Inconel 625 Buttweld Pipe Fittings
Inconel 625 / UNS N06625 / EN 2.4856 (NiCr22Mo9Nb) — 22Cr-9Mo-3.5Nb nickel superalloy for the most demanding subsea, sour gas, and seawater corrosion environments. PRE >50. Resistant to H₂S, chloride SCC, and crevice corrosion. Service from -196°C to 650°C. ASME B16.9 and EN 10253-2 Type B. EN 10204 3.1/3.2. PED 2014/68/EU.
½″–24″
Size Range
PRE >50
Pitting Index
760 MPa
Min UTS (Annealed)
-196°C to 650°C
Temp Range
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Inconel 625 Grade Equivalents
| Trade Name | UNS | EN W.Nr. | EN Name | ASTM (fittings) | ASME P-No. |
|---|---|---|---|---|---|
| Inconel 625 | N06625 | 2.4856 | NiCr22Mo9Nb | ASTM B366 / B564 UNS N06625 | 43 |
| Alloy 625 (generic) | N06625 | 2.4856 | NiCr22Mo9Nb | ASTM A403 UNS N06625 | 43 |
"Inconel 625" is a registered trademark of Special Metals Corporation. EN designation 2.4856 / NiCr22Mo9Nb. Covered by ASTM B366 for welded fittings and ASTM B564 for forgings.
Chemical Composition — UNS N06625 / EN 2.4856
| Element | Specification |
|---|---|
| Ni | ≥58.0% (balance) |
| Cr | 20.0–23.0% |
| Mo | 8.0–10.0% |
| Nb + Ta | 3.15–4.15% |
| Fe | ≤5.0% |
| C | ≤0.100% |
| Mn | ≤0.50% |
Niobium (Nb) solid-solution strengthens the matrix and prevents sensitization — carbon is tied up as stable NbC rather than as grain boundary Cr carbides. No PWHT required for most applications.
Mechanical Properties — Inconel 625 (Annealed)
| Min. UTS | Min. YS | Elongation | Hardness | Max Continuous Service |
|---|---|---|---|---|
| 760 MPa | 345 MPa | ≥30% | — | 650°C |
Work-hardened condition available — UTS up to 1380 MPa for wellhead / umbilical tubing applications, but annealed condition is standard for buttweld fittings.
Welding & Post-Weld Heat Treatment
No PWHT Required for Most Fabrications
Nb stabilisation prevents sensitization — carbon forms stable NbC rather than depleting Cr at grain boundaries. For severe corrosion service after welding, solution anneal at 1100–1180°C followed by rapid quench may be specified by the client or engineering authority.
Recommended Filler
ERNiCrMo-3 (AWS A5.14) — 625 matching filler for GTAW and GMAW. This is the designated matching filler for N06625 base metal.
Preheat
No preheat required. Nickel alloys do not suffer hydrogen cracking. Clean joint surfaces thoroughly to remove oils, grease and any sulphur-bearing compounds before welding.
Inter-pass Temperature
≤150°C maximum. Low heat input is preferred — use stringer beads, not weaving. Excessive heat input can promote precipitation hardening phases.
ASME P-Number
P-No. 43 (Ni and Ni-base alloys). Separate WPS required — cannot be qualified under austenitic SS P-8 procedures.
Alloy Selection Guide — Inconel 625 vs Alternatives
| Grade | PRE | Key Advantage | Typical Use |
|---|---|---|---|
| 316L / 1.4404 | ~24 | Cost | General chemical |
| Duplex 2205 / 1.4462 | ≥35 | Strength + cost | Offshore, desalination |
| Super Duplex 2507 / 1.4410 | ≥40 | Seawater | Subsea topsides |
| Inconel 625 / N06625 | >50 | H₂S + wide temp range | Sour gas, deep subsea |
| Hastelloy C-276 / N10276 | >50 | Reducing acids | Chemical HCl, H₂SO₄ |
Key Application Areas
Subsea Manifolds & Risers
PRE >50 and outstanding resistance to chloride SCC make 625 the preferred alloy for deep-water subsea structures where seawater exposure is continuous.
Sour Gas Injection
Resists H₂S-induced SSC (sulphide stress cracking) and HIC (hydrogen-induced cracking) meeting NACE MR0175 / ISO 15156 requirements.
Offshore Umbilicals
High strength (work-hardened) and excellent corrosion resistance for flexible and rigid umbilical lines carrying chemical injection and hydraulic control fluids.
Chemical Process — Oxidising Acids
Excellent resistance to nitric acid, phosphoric acid, and oxidising acids at elevated temperatures. Not preferred for pure HCl service — use Hastelloy C-276.
Cryogenic LNG Service
Ductility maintained to -196°C — impact properties remain acceptable at liquid nitrogen temperature. Used in LNG transfer and storage equipment.
High-Temperature Furnace & Reactor
Oxidation resistance and creep strength to 650°C for petrochemical and refinery service. Used in heat exchangers, reactor inlet/outlet piping, and fired heater components.
Available Fitting Types — Inconel 625 / UNS N06625
Sizes typically ½″–24″ for nickel alloys due to material cost and availability. Larger sizes available on enquiry with extended lead time.
Elbows — 90° & 45°
Long Radius (1.5D) and Short Radius (1D). ASME B16.9 / EN 10253-2 Type B. ½″–24″.
180° Return Bends
Long Radius. ASME B16.9. ½″–12″.
Equal & Reducing Tees
ASME B16.9 / EN 10253-2 Type B. ½″–24″.
Concentric & Eccentric Reducers
ASME B16.9 / EN 10253-2 Type B. ½″–24″.
Pipe Caps
ASME B16.9 / EN 10253-2 Type B. ½″–24″.
Lap Joint Stub Ends
ASME B16.9 Type A & B. ½″–16″. Paired with carbon steel loose flanges to reduce cost.
Crosses (4-Way)
ASME B16.9. ½″–8″.
Laterals (45° Y)
ASME B16.9. ½″–8″.
Flanges — All Types
Weld Neck, Slip-On, Blind, Socket Weld, RTJ. ASME B16.5. ASTM B564 UNS N06625. ½″–24″.
Frequently Asked Questions
What makes Inconel 625 suitable for subsea and sour gas service?
Inconel 625 (UNS N06625, EN 2.4856) has three properties that make it ideal for subsea and sour gas: (1) PRE >50 — exceptional pitting and crevice corrosion resistance in seawater; (2) very high resistance to hydrogen sulphide (H₂S) and chloride stress corrosion cracking; (3) good mechanical properties maintained at both cryogenic (-196°C) and elevated temperatures (up to 650°C). The niobium addition (3.5%) stabilises the alloy against sensitization. These properties make 625 the standard alloy for subsea manifolds, wellhead components, sour gas injection, and offshore umbilicals where super duplex (2507) is insufficient.
What is the difference between Inconel 625 and Hastelloy C-276 for pipe fittings?
Both are Ni-Cr-Mo superalloys but with different compositions. Inconel 625 (22Cr-9Mo-3.5Nb) has niobium for strengthening and is stronger at elevated temperatures; C-276 (16Cr-16Mo-4W, no Nb) has higher Mo and W, giving it superior resistance to reducing acids (HCl, H₂SO₄) and oxidizing media. 625 is the preference for seawater, sour gas and high-temperature oxidizing environments. C-276 is chosen for chemical plants with mixed acid service, especially hydrochloric acid. Both have PRE >50.
Ready to order Inconel 625 fittings?
Specify size, schedule, fitting type, standard (ASME B16.9 or EN 10253-2 Type B), and required MTR level (EN 10204 3.1 or 3.2 TPI). NACE MR0175 compliance documentation available on request.
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