304LN/316LN Nitrogen-Alloyed Stainless Steel Coil Tube for Cryogenic Applications
Product Overview
The 304LN/316LN Stainless Steel Coil Tube manufactured by Wenzhou Jixing Metal Materials Co., Ltd. represents the pinnacle of cryogenic-grade austenitic stainless steel tubing technology. This nitrogen-alloyed coil tube is specifically engineered for extreme low-temperature service environments, maintaining outstanding mechanical properties and structural integrity at temperatures as low as -196°C (-320.8°F). The strategic incorporation of nitrogen as an interstitial alloying element provides superior strength-to-weight ratios while preserving the excellent ductility and toughness inherent to the austenitic crystal structure.
Available in both 304LN and 316LN grades, this product line addresses the most demanding requirements in liquefied natural gas (LNG) storage, cryogenic fluid transport, and ultra-low-temperature industrial processing. The coil tube format offers significant advantages in downstream fabrication, including reduced material waste, improved formability, and enhanced production efficiency for pipe-making operations.
Material & Properties
The 304LN and 316LN grades are advanced nitrogen-stabilized variants of the standard 304L and 316L austenitic stainless steels. The addition of nitrogen (typically 0.03–0.10%) serves multiple critical functions in the metallurgical composition:
- Solid Solution Strengthening: Nitrogen atoms occupy interstitial sites within the austenitic FCC lattice, providing significant yield strength enhancement without compromising ductility — a combination that is exceptionally difficult to achieve through conventional alloying alone.
- Cryogenic Toughness Retention: Unlike ferritic or martensitic steels that exhibit brittle transition behavior at cryogenic temperatures, the nitrogen-alloyed austenitic structure maintains a fully face-centered cubic (FCC) phase at -196°C, ensuring no ductile-to-brittle transition occurs.
- Corrosion Resistance: The 316LN variant incorporates 2.0–2.5% molybdenum, providing enhanced resistance to pitting and crevice corrosion in chloride-containing cryogenic environments. Both grades maintain the low-carbon designation (≤0.03% C) to prevent sensitization during welding.
- Weldability: The low carbon and nitrogen-stabilized composition ensures excellent weldability with minimal risk of intergranular corrosion in heat-affected zones.
Chemical Composition (Typical)
| Element | 304LN (% max) | 316LN (% max) |
|---|---|---|
| Carbon (C) | 0.030 | 0.030 |
| Nitrogen (N) | 0.030–0.100 | 0.030–0.100 |
| Chromium (Cr) | 18.0–20.0 | 16.5–18.5 |
| Nickel (Ni) | 8.0–11.0 | 10.0–14.0 |
| Molybdenum (Mo) | — | 2.0–2.5 |
| Manganese (Mn) | 2.0 | 2.0 |
| Silicon (Si) | 1.0 | 1.0 |
| Sulfur (S) | 0.030 | 0.030 |
Mechanical Properties
| Property | Condition | 304LN | 316LN |
|---|---|---|---|
| Yield Strength (0.2% offset) | Room Temperature | ≥ 290 MPa (≥ 42 ksi) | ≥ 290 MPa (≥ 42 ksi) |
| Yield Strength (0.2% offset) | -196°C | ≥ 350 MPa (≥ 51 ksi) | ≥ 350 MPa (≥ 51 ksi) |
| Tensile Strength | Room Temperature | ≥ 520 MPa (≥ 75 ksi) | ≥ 520 MPa (≥ 75 ksi) |
| Tensile Strength | -196°C | ≥ 620 MPa (≥ 90 ksi) | ≥ 620 MPa (≥ 90 ksi) |
| Elongation | -196°C | ≥ 35% | ≥ 35% |
| Impact Energy (Charpy V-Notch) | -196°C | ≥ 200 J | ≥ 200 J |
Specifications
| Parameter | Specification |
|---|---|
| Product Form | Coil Tube (continuous length wound coil) |
| Outer Diameter Range | 6.00 mm – 60.30 mm (0.236" – 2.374") |
| Wall Thickness Range | 0.50 mm – 3.00 mm (0.020" – 0.118") |
| Coil Inner Diameter | 400 mm – 800 mm (15.7" – 31.5") |
| Coil Length | Continuous (typically 500 m – 3,000 m per coil) |
| Surface Finish | Bright Annealed (BA), Pickled & Passivated (2B), or Custom |
| Applicable Standards | ASTM A269, ASTM A312, ASME SA-269, ASME SA-312, EN 10216-5, GB/T 14976 |
| Temperature Range | -269°C to +450°C (-452°F to +842°F) |
| Maximum Design Pressure (LNG Service) | Up to 25.0 bar (362.6 psi) depending on OD/WT |
| Manufacturing Method | Precision Cold-Finishing / Hot-Finishing with Cold Drawing |
| End Condition | Plain Ends, Beveled Ends, or Custom |
Manufacturing Process
The production of 304LN/316LN coil tube at Wenzhou Jixing Metal Materials Co., Ltd. follows a rigorously controlled multi-stage manufacturing process designed to ensure consistent metallurgical quality and dimensional precision:
- Raw Material Selection: High-purity vacuum-induction-melted (VIM) or electro-slag-remelted (ESR) austenitic stainless steel billets conforming to the specified nitrogen content and trace element limits.
- Hot Rolling & Annealing: Billets are hot-rolled to the required intermediate dimensions and subsequently solution-annealed at 1,050–1,100°C (1,922–2,012°F) followed by controlled water quenching to achieve a fully austenitic microstructure.
- Precision Cold Drawing: The hot-finished tube is cold-drawn through precision tungsten carbide dies to achieve final dimensional tolerances within ±0.10 mm (±0.004") on outer diameter and ±0.05 mm (±0.002") on wall thickness.
- Intermediate Annealing: Cold-worked tube undergoes solution annealing at 1,050°C (1,922°F) to relieve residual stresses, restore full ductility, and maintain the stable austenitic phase.
- Surface Treatment: Pickling and passivation (or bright annealing) to remove scale, decarburized layers, and surface contaminants, establishing a protective chromium oxide passive film.
- Coiling: Finished tube is wound onto precision coil stands with controlled tension to prevent ovality or deformation. Protective packaging with moisture barriers is applied.
- Final Inspection: Comprehensive non-destructive testing (EDDY current, hydrostatic pressure, and ultrasonic testing) is performed on every coil before shipment.
Applications
The exceptional cryogenic performance of 304LN/316LN coil tube makes it the material of choice for the following critical industrial applications:
- LNG (Liquefied Natural Gas) Storage Tanks: Primary construction material for LNG storage vessels operating at -162°C (-219.6°F), providing reliable containment integrity over decades of service life. The nitrogen-enhanced toughness eliminates concerns about brittle fracture in the event of impact or thermal shock.
- Liquefied Nitrogen (LN₂) and Liquid Oxygen (LOX) Transport Pipelines: Cryogenic transfer lines for industrial gas supply networks, cryogenic air separation units (ASUs), and medical oxygen distribution systems operating at -196°C and -183°C respectively.
- Cryogenic Heat Exchangers: Brazed and welded heat exchanger tubes for LNG processing facilities, cryogenic distillation columns, and superconducting magnet cooling systems.
- Space Industry & Aerospace: Fuel and oxidizer lines for liquid hydrogen (-253°C) and liquid oxygen rocket propulsion systems, where weight savings and absolute reliability are paramount.
- Food & Pharmaceutical Cryogenic Processing: Freezing and preservation systems requiring rapid cooling to sub-zero temperatures with food-grade material compatibility.
- Superconducting Magnet Cables: Inner conduit tubes for high-field superconducting magnets in MRI systems and particle accelerators, where thermal contraction at helium temperatures (4.2 K / -269°C) demands exceptional dimensional stability.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system ensuring full traceability and compliance with international standards:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- EN 10204 3.1 — Full Inspection Certificate for each shipment
- ASTM/ASME — Material certification compliant with ASTM A269/A312 and ASME SA-269/SA-312 specifications
- NORSOK M-650 — Materials for use in oil and gas industry (cryogenic section)
- API 5L — Specification for line pipe (applicable for LNG pipeline applications)
- PED (Pressure Equipment Directive 2014/68/EU) — CE marking for pressure equipment components
- Mill Test Reports (MTR) — Full chemical analysis and mechanical test data provided with every coil
- Third-Party Inspection (TPI) — Available upon customer request (SGS, Bureau Veritas, Lloyd's Register)
Unique Selling Points
Superior Cryogenic Performance: Unlike conventional 304L/316L coil tubes, the nitrogen-alloyed 304LN/316LN grades deliver 20–30% higher yield strength at -196°C while maintaining elongation above 35% — enabling thinner wall designs and significant weight savings in cryogenic systems.
- Elimination of Brittle Fracture Risk: The fully austenitic FCC structure ensures no ductile-to-brittle transition at any practical cryogenic temperature, providing unmatched safety margins for LNG and cryogenic fluid containment.
- Coil Format Efficiency: Continuous coil supply eliminates butt-weld joints inherent in pipe-length deliveries, reducing leak points by up to 95% in long pipeline runs and significantly lowering installation labor costs.
- Enhanced Strength-to-Weight Ratio: Nitrogen alloying provides the highest specific strength of any austenitic stainless steel, critical for aerospace and mobile cryogenic applications where every kilogram matters.
- Proven LNG Track Record: 304LN/316LN is the globally specified material for LNG carrier tanks and onshore storage facilities, with over 40 years of successful industrial deployment worldwide.
- Full Traceability: Every coil is accompanied by complete mill documentation including chemical composition, mechanical properties, NDT results, and heat-number traceability from raw material to finished product.
Technical Support & Customization
Wenzhou Jixing Metal Materials Co., Ltd. offers comprehensive technical support for cryogenic-grade coil tube applications, including:
- Material selection engineering for specific temperature and pressure requirements
- Custom dimensional specifications including non-standard OD, wall thickness, and coil configurations
- Welding procedure qualification support (WPS/PQR) for cryogenic service
- Post-weld heat treatment recommendations for maintaining cryogenic toughness in fabricated assemblies
- Sample supply for customer qualification testing and qualification testing reports
For detailed specifications, sample requests, or technical consultation regarding 304LN/316LN cryogenic coil tube applications,