316L EP Capillary Coil Tube for IVD Analyzer Reagent Delivery Systems
Product Overview
The 316L EP (Electropolished) Capillary Coil Tube is a precision-engineered stainless steel tubing solution specifically designed for In Vitro Diagnostics (IVD) analyzers requiring critical reagent and sample transport at the microliter (μL) scale. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coil tube addresses the demanding requirements of modern automated laboratory analyzers, where minute volumes of reagents and biological samples must be delivered with absolute fidelity, zero cross-contamination, and minimal dead volume.
In contemporary IVD platforms—encompassing clinical chemistry analyzers, immunoassay systems, coagulation analyzers, and molecular diagnostics platforms—reagent tubing serves as the critical fluidic pathway connecting reagent reservoirs, sample injection ports, mixing chambers, and waste disposal systems. The integrity of this tubing directly determines assay accuracy, precision, and reliability. Any residual carryover, surface adsorption, or volumetric deviation introduced at the tubing level can propagate through the entire analytical workflow, resulting in erroneous diagnostic results.
This product line represents the pinnacle of microfluidic-grade stainless steel tubing technology, combining aerospace-grade material science with pharmaceutical-grade surface finishing to deliver a solution that meets the most stringent requirements of regulatory agencies including the U.S. Food and Drug Administration (FDA), European Medicines Agency (EMA), and China National Medical Products Administration (NMPA).
Material & Properties
Base Material: ASTM A270 / AMS 5510 316L Stainless Steel
The coil tube is fabricated from Type 316L austenitic stainless steel, a low-carbon variant of 316 stainless steel that is the gold standard material for biomedical and pharmaceutical fluid handling applications. The "L" designation denotes a maximum carbon content of 0.03% by weight, which significantly reduces the risk of intergranular corrosion during welding or heat treatment processes.
Chemical Composition (ASTM A270, Grade 316L)
| Element | Specification (%) | Function |
|---|---|---|
| Carbon (C) | ≤ 0.03 | Prevents intergranular corrosion; ensures weld integrity |
| Chromium (Cr) | 17.00 – 19.00 | Forms passive oxide layer; primary corrosion resistance element |
| Nickel (Ni) | 10.00 – 14.00 | Stabilizes austenitic structure; enhances ductility and corrosion resistance |
| Molybdenum (Mo) | 2.00 – 3.00 | Provides superior pitting and crevice corrosion resistance; critical for chloride-containing biological fluids |
| Iron (Fe) | Balance | Base matrix element |
| Silicon (Si) | ≤ 1.00 | Improves high-temperature strength and oxidation resistance |
| Manganese (Mn) | ≤ 2.00 | Deoxidizer; enhances hot workability |
| Phosphorus (P) | ≤ 0.045 | Impurity control; prevents brittleness |
| Sulfur (S) | ≤ 0.030 | Impurity control; minimizes stress corrosion cracking susceptibility |
Surface Finish: Electropolished (EP) — Ra ≤ 0.25 μm
The interior surface of the capillary tube undergoes a multi-stage electropolishing process that removes the outermost 3–10 micrometers of material through controlled anodic dissolution. This process achieves:
- Surface Roughness (Ra): ≤ 0.25 μm (typical), with premium grades achieving ≤ 0.10 μm
- Surface Pore Closure: 95%+ reduction in surface porosity, eliminating micro-cavities where biological contaminants could accumulate
- Passive Layer Enhancement: Formation of a uniform, dense chromium oxide (Cr₂O₃) passive film approximately 2–5 nm thick, providing exceptional chemical inertness
- Low Adsorption Surface: The ultra-smooth electropolished surface minimizes protein adsorption, cell adhesion, and non-specific binding of biomolecules—critical for maintaining reagent purity and assay accuracy
Key Material Properties
| Property | Value | Relevance to IVD Application |
|---|---|---|
| Density | 8.0 g/cm³ | — |
| Tensile Strength (Annealed) | ≥ 515 MPa (75,000 psi) | Ensures mechanical integrity under peristaltic pump compression |
| Yield Strength (0.2% offset) | ≥ 205 MPa (29,750 psi) | Prevents permanent deformation during fluidic pressure cycling |
| Elongation | ≥ 40% | Ensures formability during coil winding without cracking |
| Thermal Conductivity | 16.3 W/(m·K) at 20°C | Facilitates thermal uniformity in temperature-controlled reagent zones |
| Corrosion Resistance | Superior to 304 SS; resistant to chloride pitting | Withstands aggressive biological reagents, cleaning solutions (NaOH, H₂O₂), and saline-based buffers |
| Biocompatibility | ISO 10993 compliant | Non-cytotoxic; suitable for contact with biological samples |
Specifications
Geometric Dimensions
| Parameter | Specification | Tolerance | Notes |
|---|---|---|---|
| Outer Diameter (OD) | 0.51 mm – 3.18 mm (0.020" – 0.125") | ± 0.025 mm | Custom diameters available; sub-millimeter ODs optimized for μL-scale flow |
| Wall Thickness | 0.10 mm – 0.51 mm (0.004" – 0.020") | ± 10% | Thin-wall configurations minimize dead volume |
| Inner Diameter (ID) | 0.31 mm – 2.16 mm (0.012" – 0.085") | ± 0.025 mm | Capillary-grade bore; roundness ≥ 95% |
| Coil Winding Diameter | 25 mm – 150 mm (1.0" – 6.0") | ± 0.5 mm | Custom winding diameters to fit analyzer fluidic module footprints |
| Coil Length | 500 mm – 10,000 mm (per coil) | ± 2% | Continuous lengths available; spliced assemblies with welded joints |
| Coil Pitch | 1.0 mm – 5.0 mm | ± 0.1 mm | Consistent pitch prevents kinking and ensures uniform flow characteristics |
| Number of Turns | 10 – 500 turns | — | Determined by required path length and spatial constraints |
Flow Performance Characteristics
| Parameter | Specification | Test Method |
|---|---|---|
| Dead Volume (per 100 mm tube length) | ≤ 5 μL (for ID 0.51 mm); ≤ 50 μL (for ID 2.16 mm) | Volumetric displacement method per ASTM F3145 |
| Flow Rate Compatibility | 0.1 μL/min – 500 μL/min | Continuous flow with peristaltic or syringe pump |
| Maximum Operating Pressure | 0.5 – 2.0 MPa (72 – 290 psi) | Hydrostatic pressure test at 1.5× working pressure |
| Bubble-Free Flow | Verified at ≤ 0.5 μL/min | Visual inspection under magnification |
| Leak Rate | ≤ 0.01 μL/min at 0.5 MPa | Helium leak detection (ASTM F857) |
| Wetting Behavior | Complete wetting; no meniscus pinning | Contact angle measurement ≤ 10° |
Surface & Contamination Control
| Parameter | Specification | Test Method |
|---|---|---|
| Surface Roughness (Ra, Internal) | ≤ 0.25 μm (standard); ≤ 0.10 μm (premium) | White light interferometry / laser confocal profilometry |
| Surface Roughness (Rz, Internal) | ≤ 1.0 μm (standard); ≤ 0.5 μm (premium) | Profilometric measurement |
| Particulate Contamination | ≤ 5 particles ≥ 5 μm per 100 mm length | Laser particle counter (ASTM F2059) |
| Endotoxin Level | ≤ 0.25 EU/mL (after rinse) | LAL (Limulus Amebocyte Lysate) assay per USP <85> |
| Pyrogen Level | Non-pyrogenic | Rabbit pyrogen test (USP <151>) |
| Extractable Metals (1000 ppm limit) | Pb, Cd, Hg, Cr, Ni, As — all below detection limit | ICP-MS extraction test (GB/T 29761) |
| Protein Adsorption | ≤ 0.1 μg/cm² (BSA model protein, 1 hour contact) | UV absorbance method at 280 nm |
| Cell Adhesion | Non-adherent; < 5% cell attachment rate | Cell culture assay (fibroblast model) |
Manufacturing Process
The production of 316L EP capillary coil tubes for IVD applications follows a rigorously controlled, multi-stage manufacturing process designed to ensure dimensional precision, surface integrity, and contamination control at every step.
Stage 1: Raw Material Selection & Certification
- Source: Certified 316L stainless steel wire rod from approved suppliers (e.g., Outokumpu, Sandvik, or equivalent), with full mill test certificates (MTC) per EN 10204 3.1
- Incoming Inspection: Chemical composition verification via optical emission spectroscopy (OES); mechanical property verification via tensile testing per ASTM E8
- Traceability: Each batch is assigned a unique heat number and lot code for full supply chain traceability
Stage 2: Cold Drawing & Precision Bore Formation
- Process: Multi-pass cold drawing through tungsten carbide (WC) or diamond die sets to achieve precise OD and wall thickness dimensions
- Die Material: Polished tungsten carbide dies for standard diameters; diamond dies for sub-0.5 mm OD capillary tubes
- Lubricant: Food-grade or pharmaceutical-grade drawing lubricant (sodium stearate-based), subsequently removed by alkaline cleaning
- Dimensional Control: Inline optical measurement systems monitor OD and wall thickness with ± 0.01 mm resolution
Stage 3: Annealing & Stress Relief
- Process: Solution annealing at 1050°C – 1150°C in a controlled hydrogen (H₂) or vacuum atmosphere
- Purpose: Eliminates work hardening from cold drawing; restores full ductility; ensures uniform austenitic microstructure; removes residual stresses that could cause dimensional instability
- Microstructure Verification: Metallographic examination per ASTM E3 confirms fully austenitic structure with no delta ferrite or carbide precipitation
Stage 4: Coil Winding & Forming
- Equipment: CNC-controlled precision winding machines with servo-driven feed mechanisms
- Process: Continuous coil winding at controlled tension to prevent ovalization, kinking, or work hardening
- Winding Parameters: Coil diameter, pitch, and number of turns programmed to exact customer specifications
- Post-Winding Inspection: Visual and dimensional inspection for uniformity; roundness verification at multiple points along the coil length
Stage 5: Electropolishing (EP) — Interior Surface Treatment
- Process: Electrochemical anodic dissolution of the interior tube surface using a phosphoric acid–sulfuric acid electrolyte bath at controlled current density (100–300 A/dm²) and temperature (50–70°C)
- Duration: 15–45 minutes depending on target surface finish quality
- Material Removal: 3–10 μm of surface material removed uniformly, closing surface pores and achieving sub-0.25 μm Ra finish
- Passivation: Post-EP passivation treatment in nitric