High-Precision Internal Spiral Stainless Steel Coil Tube (Coiltube) for HVAC Applications
Product Overview
The High-Precision Internal Spiral Stainless Steel Coil Tube (Coiltube), manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is an advanced heat exchanger component specifically engineered for air conditioning and HVAC (Heating, Ventilation, and Air Conditioning) systems. This product integrates a micro-spiral fin structure formed internally within a seamless stainless steel coil tube, significantly enhancing turbulent flow characteristics and heat transfer efficiency while maintaining low hydraulic resistance. The coil tube is supplied in continuous coil form (Coiltube), enabling high-speed downstream processing, forming, and brazing operations with minimal material waste.
Derived from extensive research on precision internal spiral forming technologies, this product represents a state-of-the-art solution that combines the corrosion resistance and mechanical integrity of austenitic stainless steel with aerodynamic optimization achieved through internal spiral geometry. The result is a coil tube that delivers superior thermal performance compared to conventional plain-bore stainless steel tubing in heat exchanger assemblies.
Material & Properties
Base Material Composition
- Primary Grade: SUS304 / ASTM A213 TP304 (Austenitic Stainless Steel)
- Alternative Grades: SUS316 / ASTM A213 TP316 (Molybdenum-bearing, enhanced corrosion resistance)
- Composition (SUS304): Carbon (C) ≤ 0.08%, Manganese (Mn) ≤ 2.0%, Silicon (Si) ≤ 1.0%, Chromium (Cr) 18.0–20.0%, Nickel (Ni) 8.0–10.5%, Iron (Fe) balance
Mechanical Properties
- Tensile Strength (UTS): ≥ 520 MPa (75,400 psi)
- Yield Strength (0.2% Offset): ≥ 205 MPa (29,700 psi)
- Elongation at Break: ≥ 40% (50 mm gauge length)
- Hardness: ≤ 92 HRB (annealed condition)
- Operating Temperature Range: −196°C to +870°C (−320°F to +1,598°F)
Thermal & Physical Properties
- Thermal Conductivity: 16.3 W/(m·K) at 100°C
- Specific Heat: 502 J/(kg·K) at 100°C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (20–100°C)
- Density: 7,930 kg/m³
Corrosion Resistance
- Excellent resistance to atmospheric corrosion, water, and food-grade chemical exposure
- SUS316 variant provides superior resistance to chlorides, acids, and marine environments
- Passive chromium oxide layer (Cr₂O₃) self-repairs under normal oxidizing conditions
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 22.0 mm (custom sizes available) | ASTM A213 / EN 10216-5 |
| Wall Thickness (WT) | 0.3 mm – 1.2 mm | ±0.05 mm tolerance |
| Inner Diameter (ID) | 4.4 mm – 20.4 mm (dependent on OD and WT) | Calculated |
| Internal Spiral Fin Height | 0.2 mm – 0.8 mm | Custom per application |
| Spiral Fin Pitch | 3.0 mm – 12.0 mm | Custom per application |
| Number of Spiral Threads | 1 – 4 (helical land configuration) | — |
| Coil Length (per coil) | 50 m – 500 m (typical) | — |
| Coil Inner Diameter (winding) | 150 mm – 300 mm | — |
| Surface Finish (External) | Polished / Bright Annealed (BA) / 2B | Ra ≤ 0.8 μm (polished) |
| Surface Finish (Internal) | Mirror polished with spiral geometry | Ra ≤ 0.4 μm |
| Dimensional Tolerance (OD) | ±0.05 mm | ISO 4624 |
| Dimensional Tolerance (WT) | ±10% of nominal | ASTM A213 |
| Heat Transfer Enhancement Factor | 1.8 – 3.2× vs. plain tube | Experimental data |
| Pressure Drop Increase | 1.2 – 2.0× vs. plain tube | Experimental data |
| Maximum Operating Pressure | Up to 2.5 MPa (363 psi) | Application-dependent |
| Refrigerant Compatibility | R-134a, R-410A, R-32, R-290, CO₂ (R-744) | ASHRAE 34 |
Manufacturing Process
The production of High-Precision Internal Spiral Stainless Steel Coil Tubes involves a multi-stage, closely controlled manufacturing sequence that integrates traditional tube-forming techniques with advanced internal spiral forming technology:
Process Flow
- Raw Material Selection & Inspection: Cold-rolled stainless steel strip (SUS304/SUS316) is sourced from certified mills and subjected to spectroscopic analysis (OES), mechanical testing, and visual inspection to ensure compliance with ASTM A213 or EN 10216-5 specifications.
- Strip Cutting & Edge Preparation: The stainless steel strip is slit to precise width and edge-trimmed to eliminate burrs, ensuring uniform material feed into the forming station.
- Seamless Tube Forming (Roll Forming): Multi-stand roll forming equipment progressively bends and shapes the flat strip into a seamless tubular profile. Precision tooling ensures dimensional accuracy within ±0.05 mm tolerance throughout the coil length.
- Internal Spiral Fin Forming: A proprietary internal spiral forming die assembly is deployed to create micro-helical fins on the inner wall surface. This critical step employs a specialized mandrel with a helical cutting/embossing profile that is fed through the tube bore. The forming process maintains wall integrity without perforation, creating continuous spiral land structures that induce secondary flow and enhance turbulence.
- Continuous Annealing (Bright Annealing): The formed coil tube passes through a continuous annealing furnace with a protective nitrogen atmosphere (O₂ ≤ 10 ppm). This relieves forming-induced residual stresses, restores full annealed softness (≤ 92 HRB), and prevents oxidation discoloration.
- Precision Surface Polishing: Internal and external surfaces undergo mechanical or electrochemical polishing to achieve Ra ≤ 0.4 μm (internal) and Ra ≤ 0.8 μm (external), minimizing friction losses and ensuring long-term anti-fouling performance.
- Coil Winding & Packaging: The finished coil tube is wound onto precision-wound coils with controlled tension to prevent deformation. Each coil is wrapped in moisture-proof protective film and labeled with traceability documentation.
- Final Quality Inspection: 100% dimensional verification (OD, WT, spiral pitch), helium leak testing (for pressure containment), and sampling-based metallurgical analysis (grain structure, hardness mapping) are performed prior to release.
Key Process Innovations
- Online Spiral Forming: The internal spiral is formed simultaneously with tube production, eliminating secondary operations and reducing cycle time by approximately 35%.
- Finite Element Analysis (FEA) Optimization: Spiral geometry (pitch, fin height, thread count) is pre-optimized using computational fluid dynamics (CFD) and structural FEA to maximize the heat transfer enhancement-to-pressure drop ratio.
- Real-Time Dimensional Monitoring: Laser-based in-line gauging systems continuously measure OD, WT, and coil diameter, with automated feedback control maintaining tolerances throughout production.
Applications
Primary Applications
- Air Conditioning Heat Exchangers: Evaporators and condensers for split-type, central, and industrial air conditioning systems where high thermal efficiency and compact design are paramount.
- Refrigeration Systems: Evaporator and condenser tubes in commercial refrigeration, cold storage, and cryogenic applications requiring corrosion-resistant tubing.
- Heat Pump Systems: Dual-circuit heat exchangers in air-source and ground-source heat pumps, leveraging the enhanced heat transfer characteristics for improved COP (Coefficient of Performance).
- Automotive HVAC: Compact evaporator and condenser assemblies for vehicle air conditioning systems where weight reduction and thermal performance are critical.
Secondary Applications
- Food & Beverage Processing: Heat exchangers in pasteurization, sterilization, and refrigeration systems requiring sanitary-grade stainless steel tubing.
- Pharmaceutical Equipment: Process heat exchangers where GMP (Good Manufacturing Practice) compliance and corrosion resistance are mandatory.
- Marine HVAC: Air conditioning systems in vessels exposed to corrosive saltwater environments, utilizing SUS316 grade for chloride resistance.
- Solar Thermal Collectors: Absorber tubes in evacuated tube solar collectors requiring high absorptivity and thermal efficiency.
Quality Certifications & Standards Compliance
Product Standards
- ASTM A213 / A213M: Standard Specification for Seamless Austenitic Stainless Steel Tubes, Pipes, and Fittings for High-Temperature Service
- EN 10216-5: Seamless Steel Tubes for Mechanical and Thermal Uses — Part 5: Technical Delivery Conditions for Austenitic and Austenitic-Ferritic (Duplex) Stainless Steel Tubes
- ISO 4624: Metallic Materials — Tolerances on Dimensions and Geometric Features for Tubes
- ASME BPV Code: Section VIII, Division 1 (Pressure Vessel Code) — for pressure-containing applications
Management System Certifications
- ISO 9001:2015: Quality Management Systems — Design, manufacture, and supply of stainless steel coil tubes
- ISO 14001:2015: Environmental Management Systems — Sustainable manufacturing practices
- ISO 45001:2018: Occupational Health and Safety Management Systems
- CE Marking: Conformity with European Machinery Directive and Pressure Equipment Directive (PED 2014/68/EU) where applicable
Testing & Inspection Protocols
- Hydrostatic Pressure Testing: 100% of coils tested at 1.5× working pressure with minimum 10-second hold time
- Helium Leak Detection: Non-destructive leak testing at sensitivity ≤ 1×10⁻⁹ Pa·m³/s for high-integrity applications
- Intergranular Corrosion Testing: ASTM A262 Practice E (acid solution exposure) to verify resistance to sensitization
- Piezoelectric Crystal Testing: Ultrasonic wall thickness verification on sampled lengths
- Positive Material Identification (PMI): XRF (X-Ray Fluorescence) spectroscopic verification of alloy composition on each production lot
Unique Selling Points
- Superior Heat Transfer Performance: The internal spiral geometry generates secondary Dean vortices, increasing the effective heat transfer coefficient by 80–220% compared to plain tubes while maintaining manageable pressure drop penalties.
- Compact Design Enablement: Enhanced thermal performance allows for 20–35% reduction in heat exchanger surface area, resulting in lighter, more compact HVAC units.
- Full-Length Spiral Consistency: Proprietary forming technology ensures uniform spiral geometry along the entire coil length (up to 500 m), eliminating performance variation that can occur with segmented or spot-applied internal structures.
- Corrosion-Resistant Longevity: Austenitic stainless steel construction provides 2–3× the service life of copper or aluminum alternatives in corrosive environments (marine, industrial, chemical).
- Refrigerant Compatibility: Fully compatible with next-generation low-GWP (Global Warming Potential) refrigerants including R-32, R-290 (propane), and CO₂ (R-744), supporting sustainability requirements.
- Continuous Coil Supply: Delivered as continuous Coiltube, enabling high-speed downstream U-bend forming, brazing, and assembly with zero joint-induced performance loss.
- Customizable Spiral Parameters: Fin pitch, height, and thread count are tailored to specific application requirements, allowing optimization of the thermal-hydraulic performance trade-off.
Technical Support & Ordering Information
Wenzhou Jixing Metal Materials Co., Ltd. provides comprehensive technical support including:
- CFD simulation and spiral geometry optimization for specific application parameters
- Thermal-hydraulic performance testing under controlled conditions
- Custom specification development for non-standard dimensions and configurations
- Material traceability documentation and full mill certificates for each production lot
- OEM/ODM production capabilities with minimum order quantities negotiable based on configuration
All products manufactured under ISO 9001:2015 quality management systems with full traceability from raw material to finished coil. Technical data sheets and performance reports available upon request.