Stainless Steel Capillary Coil Tube (Φ0.5 mm – Φ3 mm)
Product Overview
Wenzhou Jixing Metal Materials Co., Ltd. (温州吉兴金属材料有限公司) offers a precision-engineered line of stainless steel capillary coil tubes (Stainless Steel Coil Tubes, Capillary Grade) with outer diameters ranging from Φ0.5 mm to Φ3 mm. These ultra-fine diameter tubes are manufactured to exacting tolerances and are supplied in continuous coil form, enabling high-yield downstream processing for demanding applications in analytical chemistry, microfluidic systems, precision instrumentation, and medical device engineering.
The capillary coil tube category represents the finest segment of the company's stainless steel tubing portfolio. At diameters as small as 0.5 mm, the manufacturing process demands exceptional control over dimensional accuracy, surface finish, wall uniformity, and metallurgical integrity. Each coil is produced to meet or exceed the specifications outlined in ASTM A269, ASTM A778, and ISO 15530, ensuring global compliance and interchangeability.
Material & Properties
Capillary-grade coil tubes are typically fabricated from austenitic stainless steel grades selected for their superior corrosion resistance, formability at small diameters, and biocompatibility:
- Grade 304 (UNS S30400) — General-purpose capillary applications; excellent weldability and corrosion resistance.
- Grade 316L (UNS S31603) — Enhanced pitting and crevice corrosion resistance due to 2–3% Mo (Molybdenum) addition; preferred for medical and pharmaceutical use.
- Grade 321 (UNS S32100) — Titanium-stabilized variant for elevated-temperature service up to 870 °C.
- Grade 904L (UNS N08904) — High-alloy super-austenitic option for aggressive chemical environments.
Key metallurgical properties of the standard 304/316L capillary tubing include:
- Tensile Strength (UTS): ≥ 520 MPa (annealed condition)
- Yield Strength (0.2% offset): ≥ 205 MPa
- Elongation at Break: ≥ 40%
- Hardness (annealed): ≤ 95 HRB
- Density: 8.0 g/cm³
- Thermal Conductivity (20 °C): 16.3 W/(m·K)
- Corrosion Potential: Passivates readily in oxidizing environments; pitting resistance number (PREN) of 18–20 for 316L
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ0.5 mm – Φ3.0 mm | ISO 15530-1 |
| Wall Thickness | 0.05 mm – 0.50 mm (typical) | ASTM A778 |
| OD Tolerance | ±0.005 mm (standard); ±0.002 mm (precision grade) | ISO 15530-1 |
| Wall Thickness Tolerance | ±10% of nominal (standard); ±5% (precision grade) | ASTM A269 |
| Surface Finish (Internal) | Electropolished to Ra ≤ 0.25 μm (standard); Ra ≤ 0.10 μm (chase-polished) | ASTM A269, Pass 3 |
| Surface Finish (External) | Mirror polish (Ra ≤ 0.4 μm) or commercial finish (Ra ≤ 1.6 μm) | — |
| Coil Length | Up to 500 m per coil (continuous) | — |
| Coil Winding Diameter | 100 mm – 500 mm (configurable) | — |
| Condition | Full Annealed (Solution Heat Treated) | ASTM A269 |
| End Treatment | Deburred, chamfered, or cap-sealed | — |
| Residual Stress | ≤ 50 MPa (post-anneal verification) | — |
OD Series Breakdown
| OD (mm) | Typical Wall Thickness (mm) | Inner Diameter (mm) | Primary Application |
|---|---|---|---|
| 0.5 | 0.05 – 0.15 | 0.20 – 0.40 | Microfluidic channels, GC capillary columns |
| 0.8 | 0.10 – 0.20 | 0.40 – 0.60 | HPLC columns, sensor capillaries |
| 1.0 | 0.10 – 0.25 | 0.50 – 0.80 | Chromatography, analytical tubing |
| 1.5 | 0.15 – 0.30 | 0.90 – 1.20 | Medical catheters, precision flow lines |
| 2.0 | 0.20 – 0.40 | 1.20 – 1.60 | Instrumentation, micro-dosing systems |
| 3.0 | 0.30 – 0.50 | 2.00 – 2.40 | Medical catheters, high-flow capillary lines |
Manufacturing Process
The production of capillary-grade stainless steel coil tubes follows a multi-stage metallurgical and mechanical processing sequence designed to achieve sub-micron surface quality and tight dimensional control at ultra-small diameters:
- Hot Rolling & Ring Cutting — Austenitic stainless steel billet is hot-rolled into seamless tube stock (typically Φ6–Φ10 mm OD). Rings are cut from the seamless tube and inspected for surface defects via ultrasonic testing (UT).
- Ring Rolling / Cross-Rolling — Rings are progressively reduced through cross-rolling mills to achieve the target pre-drawn diameter. This stage establishes the initial wall thickness distribution.
- Intermediate Annealing — Periodic solution heat treatment (1050–1100 °C, water quench) restores ductility and eliminates cold-work hardening between rolling passes.
- Precision Cold Drawing (Multi-Pass) — The pre-drawn tube is pulled through a series of hardened tool steel or tungsten carbide (WC-Co) dies with progressively decreasing diameters. For capillary sizes below Φ1 mm, diamond or cubic boron nitride (CBN) dies are employed. Each pass reduces the OD by 10–20%, maintaining a stable wall-to-OD ratio.
- Pipe Mandrel / Plug Drawing — A hardened plug (mandrel) is used to simultaneously reduce OD and control ID, ensuring concentricity and uniform wall thickness. For the finest capillary tubes (Φ0.5 mm), wire-drawing techniques with continuous mandrels are utilized.
- Final Annealing (Solution Treatment) — The drawn coil undergoes final solution heat treatment at 1050–1150 °C followed by controlled cooling (air or water quench depending on grade) to achieve a fully austenitic, stress-free microstructure.
- Pickling & Passivation — The coil is immersed in a citric acid or nitric acid-based pickling solution to remove scale and oxide films, followed by passivation treatment to establish a stable chromium oxide (Cr₂O₃) passive layer.
- Electropolishing (EP) — Optional — For chromatography and medical applications, the tube interior undergoes electrolytic polishing to achieve Ra ≤ 0.25 μm surface roughness. The process involves controlled dissolution of surface irregularities using an acid electrolyte (H₃PO₄/H₂SO₄/HNO₃) at 50–70 °C.
- Coil Winding & Packaging — The finished tube is wound onto a protective core (typically 150–300 mm diameter) with anti-static protective wrapping. Coils are vacuum-packaged in moisture-barrier film for shipment.
Note: At capillary diameters below Φ1 mm, the entire drawing process requires vibration-isolated equipment, temperature-controlled environments (±2 °C), and real-time dimensional monitoring via laser micrometers to maintain tolerances within ±0.005 mm.
Applications
The Φ0.5 mm – Φ3 mm capillary coil tube is engineered for applications where dimensional precision, corrosion resistance, and surface quality are critical:
Chromatography Columns (Gas Chromatography & HPLC)
Capillary stainless steel tubing serves as the structural backbone of packed-column and open-tubular chromatography systems. The ultra-smooth electropolished interior (Ra ≤ 0.25 μm) minimizes analyte adsorption and peak broadening, ensuring high column efficiency (theoretical plates per meter). 316L grade is preferred for its resistance to mobile-phase corrosion in liquid chromatography.
Microfluidic Systems
In lab-on-a-chip (LOC) and microfluidic device fabrication, stainless steel capillary tubes provide robust, chemically inert fluidic channels. Their small ID enables precise flow control at nanoliter-to-microliter flow rates, while their mechanical strength withstands pressures up to 50 MPa. Coil form allows compact integration into microfluidic manifolds and pump modules.
Precision Instrumentation
Capillary tubes are integral to pressure sensing, flow metering, and mass spectrometry sample introduction systems. The tight dimensional tolerances ensure repeatable hydraulic resistance, critical for calibration accuracy in analytical instruments. 321-grade capillary tubing is specified for high-temperature instrument lines (e.g., GC inlet liners, MS ion sources).
Medical Catheters & Diagnostic Devices
316L capillary tubing is the material of choice for vascular catheters, dialysis needles, and endoscopic instrument channels. The combination of biocompatibility (ISO 10993 compliant), fatigue resistance, and corrosion resistance in saline/blood environments makes it ideal for implantable and diagnostic medical applications. The coil form facilitates automated catheter assembly lines.
Additional Applications
- Fuel cell gas diffusion channels
- Optical fiber protective tubing (instrumentation-grade)
- Pharmaceutical aseptic filling needles
- Environmental monitoring sensor housings
- Petrochemical sampling lines (corrosive media)
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains the following quality management certifications and product standards to ensure consistent performance and regulatory compliance:
- ISO 9001:2015 — Quality Management System certification for all production facilities.
- ISO 13485:2016 — Medical device quality management system (applicable to 316L capillary tubing for medical use).
- ISO 15530 — Compliance with international seamless stainless steel tube dimensional standards.
- ASTM A269 / A778 — Material and product specifications for seamless austenitic stainless steel tubing.
- EN 10217-7 — European standard for stainless steel seamless tubes for general engineering purposes.
- JIS G3447 — Japanese Industrial Standard for seamless stainless steel tubes.
- CE Marking — European conformity for medical and pressure equipment applications.
- RoHS / REACH Compliance — Restriction of hazardous substances; full material traceability.
- Mill Test Reports (MTR) — Provided with every shipment, including chemical composition (OES/ICP), mechanical properties, and heat treatment records.
Unique Selling Points
- Ultra-Fine Diameter Capability: Consistent production at Φ0.5 mm OD with ±0.005 mm tolerance — among the finest in the industry.
- Continuous Coil Supply: Up to 500 m per coil eliminates splicing losses and reduces downstream processing time by up to 40%.
- Dual-Surface Electropolishing: Both internal and external surfaces can be independently polished to specified roughness levels for maximum functional versatility.
- Full Traceability: Heat-lot tracking from raw material to finished coil, enabling complete supply-chain auditability.
- Custom Configuration: Non-standard OD/wall combinations, special end treatments, and custom coil winding diameters available upon request with lead times as short as 15 working days.
Technical Note on Capillary Tube Performance
For capillary tubes in the Φ0.5–3.0 mm range, the Reynolds number (Re) at typical operating velocities remains well below 2300, ensuring laminar flow conditions. This is critical for chromatographic separation efficiency and microfluidic flow accuracy. The Darcy-Weisbach pressure drop (ΔP) scales inversely with the fourth power of the inner diameter (Hagen-Poiseuille equation: ΔP = 128μLQ/πd⁴), making precise ID control essential for predictable hydraulic performance. Wenzhou Jixing's precision drawing process ensures ID uniformity within ±5% along the full coil length, providing consistent flow characteristics throughout.
Recommended Storage: Store coils in a dry, vibration-free environment at 10–30 °C. Avoid exposure to chloride-containing atmospheres. For medical-grade tubing, maintain under controlled cleanroom conditions (ISO Class 8 or better) prior to assembly.