Stainless Steel Coil Tube (Coiltube) — Capillary-Wound Heat Exchanger Tube
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered continuous tube product designed primarily for capillary external winding applications in air-source heat pump water heaters (ASHPWH) and related thermal management systems. This product is categorized under the industrial literature and technical reference series (Item No. 273), representing a critical component in high-efficiency heat exchange assemblies.
The coil tube is supplied in continuous coil form, enabling efficient secondary winding into capillary tube configurations that maximize heat transfer surface area within compact envelopes. This design approach is particularly advantageous for air-source heat pump systems where volumetric efficiency and thermal performance are paramount.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its exceptional combination of corrosion resistance, mechanical strength, and thermal stability across a wide operating temperature range.
- Base Material: Austenitic Stainless Steel (typically Grade 304 / 316 / 316L per ASTM A269 / A270)
- Corrosion Resistance: Superior resistance to oxidation, chlorides, and condensation corrosion in humid atmospheric conditions
- Thermal Conductivity: Moderate thermal conductivity suitable for heat exchange applications with low thermal bridging losses
- Mechanical Properties: High tensile strength and elongation, ensuring dimensional stability during winding and long-term operational fatigue resistance
- Temperature Range: Suitable for continuous operation from cryogenic temperatures up to approximately 450°C (842°F)
- Hygienic Compatibility: Non-toxic, non-reactive, and suitable for potable water contact applications
Technical Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Form | Continuous Coil Tube (Coiltube) | — |
| Material Grade | ASTM 304 / 304L / 316 / 316L | ASTM A269 / A270 |
| Outer Diameter (OD) | 1.5 mm – 12.0 mm (customizable) | — |
| Wall Thickness | 0.2 mm – 1.0 mm (customizable) | — |
| Coil Outer Diameter | 50 mm – 300 mm | — |
| Coil Length | 50 m – 500 m per coil (standard) | — |
| Surface Finish | Polished / Bright Annealed / Pickled | ASTM A478 |
| End Condition | Deburred, squared, or threaded (optional) | — |
| Tolerance on OD | ±0.05 mm (standard) / ±0.02 mm (precision) | ISO 1128 |
| Tolerance on Wall Thickness | ±0.02 mm | — |
| Winding Tension | Controlled to prevent ovalization and stress cracking | — |
| Operating Pressure | Up to 4.0 MPa (40 bar) depending on geometry | ASME BPVC |
| Coating / Passivation | Acid passivation film (optional PTFE coating available) | — |
Manufacturing Process
1. Raw Material Selection and Verification
High-purity stainless steel strip or seamless tube stock is sourced from certified mills. Incoming material undergoes spectroscopic analysis (Optical Emission Spectroscopy, OES) and mechanical testing to verify chemical composition and tensile properties in accordance with ASTM and ISO standards.
2. Cold Drawing / Cold Forming
The tube is cold-drawn through precision tungsten carbide dies to achieve exact dimensional tolerances on outer diameter and wall thickness. This process enhances grain structure refinement, improving both mechanical strength and surface finish quality.
3. Intermediate Annealing
At defined deformation stages, the tube undergoes solution annealing in a controlled atmosphere (hydrogen or argon) to relieve cold work stresses and restore ductility, preventing cracking during subsequent forming operations.
4. Precision Coiling
The finished tube is wound into coils using computer-controlled coiling equipment that maintains consistent winding tension, layer-to-layer contact pressure, and alignment. This ensures uniformity in the final coiltube geometry and prevents localized stress concentrations.
5. Surface Treatment and Passivation
The coiltube undergoes pickling and acid passivation to remove scale, contaminants, and free iron particles, establishing a stable chromium oxide passive film. Optional polishing to achieve Ra ≤ 0.4 μm surface roughness is available for applications requiring enhanced corrosion resistance or reduced fluid friction losses.
6. Quality Inspection and Packaging
Each coil undergoes 100% visual inspection, dimensional verification (OD, wall thickness), hydrostatic pressure testing, and optional eddy current (ECT) flaw detection. Approved coils are packaged with moisture barriers, protective end caps, and identification labels specifying grade, dimensions, heat number, and test certificates.
Applications
Primary Application: Air-Source Heat Pump Water Heaters
Based on research documented in the study "Performance Investigation of Capillary External-Winding Coil-Tube Air-Source Heat Pump Water Heaters", this coiltube serves as the core heat exchange element in capillary tube external winding configurations. The capillary winding arrangement provides:
- Extremely high heat transfer area-to-volume ratio
- Uniform refrigerant distribution across the heat exchange surface
- Reduced refrigerant charge volume compared to traditional fin-and-tube designs
- Enhanced defrost performance due to uniform frost layer distribution
- Improved coefficient of performance (COP) under low-temperature ambient conditions
Additional Applications
- Industrial process heat exchangers and condensers
- Air conditioning evaporator and condenser coils
- Refrigeration system capillary tube assemblies
- Automotive thermal management components
- Medical and laboratory equipment fluid pathways
- Solar thermal collector absorber tubes
- Food and beverage industry hygienic heat exchange
Unique Selling Points
- Research-Validated Performance: The coiltube design is backed by academic performance studies demonstrating superior thermal efficiency in capillary-wound configurations for air-source heat pump applications.
- Precision Dimensional Control: Tight manufacturing tolerances (±0.02 mm wall thickness) ensure consistent capillary flow characteristics and reliable heat transfer coefficients across production batches.
- Extended Service Life: Austenitic stainless steel construction provides decades of corrosion-free service in aggressive atmospheric and condensate environments, significantly outperforming aluminum or copper alternatives.
- Environmental Sustainability: Stainless steel is 100% recyclable, non-toxic, and compatible with low-global-warming-potential (low-GWP) refrigerants mandated by current environmental regulations.
- Customization Capability: Wenzhou Jixing Metal Materials Co., Ltd. offers full customization of tube dimensions, coil configurations, surface treatments, and packaging to meet specific OEM requirements.
Quality Certifications and Standards Compliance
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| ASTM A269 / A270 | Standard Specification for Seamless and Wrought Stainless Steel Tubing |
| GB/T 14976 | Chinese National Standard — Seamless Stainless Steel Tubing for Fluid Transport |
| EN 10216-5 | European Standard — Heat Exchanger and Heat Transfer Equipment Tubing |
| ASME BPVC Section VIII | Pressure Vessel Code Compliance (for pressure-containing applications) |
| NACE MR0175 | Sour Service Resistance (for applicable grades) |
| CE Marking | European Conformity for Machinery Directive compliance |
All production batches are accompanied by a Mill Test Certificate (MTC) and Heat Treatment Certificate in accordance with EN 10204 Type 3.1 requirements, providing full traceability from raw material mill heat through to finished coil shipment.
Conclusion
Wenzhou Jixing Metal Materials Co., Ltd.'s Stainless Steel Coil Tube represents a technically advanced, research-validated product solution for high-efficiency heat exchange applications. The combination of precision manufacturing, proven material performance, and comprehensive quality assurance positions this coiltube as an optimal choice for OEM manufacturers and system integrators seeking reliable, long-life thermal management components in air-source heat pump and industrial heat exchange systems.