AL-6XN (UNS N08367) Super-Austenitic Stainless Steel: Instrumentation Fittings, Valves & Tubing
AL-6XN is a super-austenitic stainless steel with 6% molybdenum and nitrogen added, designated UNS N08367. It's built to resist chloride pitting, crevice corrosion and stress-corrosion cracking in seawater and other high-chloride service. Crestflo supplies the grade as instrumentation tube and compression fittings, instrumentation valves, and instrumentation tubing. Every piece carries heat and lot-number traceability, and each is engineered as a drop-in replacement for the majors. Delivery runs 6-8 weeks, serving customers across the US.
The composition, PREN, mechanical and corrosion figures listed below reflect standard published data for the alloy, taken from the applicable ASTM specification. They can be tailored to your requirements.
AL-6XN is a super-austenitic stainless steel, UNS N08367, used for fluid-system tube fittings, compression ferrules and instrumentation valves. It isn't a 6-series aluminum grade, not 6061 or 6XXX aluminum. Nor is it a nickel-base alloy. Crestflo offers this alloy only in instrumentation fitting, valve and tubing forms, not mill bar, sheet, plate or pipe.
Request an AL-6XN Quote · Request a Sample · sales@crestflousa.com · +1 346 594 9005 (Houston, TX)
AL-6XN® and AL-6XN PLUS® are registered trademarks belonging to ATI Properties LLC. Crestflo has no affiliation with ATI. The company builds its components in the UNS N08367 super-austenitic grade, made to the AL-6XN® specification.
AL-6XN Also Known As: UNS N08367, 6-Moly Super-Austenitic & Alloy N08367
Drawings, datasheets and purchase orders don't always agree on what to call this alloy. A print might list "AL6XN," "6-moly stainless," "N08367 alloy," or "super-austenitic stainless steel." All four point to the same grade: an iron-nickel-chromium-molybdenum super-austenitic steel.
| Designation type | Value |
|---|---|
| Trade / common names | AL-6XN, AL6XN, AL 6XN, AL-6XN PLUS, 6XN |
| UNS number | UNS N08367 (N08367) |
| Colloquial class names | 6-moly stainless, 6% molybdenum stainless, super-austenitic stainless steel, nitrogen-bearing austenitic stainless |
| Nearest EN grade (related, not identical) | 6-molybdenum super-austenitic family; EN 1.4529 (UNS N08926) is the closest 6Mo grade, not an exact equivalent |
| Alloy family | Super-austenitic (6% Mo) stainless steel, low-carbon, nitrogen-alloyed |
| Spaced / reversed forms | Alloy AL-6XN, N08367 AL-6XN, 6XN alloy, AL-6XN stainless steel |
UNS N08367 is the trademark-free designation anchoring AL-6XN, so a part specified either way names the same super-austenitic stainless steel. No European Werkstoff number matches it exactly. The closest 6Mo grade, EN 1.4529 (N08926), is a related alloy, but a distinct one, don't treat it as equivalent.
AL-6XN Chemical Composition & PREN (Super-Austenitic, per ASTM)
AL-6XN owes its corrosion performance to three things working in tandem: roughly 6.3% molybdenum, about 24% nickel, and a deliberate nitrogen addition set into an austenitic matrix. Nitrogen doesn't just do one job here. It sharpens pitting resistance and stabilizes the austenite at the same time. Low carbon content, meanwhile, keeps that resistance intact both in welds and in the metal right around them.
| Element | wt % (per ASTM B688) |
|---|---|
| Chromium (Cr) | 20.0–22.0 |
| Nickel (Ni) | 23.5–25.5 |
| Molybdenum (Mo) | 6.0–7.0 |
| Nitrogen (N) | 0.18–0.25 |
| Copper (Cu) | 0.75 max |
| Manganese (Mn) | 2.00 max |
| Silicon (Si) | 1.00 max |
| Carbon (C) | 0.030 max |
| Phosphorus (P) | 0.040 max |
| Sulfur (S) | 0.030 max |
| Iron (Fe) | Balance |
The pitting resistance equivalent number (PREN) is calculated as Cr + 3.3 × Mo + 16 × N from nominal composition, and it lands around 45 (typically 45, 47). That's well above 316/316L (~25) and 904L (~34), putting AL-6XN in the 6-molybdenum class alongside 254 SMO. Keep in mind that PREN is only a calculated ranking index; how an alloy actually performs depends on full chemistry, temperature and condition. Ranges follow the applicable ASTM product-form specification, and Crestflo confirms the actual heat chemistry on the EN 10204 material test certificate supplied with every order. For a cross-alloy view, see the PREN comparison table.
AL-6XN Mechanical & Physical Properties
Solution-annealed, AL-6XN delivers strength well above what you'd get from conventional 300-series stainless, yet it keeps the ductility and toughness that fitting and valve forming demand. The figures listed below are the alloy's standard published minimums and nominal physical properties.
Mechanical properties (solution-annealed, room temperature)
| Property | Value (per ASTM B688) |
|---|---|
| Tensile strength | ≥ 100 ksi (690 MPa) |
| Yield strength (0.2% offset) | ≥ 45 ksi (310 MPa) |
| Elongation | ≥ 30% |
| Hardness | ≤ ~241 HB (~100 HRB), annealed |
Physical properties
| Property | Value |
|---|---|
| Density | 8.06 g/cm³ (0.291 lb/in³) |
| Melting range | ~1320–1400 °C (2410–2550 °F) |
| Thermal conductivity | ~11.5 W/m·K at room temperature |
| Modulus of elasticity | ~195 GPa (28.3 × 10⁶ psi) |
| Magnetic response | Essentially non-magnetic in the annealed condition (relative permeability ~1.0) |
| Structure | Austenitic (face-centered cubic) |
Mechanical minimums follow ASTM B688 for the annealed condition. Final certified properties for a given heat are stated on the material test certificate, and they can be customized to requirement.
AL-6XN Corrosion Resistance by Media: Seawater, Chlorides & SCC
Engineers developed AL-6XN specifically for seawater exposure. Its high molybdenum content, paired with nitrogen, resists chloride pitting, crevice corrosion and chloride stress-corrosion cracking in saltwater and brine service far beyond what 316L and 904L can handle. Those are the failure modes that limit conventional stainless steel. The table below lays out typical service suitability; it's drawn from standard alloy corrosion literature.
| Media / service | Suitability | Note |
|---|---|---|
| Seawater / brackish water | Excellent | The alloy's founding application, resists chloride pitting and crevice attack |
| High-chloride process brines | Excellent | Critical pitting temperature well above 316/904L (ASTM G48 CPT typically >45 °C) |
| Crevice corrosion (CCT) | Very good | Superior to 316L/904L; sits in the 6-moly class |
| Chloride stress-corrosion cracking (SCC) | Highly resistant | High nickel + nitrogen resist Cl-SCC that cracks 300-series stainless |
| Flue-gas desulfurization (FGD) | Excellent | Scrubber and absorber environments |
| Dilute sulfuric & phosphoric acids | Good | Handles many mid-strength acid streams |
| Sour service (H₂S-containing) | Conditional | Accepted per NACE MR0175 / ISO 15156 within applicable limits |
For material selection tied to a specific process, check the corrosion-by-media × alloy matrix. Pair it with the offshore chloride selection guide for the full picture.
AL-6XN for Sour Service (NACE MR0175 / ISO 15156)
Crestflo offers AL-6XN fitting and valve material that meets NACE MR0175 / ISO 15156 requirements. UNS N08367, a nitrogen-bearing austenitic corrosion-resistant alloy, sees use in sour (H₂S-containing) production and processing environments. It can meet NACE MR0175 / ISO 15156 for applicable conditions. Check the hardness, temperature and material-condition limits in the standard before applying it to your specific case, don't assume compliance carries over automatically.
For more detail, see the NACE MR0175 and ISO 15156 standard pages, plus the sour-service selection guide.
AL-6XN Weldability & Fabrication
AL-6XN welds well. Fabricators typically use an over-alloyed nickel-base filler, something in the 625 or C-276 family, to offset molybdenum segregation and keep corrosion resistance intact across the weld; after heavy forming, a full solution anneal brings the properties back. Machining is a different story: the alloy work-hardens fast and cuts much like other high-molybdenum super-austenitics, calling for slower speeds, sharp positive-rake tooling, heavy positive feeds, rigid setups, and flood coolant. That's why it turns up so often in instrumentation tube fittings, welded tubing, and valve bodies. Welding procedures and filler choice aren't fixed, though; both get matched to the product form and the service conditions, order by order.
AL-6XN Product-Form Standards (ASTM B688, B675, B676, B690 & B691)
Crestflo covers the alloy under a family of ASTM specifications, one per product form, each paired with a matching ASME SB- designation. These define the grade. Crestflo itself supplies only instrumentation forms built to those specs, certified material in fittings, valves, and tubing. Mill sheet, plate, bar, pipe: none of that is part of the offering.
| Product form | ASTM | ASME equivalent |
|---|---|---|
| Plate, sheet & strip | B688 | SB-688 |
| Welded pipe | B675 | SB-675 |
| Welded tube | B676 | SB-676 |
| Seamless pipe & tube | B690 | SB-690 |
| Bar & wire (incl. round bar) | B691 | SB-691 |
All values and grades follow the applicable ASTM/ASME specification. Every order ships with material certificates included.
How AL-6XN Compares: vs 316L, 904L, 254 SMO & Super-Duplex 2507
AL-6XN sits above 316L and 904L when it comes to resisting chloride attack. It belongs to the 6-molybdenum super-austenitic class, with a PREN near 45. Below, you'll find it stacked against the alloys buyers most often weigh against it. Each one links to its own material or comparison page.
| Alloy | PREN (approx) | Relative chloride resistance | More detail |
|---|---|---|---|
| 316 / 316L (S31600 / S31603) | ~25 | Baseline general service | 316 / 316L · 904L vs 316 |
| 904L (N08904) | ~34 | Better than 316L; below 6-moly | 904L |
| AL-6XN (N08367) | ~45 | 6-moly super-austenitic, seawater/high-chloride | This page |
| 254 SMO (S31254) | ~43 | Peer 6-moly super-austenitic | 254 SMO |
| Super-Duplex 2507 (S32750) | ~42 | Duplex; higher strength, similar chloride class | Super-Duplex 2507 |
Where reducing acids or the harshest hot chlorides come into play, buyers move up to nickel-base alloys like Hastelloy. When higher mechanical strength is the priority, super-duplex gets weighed against AL-6XN. For the full head-to-head decision, read the 254 SMO vs super-duplex vs AL-6XN guide and the material-selection-by-service guide.
AL-6XN Applications & Industries
Wherever chlorides, seawater or high-purity acid streams beat conventional stainless, AL-6XN steps in. It just holds up where the standard grades don't. Typical instrumentation applications route to:
- Offshore and subsea production, where sampling and impulse lines sit exposed to seawater and produced fluids.
- Marine & shipbuilding and desalination or condenser systems, the alloy's original chloride duty.
- Power generation & nuclear, specifically flue-gas desulfurization (FGD) scrubber instrumentation.
- Pharmaceutical & biotech and food & beverage, where high-purity process lines demand chloride resistance.
- Water & wastewater, brackish and high-chloride treatment streams.
AL-6XN Product Forms from Crestflo: Fittings, Valves & Tubing
Crestflo supplies UNS N08367 across three instrumentation product forms. The grade goes into compression and ferrule fittings, needle, ball and manifold valves, and instrumentation tubing produced either welded or without a weld seam. Imperial and metric sizes, both covered.
- AL-6XN tube & compression fittings, single and double ferrule (twin-ferrule), hardened or non-hardened, in imperial and metric, with end connections running up to 2" (50 mm) OD. You'll also see these called AL-6XN compression fittings, 6-moly ferrule fittings, or UNS N08367 fittings. Compression tube fittings are performance-qualified per ASTM F1387.
- AL-6XN instrumentation valves, needle, ball, check, and 2/3/5-way manifold valves in N08367, sizing from 1/16" to 1". The pressure-boundary design follows ASME B16.34; seat-leak and test work follows API seat practice.
- AL-6XN instrumentation tubing, instrumentation tubing, offered in seamless and welded N08367. Both imperial and metric OD and wall combinations are available.
Every Crestflo AL-6XN part comes stamped with a heat/lot number, and it ships with an EN 10204 material test certificate. Ferrule finish options run the gamut: material finish, electropolish, passivation, silver anti-galling plating. Sizes, ferrule type and thread standard get configured to whatever the job calls for.
Why Crestflo for AL-6XN
Engineering confidence means something specific for a 6-moly super-austenitic like AL-6XN: chemistry verified through PMI, honest sourcing and real interchange you can actually use. It shows up in extractable specs, not a buried PDF.
Drop-in interchange for Swagelok®, Parker®, Hoke® and Hy-Lok®: dimensions match, and compression fitting ends carry ASTM F1387 performance qualification. These are interchange/equivalent parts, not "compatible/intermix." Need a Swagelok®/Parker® cross-reference? Our engineering team can pull one together for you. Visit the Swagelok cross-reference page to request it.
Lead time runs 6-8 weeks, against 20+ weeks typical from the major suppliers. Details sit on the lead-time capability and tariff-cost advantage pages.
Traceability is complete. Every part carries a heat/lot number, EN 10204 MTC 3.1 comes standard (3.2 available on request), and PMI confirms the material really is N08367. In-house testing backs all of it.
NACE MR0175 / ISO 15156 material options are available across all fittings, along with single and double ferrules (hardened or non-hardened) in both imperial and metric.
Certified to ISO 9001 / 14001 / 45001 and PED. Machining happens in-house via CNC / VMC / EDM, and small MOQ runs plus private-label options are on the table.
The heritage behind the brand. Crestflo is the instrumentation division of an export house that's been running for four decades, recognized by the Government of India, with a solid delivery record across the Middle East. New in manufacturing, but the export pedigree runs deep. Read more about Crestflo.
Stock & delivery: Standard items ship from ready stock. Specials are made to order, with a 6-8 week delivery window. Origin: Material is of Indian origin; US or European melt is available on request, and full material traceability comes standard (origin & compliance).
Buyers: Request a Quote or Sample, for end users, EPC firms and panel fabricators. Equipment manufacturers and OEMs should talk to an engineer or send a print. Want to become a distributor? We serve offshore and marine systems across the US.
AL-6XN FAQs
What is AL-6XN?
AL-6XN (UNS N08367) is a super-austenitic, 6% molybdenum, nitrogen-bearing stainless steel built for high-chloride and seawater service. It resists chloride pitting, crevice corrosion and stress-corrosion cracking far better than 316L and 904L. You'll find it in instrumentation fittings, valves and tubing.
Is AL-6XN aluminum or stainless steel?
This is a stainless steel. The "6XN" in its name is a bit misleading: AL-6XN (UNS N08367) is actually a super-austenitic stainless steel, an iron-nickel-chromium-molybdenum alloy. It isn't a 6-series aluminum grade like 6061, and it isn't a nickel-base alloy either.
What is the UNS number for AL-6XN?
UNS N08367 is the trademark-free anchor designation. No single exact European Werkstoff number matches it, and the closest 6-molybdenum grade, EN 1.4529 (N08926), is related but not the same thing.
What is the chemical composition of AL-6XN?
The alloy runs nominally 24% nickel, 21% chromium, 6.3% molybdenum and 0.22% nitrogen. Carbon stays low, capped at 0.030%, with iron making up the balance. Full ASTM B688 ranges are in the composition table above.
What is the PREN of AL-6XN?
PREN comes out to roughly 45, using the formula Cr + 3.3 × Mo + 16 × N applied to the nominal composition. That's well above 316 and 316L, which sit around 25, and above 904L at about 34. It puts this alloy in the 6-molybdenum super-austenitic class, right alongside 254 SMO. Worth remembering: PREN is just a calculated ranking index. It doesn't guarantee corrosion performance on its own.
AL-6XN vs 316L, 904L or 254 SMO, which is better for chlorides?
AL-6XN beats 316L and 904L on pitting, crevice attack and chloride stress-corrosion resistance, and it's in the same 6-moly class as 254 SMO. Go with 316L or 904L for milder service. For seawater and high chlorides, AL-6XN or 254 SMO is the better call. Take a look at the comparison of 254 SMO, super-duplex and AL-6XN.
Is AL-6XN suitable for seawater and offshore service?
Yes, it was built as a seawater-resistant alloy for marine, desalination and offshore systems, and it meets PED requirements while standing up to the chloride pitting and crevice corrosion that hold back conventional stainless in those environments.
Is AL-6XN acceptable for sour (NACE) service?
N08367, a nitrogen-bearing austenitic corrosion-resistant alloy, can meet NACE MR0175 / ISO 15156 for applicable conditions. Check the standard for the hardness, temperature and material-condition limits that apply to your specific use. Crestflo offers NACE-compliant AL-6XN fitting and valve material options.
Which ASTM/ASME specs cover AL-6XN product forms?
Plate, sheet and strip fall under ASTM B688. Welded pipe carries the B675 designation, welded tube B676, and seamless pipe and tube B690. Bar and wire round out the list at B691. Each one carries a matching ASME SB designation. Crestflo builds its instrumentation forms only from material that's certified to these specs.
Is AL-6XN weldable?
Yes, it has good weldability and is typically welded with an over-alloyed nickel-base filler (of the ~625 / C-276 type) to preserve corrosion resistance across the weld, with a solution anneal after heavy forming.
Does Crestflo supply AL-6XN as fittings, valves and tubing?
Yes. N08367 tube and compression fittings are available up to 2" (50 mm) OD, in single or double ferrule, hardened or non-hardened. Valves for instrumentation run from 1/16" to 1", and the tubing comes seamless or welded, in imperial or metric, all of it customizable to what you need. That said, Crestflo doesn't sell mill bar, sheet, plate or pipe.
Can Crestflo AL-6XN fittings replace Swagelok or Parker parts?
Yes. Crestflo AL-6XN fittings match the major brands dimensionally and count as equivalents, with compression fitting ends qualified to ASTM F1387 performance standards. Swagelok and Parker are trademarks of their respective owners. Crestflo parts are interchange and equivalent, not compatible or intermix. Ask for a cross-reference on any brand, and we'll send it over.
What is the price and lead time for AL-6XN components?
Pricing works by quotation only, there's no online cart. Standard items ship from ready stock; specials are made to order, with delivery running 6-8 weeks. Standard product comes from India. US or European melt is available on request, and full traceability comes with it. To get a configured part number and price, submit an RFQ with size, form, material and rating.
Related Alloys & Resources
- 254 SMO, peer 6-molybdenum super-austenitic stainless for chloride service.
- 904L, the step below the 6-moly class for moderate chlorides and acids.
- Super-Duplex 2507 · Duplex 2205, higher-strength duplex alternatives.
- Alloy 20 · 316 / 316L, related corrosion-resistant grades.
- Check the 254 SMO vs super-duplex vs AL-6XN and corrosion-alloy matrix guides before you decide.
- For the full lineup, head to the materials hub or the instrumentation valves hub.
Request an AL-6XN Quote
Send us your form: fittings, valves or tubing. Include the size, end connections and line conditions too. From there, the Crestflo Engineering Team will turn it around into a configured part number, ratings and price.
Request a Quote · Request a Sample · Browse the materials hub Reach the Crestflo team at sales@crestflousa.com or +1 346 594 9005. We're based in Houston, TX.
Datasheets and CAD files are available to customers on request, reviewed beforehand by the Crestflo Engineering Team. AL-6XN® and AL-6XN PLUS® are registered trademarks of ATI Properties LLC. Swagelok® and Parker®, meanwhile, are trademarks of their respective owners.