ASTM B676 UNS N08367 Welded Pipe | AL-6XN Super Austenitic Stainless Steel Tube
In harsh working conditions coupled with high chloride ions, strong acidity and elevated temperatures, such as seawater desalination, offshore oil & gas, flue gas desulfurization (FGD) and fine chemical industries, conventional austenitic stainless steels like 316L and 904L often suffer premature failure due to pitting corrosion, crevice corrosion or stress corrosion cracking (SCC), while nickel-based alloys remain costly.
Manufactured to ASTM B676, UNS N08367 (commercial grade AL-6XN, 1.4547) welded pipe adopts a super austenitic stainless steel design with high molybdenum (6%), high nitrogen, chromium and nickel contents. It delivers an optimal balance of superior corrosion resistance and high mechanical strength at only 1/3 to 1/2 the cost of nickel-based alloys, making it the preferred cost-effective piping solution for highly corrosive service environments.
Core Material Characteristics of UNS N08367
UNS N08367 is a Ni-Cr-Mo-N super austenitic stainless steel with a stable single austenitic microstructure and no harmful intermetallic phases. Its key advantages include outstanding corrosion resistance, high strength and excellent low-temperature toughness.
| Element | C | Mn | Si | P | S | Cr | Ni | Mo | N | Cu | Fe |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Range | ≤0.03 | ≤2.00 | ≤1.00 | ≤0.04 | ≤0.03 | 20.0–22.0 | 23.5–25.5 | 6.0–7.0 | 0.18–0.25 | ≤0.75 | Balance |
Physical Properties
- • Density: 8.24 g/cm³
- • Melting Point: 1320–1400℃
- • Thermal Conductivity: ~15 W/(m·K)
- • Linear Expansion Coef: ~13×10⁻⁶ /℃
- • Modulus of Elasticity: ~200 GPa
Mechanical Properties (Solution Annealed)
- • Tensile Strength: ≥655 MPa
- • Yield Strength: ≥295 MPa (≈2x 316L)
- • Elongation: ≥30%
- • Low-temp Toughness: Excellent down to -196℃
Pitting Resistance & Corrosion Advantage
PREN = Cr+3.3Mo+16N ≈ 45–48, far higher than 316L (≈24) and close to nickel-based alloys. Superior resistance to pitting/crevice/SCC in high-chloride environments, dilute acids & alkaline media.
Overview of ASTM B676 Standard
ASTM B676-19 (Reapproved 2024) is the dedicated standard for UNS N08367 welded pipe. Size range: OD 1/8–5 in (3.2–127 mm), wall 0.015–0.320 in (0.38–8.13 mm).
Manufacturing
Base material: UNS N08367 plate. Automatic GTAW without filler. Solution annealing 1050–1150℃ + rapid cooling. Descaling & passivation.
Product Grades
Grade 1: 100% NDT (hydrostatic, eddy current). Grade 2: batch sampling NDT. Mandatory tests include chemical, tensile, flattening, intergranular corrosion test.
Welding Procedure & Filler Metal Selection
Challenges & Control
High Ni/Mo content → low thermal conductivity, high expansion → control heat input (10–15 kJ/cm), interpass ≤150°C. No preheat needed above 5°C. Shielding: ≥99.99% Ar + back purge.
Recommended Filler Metals
✔ Solid Wire: ERNiCrMo-3 (AWS A5.14) e.g., COR-MET 182
✔ Covered Electrode: ENiCrMo-3 (AWS A5.11) e.g., COR-MET 183
✔ Process: GTAW (primary), SMAW optional.
Typical Application Fields
Offshore & Marine
Seawater desalination, offshore platforms cooling, shipbuilding ballast systems.
Env. & Energy
Flue gas desulfurization, nuclear seawater cooling, waste-to-energy plants.
Chemical / Fine Chem
Chloride media evaporators, wet-process phosphoric acid, high-salinity wastewater.
Pulp, Paper & Food
Chlorine dioxide bleaching, food processing high-salinity piping.
Product Advantages Summary
Superior Corrosion
High Strength
Outstanding Toughness
High Cost Performance: Comparable to premium nickel-based alloys at much lower material cost, fully regulated under ASTM B676.
Conclusion
ASTM B676 UNS N08367 welded pipe, as a premium super austenitic stainless steel product, solves the dual pain points of premature failure of conventional stainless steels and high cost of nickel-based alloys in severe high-chloride corrosive environments. Widely applied in marine engineering, environmental energy and chemical industries, it delivers reliable long-term operation when paired with matched welding consumables and controlled welding procedures.
Related resources: Explore more about ASTM B676 stainless steel tube and UNS N08367 welded pipe for further technical specifications.