Stainless Steel Coil Tube (Coiltube) for Fan Coil Unit Applications
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled tubing product designed specifically for use in fan coil unit (FCU) systems and related HVAC (Heating, Ventilation, and Air Conditioning) applications. This product is developed in strict compliance with the national standards governing domestic fan coil units in China, ensuring dimensional accuracy, thermal performance, and long-term reliability under demanding operating conditions.
The coil tube serves as the core heat exchange element within fan coil units, facilitating efficient thermal transfer between the circulating fluid (typically water or refrigerant) and the surrounding air. The coiled geometry maximizes surface area within a compact envelope, delivering superior heat exchange efficiency compared to straight-tube alternatives.
Material & Properties
Material Composition
The coil tube is fabricated from high-grade stainless steel, typically conforming to AISI 304 (UNS S30400) or AISI 316 (UNS S31600) grades, selected based on the specific corrosion resistance and mechanical performance requirements of the application environment.
- Base Metal: Austenitic stainless steel with minimum chromium (Cr) content of 18% and nickel (Ni) content of 8% (304 grade) or enhanced molybdenum (Mo) content of 2–3% (316 grade)
- Surface Finish: Cold-rolled and annealed (2B finish) or polished finish (RA ≤ 0.4 μm) depending on application requirements
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, water scale, and mild chemical environments; 316 grade provides additional resistance to chlorides and marine atmospheres
Key Physical and Mechanical Properties
| Property | Specification | Test Standard |
|---|---|---|
| Density | 7.93 g/cm³ | ASTM A968 |
| Tensile Strength (UTS) | ≥ 515 MPa | ASTM A240 / GB/T 24511 |
| Yield Strength (0.2% Offset) | ≥ 205 MPa | ASTM A240 / GB/T 24511 |
| Elongation (A50mm) | ≥ 40% | ASTM A240 |
| Thermal Conductivity (at 20°C) | 16.3 W/(m·K) | ASTM A968 |
| Thermal Expansion Coefficient | 17.3 × 10⁻⁶ /°C | ASTM A968 |
| Operating Temperature Range | −196°C to +870°C | — |
| Maximum Working Pressure | 1.6 MPa (standard); up to 2.5 MPa (reinforced) | GB/T 18431 |
Specifications
| Parameter | Specification | Remarks |
|---|---|---|
| Outer Diameter (OD) | 6 mm, 8 mm, 10 mm, 12 mm (custom available) | ±0.1 mm tolerance |
| Wall Thickness (WT) | 0.5 mm, 0.6 mm, 0.8 mm, 1.0 mm | ±0.05 mm tolerance |
| Coil Inner Diameter (CID) | 50 mm – 200 mm (configurable) | Based on FCU design requirements |
| Tube Length per Coil | Up to 100 m (continuous coil) | Custom lengths available |
| Number of Coils (Rows) | 1 – 6 rows (standard configurations) | Per GB/T 19232 |
| Bend Radius (Minimum) | ≥ 3 × OD | Prevents ovality and collapse |
| Fin Pitch (with fins) | 2.0 mm – 3.5 mm (aluminum fins, if applicable) | Enhanced heat transfer configuration |
| Surface Treatment | Passivated / Pickled and Passivated | GB/T 4237 |
| Hydrostatic Test Pressure | 1.5 × Maximum Working Pressure | 100% inline testing |
| Refrigerant Compatibility | R410A, R32, R404A, R134a, Water/Glycol | — |
| Standards Compliance | GB/T 19232, GB/T 18431, GB/T 24511, GB/T 4237 | Chinese National Standards |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing process to ensure dimensional precision, mechanical integrity, and corrosion resistance:
- Raw Material Inspection: Incoming stainless steel strip or seamless pipe stock is verified for chemical composition (via XRF or spectroscopic analysis) and mechanical properties per ASTM A240 / GB/T 24511 requirements.
- Coil Forming / Pipe Winding: High-precision CNC winding machines form the straight stainless steel tubing into the specified coil geometry. The winding process maintains controlled tension to prevent material deformation, ovality, or stress concentration at bend points.
- Welding (if applicable): For coil tubes requiring longitudinal seams, TIG (Tungsten Inert Gas) welding or orbital welding is employed with argon (Ar) shielding gas to ensure clean, penetration-free welds. Weld bead height is controlled to ≤ 0.1 mm to minimize internal flow resistance.
- Heat Treatment / Stress Relief: Post-forming annealing at 1050°C – 1150°C followed by controlled cooling eliminates residual stresses introduced during the forming process, restoring full austenitic microstructure and mechanical properties.
- Pickling and Passivation: The coil tube undergoes acid pickling (HNO₃ + HF mixture) to remove oxidation scale, followed by passivation treatment (HNO₃-based) to form a stable chromium oxide (Cr₂O₃) protective film on the surface, enhancing corrosion resistance per GB/T 4237.
- Hydrostatic Pressure Testing: Each coil tube assembly is subjected to 100% hydrostatic testing at 1.5 × the maximum working pressure (typically 2.4 MPa for 1.6 MPa rated coils) to verify weld integrity and structural soundness. Hold time: minimum 30 seconds.
- Dimensional Inspection: Final inspection verifies outer diameter, wall thickness, coil diameter, straightness, and bend radius using laser measurement systems and calibrated gauges. Acceptance criteria per GB/T 18431.
- Packaging and Dispatch: Qualified products are wrapped in protective film, secured on wooden pallets, and labeled with material certificates, batch traceability codes, and inspection reports.
Applications
Primary Applications
- Fan Coil Units (FCU): The primary application domain. The coil tube serves as the heat exchanger core in both water-cooled and direct-expansion (DX) fan coil units used in commercial buildings, hotels, hospitals, and office complexes.
- HVAC Systems: Integration into Variable Air Volume (VAV) systems, Constant Air Volume (CAV) systems, and chilled water distribution networks.
- Air Handling Units (AHU): Use as coil elements in large-capacity air handling units for centralized air conditioning.
Secondary Applications
- Industrial Process Cooling/Heating: Precision temperature control in pharmaceutical manufacturing, food processing, and electronics production.
- Water-to-Water Heat Exchangers: Compact heat exchange elements in industrial thermal management systems.
- Refrigeration Systems: Evaporator and condenser coils in commercial refrigeration equipment.
- Geothermal Heat Pump Systems: Coil tubes for ground-source heat exchanger loops.
- Marine and Offshore HVAC: Corrosion-resistant coil tubes for marine air conditioning systems (316 grade recommended).
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality assurance and certification systems to ensure product conformity with national and international standards:
- ISO 9001:2015 — Quality Management System certification, demonstrating systematic commitment to quality throughout the manufacturing lifecycle.
- ISO 14001:2015 — Environmental Management System certification, confirming environmentally responsible production practices.
- GB/T 19232 Compliance — Full compliance with the Chinese National Standard for Fan Coil Units (风机盘管机组), covering thermal performance, air flow characteristics, and noise levels.
- GB/T 18431 Compliance — Conformity with the standard for stainless steel welded pipes, ensuring mechanical integrity and dimensional accuracy.
- GB/T 24511 Compliance — Compliance with the standard for steel tubes and fittings for pressure purposes, validating pressure containment capability.
- Material Mill Certificates (EN 10204 Type 3.1) — Each batch is accompanied by a certified material test report from the mill of origin, verifying chemical composition and mechanical properties.
- Hydrostatic Test Reports — 100% inline testing documentation for each production batch.
- Third-Party Inspection — Available upon request (SGS, Bureau Veritas, or TÜV inspection).
Unique Selling Points
- Full Standard Compliance: Products are engineered and manufactured in strict accordance with the domestic fan coil unit national standards (GB/T 19232), ensuring seamless integration into certified HVAC systems and compliance with building code requirements.
- Precision Coil Geometry: CNC-controlled winding ensures consistent coil diameter and pitch, optimizing heat transfer surface area and minimizing flow maldistribution within the heat exchanger.
- Superior Corrosion Resistance: The austenitic stainless steel construction with pickled and passivated finish provides exceptional longevity in humid, chemically aggressive, or saline environments where carbon steel alternatives would fail prematurely.
- Full Traceability: Each coil tube carries batch traceability documentation from raw material mill certificate through final hydrostatic testing, enabling complete supply chain accountability.
- Customization Capability: Flexible configuration of outer diameter, wall thickness, coil diameter, row count, and length to meet specific OEM and project requirements.
- Pressure Integrity Assurance: 100% hydrostatic pressure testing at 1.5× working pressure guarantees zero-defect delivery and eliminates field failure risk.
- Energy Efficiency Contribution: The optimized coil geometry and high thermal conductivity of stainless steel contribute to reduced fan power consumption and improved COP (Coefficient of Performance) in the overall FCU system.
Standards Reference
| Standard Number | Title | Relevance |
|---|---|---|
| GB/T 19232 | Fan Coil Units (风机盘管机组) | Primary product performance standard |
| GB/T 18431 | Stainless Steel Welded Pipes | Material and dimensional specification |
| GB/T 24511 | Steel Tubes and Fittings for Pressure Purposes | Mechanical property requirements |
| GB/T 4237 | Technical Requirements for Hot/Cold Rolled Steel Plates | Surface treatment and passivation |
| ASTM A240 | Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plate, Sheet, and Strip | International material benchmark |
| EN 10204 | Steel Products — Types of Delivery Documents | Certification documentation standard |