Stainless Steel Coil Tube — HVAC Fan Coil Unit (FCU) Application
Wenzhou Jixing Metal Materials Co., Ltd. (Product No. 1414) offers a premium-grade stainless steel coil tube engineered specifically for dual-water-pipe fan coil unit (Fan Coil Unit, FCU) systems integrated with fresh air ventilation. This product represents a critical component in modern hydronic HVAC (Heating, Ventilation, and Air Conditioning) infrastructure, providing superior thermal exchange efficiency, extended service life, and resistance to corrosion in both heating and cooling operating modes.
Product Overview
The stainless steel coil tube is a coiled, serpentine heat exchanger element manufactured from austenitic stainless steel wire or tube stock, formed into a precise helical geometry to maximize surface area-to-volume ratio. In dual-water-pipe FCU systems, the coil tube serves as the primary heat transfer medium, circulating either chilled water or hot water through the coil to condition indoor air temperature. The dual-pipe configuration enables independent control of heating and cooling circuits, facilitating simultaneous temperature regulation and humidity management when paired with a dedicated fresh air handling unit (Fresh Air Handling Unit, FAHU).
This product line is designed to meet the rigorous demands of commercial and industrial HVAC installations where reliability, energy efficiency, and long-term durability are paramount. The coil tube geometry is optimized for laminar and transitional flow regimes, ensuring consistent heat transfer coefficients across a wide range of operating conditions.
Material and Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its exceptional combination of mechanical strength, corrosion resistance, and thermal conductivity.
- Base Material: Austenitic Stainless Steel (SAE 304 / AISI 304 or SAE 316 / AISI 316)
- Composition (304 Grade): Chromium (Cr) 18–20%, Nickel (Ni) 8–10.5%, Manganese (Mn) ≤2%, Carbon (C) ≤0.08%, Silicon (Si) ≤1%
- Composition (316 Grade): Chromium (Cr) 16–18%, Nickel (Ni) 10–14%, Molybdenum (Mo) 2–3%, Carbon (C) ≤0.08%
- Surface Finish: Polished or pickled and passivated surface to minimize fouling and facilitate cleaning
- Operating Temperature Range: −40°C to +250°C (−40°F to +482°F)
- Maximum Operating Pressure: Up to 1.6 MPa (232 PSI), depending on coil diameter and wall thickness
- Thermal Conductivity: Approximately 16–18 W/(m·K) at 20°C
- Tensile Strength: ≥520 MPa (annealed condition)
- Elongation: ≥40% at break
Technical Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Name | Stainless Steel Coil Tube (盘管) | — |
| Product Code | 1414 | — |
| Outer Diameter (OD) | 6.35 mm – 12.70 mm (¼" – ½") | ASTM A213 / ASTM A269 |
| Wall Thickness | 0.50 mm – 1.20 mm | ASTM A269 |
| Coil Pitch | 12 mm – 25 mm (adjustable per design) | Custom |
| Row Configuration | Single-row, double-row, or multi-row serpentine | ASHRAE Standard 90.1 |
| Tube Length per Row | Up to 1,500 mm (configurable) | Custom |
| Material Grade | AISI 304 / AISI 316 / Custom Alloy | ASTM A213 TP304 / TP316 |
| Surface Treatment | Pickled and Passivated (PP) or Electropolished | ASTM A967 |
| Hydrostatic Test Pressure | 1.5 × Maximum Working Pressure | ISO 4434 |
| Flow Rate Capacity | Up to 20 L/min per coil circuit | Design-dependent |
| Heat Transfer Coefficient | 2,000 – 4,500 W/(m²·K) (water-side) | ASHRAE Fundamentals |
| Compliance | EN 12828, ISO 9001, CE Marked | EN 12828 / ISO 9001:2015 |
Manufacturing Process
The production of stainless steel coil tubes follows a rigorous, multi-stage manufacturing protocol to ensure dimensional accuracy, material integrity, and consistent performance.
- Material Selection and Inspection: Raw stainless steel tube stock is sourced from certified mills and subjected to incoming quality control (Incoming Quality Control, IQC) including visual inspection, dimensional measurement, and chemical composition verification via optical emission spectroscopy (Optical Emission Spectroscopy, OES).
- Pre-Forming Preparation: Tubes are cut to specified lengths using precision shearing or laser cutting equipment. Ends are deburred and chamfered to prevent turbulence and ensure smooth fluid entry and exit.
- Coil Forming: The tube is formed into a helical coil using CNC-controlled coiling machinery. The forming process is performed in an annealed or solution-treated condition to prevent work hardening and cracking. Tight tolerances on coil pitch and diameter are maintained through real-time feedback systems.
- Serpentine Bending: For multi-row coil configurations, the helical coil is further bent into a serpentine (zig-zag) pattern using hydraulic bending equipment. Bend radii are calculated to minimize flow resistance while maximizing heat transfer surface area.
- Welding and Joining: End connections and manifold joints are welded using Gas Tungsten Arc Welding (Gas Tungsten Arc Welding, GTAW / TIG) or Orbital Welding to ensure leak-tight, high-integrity joints. Weld parameters are optimized for the specific alloy grade to prevent sensitization and intergranular corrosion.
- Pickling and Passivation: The completed coil assembly undergoes pickling to remove oxide scale and passivation to restore the chromium oxide passive film, ensuring maximum corrosion resistance. This process conforms to ASTM A967.
- Pressure Testing: Each coil unit is hydrostatically tested at 1.5 times the maximum working pressure to verify weld integrity and structural soundness. Leak detection is performed using helium sniffing or ultrasonic methods.
- Final Inspection and Packaging: Finished products undergo dimensional verification, surface quality assessment, and material certification traceability checks. Coils are packaged with protective end caps and corrosion inhibitors for safe transport.
Applications
The stainless steel coil tube from Wenzhou Jixing Metal Materials Co., Ltd. is designed for a wide spectrum of HVAC and thermal management applications:
- Commercial HVAC Systems: Dual-water-pipe fan coil units in office buildings, hotels, hospitals, and shopping centers where simultaneous heating and cooling zones require independent circuit control.
- Integrated Fresh Air Systems: Coil tubes paired with Fresh Air Handling Units (FAHU) to provide conditioned ventilation air, maintaining indoor air quality (Indoor Air Quality, IAQ) while managing thermal loads efficiently.
- Industrial Process Cooling: Precision temperature control in manufacturing facilities, cleanrooms, and data centers requiring corrosion-resistant heat exchange components.
- Marine and Coastal Environments: 316-grade coil tubes provide superior resistance to chloride-induced pitting corrosion, making them ideal for coastal and marine HVAC installations.
- Food and Pharmaceutical Industries: Hygienic-grade coil tubes meet the stringent sanitation requirements of food processing and pharmaceutical manufacturing facilities.
- Residential High-End Systems: Compact coil units for premium residential HVAC installations where long service life and low maintenance are prioritized.
Quality Certifications and Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system aligned with international standards:
- ISO 9001:2015 — Quality Management Systems certification, ensuring consistent product quality and customer satisfaction.
- ISO 14001:2015 — Environmental Management Systems certification, demonstrating commitment to sustainable manufacturing practices.
- CE Marking — Conformity with European health, safety, and environmental protection standards per the Pressure Equipment Directive (PED) 2014/68/EU.
- EN 12828 — Compliance with European standards for heating systems in buildings and their components.
- ASTM A213 / ASTM A269 — Material specification compliance for austenitic stainless steel seamless tubes.
- ASTM A967 — Compliance with pickling and passivation process requirements.
- ASME B31.9 — Compliance with pressure piping code for refrigeration and air-conditioning systems.
Unique Selling Points
- Superior Corrosion Resistance: Austenitic stainless steel construction provides exceptional resistance to oxidation, scaling, and chemical attack, significantly extending service life compared to carbon steel or copper alternatives.
- Thermal Efficiency Optimization: Precision-engineered coil geometry maximizes heat transfer surface area while minimizing pressure drop, reducing pump energy consumption by up to 15–20% in dual-pipe FCU configurations.
- Dual-Pipe System Compatibility: Specifically designed for integration with dual-water-pipe fan coil unit systems, enabling independent heating and cooling circuit operation with a dedicated fresh air supply.
- Customizable Configurations: Flexible manufacturing capabilities allow customization of coil diameter, pitch, row count, and length to meet specific project requirements and space constraints.
- Traceable Quality Assurance: Full material traceability from mill certification to final product testing, ensuring compliance with all applicable international standards.
- Low Maintenance Design: Smooth, passivated surfaces resist fouling and biofilm formation, reducing maintenance frequency and total cost of ownership over the system lifecycle.
Note: The dual-water-pipe fan coil unit with fresh air system (双水管风机盘管加新风系统) represents an advanced HVAC configuration where the coil tube serves as the thermal core. The separation of heating and cooling water circuits, combined with a dedicated fresh air pathway, enables precise indoor climate control while maintaining optimal indoor air quality — a configuration increasingly mandated in high-performance building standards such as LEED (Leadership in Energy and Environmental Design) and Green Star ratings.