316LVM Stainless Steel Capillary Coiltube for Catheter Sheaths & Balloon Dilation Tubes
Product Overview
This precision-engineered stainless steel capillary coiltube is purpose-designed for the fabrication of interventional medical devices, specifically catheter sheaths and balloon dilation tubes intended for in-vivo implantation within the human vasculature and soft tissue. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product represents the intersection of advanced metallurgy and minimally invasive medical engineering, delivering the critical combination of biocompatibility, miniaturization, and mechanical reliability demanded by the interventional cardiology and peripheral intervention markets.
The coiltube form factor—supplied as continuous coil stock—enables high-efficiency downstream processing, including laser cutting, precision welding, and automated catheter assembly, while maintaining the dimensional integrity and surface finish required for devices navigating tortuous anatomical pathways.
Material & Properties
The base material is 316LVM (316L Vacuum Melted) austenitic stainless steel, a high-purity variant of 316L grade refined through vacuum induction melting (VIM) or vacuum arc remelting (VAR) to achieve ultra-low interstitial carbon and nitrogen levels. This metallurgical refinement is critical for medical implant applications, as it significantly reduces the risk of stress corrosion cracking (SCC), eliminates surface inclusions that could trigger inflammatory responses, and ensures long-term corrosion resistance in the chloride-rich environment of human blood and interstitial fluid.
Key Metallurgical Characteristics
- Ultra-low carbon content (≤ 0.015% C): Minimizes sensitization and carbide precipitation at grain boundaries, ensuring weldability and resistance to intergranular corrosion.
- High nickel (Ni) and molybdenum (Mo) content: Provides superior pitting and crevice corrosion resistance in physiological environments.
- Low surface roughness (Ra ≤ 0.1 μm achievable): Critical for reducing thrombogenicity and ensuring smooth blood flow through catheter lumens.
- Full austenitic microstructure (non-magnetic): Ensures compatibility with MRI environments and eliminates magnetic interference during imaging-guided procedures.
- Excellent cold workability: Allows precision drawing to micro-diameters without cracking or loss of ductility.
Chemical Composition (ASTM F138 / ASTM F139)
| Element | Specification (%) | Notes |
|---|---|---|
| Carbon (C) | ≤ 0.015 | Vacuum melted; ultra-low for implant grade |
| Nickel (Ni) | 11.0 – 14.0 | Stabilizes austenite; enhances corrosion resistance |
| Chromium (Cr) | 17.0 – 19.0 | Passive film formation; primary corrosion defense |
| Molybdenum (Mo) | 2.0 – 3.0 | Pitting and crevice corrosion resistance |
| Manganese (Mn) | ≤ 2.0 | — |
| Phosphorus (P) | ≤ 0.035 | — |
| Sulfur (S) | ≤ 0.030 | — |
| Silicon (Si) | ≤ 1.0 | — |
| Nitrogen (N) | ≤ 0.030 | Ultra-low in VIM process |
| Iron (Fe) | Balance | — |
Specifications
| Parameter | Specification | Testing Standard |
|---|---|---|
| Outer Diameter (OD) | 0.30 mm – 3.00 mm (customizable) | ISO 13485 dimensional control |
| Wall Thickness | 0.05 mm – 0.50 mm | — |
| OD Tolerance | ± 0.01 mm | ASTM F138 |
| Wall Thickness Tolerance | ± 0.01 mm | ASTM F138 |
| Surface Finish | Ra ≤ 0.25 μm (standard); Ra ≤ 0.10 μm (upon request) | — |
| Delivery Condition | Annealed (soft); Hard-tempered available | — |
| Coil Length | Up to 500 m continuous (spool) | — |
| Roundness | ≥ 98% of nominal OD | — |
| Leak Tightness | 100% helium leak test pass (≤ 1 × 10⁻⁹ atm·cc/s) | ASTM F86 |
| Hardness | ≤ 180 HV (annealed); 250–350 HV (hard-tempered) | ASTM F138 |
| Yield Strength | ≥ 170 MPa (annealed); ≥ 620 MPa (hard-tempered) | ASTM F138 |
| Corrosion Resistance | ASTM F86 immersion test; ASTM G48 pitting test | ASTM F86 / ASTM G48 |
Manufacturing Process
The production of 316LVM capillary coiltube follows a rigorous multi-stage process designed to ensure metallurgical purity, dimensional precision, and surface quality at the micro-scale:
- Vacuum Induction Melting (VIM): Raw alloy stock is melted under high vacuum (≤ 10⁻³ mbar) to remove interstitial gases (O₂, N₂, H₂) and segregate impurities. This step is the defining differentiator of 316LVM over conventional 316L, ensuring the ultra-low carbon and nitrogen levels mandated by implant-grade specifications.
- Secondary Refining (VAR / ESR): Optional vacuum arc remelting or electroslag remelting further homogenizes the microstructure and eliminates macrosegregation, producing a fully dense ingot.
- Hot Rolling & Piercing: The refined ingot is hot-rolled into hollow bar stock and pierced to create the initial tube geometry.
- Multi-Pass Cold Drawing: The hollow bar is progressively drawn through precision tungsten carbide (WC) dies to achieve the target micro-diameter and wall thickness. Each drawing pass reduces the cross-section incrementally while maintaining roundness and concentricity.
- Intermediate Annealing: Periodic annealing at 1050–1100 °C in a controlled argon atmosphere restores ductility between cold-drawing passes, preventing work hardening and ensuring uniform microstructure.
- Final Annealing (Solution Treatment): The finished tube is solution-annealed to achieve the fully austenitic, soft delivery condition, followed by controlled cooling to prevent sensitization.
- Surface Treatment & Passivation: The tube undergoes acid pickling (HNO₃ + HF) and passivation to remove surface contaminants, restore the chromium oxide passive film, and achieve the required surface roughness.
- Coiling & Packaging: The continuous tube is wound onto precision spools and packaged in cleanroom-rated, moisture-barrier packaging to maintain surface integrity until downstream processing.
Applications
This 316LVM capillary coiltube is the foundational raw material for a range of interventional medical devices:
- Catheter Sheaths: The capillary tube forms the structural backbone of vascular access sheaths used in percutaneous coronary intervention (PCI), peripheral arterial intervention (PAI), and neuroradiological procedures. The tube's micro-diameter enables sub-millimeter sheath profiles that minimize vascular trauma during insertion.
- Balloon Dilation Tubes: The stainless steel capillary serves as the inflation lumen and structural support for balloon catheters used in angioplasty, stent deployment, and stricturoplasty. The tube's fatigue resistance and leak tightness are critical for withstanding repeated balloon inflation/deflation cycles.
- Guide Wires & Micro-Catheters: The coiltube stock can be further processed into guide wire cores and micro-catheter shafts for navigating complex vascular anatomy.
- Endovascular Stent Delivery Systems: The tube forms the sheath and pusher components of stent delivery catheters, requiring high radial strength and precise inner diameter control.
- Implantable Devices: The tube's biocompatibility and corrosion resistance qualify it for use in permanently implanted vascular components, including intravascular shunts and valve frames.
Quality Certifications & Compliance
Every batch of 316LVM capillary coiltube produced by Wenzhou Jixing Metal Materials Co., Ltd. is manufactured and tested under a comprehensive quality management framework:
- ASTM F138: Standard Specification for Chromium-Nickel Stainless Steel Wire and Bar for General Surgical Implants—covers chemical composition, mechanical properties, and acceptance criteria for implant-grade stainless steel.
- ASTM F139: Standard Specification for Chromium-Nickel-Iron-Molybdenum Stainless Steel Wire and Bar for Surgical Implants—alternative implant-grade specification.
- ASTM F86: Standard Specification for Stainless Steel Tubing for Surgical Implants—specifically governs the chemical, mechanical, and dimensional requirements for implant tubing.
- ISO 13485: Quality Management Systems for Medical Devices—ensures the manufacturing process meets regulatory expectations for device-grade raw materials.
- ISO 9001: General quality management system certification for manufacturing excellence.
- RoHS & REACH Compliance: Ensures freedom from restricted hazardous substances in the material composition.
- MTC 3.1 Certification: Full material test certificate (EN 10204 Type 3.1) provided with every shipment, including chemical analysis, mechanical test results, and heat traceability.
Unique Selling Points
1. True Vacuum-Melted Purity: Unlike standard 316L stock, the 316LVM designation guarantees ultra-low interstitial gas content achieved through VIM/VAR refining—reducing the risk of late-stage implant failure by up to 90% compared to conventional grades.
2. Sub-Millimeter Precision: Capillary diameters as small as 0.30 mm with ±0.01 mm tolerance enable the fabrication of ultra-low-profile catheters that reduce vascular access complications.
3. Continuous Coil Supply: The coiltube format eliminates butt joints and enables automated, high-throughput catheter manufacturing with 100% traceability from raw material to finished device.
4. Dual Condition Availability: Both annealed (soft) and hard-tempered conditions are available from the same coil stock, allowing manufacturers to select the optimal mechanical state for each device component.
5. Full Regulatory Readiness: ASTM F138/F86 compliance with complete MTC 3.1 documentation provides medical device OEMs with the material qualification data required for FDA 510(k), EU MDR, and NMPA submissions.