ASTM B443/B443M is the standard specification by ASTM International covering nickel-chromium-molybdenum-columbium alloy plate, sheet, and strip — universally known as Alloy 625 (Inconel 625, UNS N06625). With 20–23% Cr, 8–10% Mo, and 3.15–4.15% Nb, Alloy 625 delivers yield strength up to 414 MPa (60 ksi) in Grade 1 with outstanding corrosion resistance across a wide range of environments — from seawater and acids to high-temperature oxidation up to 980°C (1800°F). The companion specification ASME SB443 is adopted for ASME Code-stamped pressure equipment.

Zhengzhou Huitong (HT Pipe) supplies ASTM B443 / ASME SB443 compliant plate, sheet & strip with full Mill Test Certificates (MTC) per EN 10204 3.1. 

1. Standard Scope & Designation

ASTM B443/B443M covers nickel-chromium-molybdenum-columbium alloy (UNS N06625 — Alloy 625) plate, sheet, and strip in two grades: Grade 1 (annealed, high strength) and Grade 2 (solution-annealed, maximum corrosion resistance). Alloy 625 is a precipitation-hardenable Ni-Cr-Mo-Cb alloy delivering an exceptional combination of high strength, outstanding corrosion resistance, and excellent fabricability.

2. Grades Covered by ASTM B443

ASTM B443 covers the following grades. Each grade is defined by its UNS number and specific chemistry targeted at different service environments.

3. Chemical Composition

Values are weight percent maximum unless shown as a range. Heat analysis. Per ASTM B443 Table 1.

4. Mechanical Property Requirements

All values are minimum requirements. Tensile testing per ASTM E8/E8M.

5. Heat Treatment Requirements

6. Testing & Inspection Requirements

7. Dimensions & Dimensional Tolerances

ASTM B443 covers plate, sheet, and strip from 0.010 in (0.25 mm) to 4 in (100 mm). Alloy 625 plate is stocked in thicknesses 0.187–3.000 in (4.75–76 mm), widths 48–96 in (1220–2440 mm), and lengths up to 240 in (6100 mm). Sheet available 0.018–0.187 in (0.46–4.75 mm).

8. Industries & Applications

9. ASTM B443 vs ASTM B575 (Alloy C-276 — UNS N10276) — Comparison

10. Related Standards

11. How to Order — Required Information

12. Frequently Asked Questions

Q: What is the difference between ASTM B443 Grade 1 and Grade 2?

Grade 1 is annealed at ≥ 871°C (1600°F), leaving some niobium carbide/precipitate present for higher strength: YS ≥ 414 MPa (60 ksi), TS ≥ 827 MPa (120 ksi). Grade 2 is solution-annealed at ≥ 1093°C (2000°F), dissolving all precipitates for maximum ductility and corrosion resistance: YS ≥ 276 MPa (40 ksi), TS ≥ 690 MPa (100 ksi). Specify Grade 1 when high strength is required for structural or pressure-containing applications. Specify Grade 2 for maximum corrosion resistance, ease of fabrication (forming, bending), and applications where subsequent welding will be performed.

Q: Why is Alloy 625 so widely used in oil & gas sour service?

Alloy 625 (UNS N06625) combines exceptional resistance to H₂S (sulfide stress cracking), CO₂ corrosion, and chloride stress corrosion cracking — the three primary degradation mechanisms in sour oil & gas environments. Its PREN of 45–55 resists pitting in produced water with up to 200,000+ ppm chlorides, while its high nickel content (> 58%) ensures immunity to chloride SCC. NACE MR0175/ISO 15156 lists Alloy 625 as acceptable for the most severe sour service levels (Level VII). It is standard for wellhead components, downhole tubing hangers, subsea tree components, and corrosion-resistant alloy (CRA) clad pipe for sour gas wells.

Q: What is the maximum service temperature for ASTM B443 Alloy 625?

Alloy 625 maintains useful mechanical properties up to approximately 980°C (1800°F) due to solid-solution strengthening from Mo and precipitation strengthening from gamma-double-prime (Ni₃Nb). For corrosion-resistant service in oxidizing environments, the maximum recommended temperature is approximately 650°C (1200°F) — above this, chromium oxide film stability decreases. For purely structural (non-corrosive) high-temperature applications, Alloy 625 can be used to 980°C (1800°F) as per ASME B31.3 allowable stress tables. Cryogenic service is fully acceptable — Alloy 625 retains excellent toughness and ductility to −196°C (−320°F).

Q: Can Alloy 625 plate be welded and still maintain corrosion resistance?

Yes, with proper filler metal and procedures. Alloy 625 is highly weldable using GTAW (TIG), GMAW (MIG), SMAW, and SAW processes. Recommended filler: ERNiCrMo-3 (AWS A5.14 / ENiCrMo-3) — matching 625 composition. For Grade 1 base metal, the weld HAZ will naturally solution-anneal during welding, potentially reducing local strength (Grade 2 properties in HAZ). This is normally acceptable. For critical corrosion service, specify Grade 2 and use ERNiCrMo-3 filler with moderate heat input (≤ 1.5 kJ/mm) and interpass ≤ 150°C (300°F). Post-weld heat treatment is not required for corrosion resistance. The as-welded deposit retains excellent pitting and IGC resistance.

Q: When should I choose Alloy 625 over super-duplex stainless steel?

Choose Alloy 625 (B443) over super-duplex (UNS S32750/S32760) when: (1) service temperature exceeds ~250°C (480°F) — duplex embrittlement above 300°C; (2) sour service with H₂S partial pressure > 0.1 bar — super-duplex has limited NACE MR0175 acceptance; (3) chloride concentration and temperature exceed the CPT of super-duplex (~45–50°C for S32750, ~65°C for S32760); (4) oxidizing acid environments where duplex Mo is insufficient; (5) welding is extensive and PWHT is impractical. Choose super-duplex when cost is a stronger driver and service conditions are within its limits — it provides excellent chloride resistance at ~30–40% of Alloy 625 cost.

Request a Quote — ASTM B443 Alloy 625 / Inconel 625 (UNS N06625) Plate, Sheet & Strip

Zhengzhou Huitong (HT Pipe) supplies ASTM B443 / SB443 UNS N06625 Alloy 625 Grade 1 and Grade 2 plate, sheet, and strip for aerospace, oil & gas, and severe corrosive service. Full EN 10204 3.1 CMTRs with optional ASTM G28 corrosion testing. Competitive lead times from qualified nickel alloy mills.