F2 Series Stainless Steel Coil Tube for Fan Coil Units
Product Overview
The F2 Series Stainless Steel Coil Tube (Product Code: 1712) is a precision-engineered coiled tubing product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This coil tube is specifically designed for integration into fan coil unit (FCU) air conditioning systems, serving as the core heat exchange element within evaporator and condenser assemblies. The product combines the corrosion resistance and mechanical integrity of austenitic stainless steel with the compact, high-efficiency geometry of a continuously wound coil, making it an ideal solution for modern HVAC (Heating, Ventilation, and Air Conditioning) applications.
As a specialized component in the HVAC supply chain, this coil tube addresses the critical demand for long service life, thermal efficiency, and resistance to scaling and corrosion in humid and chemically aggressive environments. The coiled configuration maximizes the heat transfer surface area within a confined volume, enabling compact system design without compromising thermal performance.
Material & Properties
Base Material Composition
The coil tube is fabricated from high-grade austenitic stainless steel, conforming to industry-standard grades suitable for HVAC heat exchanger applications. The primary material grades include:
- 304 Stainless Steel (AISI 304 / UNS S30408) — the standard grade offering excellent general corrosion resistance, with a minimum nickel content of 8% and chromium content of 18%.
- 316 Stainless Steel (AISI 316 / UNS S31608) — enhanced grade with added molybdenum (2–3%) for superior resistance to pitting and crevice corrosion, particularly in coastal or chemically exposed environments.
- 304L / 316L Low-Carbon Variants — reduced carbon content (≤0.03%) to prevent sensitization during welding, ensuring long-term structural integrity at weld joints.
Key Physical and Mechanical Properties
- Density: 7.93 g/cm³ (304); 8.00 g/cm³ (316)
- Thermal Conductivity: 16.3 W/(m·K) at 25°C (304); 16.3 W/(m·K) at 25°C (316)
- Specific Heat Capacity: 0.50 J/(g·K) at 25°C
- Coefficient of Thermal Expansion: 17.3 × 10⁻⁶ /°C (304); 17.7 × 10⁻⁶ /°C (316)
- Tensile Strength: ≥ 515 MPa (annealed condition)
- Yield Strength: ≥ 205 MPa (0.2% offset)
- Elongation: ≥ 40% at break
- Operating Temperature Range: −196°C to +870°C (intermittent); continuous service up to +500°C
- Maximum Operating Pressure: Typically up to 1.6 MPa (design pressure varies by coil geometry and wall thickness)
Corrosion Resistance Characteristics
The austenitic stainless steel matrix provides exceptional resistance to:
- Atmospheric and industrial corrosion
- Scaling and fouling from circulating water
- Microbiologically Influenced Corrosion (MIC) in water-bearing systems
- Pitting and crevice corrosion (particularly in 316 grade)
- Intergranular corrosion in welded assemblies (with L-grades)
Specifications
| Parameter | Specification | Notes |
|---|---|---|
| Product Code | 1712 | Internal reference number |
| Product Name | F2 Series Coil Tube (盘管) | Designed for fan coil unit integration |
| Material Grade | AISI 304 / 316 / 304L / 316L | Selectable per application requirements |
| Outer Diameter (OD) | 6.35 mm / 8.00 mm / 9.53 mm / 12.70 mm | Standard sizes; custom diameters available |
| Wall Thickness | 0.30 mm – 1.20 mm | Dependent on OD and pressure rating |
| Inner Diameter (ID) | 5.75 mm – 10.50 mm | Calculated from OD and wall thickness |
| Coil Length | 3 m – 50 m (standard); up to 100 m (custom) | Delivered in continuous coil form |
| Coil Winding Diameter | ≥ 200 mm | Minimum winding diameter to prevent kinking |
| Surface Finish | Pickled & Passivated (P&P); Mirror Polish (Ra ≤ 0.4 μm) | P&P is standard; mirror finish on request |
| Tolerance – OD | ±0.05 mm (precision grade); ±0.10 mm (standard) | Per ASTM A778 / EN 10217 |
| Tolerance – Wall Thickness | ±10% (standard); ±5% (precision grade) | Per ASTM A778 |
| Surface Roughness | Ra ≤ 0.8 μm (inner surface); Ra ≤ 0.4 μm (mirror finish) | Smooth bore reduces flow resistance |
| Hydrostatic Test Pressure | 1.5 × Maximum Working Pressure (MWP) | Each coil tested prior to shipment |
| Maximum Flow Velocity | 2.0 – 3.0 m/s (water); 30 – 50 m/s (refrigerant) | Optimized for turbulent flow and heat transfer |
| Design Life | ≥ 25 years (indoor); ≥ 15 years (coastal/outdoor) | Under normal maintenance conditions |
Manufacturing Process
The production of the F2 Series Coil Tube follows a rigorous, multi-stage manufacturing process to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection and Incoming Inspection: Stainless steel strip or seamless tube blanks are sourced from certified mill suppliers. Incoming materials undergo spectroscopic analysis (OES) to verify chemical composition, along with mechanical property testing (tensile, hardness) to confirm conformance to the specified grade.
- Hot or Cold Forming: For seamless tube production, the material is hot-rolled into a round billet and then pierced. Cold-rolled forming follows to achieve precise outer diameter and wall thickness tolerances. Alternatively, welded tube production involves cold-rolled strip being formed into a round profile and welded using TIG (Tungsten Inert Gas) welding.
- Solution Annealing: The formed tube is solution-annealed at 1010–1150°C followed by rapid water quenching. This process dissolves carbide precipitates, restores full austenitic structure, and achieves the soft, ductile condition required for coiling.
- Pickling and Passivation: The annealed tube undergoes acid pickling (typically using nitric/hydrofluoric acid blend) to remove oxide scale, followed by passivation to re-establish a chromium-rich passive film on the surface. This ensures optimal corrosion resistance.
- Precision Coiling: The straight tube is wound into a continuous coil using a CNC-controlled coiling machine. The winding diameter, pitch, and number of turns are precisely controlled to meet the specified coil geometry. The coil is wound in a single continuous length to minimize joints and potential leak points.
- End Finishing and Deburring: Tube ends are cut to length, deburred, and chamfered to facilitate brazing or mechanical connection during assembly into the fan coil unit. End surfaces are inspected for burr-free, smooth finish.
- Quality Inspection and Testing: Each coil undergoes comprehensive testing including:
- Dimensional inspection (OD, wall thickness, coil length, winding diameter)
- Hydrostatic pressure testing at 1.5× MWP for a minimum hold time of 30 seconds
- Surface inspection (visual and, where required, magnetic particle or eddy current testing)
- Chemical composition verification via portable XRF (X-ray Fluorescence) analyzer
- Surface roughness measurement (where mirror polish is specified)
- Packaging and Dispatch: Coils are wrapped in protective film, placed in wooden or steel crates with desiccant packs, and labeled with product identification, material certificate, and traceability information.
Applications
The F2 Series Stainless Steel Coil Tube is engineered for a wide range of HVAC and thermal management applications:
- Fan Coil Units (FCUs): Primary application — serving as the evaporator coil in commercial and residential FCU air conditioning systems, where it exchanges heat between circulating chilled water and ambient air.
- Chilled Water Systems: Used in central air conditioning plants for chilled water distribution loops, where corrosion resistance extends system life significantly compared to copper or carbon steel alternatives.
- Heat Recovery Units: Employed in energy recovery ventilators (ERV) and heat recovery ventilators (HRV) for efficient thermal exchange between exhaust and supply air streams.
- Industrial Process Cooling: Suitable for cooling loops in manufacturing facilities where process fluids may be corrosive or where hygiene requirements demand stainless steel construction.
- Marine and Coastal HVAC: The 316 grade variant provides excellent resistance to salt-laden air, making it ideal for shipboard HVAC systems, offshore platforms, and coastal facility air conditioning.
- Food and Pharmaceutical Processing: Sanitary-grade applications where the non-toxic, non-contaminating properties of stainless steel are critical for product safety.
- Geothermal Heat Exchange: Used in ground-source heat pump systems for fluid circulation through borehole heat exchangers, benefiting from the material's resistance to geothermal water chemistry.
Quality Certifications and Standards
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework to ensure product conformance and traceability:
- ISO 9001:2015 — Quality Management Systems certification covering all manufacturing and quality control processes.
- ISO 14001:2015 — Environmental Management Systems certification, demonstrating commitment to sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management Systems certification.
- ASTM A778 / A778M — Standard specification for seamless austenitic stainless steel tube for heat exchangers and similar service.
- ASTM A269 — Standard specification for seamless and welded austenitic stainless steel sanitary tubing.
- EN 10217-7 — European standard for non-ferrous and stainless steel tubes for pressure purposes.
- GB/T 12771 — Chinese national standard for stainless steel seamless tubes for general use.
- GB/T 14976 — Chinese national standard for cold-rolled stainless steel seamless tubes.
- SUS 304 / 316 (JIS G4305) — Japanese Industrial Standard for stainless steel wire rod, bar, and section.
- Third-Party Inspection: Products are available for independent verification by SGS, Bureau Veritas, or TÜV upon customer request.
Unique Selling Points
- Superior Corrosion Resistance: Compared to traditional copper coil tubes, the stainless steel construction eliminates concerns about dezincification, stress corrosion cracking, and galvanic corrosion when in contact with dissimilar metals or aggressive water chemistries.
- Extended Service Life: The F2 Series coil tube offers a design life exceeding 25 years under indoor conditions, significantly outperforming copper coils (10–15 years) in corrosive environments.
- Hygienic and Non-Toxic: The inert surface of austenitic stainless steel ensures no leaching of heavy metals into the fluid stream, making it ideal for food-grade, pharmaceutical, and potable water applications.
- Customizable Geometry: The coil can be wound to precise dimensions and lengths tailored to specific FCU heat exchanger designs, enabling optimized thermal performance and compact installation.
- Low Maintenance: The passive film self-repairs in the presence of oxygen, minimizing maintenance requirements and reducing total cost of ownership over the product lifecycle.
- Full Traceability: Each coil is accompanied by a Material Test Certificate (MTC) per EN 10204 3.1, providing complete traceability from mill heat number to finished product.
Conclusion
The F2 Series Stainless Steel Coil Tube (Product Code: 1712) represents a premium solution for heat exchange applications in modern HVAC systems. By leveraging the inherent corrosion resistance, mechanical strength, and thermal performance of austenitic stainless steel in a precisely wound coil configuration, this product delivers exceptional reliability, longevity, and efficiency. Wenzhou Jixing Metal Materials Co., Ltd. is committed to delivering consistently high-quality products backed by rigorous quality control, international certifications, and full technical support to ensure optimal performance in every application.