Project Description
Inconel 625, designated UNS N06625 (EN 2.4856 / NiCr22Mo9Nb), is a nickel-chromium-molybdenum solid-solution superalloy strengthened by niobium (3.15–4.15%) without precipitation-hardening heat treatment. Invented by Special Metals in 1964, it delivers exceptional corrosion resistance—PREN ~50—with 930 MPa tensile strength in Grade 1 annealed condition. For oil & gas operators, 625 is the benchmark CRA for H₂S/CO₂ sour service, subsea cladding, and deepwater NACE MR0175 / ISO 15156 Level VII environments. At SHUNFU METAL, every heat is produced via EAF + VOD followed by electroslag remelting (ESR) to suppress niobium segregation, with 100% positive material identification (PMI), ultrasonic testing (UT), eddy current, and hydrostatic test per order.
Equivalent Grades of Alloy 625 / N06625
| Alloy | UNS | EN / DIN | GB | JIS | ASTM Pipe | PREN |
|---|---|---|---|---|---|---|
| Alloy 625 | N06625 | 2.4856 | NS3306 | NCF 625 | B444/B705 | ~50 |
| Alloy C-276 | N10276 | 2.4819 | NS3304 | NW 0276 | B622 | ~74 |
| Alloy C-22 | N06022 | 2.4602 | NS3308 | — | B622 | ~65 |
| Alloy 825 | N08825 | 2.4858 | NS1402 | NCF 825 | B423 | ~32 |
| Inconel 718 | N07718 | 2.4668 | GH4169 | NCF 718 | B983 | ~28 |
| Alloy 59 | N06059 | 2.4605 | NS3311 | — | B622 | ~74 |
Oil & Gas Applications of Alloy 625 Pipe
Clad risers, jumpers, and flowline spools in deepwater H₂S + CO₂ + Cl⁻ fields per API 17D
Unbonded flexible riser pressure sheaths and carcass profiles for dynamic service in FPSO
Production tubing and liner hangers in high-H₂S gas wells, NACE Level VII per ISO 15156
Valve stems, seats, ring gaskets, and choke trim in 20K subsea wellheads exposed to aggressive brines
Hydraulic and chemical injection tubes in deepwater umbilicals, API 17E fatigue-qualified
Amine contactors, lean/rich exchangers, and reflux piping in gas-sweetening megaprojects
Internal cladding of carbon-steel flowlines and forgings by GTAW/GMAW overlay, 3 mm minimum per DNV-OS-F101
Offshore seawater caissons and firewater ring mains where crevice corrosion under biofouling demands high PREN
Methanol, MEG, and corrosion inhibitor injection lines, manifolds, and quill assemblies
Alloy 625 Pipe Supply Range at SHUNFU METAL
Seamless Pipe (ASTM B444 / ASME SB444): OD 4–219 mm, WT 0.5–20 mm, up to 70 ft length. Grade 1 annealed or Grade 2 solution-annealed. Cold pilger finish Ra ≤1.6 μm for clad-ready weld quality.
Welded Pipe (ASTM B705 / ASME SB705): OD 5–1219.2 mm, WT 0.5–20 mm, GTAW/PAW longitudinal seam with 100% radiography. EFW up to 1219.2 mm. Beveled, plain, or threaded ends.
Thick-wall & Hollow Bar: OD 10–600 mm, WT up to 150 mm. Custom machined trepanning from solid bar.
Capillary & Instrument Tube: OD 0.5–25.4 mm, WT 0.1–5 mm, coiled lengths up to 10,000 m.
Schedule: SCH 5S through SCH 160 & XXS. NACE MR0175 / ISO 15156-3 Level VII certified. API 6ACRA, DNV-OS-F101, PED 2014/68/EU, EN 10204 3.2.
Chemical Composition of N06625 per ASTM B444 / B705
| Element | Ni | Cr | Mo | Nb+Ta | Fe | C | Mn | Si | Ti | Al | P | S | Co |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Wt% | ≥58.0 | 20.0–23.0 | 8.0–10.0 | 3.15–4.15 | ≤5.0 | ≤0.10 | ≤0.50 | ≤0.50 | ≤0.40 | ≤0.40 | ≤0.015 | ≤0.015 | ≤1.0* |
*If determined. The 3.15–4.15% Nb+Ta is the alloy’s defining feature—niobium forms stable NbC carbides at grain boundaries during welding, suppressing chromium depletion and preserving intergranular corrosion resistance in as-welded condition. Molybdenum (8–10%) and chromium (20–23%) together deliver PREN ~50, resisting pitting in chloride concentrations exceeding 50,000 ppm. Niobium also contributes powerful solid-solution strengthening without age-hardening, so the alloy retains toughness from −196 °C to +980 °C. SHUNFU METAL verifies every heat by optical emission spectroscopy (OES), inductively coupled plasma analysis, and inert gas fusion for C/S/N.
Mechanical Properties of Alloy 625 Pipe
Grade 1 annealed (871–1037 °C): maximum strength. Grade 2 solution-annealed (1093–1204 °C): optimal creep resistance for elevated-temperature service. Cooling rate after annealing does not affect mechanical properties, making fabrication straightforward.
| Condition | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) | Hardness (HRB) |
|---|---|---|---|---|
| Grade 1 — Annealed | ≥827 (120 ksi) | ≥414 (60 ksi) | ≥30 | ≤95 |
| Grade 2 — Solution Annealed | ≥690 (100 ksi) | ≥276 (40 ksi) | ≥30 | ≤90 |
| Cold Pilgered (Optional) | up to 1200 | up to 1100 | ≥12 | 20–35 HRC |
Physical properties: Density 8.44 g/cm³ (0.305 lb/in³) | Melting range 1290–1350 °C | Modulus of elasticity 207 GPa (30.1×10³ ksi) | Thermal conductivity 9.8 W/m·K at 21 °C | Specific heat 410 J/kg·K | CTE 12.8 μm/m·°C (20–100 °C) | Permeability <1.002 (virtually non-magnetic). Low-temperature toughness: Charpy V-notch >60 J at −196 °C. Service range: −196 °C to +980 °C (oxidation limit). At 540 °C, yield strength retains ≥350 MPa. NORSOK M-DP-001 and API 17E fatigue-qualified for dynamic umbilical applications. SHUNFU METAL performs batch tensile testing at room temperature, hardness per ASTM E18/E92, ASTM E112 grain-size metallography, and ASTM G28 Method A intergranular corrosion verification on every heat lot.
