Stainless Steel Coil Tube for Fan Coil Unit (FCU) Systems
Product Code: 1418 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
1. Product Overview
The stainless steel coil tube is a precision-engineered heat exchange component designed specifically for Fan Coil Unit (FCU) air conditioning systems. As a core element within the hydronic coil assembly, this product facilitates efficient heat transfer between circulating water and ambient air, enabling precise temperature regulation in commercial and residential HVAC (Heating, Ventilation, and Air Conditioning) applications. The coil tube is manufactured to meet rigorous industry standards and is engineered to withstand prolonged exposure to water-borne chemicals, thermal cycling, and mechanical vibration inherent in continuous-duty HVAC operation.
Wenzhou Jixing Metal Materials Co., Ltd. has developed advanced water flow control methodologies for FCU systems, integrating intelligent hydraulic management strategies that optimize coil tube performance, reduce energy consumption, and extend service life. The company's expertise in metallurgy and precision forming ensures that each coil tube delivers superior thermal conductivity, structural integrity, and corrosion resistance under demanding operating conditions.
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from austenitic stainless steel, predominantly conforming to the following grades:
- AISI 304 (UNS S30408): The standard grade offering excellent general corrosion resistance, suitable for most indoor HVAC applications with clean water systems.
- AISI 316 (UNS S31608): Enhanced grade with molybdenum addition (2–3%), providing superior resistance to chlorides and aggressive water chemistries, recommended for coastal environments or systems with elevated chloride content.
- AISI 316L (UNS S31603): Low-carbon variant of 316, offering improved weldability and resistance to intergranular corrosion, ideal for welded coil assemblies.
2.2 Mechanical Properties
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (UTS) | ≥ 520 MPa (AISI 304) / ≥ 515 MPa (AISI 316) | ASTM A269 / GB/T 12771 |
| Yield Strength (0.2% offset) | ≥ 205 MPa | ASTM A269 |
| Elongation (at break) | ≥ 40% (as-delivered condition) | ASTM A269 |
| Hardness (Rockwell B) | ≤ 95 HRB (annealed) | ASTM A269 |
| Thermal Conductivity (at 20°C) | 16.3 W/(m·K) (AISI 304) / 14.6 W/(m·K) (AISI 316) | ASTM E153 |
| Thermal Expansion Coefficient (20–100°C) | 17.3 × 10⁻⁶ /K | ASTM E153 |
2.3 Chemical Composition (Typical, wt%)
| Element | AISI 304 | AISI 316 |
|---|---|---|
| Carbon (C) max | 0.08 | 0.08 |
| Chromium (Cr) | 18.0–20.0 | 16.0–18.0 |
| Nickel (Ni) | 8.0–10.5 | 10.0–14.0 |
| Molybdenum (Mo) | — | 2.0–3.0 |
| Manganese (Mn) max | 2.0 | 2.0 |
| Silicon (Si) max | 0.75 | 0.75 |
| Sulfur (S) max | 0.03 | 0.03 |
3. Technical Specifications
| Parameter | Specification | Notes |
|---|---|---|
| Outer Diameter (OD) | Φ9.52 mm (3/8") / Φ12.70 mm (1/2") / Φ15.88 mm (5/8") | Standard FCU coil sizes |
| Wall Thickness (WT) | 0.40–1.00 mm (adjustable per application) | Thinner wall for higher heat transfer; thicker for pressure resistance |
| Coil Length (per bank) | 1.0–6.0 meters (customizable) | Determined by heat load requirement |
| Coil Configuration | Single-row, double-row, or multi-row serpentine | Row count based on capacity demand |
| Fin Type | Aluminum or stainless steel plate fins | Fin density: 8–14 FPI (Fins Per Inch) |
| Operating Pressure | ≤ 1.6 MPa (232 psi) typical; up to 2.5 MPa on request | Hydrostatic test at 1.5× working pressure |
| Operating Temperature Range | −20°C to +120°C (water side) | Continuous duty rating |
| Surface Finish | Mirror polished (Ra ≤ 0.4 μm) or brushed (Ra ≤ 1.6 μm) | Reduces fouling and biofilm adhesion |
| Connection Method | Soldered, brazed, or welded (TIG) headers | Brazing alloy: Cu-P or Ni-based for SS compatibility |
| Material Standard | ASTM A269 / ASME SA269 / GB/T 12771 / EN 10217-7 | Mutually equivalent certifications |
| Maximum Flow Velocity | ≤ 2.5 m/s (recommended) / ≤ 3.5 m/s (maximum) | Exceeding limits may cause erosion-corrosion |
4. Manufacturing Process
The production of stainless steel coil tubes for FCU applications follows a rigorous multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical soundness, and surface quality:
- Raw Material Selection & Inspection: Cold-rolled stainless steel strip is procured from certified mills. Incoming material undergoes spectrographic analysis (OES), mechanical property verification, and visual surface inspection in accordance with ASTM A269 requirements.
- Tube Forming (Cold Draw & Butt Weld): Strip is fed through a precision die set to form seamless or welded tubular stock. For welded tubes, high-frequency induction welding (HF) or orbital TIG welding is employed, followed by inside/outside welding bead grinding and pickling to restore corrosion resistance.
- Heat Treatment & Annealing: Tubes are solution-annealed at 1050–1150°C in a controlled atmosphere (argon or vacuum) furnace, followed by rapid quenching. This process dissolves carbides, relieves residual stresses, and establishes the desired austenitic microstructure.
- Precision Sizing & Straightening: Cold sizing passes through calibrated mandrels ensure uniform wall thickness and roundness tolerance within ±0.05 mm.
- Coil Forming (Tube Bending): The straight tube is cold-bent into the required serpentine coil geometry using CNC-controlled roll-bending or press-bending equipment. Bend radii are maintained at ≥ 3× tube OD to prevent wall thinning and buckling. Springback compensation is algorithmically applied.
- Fin Insertion & Header Assembly: Fins are inserted into the formed coil tubes, and the coil bank is assembled between inlet and outlet headers. Brazing or welding is performed to create a hermetic fluid circuit.
- Surface Passivation & Cleaning: The completed coil assembly undergoes acid pickling and passivation treatment (nitric-hydrofluoric acid blend or citric acid solution) to remove heat scale, oxidation, and contaminants, forming a protective chromium oxide passive layer.
- Pressure Testing & Non-Destructive Inspection: Each coil assembly is hydrostatically tested at 1.5× the maximum working pressure for a minimum dwell time of 10 minutes. Leak detection employs visual inspection, ultrasonic testing (UT), or dye penetrant testing (PT) on weld joints.
- Final Inspection & Packaging: Dimensional verification, surface roughness measurement, and material certification documentation are completed. Coils are protected with desiccant bags, foam end caps, and export-grade wooden crates or corrugated cartons.
5. Applications
The stainless steel coil tube finds extensive application across diverse HVAC and thermal management sectors:
- Commercial HVAC Systems: Primary heat exchange component in ceiling-mounted, wall-mounted, and ducted fan coil units for office buildings, hotels, hospitals, and shopping centers.
- Residential Air Conditioning: Used in high-end residential FCU systems where corrosion resistance and long service life are prioritized.
- Cleanroom & Laboratory HVAC: Stainless steel coil tubes meet the stringent cleanliness requirements of pharmaceutical manufacturing, semiconductor fabrication, and research laboratories.
- Marine & Coastal HVAC: AISI 316-grade coil tubes provide essential chloride resistance for HVAC systems installed in coastal regions, marine vessels, and offshore platforms.
- Food & Beverage Processing: Hygienic-grade stainless steel coils comply with FDA and EU regulations for HVAC systems in food processing facilities.
- Refrigeration Systems: Low-temperature coil tubes for cold storage, refrigeration condensers, and evaporator units.
5.1 Advanced Water Flow Control Integration
Wenzhou Jixing Metal Materials Co., Ltd. has pioneered novel water flow control methodologies for FCU systems that directly enhance coil tube performance. These innovations include:
- Variable Flow Modulation: Integration of smart flow control valves enables precise water flow rate adjustment matched to real-time thermal loads, preventing over-cooling and under-cooling while optimizing coil tube efficiency.
- Anti-Fouling Flow Dynamics: Optimized flow velocity profiles within the coil tubes minimize deposit formation and biofilm accumulation, maintaining heat transfer coefficients over extended operating cycles.
- Thermal Stratification Mitigation: Advanced manifold distribution ensures uniform water temperature across all coil tube rows, eliminating cold spots and improving overall system COP (Coefficient of Performance).
6. Quality Certifications & Standards Compliance
All products manufactured by Wenzhou Jixing Metal Materials Co., Ltd. are subject to comprehensive quality assurance programs aligned with international standards:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent product quality and continuous improvement |
| ISO 14001:2015 | Environmental Management System certification for sustainable manufacturing practices |
| ISO 45001:2018 | Occupational Health and Safety Management System |
| CE Marking (EU) | Compliance with European Pressure Equipment Directive (PED 2014/68/EU) for pressure-containing components |
| EN 12828 | European standard for heating systems in buildings, covering component requirements |
| ASME SA269 | American Society of Mechanical Engineers standard for seamless and welded austenitic stainless steel tubing |
| GB/T 12771 | Chinese national standard for welded austenitic stainless steel seamless tubes for general use |
| NSF/ANSI 61 | Health Effects Standard for Drinking Water System Components (where applicable for potable water loops) |
| Third-Party Mill Test Reports (MTR) | <