1.2 | ≤0.20 | ≤1.00 | ≤0.05 | ≤0.50 | ≤0.030 | ≤0.030 |
Chemical requirements per ASTM B163-22, Table 1. Single values are maximum content unless a range or minimum is indicated. B163 does not specify a phosphorus limit for UNS N08825 (shown as –); iron is determined arithmetically by difference (22.0% minimum).
Typical Mechanical Properties
Values below are specification minimums for the delivery condition; they define the acceptance basis for UNS N08825 seamless tube.
| Condition | Tensile Strength, min, ksi (MPa) | Yield Strength, min, ksi (MPa) | Elongation in 2 in., min, % |
|---|---|---|---|
| Annealed | 85 (586) | 35 (241) | 30 |
Mechanical properties per ASTM B163-22, Table 3, annealed condition. B163 does not impose a hardness limit for annealed UNS N08825 tube.
Typical Physical Properties
These physical properties highlight the material’s ability to perform reliably across a range of environments.
| Density | Melting Range | Thermal Expansion | Thermal Conductivity | Modulus of Elasticity | Electrical Resistivity |
|---|---|---|---|---|---|
| 8.14 g/cm3 | 1370 – 1400 °C | 14.0 μm/m·°C (20–100°C) | 11.1 W/m·K | 195 GPa | 1.13 μΩ·m (20°C) |
Size Tolerance Chart (mm)
Permissible variations for seamless nickel alloy tube in accordance with ASTM B163-22, Table 4:
| Outside Diameter, mm | Permissible Variation in OD, mm | Average Wall, % | Minimum Wall |
|---|---|---|---|
| 12.7 to 15.9, excl | ±0.13 | ±12.5 | +25% / −0 |
| 15.9 to 38.1, incl | ±0.19 | ±10 | +20% / −0 |
| over 38.1 to 76.2, incl | ±0.25 | ±10 | +22% / −0 |
Notes (ASTM B163-22, Table 4): tolerances apply to individual measurements of outside diameter and include ovality. For thin-wall tube (nominal wall 3% or less of the OD), the mean OD shall comply with the table and individual measurements are increased by ½% of the nominal OD. Wall variation in any cross section (eccentricity) shall not exceed ±10% of the actual average wall. Wall variations apply to the wall as ordered (minimum or average), but not to both.
Length Tolerance
- When tube is ordered cut-to-length, the length shall not be less than that specified; a variation of +3.2 mm is permitted, and +6.4 mm for lengths over 9.1 m (30 ft) (ASTM B163-22, 7.2).
- Tube is normally supplied in mill lengths or specific cut lengths as agreed in the order.
Disclaimer: Dimensional data above are summarized from ASTM B163-22, Table 4. The full and most current specification document must always be consulted for official design and procurement purposes.
Common Industrial Applications
The combination of corrosion resistance, mechanical strength and manufacturing quality makes UNS N08825 seamless tube a preferred choice for:
Sulfuric and Phosphoric Acid Plants
Coolers, heaters and transfer tubing across the acid concentration range.
Sour Oil and Gas
Downhole and surface tubulars, valves and fittings in H2S/CO2 production service.
Pollution Control
Flue-gas desulfurization and scrubber components handling wet acid gases.
Nuclear Fuel Reprocessing and Seawater
Deep-sea and nuclear process equipment where reliability is paramount.
Frequently Asked Questions
What sizes are available for Incoloy 825 seamless tube?
Continuous supply covers OD 6–257 mm and WT 0.5–35 mm. Requirements outside this range are reviewed against mill capability on request.
Which specification governs Incoloy 825 seamless tube?
ASTM B163 applies to Incoloy 825 heat-exchanger tube (B163-26a limits outside diameter to 76.2 mm). Larger sizes are supplied to ASTM B423 / B829 or to tolerances agreed in the purchase order.
What inspection documents are provided?
Each order is documented with a mill test certificate stating heat chemistry and mechanical test results. EN 10204 3.1 certification, hydrostatic testing, eddy-current or ultrasonic inspection and PMI are performed when specified in the purchase order.
Technical review: page data reviewed by the Xinzhe technical desk on 2026-09-27. Property values are typical reference data compiled from Special Metals Corporation alloy data sheets and the governing ASTM specifications; they are not acceptance guarantees unless stated in the purchase order. “Incoloy” is a trademark of Special Metals Corporation, used here to identify the alloy family only.
Ready to Request a Quotation?
Send the NPS and schedule (or actual OD and wall), quantity, length, end finish and the inspection items you need as acceptance criteria — you will get a written quotation stating the specification and edition, delivery condition, documents included and lead time.
