UNS N09925 | Precipitation-Hardened | NACE MR0175 / ISO 15156 Compliant | Sour Gas & H₂S Service
Incoloy 925 (UNS N09925) is a precipitation-hardenable nickel-iron-chromium alloy containing molybdenum, copper, titanium, and aluminium, engineered specifically for service in aggressive oil and gas environments where resistance to both hydrogen sulphide (H₂S) stress cracking and chloride-induced stress corrosion cracking (SCC) is simultaneously required. Unlike solid-solution nickel alloys such as Incoloy 825, the age-hardening mechanism of Incoloy 925 — driven by the precipitation of Ni₃(Ti,Al) gamma-prime (γ') particles during a controlled two-stage ageing heat treatment — delivers tensile strengths exceeding 1000 MPa and yield strengths above 793 MPa while maintaining hardness below 35 HRC, satisfying the stringent requirements of NACE MR0175 / ISO 15156-3 for sour service. An Incoloy 925 blind flange is used to terminate or isolate a pipeline or pressure vessel nozzle in these demanding environments — from sub-sea wellhead christmas trees and high-pressure sour gas separators to downhole completion equipment — where no other flange material simultaneously meets the strength, corrosion resistance, and NACE compliance requirements.
Tesco Steel & Engineering manufactures Incoloy 925 blind flanges to ASME B16.5 (NPS ½″ to 24″, Class 150 to 2500), ASME B16.47 Series A & B (NPS 26″ to 60″), and DIN/EN flanges in PN 10 through PN 400 pressure ratings. Each blind flange is forged from ASTM B805 / AMS 5719 qualified Incoloy 925 billet stock, solution-annealed and precipitation-hardened (double-aged) in controlled furnaces, then CNC-machined to ASME dimensional tolerances. Face types include Raised Face (RF), Flat Face (FF), and Ring Type Joint (RTJ) with API BX or RX ring grooves for subsea applications. Full documentation — EN 10204 3.1 mill test reports, NACE MR0175 compliance certificates, hardness test reports (Rockwell C), and hydrostatic test certificates — is supplied standard. Tesco exports Incoloy 925 blind flanges to oil and gas operators, subsea system integrators, and EPC contractors in 96 countries.
| Parameter | Details |
|---|---|
| Alloy Designation | Incoloy 925 (proprietary name, Special Metals / Precision Castparts) |
| UNS Number | N09925 |
| Alloy Type | Precipitation-hardenable (age-hardened) nickel-iron-chromium alloy |
| Material Standard | ASTM B805 (forgings), ASTM B425 (rod & bar), AMS 5718 / AMS 5719 |
| Flange Standard | ASME B16.5, ASME B16.47 Series A & B, DIN 2573–2638, EN 1092-1 |
| Size Range | NPS ½″ to NPS 60″ (DN 15 to DN 1500) |
| Pressure Classes | ASME Class 150, 300, 600, 900, 1500, 2500 | DIN PN 10 to PN 400 |
| Face Types | Raised Face (RF), Flat Face (FF), Ring Type Joint (RTJ — API RX / BX grooves) |
| Heat Treatment | Solution annealed + precipitation hardened (double-aged: 940°C + 720°C) |
| NACE Compliance | NACE MR0175 / ISO 15156-3 — hardness ≤ 35 HRC (sour service certified) |
| Key Advantage | High strength + H₂S SCC resistance + chloride SCC resistance — all in one alloy |
| Testing | Hydrostatic, PMI, hardness (Rockwell C & Vickers), UT/MT/PT NDT |
| Documentation | EN 10204 3.1 MTR, NACE compliance cert, hardness test report, heat treatment records |
Incoloy 925 is a proprietary alloy designation originally developed by Special Metals Corporation (now part of Precision Castparts Corp.). It belongs to the nickel-iron-chromium-molybdenum family but is distinguished from alloys such as Incoloy 825 (UNS N08825) by the addition of titanium (Ti ~2.1%) and aluminium (Al ~0.3%), which enable precipitation (age) hardening.
During the two-stage ageing heat treatment — typically 940°C for 1 hour followed by 720°C for 8 hours — fine Ni₃(Ti,Al) gamma-prime particles precipitate coherently within the nickel-rich austenitic matrix, blocking dislocation movement and raising the yield strength from approximately 300 MPa (annealed) to over 793 MPa (aged). This combination of high mechanical strength with an ordered FCC crystal structure provides a unique immunity to sulphide stress cracking (SSC) — the primary failure mode in sour gas environments — which makes Incoloy 925 one of the few high-strength alloys that fully satisfies NACE MR0175 / ISO 15156-3 for use in H₂S-containing environments.
The chromium (19.5–22.5%), molybdenum (2.5–3.5%), and copper (1.5–3.0%) additions provide excellent resistance to pitting, crevice corrosion, and general corrosion in chloride brines, CO₂, and mixed sour/chloride environments typical of deep offshore and HPHT wells — making the alloy uniquely suited for wellhead flanges, christmas tree connectors, and subsea isolation valves.
| Element | Ni | Cr | Fe | Mo | Cu | Ti | Al | Mn | Si | C | S |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Wt% (per ASTM B805) | 38.0–46.0 | 19.5–22.5 | Balance (min ~22) | 2.50–3.50 | 1.50–3.00 | 1.90–2.40 | 0.10–0.50 | 1.00 max | 0.50 max | 0.030 max | 0.030 max |
Note: Titanium (Ti 1.90–2.40%) and Aluminium (Al 0.10–0.50%) are the precipitation-hardening agents in Incoloy 925 — these elements form Ni₃(Ti,Al) gamma-prime precipitates during ageing. They are essential to the alloy's NACE MR0175 qualification and distinguish 925 from the solid-solution Incoloy 825 (UNS N08825).
Incoloy 925 flanges are always supplied in the precipitation-hardened (aged) condition for sour service compliance. The annealed condition values are shown for reference only and do not meet NACE MR0175 requirements.
| Condition | Tensile Strength (MPa / ksi) | 0.2% Proof Stress / Yield (MPa / ksi) | Elongation % (min) | Hardness (max) | NACE MR0175 Compliant? |
|---|---|---|---|---|---|
| Precipitation Hardened (Aged) | ≥ 1000 MPa / ≥ 145 ksi | ≥ 793 MPa / ≥ 115 ksi | ≥ 15% | ≤ 35 HRC / ≤ 331 HV | Yes — per ISO 15156-3 |
| Annealed (Solution Treated only) | ~690 MPa / ~100 ksi | ~310 MPa / ~45 ksi | ≥ 30% | ~85 HRB | No — annealed condition not approved for H₂S service |
Important: Always verify that Incoloy 925 blind flanges supplied for sour service are in the precipitation-hardened condition. Request the hardness test report (Rockwell C, individual piece) as part of the inspection documentation — NACE MR0175 requires hardness ≤ 35 HRC per tested piece, not just per heat.
| Standard / System | Designation |
|---|---|
| Proprietary Name | Incoloy® 925 (Special Metals Corporation / Precision Castparts) |
| UNS (USA) | N09925 |
| ASTM (Forgings) | ASTM B805 — Ni-Fe-Cr-Mo-Cu-Ti-Al alloy forgings |
| ASTM (Bar / Rod) | ASTM B425 — Ni-Fe-Cr-Mo-Cu alloy rod and bar |
| AMS (Aerospace) | AMS 5718 (annealed), AMS 5719 (precipitation hardened) |
| W. Nr. / EN | 2.4858 (closest — Incoloy 825 / NiCr21Mo; note: 925 has no exact EN equivalent) |
| NACE / ISO | Approved under NACE MR0175 / ISO 15156-3 Table B.5 for sour service |
| API | Referenced in API 6A (Wellhead & Christmas Tree Equipment) for HPHT sour service flanges |
| Common Trade Names | Incoloy 925, Alloy 925, N09925 |
| Property | Incoloy 925 (N09925) | Incoloy 825 (N08825) | Inconel 625 (N06625) |
|---|---|---|---|
| Alloy Type | Precipitation-hardened Ni-Fe-Cr | Solid-solution Ni-Fe-Cr-Mo-Cu | Solid-solution Ni-Cr-Mo-Nb |
| Tensile Strength (aged/annealed) | ≥ 1000 MPa (aged) | ~690 MPa (annealed) | ~827 MPa (annealed) |
| Yield Strength | ≥ 793 MPa | ~310 MPa | ~414 MPa |
| Hardness | ≤ 35 HRC (NACE controlled) | ~85 HRB (~175 HB) | ~88 HRB (~190 HB) |
| NACE MR0175 / ISO 15156 Approval | Yes (precipitation hardened) | Yes (annealed only, limited H₂S) | Yes (annealed, high corrosion resistance) |
| H₂S Stress Cracking Resistance | Excellent (primary design driver) | Good (limited to lower severity) | Very good |
| Chloride SCC Resistance | Excellent | Excellent | Excellent |
| Pitting Resistance (PREN) | ~32–35 | ~32–35 | ~51 (superior) |
| Seawater / Marine Corrosion | Very good (Cu addition helps) | Very good (Cu addition) | Excellent |
| Relative Cost | High | Moderate–High | High–Very High |
| Primary Application | HPHT wellheads, sour gas flanges, downhole completions | Sour service (moderate HPHT), chemical plant | Subsea, CRA cladding, high-corrosion chemical service |
| Key Limitation | No exact EN equivalent; specialised heat treatment required | Lower strength — not suited to HPHT applications | Very high cost; lower yield strength than 925 aged |
| Parameter | Details |
|---|---|
| Size Range (NPS) | ½″ NB to 60″ NB (DN 15 to DN 1500) |
| ASME Classes | Class 150, 300, 600, 900, 1500, 2500 |
| DIN / EN Pressure Ratings | PN 10, PN 16, PN 25, PN 40, PN 64, PN 100, PN 160, PN 250, PN 320, PN 400 |
| Dimensional Standards | ASME B16.5 (NPS ½″–24″), ASME B16.47 Series A & B (NPS 26″–60″), DIN 2573–2638, EN 1092-1 |
| Face Types | Raised Face (RF), Flat Face (FF), Ring Type Joint (RTJ) — API RX or BX ring grooves for subsea |
| Material Standards | ASTM B805 (forgings), ASTM B425 (bar/rod), AMS 5718, AMS 5719 |
| Manufacturing Method | Open-die or closed-die forging from qualified billet; solution anneal + double-age heat treatment; CNC machining |
| Bore Options | Standard bore (as per ASME B16.5 Table E1.1) or custom bore to pipe schedule |
| Surface Finishes | Machined (standard), electropolished, passivated |
| Testing | Hydrostatic, PMI (Positive Material Identification), hardness (Rockwell C per piece), UT, MT, PT, IGC test |
| Third-Party Inspection | SGS, Bureau Veritas, Lloyd's Register, TÜV, DNV, Intertek available |
Incoloy 925 blind flanges are manufactured to ASME B16.5 dimensions. Select the pressure class for full dimensional data including OD, thickness, bolt circle, bolt holes, and raised face diameter:
| Pressure Class | Dimensional Standard | NPS Range | Approximate Rating (CS, ambient) |
|---|---|---|---|
| ASME / ANSI Class 150 Incoloy 925 Blind Flange | ASME B16.5 | ½″ to 24″ | ~285 psi (20 bar) at ambient |
| ASME / ANSI Class 300 Incoloy 925 Blind Flange | ASME B16.5 | ½″ to 24″ | ~740 psi (51 bar) at ambient |
| ASME / ANSI Class 600 Incoloy 925 Blind Flange | ASME B16.5 | ½″ to 24″ | ~1480 psi (102 bar) at ambient |
| ASME / ANSI Class 1500 Incoloy 925 Blind Flange | ASME B16.5 | ½″ to 24″ | ~3705 psi (255 bar) at ambient |
Class 2500 and DIN/EN PN-rated blind flanges available on request. Contact us with your NPS, pressure class, and face type for a quote.
| Standard | Scope |
|---|---|
| ASTM B805 | Ni-Fe-Cr-Mo-Cu-Ti-Al alloy forgings (covers UNS N09925 Incoloy 925 forged flanges) |
| ASTM B425 | Ni-Fe-Cr-Mo-Cu alloy rod and bar — billet source material for machined flanges |
| AMS 5718 | Incoloy 925 bar, forgings, and rings — annealed condition (aerospace specification) |
| AMS 5719 | Incoloy 925 bar, forgings, and rings — precipitation-hardened condition |
| ASME B16.5 | Pipe flanges and flanged fittings — NPS ½ through NPS 24, Class 150 to 2500 |
| ASME B16.47 | Large diameter steel flanges — NPS 26 through NPS 60 (Series A and Series B) |
| ASME B16.20 | Metallic gaskets for pipe flanges — ring-joint, spiral-wound, jacketed types |
| NACE MR0175 / ISO 15156-3 | Materials for use in H₂S-containing environments in oil and gas production — Part 3 covers CRAs (Corrosion Resistant Alloys). Incoloy 925 (N09925) is approved in precipitation-hardened condition under Table B.5 |
| API 6A | Wellhead and christmas tree equipment — specifies CRA flange requirements for HPHT sour service |
| API 6ACRA | Corrosion resistant alloys for use as wellhead and christmas tree equipment (references NACE MR0175 compliance) |
| EN 10204 Type 3.1 | Inspection and test documentation — mill test report issued by manufacturer's own laboratory |
| ISO 9001:2015 | Quality management system — Tesco's manufacturing QMS certification |
| Industry / System | Specific Application | Why Incoloy 925? |
|---|---|---|
| Oil & Gas — Wellhead Equipment | Christmas tree isolation valves, wellhead flange connectors, blind flanges on test ports and kill lines | NACE MR0175 compliance + high strength for HPHT wellhead pressures (up to 15,000 psi API 6A rating) |
| Sour Gas Processing | Blind flanges on sour gas separators, amine absorber nozzles, H₂S removal unit vessels | Resistant to sulphide stress cracking (SSC) in wet H₂S environments up to 10% H₂S partial pressure |
| Subsea Systems | Subsea tree connectors, pipeline end manifolds (PLEMs), subsea isolation blind flanges | High strength + seawater corrosion resistance + RTJ ring groove face type for metal-to-metal subsea sealing |
| HPHT (High-Pressure High-Temperature) Wells | Downhole completion equipment, tubing hanger flanges, production packer isolation | Retains strength and NACE compliance at temperatures up to 232°C (450°F) per ISO 15156-3 |
| Deep Offshore / Floating Production (FPSO) | Sour crude production manifolds, high-pressure riser flanges, CRA flange joints in corrosive service | Combined chloride SCC resistance + H₂S resistance — unique to precipitation-hardened alloys in this class |
| Gas Injection Systems | Sour gas reinjection headers, CO₂ injection blind flanges, downhole injection valves | Resists CO₂ corrosion and H₂S simultaneously; suitable for mixed sour/CO₂ environments |
| Chemical Processing | Blind flanges on vessels handling halide-containing acids, chlorinated solvents, reducing acids | Molybdenum (2.5–3.5%) and copper (1.5–3.0%) additions provide broad chemical corrosion resistance |
| Desalination Plants | High-pressure brine system blind flanges, pump isolation in seawater reverse osmosis systems | Excellent seawater and brine corrosion resistance; copper addition inhibits biofouling |
Incoloy 925 (UNS N09925) is a precipitation-hardenable nickel-iron-chromium alloy containing molybdenum (2.5–3.5%), copper (1.5–3.0%), titanium (1.9–2.4%), and aluminium (0.1–0.5%). The titanium and aluminium enable age hardening through the precipitation of Ni₃(Ti,Al) gamma-prime particles, raising yield strength to over 793 MPa while keeping hardness below 35 HRC — making it NACE MR0175 / ISO 15156-3 compliant for sour service. It is primarily specified for oil and gas wellhead flanges, christmas tree equipment, and downhole completions in H₂S-containing environments.
Yes. Incoloy 925 in the precipitation-hardened (aged) condition is approved under NACE MR0175 / ISO 15156-3, Table B.5 for use in H₂S-containing oil and gas environments. The key compliance requirement is that hardness must not exceed 35 HRC on any individual tested piece. The alloy must be in the aged (not annealed) condition — annealed Incoloy 925 does not meet NACE hardness requirements for SSC resistance at high strength levels. Always request per-piece hardness test reports when ordering Incoloy 925 blind flanges for sour service.
The fundamental difference is in strengthening mechanism and resulting mechanical properties. Incoloy 825 (UNS N08825) is a solid-solution alloy — it cannot be age hardened, and its maximum yield strength is approximately 310 MPa. Incoloy 925 (UNS N09925) contains titanium and aluminium which allow precipitation hardening to yield strengths above 793 MPa. As a result, Incoloy 925 is used for high-pressure, high-strength applications (HPHT wells, Class 900/1500/2500 flanges) while Incoloy 825 is suited to moderate-pressure corrosion-resistant applications. Both alloys are NACE MR0175 approved, but 925 is essential where high strength and sour service compliance must coexist.
Choose Incoloy 925 over Inconel 625 when your design requires both high mechanical strength and NACE MR0175 sour service compliance, particularly in HPHT applications (Class 900, 1500, or 2500 flanges at wellheads). Incoloy 925 in aged condition delivers yield strength of ≥793 MPa versus ~414 MPa for Inconel 625 annealed — a near-doubling of strength. However, choose Inconel 625 when maximum pitting resistance (PREN ~51 vs ~33 for 925) and crevice corrosion resistance in extremely aggressive chloride environments are the primary concern, or when the design temperature exceeds 232°C where 925's NACE approval has limits. Cost-wise, 925 and 625 are in a similar price range.
Incoloy 925 blind flanges for sour service must be in the double-aged precipitation-hardened condition. The standard heat treatment cycle is: (1) Solution anneal at approximately 980–1010°C, water quench; (2) First age at approximately 940°C for 1 hour, air cool; (3) Second age at approximately 720°C for 8 hours, air cool. This two-stage ageing cycle produces a uniform distribution of fine Ni₃(Ti,Al) gamma-prime precipitates that provides the combination of high strength (≥793 MPa yield) and controlled hardness (≤35 HRC) required for NACE compliance. Heat treatment records and hardness test reports must be included in the documentation package.
Subsea Incoloy 925 blind flanges are typically specified with Ring Type Joint (RTJ) face — either API RX or BX ring groove profiles for compact hub connectors, or ASME B16.20 R/RX/BX grooves for standard flanged connections. The RTJ face creates a metal-to-metal seal using a solid alloy ring gasket (typically Incoloy 825 or 625 ring) which is essential subsea because elastomeric gaskets can extrude under deep-water hydrostatic pressure, and the joint must maintain integrity over the well lifetime without the ability for easy re-torqueing. Raised face (RF) with spiral-wound gaskets is used for surface and topside Incoloy 925 blind flanges in most process systems.
The primary ASTM standard for Incoloy 925 forgings (including blind flanges) is ASTM B805 — "Standard Specification for Age-Hardenable Nickel-Iron-Chromium-Molybdenum-Columbium Alloy, and Nickel-Iron-Chromium-Molybdenum-Copper-Titanium-Aluminum Alloy Forgings." The material for bar-stock machined flanges is covered by ASTM B425. For aerospace-critical applications, AMS 5718 (annealed) and AMS 5719 (precipitation hardened) apply. The flange dimensions are per ASME B16.5 (up to NPS 24) or ASME B16.47 (NPS 26–60).
Yes, but with important precautions. Incoloy 925 is weldable using GTAW (TIG) or GMAW processes. The recommended filler metal is ERNiCrMo-3 (Inconel 625 filler) or ERNiCrCoMo-1 (Inconel 617), as there is no matching 925 filler wire available. Because blind flanges do not require a weld to pipe (they seal a pipe end), welding is typically limited to attaching boss connections, instrument nozzles, or test ports — these welds should be performed before final age hardening, or if post-weld ageing is not possible, the weld should be stress-relief annealed to ensure NACE compliance of the HAZ. Always consult NACE MR0175 / ISO 15156-3 and your welding engineer for sour-service weld procedure qualification.
Incoloy 925 blind flanges are not a stock item due to the specialised alloy, heat treatment, and testing requirements. Typical lead time from Tesco Steel & Engineering is 4–8 weeks for standard sizes (NPS ½″–8″, Class 600–1500) and 8–14 weeks for large bore (NPS 10″ and above) or high-pressure classes (Class 2500) depending on billet availability. For urgent orders, please provide full specifications including NACE compliance requirements at time of enquiry so we can source billet and schedule heat treatment capacity.
NACE MR0175 / ISO 15156-3 requires that every individual piece of CRA flange material used in sour service be hardness-tested and verified to ≤ 35 HRC — not just the heat or lot. Hardness testing by heat alone is insufficient because variations in section thickness, forging ratio, and heat treatment uniformity within a production batch can produce individual pieces with hardness above the limit, even if the average is compliant. Requesting per-piece Rockwell C hardness test reports is therefore essential to ensure the specific Incoloy 925 blind flanges you receive are individually NACE-qualified, not just statistically likely to comply.
The minimum documentation package for Incoloy 925 blind flanges supplied for NACE MR0175 / ISO 15156 compliant sour service should include: EN 10204 Type 3.1 mill test report (chemical composition and mechanical properties); heat treatment records (solution anneal + both ageing cycles with furnace temperatures and times); per-piece Rockwell C hardness test report (confirming ≤ 35 HRC); dimensional inspection report (confirming ASME B16.5 / B16.47 compliance); hydrostatic pressure test certificate; PMI (positive material identification) report by XRF; and NACE MR0175 / ISO 15156-3 compliance certificate. Third-party inspection reports from SGS, Bureau Veritas, or Lloyd's Register should be added for critical service applications.
Incoloy 925 blind flange pricing is driven by alloy content (high nickel, titanium, and molybdenum), forging or bar billet cost, and the specialised heat treatment and NACE testing requirements. Prices are quoted on request based on size, pressure class, quantity, face type, and documentation requirements.
To receive a competitive quotation, please share the following with your inquiry:
Global Export: Tesco Steel & Engineering exports Incoloy 925 Blind Flanges to 96 countries including the USA, UK, Germany, France, Netherlands, Norway, Italy, Saudi Arabia, UAE, Qatar, Kuwait, Oman, Bahrain, Iraq, Singapore, Malaysia, Thailand, Indonesia, Vietnam, South Korea, Japan, Australia, Canada, Brazil, Mexico, South Africa, Nigeria, Kenya, Egypt, Turkey, Kazakhstan, Russia, and across the EU, Middle East, Southeast Asia, Africa, and the Americas. All shipments include full NACE MR0175 compliance documentation, EN 10204 3.1 mill test reports, heat treatment records, per-piece hardness test reports, and dimensional inspection certificates.
