316L Electropolished Capillary Coiled Tube for GC Carrier Gas Lines
Product Overview
This precision-engineered 316L stainless steel coiled capillary tube is purpose-built for gas chromatography (GC) carrier gas delivery systems. Designed to transport high-purity helium (He), hydrogen (H₂), and nitrogen (N₂) carrier gases with exceptional flow stability, this coiled tube ensures reliable, contamination-free gas delivery in process analysis instrumentation. The product is manufactured to the rigorous standards demanded by analytical laboratories, petrochemical facilities, and environmental monitoring stations where trace-level analytical accuracy is paramount.
Coiled capillary tubing in GC systems serves as the critical pathway between the gas cylinder/regulator and the chromatograph injector or column inlet. Any deviation in flow rate, contamination, or leak integrity directly compromises analytical results. This product addresses every one of these concerns through advanced metallurgy, precision drawing, and exhaustive quality verification.
Material & Properties
The tube is fabricated from UNS S316L / 1.4404 austenitic stainless steel, the gold standard for high-purity gas service. The low-carbon "L" grade (carbon ≤ 0.03%) provides superior resistance to intergranular corrosion, ensuring long-term structural integrity even in aggressive or trace-contaminant environments. The 2–3% molybdenum content further enhances resistance to chloride pitting and general corrosion.
- Grade: 316L (UNS S316L / EN 1.4404)
- Outer Diameter (OD): ≤ 3 mm (typical range: 0.5 mm – 3.0 mm)
- Wall Thickness: 0.1 mm – 0.5 mm (available in multiple configurations)
- Inner Surface Finish: Electropolished (EP), Ra ≤ 0.1 μm
- Outer Surface Finish: Cold-drawn, smooth finish
- Maximum Operating Temperature: Up to 870 °C (continuous)
- Operating Pressure: Up to 100 bar (N₂ equivalent), subject to wall thickness
- Outgassing Rate: Ultra-low, suitable for high-purity gas service
- Form: Coiled (spooled) for easy handling, installation, and column integration
Specifications
| Parameter | Specification | Standard / Method |
|---|---|---|
| Material Grade | 316L Austenitic Stainless Steel | ASTM A269 / ASTM A213 |
| Outer Diameter (OD) | ≤ 3.0 mm | — |
| Inner Diameter (ID) | 0.1 mm – 2.8 mm (configurable) | — |
| Wall Thickness Tolerance | ±10% of nominal | ASTM A269 |
| OD Tolerance | ±0.05 mm | ASTM A269 |
| Inner Surface Finish | Electropolished (EP), Ra ≤ 0.1 μm | ASTM A269 / ASTM B915 |
| Leak Rate | ≤ 1×10⁻⁹ Pa·m³/s (helium leak test) | ISO 14623 / ASTM E1202 |
| Coil Winding Diameter | Configurable per application requirement | — |
| Length per Coil | Custom (typically 5 m – 50 m per spool) | — |
| End Preparation | Flush cut, burr-free; optional threaded or compression fitting | — |
| Chemical Purity | High-purity gas compatible (He 6.0N, H₂ 6.0N, N₂ 6.0N) | — |
| Flow Stability | Uniform cross-section ensures laminar, repeatable flow profiles | — |
Manufacturing Process
The production of this GC-grade capillary coiled tube follows a multi-stage precision manufacturing workflow to ensure dimensional accuracy, surface integrity, and leak-tight performance:
- Material Selection & Certification: 316L stainless steel wire rod sourced from certified mills, accompanied by full chemical composition and mechanical property documentation (Mill Test Certificate / EN 10204 3.1).
- Multi-Pass Cold Re-Drawn Drawing: The tube undergoes successive cold-drawing passes through precision tungsten carbide dies to achieve the target OD, ID, and wall thickness with tight tolerances. This re-drawing process simultaneously imparts beneficial work-hardening, improving mechanical strength and pressure resistance.
- Electropolishing (EP): The inner surface is electropolished using a controlled electrolytic process that removes the surface layer to a depth of approximately 1–5 μm. This eliminates micro-roughness, embedded impurities, and residual drawing debris, producing a smooth, passive, and chemically inert inner surface (Ra ≤ 0.1 μm). The EP process is critical for preventing gas adsorption and maintaining carrier gas purity.
- Acid Pickling & Passivation: Post-electropolishing, the tube is subjected to citric or nitric acid pickling and passivation to remove any residual iron contamination and restore the full Cr₂O₃ passive film, ensuring maximum corrosion resistance.
- Precision Coiling: The tube is wound onto a clean, controlled-diameter mandrel using an automated coiling machine. The winding tension and diameter are carefully controlled to prevent kinking, ovality, or mechanical stress that could compromise flow uniformity or introduce stress-corrosion vulnerabilities.
- Helium Leak Testing: Every coil is subjected to a rigorous helium mass spectrometric leak test in accordance with ISO 14623. The tube is pressurized with helium and scanned under vacuum; any leakage exceeding the specified threshold (≤ 1×10⁻⁹ Pa·m³/s) results in rejection of the entire coil. This ensures absolute integrity of the carrier gas pathway.
- Final Inspection & Packaging: Each coil is inspected for dimensional accuracy, surface condition, and visual defects. The coil is then packaged in clean, moisture-barrier packaging with desiccant to preserve surface integrity until installation.
Applications
This 316L electropolished capillary coiled tube is specifically engineered for the following applications within gas chromatography and process analysis instrumentation:
- GC Carrier Gas Lines: Primary application — connecting high-purity gas cylinders (He, H₂, N₂) to gas chromatograph injectors, split/splitless valves, and column inlets with maximum flow stability and zero contamination risk.
- Process Analysis Systems: Integration into online process gas analysis systems in petrochemical, pharmaceutical, semiconductor, and food/beverage manufacturing environments.
- Capillary Column Connections: Use as connecting tubing between GC column ovens and detector interfaces (FID, TCD, ECD, MS) where ultra-clean, leak-free pathways are required.
- Sample Conditioning & Purification Lines: Routing high-purity gases through drying tubes, oxygen/moisture traps, and gas purification systems.
- Instrumentation & Laboratory Automation: Integration into automated analytical workflows where consistent carrier gas delivery is essential for reproducible chromatographic results.
- Environmental & Safety Monitoring: Carrier gas delivery in portable and fixed GC-based air quality and emissions monitoring instruments.
Quality Certifications & Compliance
Every batch of this product is manufactured and tested under a certified quality management system, ensuring full traceability and compliance with international standards:
- ISO 9001:2015 — Quality Management System certification for manufacturing processes
- ISO 14623 — Helium leak detection and testing procedures
- ASTM A269 — Standard specification for seamless austenitic stainless steel tubing
- ASTM A213 — Standard specification for austenitic stainless steel boiler, heat exchanger, and heat-treating tubing
- ASTM B915 — Standard specification for electropolished stainless steel tubing
- EN 10204 Type 3.1 — Full material test documentation (Mill Certificate)
- RoHS / REACH Compliance — Restricted hazardous substances compliant for global distribution
Key Selling Points:
- Ultra-low outgassing 316L electropolished inner surface (Ra ≤ 0.1 μm) — preserves carrier gas purity at the 6N level
- Helium mass-spectrometric leak-tested to ≤ 1×10⁻⁹ Pa·m³/s — guaranteed zero-leak integrity
- Precision cold re-drawn for uniform cross-section and exceptional flow stability
- Compact OD ≤ 3 mm design — ideal for tight instrument layouts and column integration
- Coiled format for easy handling, storage, and on-site installation
- Full material traceability with EN 10204 3.1 certification