Stainless Steel Coil Tube (Coiltube) – Fan Coil Unit Application Grade
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled piping solution specifically designed for high-performance Fan Coil Units (FCUs) and HVAC (Heating, Ventilation, and Air Conditioning) systems. This product represents a critical component in modern building climate control infrastructure, where the thermal efficiency, corrosion resistance, and structural integrity of coil tubing directly determine system performance, service life, and energy consumption metrics.
Unlike conventional carbon steel or copper coil tubes, the stainless steel variant offers superior resistance to chemical attack, thermal cycling fatigue, and long-term degradation, making it particularly suitable for applications involving aggressive refrigerants, high-humidity environments, and extended operational cycles. The coil geometry is optimized to maximize heat transfer surface area within a compact footprint, aligning with the design principles outlined in performance-enhancement methodologies for fan coil unit systems.
Material & Properties
The coil tube is fabricated from austenitic stainless steel grades, with primary specifications based on the following material compositions:
- Grade 304 (UNS S30400): Contains approximately 18% Chromium (Cr) and 8% Nickel (Ni), providing excellent general corrosion resistance and formability. This is the standard grade for most HVAC coil applications.
- Grade 316 (UNS S31600): Includes 2–3% Molybdenum (Mo) in addition to Cr and Ni, offering enhanced resistance to pitting corrosion and chloride attack—ideal for coastal or chemically aggressive environments.
- Grade 321 (UNS S32100): Stabilized with Titanium (Ti), providing superior resistance to intergranular corrosion during welding and high-temperature exposure.
Mechanical Properties (Annealed Condition)
- Tensile Strength: ≥ 520 MPa (Grade 304); ≥ 570 MPa (Grade 316)
- Yield Strength (0.2% offset): ≥ 205 MPa
- Elongation: ≥ 40%
- Hardness: ≤ 217 HB (annealed condition)
- Thermal Conductivity: ~16.3 W/(m·K) at 20°C
- Thermal Expansion Coefficient: ~17.3 × 10⁻⁶ /K (20–100°C)
- Operating Temperature Range: −196°C to +870°C
Corrosion Resistance Characteristics
- Excellent resistance to atmospheric corrosion and industrial pollution
- High resistance to acidic and alkaline solutions (pH range 3–11)
- Superior performance against refrigerant-induced stress corrosion cracking compared to copper alternatives
- Non-toxic and hygienic surface suitable for potable water systems
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) |
| Item Number | 1526 |
| Material Grade | 304 / 316 / 321 (Austenitic Stainless Steel) |
| Outer Diameter (OD) | 6.0 mm / 8.0 mm / 9.5 mm / 10.0 mm / 12.0 mm (customizable) |
| Wall Thickness | 0.3 mm / 0.4 mm / 0.5 mm / 0.6 mm / 0.8 mm (customizable) |
| Coil Diameter | 150 mm – 600 mm (standard range) |
| Coil Length | Up to 200 m per coil (continuous) |
| Surface Finish | 2B / BA (Bright Annealed) / No.4 Brushed / Mirror (Ra ≤ 0.2 μm) |
| Dimensional Tolerance | ±0.05 mm (OD); ±0.02 mm (Wall Thickness) |
| Coil Pitch | 5.0 mm – 15.0 mm (configurable for heat exchanger design) |
| Standard Compliance | ASTM A213 / A269 / GB/T 14976 / EN 10216-5 |
| Packaging | Wooden pallet with moisture-proof wrapping; export-grade crating available |
Manufacturing Process
The production of high-performance stainless steel coil tubes follows a rigorous multi-stage manufacturing process designed to ensure dimensional accuracy, metallurgical homogeneity, and surface integrity:
- Raw Material Selection & Incoming Inspection: Only certified stainless steel strip material from approved mill sources is accepted. Incoming material undergoes spectroscopic analysis (OES) to verify chemical composition and mechanical property testing to confirm compliance with ASTM/GB standards.
- Slitting & Leveling: Coil strip is precision-slitted to the required width using high-tension slitting lines, followed by leveling to eliminate coil set and ensure flatness within ±0.1 mm/m.
- Tube Forming (Roll Forming): Multi-stand roll-forming machines progressively bend the flat strip into a circular cross-section. The forming stations are computer-controlled to maintain consistent wall thickness distribution and minimize ovality (≤ 0.15% of OD).
- Welding (TIG/Orbital): The longitudinal seam is welded using Gas Tungsten Arc Welding (GTAW/TIG) with high-purity Argon (Ar, ≥ 99.995%) shielding. Orbital welding ensures consistent weld quality around the entire tube circumference.
- Heat Treatment (Annealing): Welded tubes undergo solution annealing at 1050–1100°C in a controlled-atmosphere furnace (hydrogen or vacuum) to relieve welding stresses, restore full austenitic structure, and achieve maximum corrosion resistance.
- Pickling & Passivation: Tubes are cleaned via acid pickling (HNO₃/HF blend) to remove oxide scale, followed by passivation treatment to restore the chromium oxide protective layer.
- Coiling & Pitch Winding: Straight tubes are coiled at specified diameters and pitches using CNC-controlled coiling machines. The winding process ensures uniform coil geometry critical for heat exchanger packing density.
- Final Quality Inspection: Each coil undergoes hydrostatic pressure testing (2.0× working pressure), dimensional verification (CMM/optical measurement), surface inspection, and chemical composition re-verification.
Applications
The stainless steel coil tube from Wenzhou Jixing Metal Materials is engineered for demanding applications where performance, reliability, and longevity are paramount:
Primary Applications
- Fan Coil Units (FCUs): Serves as the core heat exchange element in commercial and residential HVAC systems. The stainless steel material eliminates the risk of stress corrosion cracking that plagues copper coils when exposed to certain refrigerants (e.g., R-134a, R-410A) and humid air, directly addressing the performance degradation issues discussed in fan coil unit optimization literature.
- Chilled Water & Hot Water Systems: Ideal for hydronic heating and cooling distribution where water quality variability and long-term operation require corrosion-resistant piping.
- Refrigeration & Heat Pump Systems: Provides reliable heat transfer surfaces in evaporators and condensers operating with various refrigerant types.
- Plate Heat Exchanger Alternatives: Used in shell-and-tube heat exchangers requiring corrosion-resistant internals for chemical processing, food and beverage, and pharmaceutical applications.
Industry-Specific Applications
- Marine & Offshore: Resistant to saltwater corrosion for shipboard HVAC systems
- Food & Beverage Processing: Hygienic surface finish meets FDA and 3-A sanitary standards
- Pharmaceutical & Biotech: Non-reactive surface prevents product contamination
- Power Generation: Condenser tubes in steam turbine systems
- Chemical Processing: Resistant to acidic process fluids and aggressive environments
Unique Selling Points
- Enhanced Fan Coil Unit Performance: The superior thermal conductivity-to-corrosion-resistance ratio of stainless steel coil tubes enables sustained heat transfer efficiency throughout the system lifecycle, directly addressing the performance decline issues documented in HVAC optimization research.
- Extended Service Life: Elimination of internal corrosion and scale buildup maintains design heat transfer capacity for 20+ years, compared to 8–12 years for standard copper coils in aggressive environments.
- Refrigerant Compatibility: Full compatibility with all modern HFC and HFO refrigerants without risk of stress corrosion cracking or ammonia-induced degradation.
- Customizable Geometry: Flexible coil diameter, pitch, and tube dimension customization allows OEM integration into specific FCU designs without compromising performance.
- Hygienic Surface: Low surface roughness (Ra ≤ 0.2 μm available) prevents microbial adhesion and biofilm formation, reducing maintenance requirements.
- Environmental Sustainability: Stainless steel is 100% recyclable with no loss of material properties, supporting circular economy goals in building HVAC systems.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems and holds the following certifications and compliances:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent product quality and process control |
| ISO 14001:2015 | Environmental Management System certification for sustainable manufacturing practices |
| ISO 45001:2018 | Occupational Health and Safety Management System |
| CE Marking | European Conformity certification for market access in EU member states |
| ASTM A213 / A269 | Compliance with American Society for Testing and Materials standards for seamless and welded austenitic stainless steel tubing |
| GB/T 14976 | Chinese National Standard for seamless stainless steel hydraulic and pneumatic tubing |
| EN 10216-5 | European Standard for non-alloy and alloy steel tubes for technical purposes |
| Third-Party Inspection | Available SGS / BV / TÜV inspection services for export orders |
Quality Assurance Protocol
Every production batch undergoes a comprehensive quality assurance protocol including: chemical composition verification via Optical Emission Spectroscopy (OES), mechanical property testing (tensile, hardness, impact), hydrostatic pressure testing, dimensional measurement using Coordinate Measuring Machines (CMM), surface finish measurement (profilometry), and visual inspection under controlled lighting conditions. Mill Test Certificates (MTC) conforming to EN 10204 3.1 are provided with each shipment.
Technical Notes for FCU Integration
Based on performance optimization research for fan coil unit systems, the following design considerations are recommended when integrating stainless steel coil tubes:
- Fin-to-Tube Bonding: Utilize mechanical bonding (mechanical bonding) or brazing with compatible filler metals (e.g., copper-phosphorus brazing alloy) to achieve thermal contact resistance below 10 m²·K/W.
- Flow Distribution: Design inlet/outlet headers to ensure uniform flow distribution across all tube passes, minimizing bypass flow that reduces effective heat transfer area.
- Anti-Vibration Mounting: Implement flexible connections and vibration-isolating supports to prevent fatigue failure at tube sheet interfaces.
- Water Treatment: While stainless steel offers superior corrosion resistance, maintaining water quality (conductivity < 50 μS/cm, pH 6.5–8.5) further extends service life and prevents scale formation.
Wenzhou Jixing Metal Materials Co., Ltd. provides comprehensive technical support, including coil tube design consultation, thermal performance simulation data, and application engineering guidance to ensure optimal integration into fan coil unit and heat exchange systems.