Stainless Steel Coil Tube for Fan Coil Units — Model FP5WA Series
Product Overview
The Stainless Steel Coil Tube (盘管) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered heat exchange coil component designed specifically for concealed horizontal fan coil units (FCU), including the FP5WA series. This coil tube serves as the core thermal transfer element within HVAC (Heating, Ventilation, and Air Conditioning) systems, facilitating efficient heat exchange between circulating refrigerant or hot water and ambient air.
The product, catalogued under serial number 1711, represents a specialized grade of stainless steel tubing formed into compact serpentine coil configurations. It is engineered to meet the demanding thermal, mechanical, and corrosion resistance requirements of commercial and residential HVAC installations, ensuring long-term operational reliability in concealed ceiling-mounted applications.
Material & Properties
The coil tube is fabricated from high-purity austenitic stainless steel, selected for its exceptional combination of corrosion resistance, thermal conductivity, and mechanical strength under cyclic thermal loading conditions.
Primary Alloy Composition
- Base Material: Austenitic Stainless Steel (Type 304 / 316L equivalent)
- Chromium (Cr): 18.0–20.0% — provides passive oxide layer for corrosion protection
- Nickel (Ni): 8.0–10.5% — stabilizes austenitic structure, enhances ductility
- Molybdenum (Mo): 2.0–3.0% (316L grade) — improves resistance to pitting and crevice corrosion
- Carbon (C): ≤ 0.03% (L-grade) — minimizes intergranular corrosion risk
- Manganese (Mn): ≤ 2.0%
- Phosphorus (P): ≤ 0.045%
- Sulfur (S): ≤ 0.030%
Mechanical Properties
- Tensile Strength (UTS): ≥ 520 MPa (annealed condition)
- Yield Strength (0.2% Proof Stress): ≥ 205 MPa
- Elongation at Break: ≥ 40%
- Hardness (Brinell): 120–180 HB (annealed)
- Thermal Conductivity: 16.3 W/(m·K) at 20°C
- Operating Temperature Range: −196°C to +450°C
Corrosion Resistance Characteristics
- Excellent resistance to atmospheric corrosion and condensate (acidic) environments
- Superior performance in chlorinated water and marine-influenced HVAC applications (316L grade)
- Resistance to stress corrosion cracking (SCC) under normal service temperatures
- Long-term stability against microbiologically influenced corrosion (MIC)
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Designation | Coil Tube (盘管) — FP5WA Series | Internal Catalog No. 1711 |
| Tube Outer Diameter (OD) | 6.35 mm / 9.52 mm / 12.70 mm | ASTM A269 / A213 |
| Tube Wall Thickness | 0.50 – 1.00 mm | ASME B36.19M |
| Tube Material Grade | SUS304 / SUS316L (UNS S30400 / S31603) | ASTM A269 / EN 10217-7 |
| Coil Length (per Unit) | 15.0 – 35.0 m (variable by FCU capacity) | — |
| Fin Material | Aluminum (Al-Mg1) or Copper-clad Aluminum | ASTM B209 |
| Fin Pitch | 1.50 – 2.50 mm (10–16 fins per inch) | — |
| Tube Layout | Staggered / In-line serpentine configuration | ASHRAE Standard 15 |
| Number of Circuits | 1 – 4 circuits (configurable) | — |
| Connection Method | Brazed joints / Mechanical flared fittings | ASTM B815 (solder) / ASME B31.5 |
| Operating Pressure (Design) | ≤ 1.6 MPa (water side) / ≤ 2.5 MPa (refrigerant side) | EN 12828 / ISO 5149 |
| Refrigerant Compatibility | R410A, R32, R134a, R22 (legacy) | ASHRAE 34 |
| Surface Treatment | Passivated / Electropolished (optional) | ASTM A967 |
| Weight (Typical) | 2.5 – 8.0 kg per coil assembly | — |
Manufacturing Process
The production of the stainless steel coil tube for FP5WA fan coil units follows a rigorous multi-stage manufacturing sequence to ensure dimensional accuracy, thermal performance, and structural integrity:
- Material Preparation: Cold-rolled stainless steel strip (SUS304/316L) is inspected for surface quality, alloy composition (via XRF spectroscopy), and mechanical properties. Strip is annealed to relieve residual stresses and achieve the required ductility for forming operations.
- Tube Forming (Cold Drawing): The strip is fed through sequential die sets in a cold-drawing or cold-rolling machine to form seamless round tubes with precise wall thickness tolerances (±0.05 mm). This process enhances grain structure alignment and surface finish quality.
- Heat Treatment (Solution Annealing): Tubes are subjected to solution annealing at 1050–1150°C followed by rapid quenching (air or water) to restore full austenitic microstructure and maximize corrosion resistance properties.
- Coil Bending / Serpentine Forming: The formed tubes are cold-bent into precise serpentine coil configurations using CNC-controlled bending machinery. Bend radii are maintained at a minimum of 3× tube OD to prevent wall thinning and micro-cracking. Bend angles are controlled to ±0.5°.
- Fin Insertion (Fin-And-Tube Assembly): Pre-stretched aluminum fins are inserted into the formed tube array using a hydraulic fin-insertion machine. The fins are compressed between tube rows to achieve metal-to-metal contact, ensuring optimal thermal conductivity across the heat exchange interface.
- Header Assembly: Inlet and outlet headers (manifolds) are welded or brazed to the coil ends, forming the complete circuit configuration. Brazing is performed under nitrogen atmosphere to prevent oxidation and ensure clean, leak-free joints.
- Surface Passivation: The completed coil assembly undergoes chemical passivation (nitric acid or citric acid bath) to remove any free iron contamination and establish a stable chromium oxide passive layer.
- Pressure Testing & Leak Detection: Each coil unit is hydrostatically tested at 1.5× design pressure (typically 2.4–3.75 MPa) for a minimum of 30 minutes. Helium leak detection (sensitivity ≤ 1×10⁻⁹ mbar·L/s) is performed on critical joints.
- Final Inspection & Packaging: Dimensional verification (laser scanning), visual inspection, and performance coefficient (K-factor) validation are conducted. Coils are packaged in protective foam-lined cartons with desiccant packs for shipment.
Applications
The FP5WA-series stainless steel coil tube is designed for concealed horizontal fan coil units installed in a wide range of HVAC applications:
- Commercial Buildings: Office towers, hotels, retail centers, and hospitals requiring concealed ceiling-mounted cooling/heating units with high air quality standards
- Residential HVAC: High-end residential installations where silent operation and compact form factor are prioritized
- Clean Room Environments: Pharmaceutical manufacturing, semiconductor fabrication, and laboratory facilities requiring corrosion-resistant, low-particulate heat exchangers
- Marine & Coastal Installations: 316L-grade coils suitable for marine HVAC systems exposed to salt-laden atmospheres
- Food & Beverage Processing: Facilities requiring hygienic, cleanable, and corrosion-resistant heat exchange components compliant with food safety regulations
- Industrial Process Cooling: Precision temperature control for machinery enclosures and process equipment
Integration with FP5WA Concealed Horizontal Fan Coil Unit
The coil tube integrates as the primary heat exchange element within the FP5WA concealed horizontal fan coil unit. The unit is designed for installation within ceiling plenums, directing conditioned air through supply diffusers below. Key integration features include:
- Compact coil footprint optimized for ceiling plenum space constraints
- Low-profile design compatible with standard 250–400 mm ceiling cavity depths
- Modular circuit design allowing capacity matching from 2.0 kW to 12.0 kW cooling output
- Condensate drain pan compatibility with corrosion-resistant stainless steel construction
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management systems and holds the following certifications and complies with international standards:
| Certification / Standard | Scope of Compliance |
|---|---|
| ISO 9001:2015 | Quality Management System — full manufacturing process coverage |
| ISO 14001:2015 | Environmental Management System — production sustainability |
| ISO 45001:2018 | Occupational Health & Safety Management |
| CE Marking (EU) | Compliance with European Machinery Directive and Pressure Equipment Directive (PED 2014/68/EU) |
| UL / CSA Listed | North American safety standards for HVAC components |
| ASME B31.5 | Pressure Piping and Tubing — Industrial piping systems |
| ASHRAE Standard 15 | Minimum requirements for safely handling refrigerants |
| RoHS 2011/65/EU | Restriction of hazardous substances in electrical/electronic equipment |
| EN 12828 | Heating systems in buildings — component requirements |
Unique Selling Points
1. Premium Austenitic Stainless Steel Construction: Unlike conventional copper tube-and-fin heat exchangers, this product employs 304/316L stainless steel tubing, offering 5–10× longer service life in corrosive condensate environments and eliminating copper-induced microbiological contamination concerns.
2. Precision CNC Serpentine Forming: Computer-controlled bending ensures repeatable coil geometry with bend radii maintained to ±0.3 mm tolerance, maximizing airflow uniformity and thermal performance coefficient (K-factor).
3. Enhanced Thermal Performance: The combination of high-conductivity stainless steel tubing with optimized aluminum fin geometry (fin pitch 1.5–2.5 mm) achieves a heat transfer coefficient exceeding 65 W/(m²·K) for air-to-water applications.
4. Full Traceability: Each coil tube is laser-marked with batch identification, material heat number, and manufacturing date code, enabling complete supply chain traceability and quality audit compliance.
5. Integrated FP5WA Design Optimization: The coil is specifically engineered for seamless integration with the FP5WA concealed horizontal fan coil unit platform, providing factory-matched performance characteristics and simplified field installation.
6. Nitrogen-Protected Brazing: All joints are brazed under inert nitrogen atmosphere, producing oxidation-free, structurally sound connections that withstand thousands of thermal cycles without degradation.
Technical Notes & Recommendations
- For applications involving chlorinated water or high-chloride environments, specify 316L grade (Mo-containing) to ensure long-term resistance to pitting corrosion.
- Periodic inspection of coil surfaces is recommended at 24-month intervals to verify passive film integrity and detect any localized corrosion initiation.
- System water quality should be maintained with pH 6.5–8.5 and total dissolved solids (TDS) below 1000 ppm to maximize coil service life.
- When retrofitting into existing FP5WA units, verify coil circuit count and connection port dimensions match the original equipment specification to prevent flow maldistribution.