UNS N08367, commercially known as AL-6XN (a registered trademark of ATI Allegheny Ludlum) and also designated Incoloy 25-6HN, is a 6% molybdenum super-austenitic stainless steel engineered for seawater and chloride-dominated corrosive environments. With a PREN of approximately 47 — driven by high Cr 20–22%, Mo 6–7%, and N 0.18–0.25% — AL-6XN delivers superior resistance to chloride pitting, crevice corrosion, and stress corrosion cracking (SCC). Its high nickel content (24%) provides exceptional chloride SCC immunity, making it a preferred CRA for offshore seawater, FGD, and reverse osmosis desalination systems. At SHUNFU METAL, every heat of AL-6XN is produced via VIM + ESR dual refining and undergoes 100% PMI, ultrasonic testing (UT), eddy current inspection (ET), and hydrostatic pressure verification before dispatch.

AL-6XN / N08367 CRA Seamless Pipe
UNS designationN08367
Alloy family6% Mo super-austenitic
Primary standardASTM A312
PREN47

Equivalent Grades — AL-6XN / N08367

Grade UNS EN / W.Nr. GB ASTM Pipe Mo% PREN
AL-6XN N08367 (X1NiCrMoCuN25-20-6) — A312 / B690 6.0–7.0 ~47
254 SMO S31254 1.4547 015Cr20Ni18Mo6CuN A312 6.0–6.5 ~43
Alloy 926 N08926 1.4529 015Cr21Ni26Mo6Cu2N B677 6.0–7.0 ~46
904L N08904 1.4539 015Cr21Ni26Mo5Cu2 B677 4.0–5.0 ~36
Alloy 31 N08031 1.4562 NS1404 B622 6.0–7.0 ~48
Alloy 625 N06625 2.4856 NS3306 B444 8.0–10.0 ~50

Oil & Gas Applications — AL-6XN / N08367 CRA Pipe

Seawater Lift & Cooling Systems

Vertical seawater lift risers, cooling water return lines, and heat exchanger tube bundles on offshore platforms and FPSO units exposed to untreated, oxygenated seawater.

Reverse Osmosis Desalination

High-pressure RO feed manifolds, brine reject piping, and multi-stage flash (MSF) evaporator heat recovery sections in thermal and membrane desalination plants.

FGD Scrubber Systems

Absorber recirculation piping, mist eliminator wash lines, and slurry spray headers in coal and fuel-oil power plant FGD units handling hot acidic chloride condensate.

Offshore Topside Process Piping

Sea chest suction screens, overboard discharge lines, produced water treatment pipework, and open-drain caustic/chloride systems on FPSOs and fixed platforms.

Firewater & Ballast Water Systems

Firewater ring mains, deluge valves, jockey pump suction/discharge piping, and ballast water treatment (BWTS) filter and UV reactor housings on marine vessels and platforms.

Deepwater Riser & Umbilical Systems

Control line conduits, methanol injection tubing, and small-bore hydraulic umbilicals in subsea production systems demanding sustained PREN ≥ 43 under high external pressure.

Chemical Injection Distribution

Corrosion inhibitor, scale inhibitor, and oxygen scavenger injection quills and distribution manifolds in topside chemical delivery and subsea well annulus injection systems.

Refinery Tall Oil Distillation

Fractionation column internals, structured packing supports, and reboiler tube bundles in crude tall oil (CTO) distillation units processing acidic, high-chloride organic streams.

Sour Gas AGR Amine Systems

Intermediate-pressure amine contactor and regenerator piping, rich/lean amine exchanger tubes under NACE MR0175 Level I–IV where chloride SCC immunity is critical.

Pipe Supply Range — AL-6XN / N08367

Product Form Seamless Pipe, Welded Pipe (ERW / EFW), Capillary Tube, Heat-Exchanger Tube
OD Range (Seamless) 12.7 mm – 356 mm (1/2″ – 14″)
OD Range (Welded) 12.7 mm – 914 mm (1/2″ – 36″)
Wall Thickness 0.5 mm – 50 mm (SCH 5S – SCH XXS)
Tube OD & WT Seamless: 3.18–127 mm × 0.38–12.7 mm; Welded: 6.35–610 mm × 0.38–12.7 mm
Length Up to 12,192 mm (480″); Single Random, Double Random, Cut-to-Length
End Finish Plain End (PE), Bevel End (BE), Threaded
Surface Pickled & Passivated, Bright Annealed, Polished
Standards ASTM A312 / ASME SA312, ASTM A249, ASTM A269, ASTM B690, ASTM B676, ASTM A358, ASTM A409, ASTM A813, ASTM A814, ASTM B804
Certification EN 10204 3.1 / 3.2, PED 2014/68/EU, NACE MR0175 / ISO 15156, NORSOK M-DP-001

SHUNFU METAL stocks AL-6XN pipe in key diameters and schedules. Non-standard sizes, large OD welded pipe (up to 36″), and heavy-wall sections are manufactured to order. Every weld receives 100% radiography (RT) or UT per ASME B31.3, and all pipe is shipped with full mill test certification per EN 10204 3.1 or 3.2. NORSOK M-DP-001 qualification is available for Norwegian-sector offshore projects.

Chemical Composition — AL-6XN / N08367

Cr 20.00–22.00 Ni 23.50–25.50
Mo 6.00–7.00 N 0.18–0.25
Cu ≤0.75 Fe Bal.
C ≤0.030 Mn ≤2.00
Si ≤1.00 P ≤0.040
S ≤0.030

Composition per ASTM A240 / A312 / B688, UNS N08367. AL-6XN’s alloy design rests on three pillars: high nickel (24%) suppresses chloride SCC through elevated austenite stability; molybdenum (6–7%) raises the critical pitting temperature (CPT) and enables seawater service; and nitrogen (0.18–0.25%) provides solid-solution strengthening (~50% higher yield vs 316L) while delaying sigma-phase precipitation during fabrication. The 2.00% Mn maximum and low carbon (≤0.030%) preserve weld-zone corrosion resistance. Unlike some Ni-Cr-Mo grades, AL-6XN contains no tungsten — avoiding hot-workability constraints — and its copper content (≤0.75%) contributes secondary resistance in dilute sulphuric acid condensates. At SHUNFU METAL, all melt compositions are verified via optical emission spectroscopy (OES) and inert gas fusion nitrogen analysis before release to production.

Mechanical Properties — AL-6XN / N08367

Solution-annealed at ≥1110 °C (≥2025 °F) followed by rapid water quenching. Data per ASTM A312 / A240 at room temperature unless noted.

Tensile Strength, Rm ≥ 744 MPa (≥ 108 ksi)
Yield Strength, Rp0.2 ≥ 365 MPa (≥ 53 ksi)
Elongation (2 in / 50 mm) ≥ 44%
Hardness (Typical) ≤ 89 HRB (≤ 180 HBW)
Modulus of Elasticity ~200 GPa (29.0×10⁶ psi)
Density 8.06 g/cm³ (0.291 lb/in³)
Melting Range 1320–1400 °C (2408–2552 °F)
Thermal Conductivity ~12 W/m·K at 20 °C
Cryo Toughness −196 °C Charpy V-notch ≥ 85 ft·lb (115 J)

AL-6XN maintains exceptional cryogenic toughness: Charpy V-notch impact energy exceeds 85 ft·lb (115 J) at −196 °C and reaches 140 ft·lb (190 J) at room temperature — enabling use in LNG liquefaction cold-boxes and cryogenic process piping. At elevated temperatures, the ASME Section II Part D maximum allowable stress is 180.6 MPa at 93 °C and 124.6 MPa at 316 °C. SHUNFU METAL conducts furnace-chart-controlled solution annealing on every batch: soak temperature and duration are continuously logged, followed by rapid water quenching to suppress intermetallic precipitation. Per-heat-lot hardness testing confirms uniform grain structure per ASTM E112, and NACE-qualified heats undergo ASTM A262 Practice C (intergranular corrosion) and ASTM G48 Method C & D (critical pitting/crevice temperature) verification.

Welding is performed with matching-composition or over-alloyed nickel-base fillers (AWS ERNiCrMo-3 / ERNiCrMo-10). Post-weld heat treatment is not required due to the ultra-low carbon content and high nitrogen stabilization. Weld procedure qualification includes G48 Method C testing of weld metal, HAZ, and base metal per NACE MR0175 Level VI–VII requirements.

Service temperature range: −196 °C to +400 °C in chloride-bearing environments. Design codes: ASME B31.3 (Process Piping), ASME B31.1 (Power Piping), ASME Section VIII Div. 1 (Pressure Vessels). For subsea umbilical applications, material is qualified to NORSOK M-DP-001 and API 17E / 17I specifications.

Need AL-6XN / N08367 CRA to the specification above?

Send the size, condition, quantity and any NACE or PMI requirements — we reply with mill availability, lead time and a priced offer, usually within one working day.

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