Incoloy 925
Incoloy 925 (UNS N09925) is a precipitation-hardenable iron-nickel-chromium alloy with molybdenum, copper, titanium, and aluminum. It was developed to combine the aqueous corrosion resistance of Incoloy 825 with high strength from age hardening. This makes it the primary candidate for HPHT oil and gas components that need both corrosion resistance and structural load-bearing capacity.
1. Chemical Composition
The table below shows the elemental specification for Incoloy 925. Titanium and aluminum are the precipitation-hardening agents that separate it from the non-hardenable Incoloy 825.
| Grade | Standard | C | Mn | Si | S | Cr | Mo | Nb | Ti | AI | Ni | Fe | Cu |
| N09925 | B983 | =0.03 | =1.0 | =0.50 | =0.03 | 19.5-23.5 | 2.50-3.50 | =0.50 | 1.90-2.40 | 0.10-0.50 | 38.0-46.0 | =22 | 1.5-3.0 |
2. Mechanical Properties
The values below are for Incoloy 925 in the precipitation-hardened (aged) condition. This is the mandatory delivery condition for all oil and gas structural applications under NACE MR0175.
| Grade | Condition & Size | Standard | Tensile Strength , MPa (ksi) |
Yield Strength, MPa (ksi) |
Elongation , % |
Hardness Rc |
| N09925 | Solution Annealed+prec hard | B983 | =965(140) | =758(110) | =18 | =38 |
3. Equivalent Grade
The table below cross-references Incoloy 925 (UNS N09925) with international standard designations used in procurement and material qualification.
| GRADE | UNS | GB | JIS | ISO | DIN/EN | GOST | |
| ISC | NEW | ||||||
| Incoloy 925 | N09925 | GH169 | - | NCF925 | 9825 | 1.4883 | ??760 |
4. Key Technical Advantages
- Precipitation Hardening for High Structural Strength: Titanium (1.9–2.4%) and aluminum (0.1–0.5%) combine with nickel to form gamma-prime precipitates during aging heat treatment. This raises the yield strength to 827 MPa minimum while keeping the corrosion resistance of the Alloy 825 chemistry. Solution-annealed Alloy 825 cannot reach these strength levels.
- NACE MR0175 / ISO 15156 Compliance: Incoloy 925 is qualified under NACE MR0175/ISO 15156 Part 3 for H2S-containing oil and gas production environments as a corrosion-resistant alloy (CRA) at hardness values up to 40 HRC. It can operate at high partial pressures of H2S where high-strength low-alloy steels are prone to sulfide stress cracking.
- Resistance to Chloride Stress Corrosion Cracking: The high nickel content (42–46%) makes Incoloy 925 resistant to chloride-induced SCC at the strength levels needed for downhole pressure containment. Lower-nickel precipitation-hardened stainless steels such as 17-4PH and 15-5PH cannot match this performance.
Technical Note: Maximum service temperature for Incoloy 925 in aged condition is approximately 450°C. Above this temperature, gamma-prime over-aging occurs progressively, reducing yield strength. For HPHT applications above this threshold, Inconel 718 or 725 should be evaluated as the appropriate grade.
5. Common Manufacturing Standards
ASTM B983: Standard Specification for Precipitation Hardened or Cold Worked, Seamless Nickel Alloy Pipe and Tube
NACE / ISO Standards (Non-linked):
- NACE MR0175 / ISO 15156-3: Materials for use in H2S-containing environments in oil and gas production — qualification requirements for CRAs including N09925
- ISO 13680: Petroleum and natural gas industries — corrosion-resistant alloy (CRA) seamless tubes for use as casing, tubing, and coupling stock
JIS Standards:
- JIS H 4552: Nickel and nickel alloy seamless pipes and tubes
Summary Table — Standard Equivalents:
| ASTM | ISO | EN/DIN | JIS | NACE |
| ASTM B983 | ISO 13680 | - | JIS H 4552 | MR0175/ISO 15156 |
6. Primary Applications
- HPHT Downhole Tubing and Casing: Completion tubing and production casing in high-pressure, high-temperature sour gas wells. These environments demand simultaneous resistance to H2S, CO2, chlorides, and elemental sulfur, along with high yield strength for pressure containment.
- Subsurface Safety Valves (SSSSVs): Valve bodies, stems, and mandrels in downhole safety systems. These components need NACE-compliant high-strength CRA material that can handle both well fluid chemistry and mechanical cycling.
- Surface Wellhead and Christmas Tree Equipment: Valve bodies, flanges, and flow tees in corrosive produced fluids service, where both API 6A and NACE MR0175 qualification are required for material and dimensional standards.
- High-Pressure Umbilical and Control Line Tubing: Hydraulic control tubing for deepwater subsea trees and manifolds. Thin-wall, high-strength, corrosion-resistant tubing is needed to transmit hydraulic control pressure over long distances under seawater exposure.
- Gas Compression Station Piping: High-strength process piping and fittings in gas gathering and processing systems handling sour gas streams at elevated pressure. SCC resistance and mechanical strength both govern material selection in these applications.