Stainless Steel Coil Tube for Fan Coil Unit (FCU) HVAC Systems
Product Overview
The Stainless Steel Coil Tube (Product No. 334) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled tubing product designed for integration into Fan Coil Units (FCU) within commercial and industrial HVAC (Heating, Ventilation, and Air Conditioning) systems. This product serves as a critical heat exchange medium in demand-response air conditioning architectures, particularly in high-capacity environments such as cinema halls, convention centers, and entertainment venues where precise thermal regulation and energy efficiency are paramount.
Unlike conventional copper coil tubes, the stainless steel variant offers superior resistance to corrosion, thermal cycling fatigue, and chemical degradation, making it an ideal solution for long-duration, high-uptime HVAC applications where system reliability directly impacts operational revenue.
Material & Properties
The coil tube is fabricated from high-grade Stainless Steel (AISI 304 / 316L) austenitic alloy, selected for its optimal balance of mechanical strength, thermal conductivity, and corrosion resistance. Key material properties include:
- Base Alloy: AISI 304 (UNS S30400) or AISI 316L (UNS S31603) — the latter offering enhanced resistance to chloride-induced pitting corrosion in humid coastal environments
- Carbon Content: ≤ 0.08% (304) / ≤ 0.03% (316L), ensuring resistance to intergranular sensitization during welding
- Nickel Content: 8.0–10.5%, providing stable austenitic microstructure and ductility
- Chromium Content: 18.0–20.0%, forming a passive oxide layer for oxidation resistance
- Molybdenum Content: 2.0–3.0% (316L only), enhancing resistance to sulfidic and chloridic attack
- Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C, sufficient for efficient heat transfer in chilled water and hot water loops
- Tensile Strength: ≥ 520 MPa (304) / ≥ 485 MPa (316L)
- Operating Temperature Range: −196°C to +870°C (304) / −273°C to +870°C (316L)
- Surface Finish: Electropolished or mechanically polished, Ra ≤ 0.8 μm, minimizing flow resistance and biofilm accumulation
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (盘管) |
| Product Code | No. 334 |
| Material Grade | AISI 304 / AISI 316L |
| Outer Diameter (OD) | 6.35 mm (¼") / 9.53 mm (⅜") / 12.70 mm (½") — customizable |
| Wall Thickness | 0.50 mm – 1.20 mm |
| Coil Pitch (Spacing) | 12 mm – 25 mm (adjustable per heat exchanger design) |
| Coil Diameter | 150 mm – 600 mm |
| Tube Length per Coil | Up to 12,000 mm (continuous forming) |
| Heat Transfer Coefficient (U-value) | ≥ 400 W/(m²·K) (air-to-water configuration) |
| Pressure Rating | ≤ 1.6 MPa (PN16) at 25°C; ≤ 1.0 MPa at 100°C |
| Surface Treatment | Pickled & Passivated (P&P) / Electropolished |
| Welding Method | TIG (Tungsten Inert Gas) / Orbital Automated Welding |
| Fin Configuration | Aluminum plate fins, 2.5 mm – 4.0 mm pitch, hydrophobic coating available |
| Maximum Operating Pressure | 2.5 MPa (burst test: ≥ 6.0 MPa) |
| Design Life | ≥ 25 years (commercial HVAC duty cycle) |
Manufacturing Process
The production of stainless steel coil tubes follows a rigorous multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical integrity, and thermal performance:
- Material Selection & Incoming Inspection: Hot-rolled stainless steel coil stock is sourced from certified mills and subjected to spectrographic analysis (PMI — Positive Material Identification) to verify alloy composition compliance with ASTM A269 / ASTM A312 standards.
- Coil Cutting & Deburring: The master coil is precision-cut to required lengths using hydraulic shearing or laser cutting, followed by mechanical deburring to eliminate edge burrs that could cause flow turbulence or stress concentration.
- Tube Forming & Cold Drawing: Seamless stainless steel tubes are cold-drawn through calibrated dies to achieve precise OD and wall thickness tolerances (±0.05 mm). This process enhances grain alignment and surface finish.
- Coil Winding (Coiling): Tubes are wound into helical coils using CNC-controlled coiling machines with programmable pitch and diameter. The coiling process maintains consistent tension to prevent ovality and distortion.
- Fin Insertion: Aluminum fins are inserted between coil passes at pre-determined pitch intervals using automated fin-insertion machinery, ensuring uniform fin spacing critical for consistent airflow distribution.
- Header Welding: End connections (headers) are formed via automated TIG welding with argon gas shielding (internal and external). Weld joints undergo 100% visual inspection and spot radiographic testing (RT) to verify full penetration and absence of porosity.
- Pickling & Passivation: The assembled coil tube undergoes acid pickling (nitric-hydrofluoric acid bath) to remove heat tint and surface contaminants, followed by passivation to restore the chromium oxide protective layer.
- Pressure Testing: Each unit is hydrostatically tested at 1.5× the maximum operating pressure (minimum 3.75 MPa) for a minimum dwell time of 10 minutes to verify leak-tightness and structural integrity.
- Final Inspection & Packaging: Products pass through dimensional verification, surface roughness measurement, and functional testing before protective end-caps are applied and units are packaged for shipment.
Applications
The stainless steel coil tube is engineered for demanding thermal management applications where reliability, hygiene, and longevity are non-negotiable:
- Cinema & Entertainment Venue HVAC: In large-scale cinema halls with high occupant density and continuous operational cycles, the coil tube enables demand-response air conditioning strategies that dynamically adjust cooling capacity based on real-time thermal load, optimizing energy consumption while maintaining thermal comfort (ASHRAE Class 1).
- Commercial Building Fan Coil Units: Integrated into ceiling-mounted, floor-standing, and concealed FCUs for office buildings, hotels, and shopping malls, providing zone-level temperature control.
- Pharmaceutical & Cleanroom Systems: The electropolished surface and corrosion-resistant alloy make this product suitable for HVAC systems in GMP (Good Manufacturing Practice) environments where particulate control is critical.
- Food & Beverage Processing Plants: Resistant to CIP (Clean-In-Place) chemical agents and humid processing environments, ensuring sanitary compliance.
- Coastal & Marine HVAC Systems: The 316L grade offers exceptional resistance to salt-laden air, making it ideal for coastal facilities, offshore platforms, and marine vessels.
- Data Center Cooling: High-thermal-conductivity configurations deployed in precision air handling units for server room temperature regulation.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality assurance framework ensuring that every coil tube product meets or exceeds international performance standards:
- ISO 9001:2015 — Quality Management System certification, ensuring systematic process control from raw material intake through final dispatch
- ISO 14001:2015 — Environmental Management System certification, demonstrating commitment to sustainable manufacturing practices
- ASTM A269 / ASTM A312 — Material and manufacturing compliance for stainless steel tubing and pipe
- EN 10217-7 — European standard for seamless stainless steel tubes for general engineering purposes
- GB/T 14976 — Chinese national standard for cold-rolled stainless steel seamless tubes
- GB/T 4730 — Chinese standard for non-destructive testing methods
- TÜV / SGS Inspection Reports — Third-party verification of material composition, dimensional accuracy, and pressure test results
- Mill Test Certificates (MTC) — Full traceability documentation per EN 10204 Type 3.1 for each production batch
Unique Selling Points
1. Superior Corrosion Resistance: Unlike copper coil tubes susceptible to dezincification and ammonia corrosion in humid HVAC condensate environments, the stainless steel construction provides decades of service life without degradation.
2. Demand-Response Compatibility: Engineered for integration with intelligent building management systems (BMS), enabling dynamic air supply strategy optimization — critical for cinema and entertainment venue energy management as demonstrated in advanced HVAC research.
3. Hygienic Surface Finish: Electropolished Ra ≤ 0.8 μm surface eliminates micro-crevices where microbial growth occurs, ensuring indoor air quality (IAQ) compliance with WHO and ASHRAE 62.1 standards.
4. Full Traceability: Each production batch is accompanied by complete material traceability documentation, enabling lifecycle management and predictive maintenance planning.
5. Customizable Engineering: Coil pitch, diameter, tube OD, wall thickness, and fin configuration are all customizable to match specific FCU thermal load requirements, ensuring optimal heat transfer efficiency for each application.
Technical Reference
This product specification is informed by research into Fan Coil Unit Demand Response and Air Supply Strategy Optimization, particularly as applied to large-scale cinema HVAC systems. The stainless steel coil tube represents the core thermal exchange element whose performance characteristics directly determine the efficacy of demand-response control algorithms, including variable air volume (VAV) modulation, setpoint temperature optimization, and predictive load forecasting. The selection of stainless steel over conventional copper or aluminum tubing is justified by the extended service life, reduced maintenance frequency, and enhanced reliability required for 24/7 commercial entertainment facility operations.