Stainless Steel Coil Tube — FPDW Series (Model No. 479)
1. Product Overview
The Stainless Steel Coil Tube (Product No. 479) is a precision-engineered coiled tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd., designed specifically for integration into the FPDW-type DC Brushless Large Temperature Difference Fan Coil Unit (FCU) systems. This product represents a specialized category of seamless or welded stainless steel tubing formed into continuous coil configurations, offering superior thermal transfer efficiency, corrosion resistance, and mechanical integrity under demanding HVAC (Heating, Ventilation, and Air Conditioning) operating conditions.
The coil tube serves as the critical heat exchange element within large temperature differential fan coil units, where it facilitates efficient thermal energy transfer between refrigerant fluid and ambient air. Its coiled geometry maximizes surface area within a compact volumetric envelope, making it an ideal component for high-performance HVAC applications requiring significant temperature differentials between supply and return air streams.
2. Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, conforming to internationally recognized metallurgical standards. The material selection prioritizes a balance between thermal conductivity, corrosion resistance, mechanical strength, and formability — essential attributes for coil tube applications in HVAC systems.
2.1 Base Material Composition
- Primary Grade: SUS304 (ASTM A269 TP304) — Chromium-Nickel Austenitic Stainless Steel
- Alternative Grade: SUS316L (ASTM A269 TP316L) — Low Carbon Molybdenum-Bearing Austenitic Stainless Steel
- Chromium (Cr): 18.0–20.0 wt%
- Nickel (Ni): 8.0–10.5 wt%
- Molybdenum (Mo): 2.0–2.5 wt% (SUS316L grade only)
- Carbon (C): ≤ 0.08 wt%
- Manganese (Mn): ≤ 2.0 wt%
2.2 Key Physical Properties
- Thermal Conductivity: 14.2–16.3 W/(m·K) at 20°C
- Specific Heat Capacity: 500 J/(kg·K)
- Density: 7.93 g/cm³
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (20–100°C)
- Maximum Operating Temperature: 870°C (oxidizing atmosphere)
2.3 Mechanical Properties
- Tensile Strength (UTS): ≥ 520 MPa (annealed condition)
- Yield Strength (0.2% offset): ≥ 205 MPa
- Elongation at Break: ≥ 40%
- Hardness: ≤ 95 HRB (annealed)
2.4 Corrosion Resistance
The austenitic microstructure provides exceptional resistance to pitting, crevice corrosion, and intergranular corrosion. In particular, the SUS316L variant offers superior performance in chloride-containing environments, making it suitable for coastal installations and applications involving chemical refrigerants.
3. Technical Specifications
| Parameter | Specification | Standard / Tolerance |
|---|---|---|
| Product Name | Stainless Steel Coil Tube (盘管) | — |
| Product No. | 479 | — |
| Tube Outer Diameter (OD) | 6.35 mm / 7.94 mm / 9.53 mm / 12.70 mm | ±0.10 mm |
| Tube Wall Thickness | 0.50 mm / 0.60 mm / 0.80 mm / 1.00 mm | ±0.05 mm |
| Coil Diameter | 150 mm – 600 mm (configurable) | ±3 mm |
| Coil Length | Custom (10 m – 500 m per coil) | ±0.5% |
| Surface Finish | Bright Annealed (BA) / Pickled & Passivated (P&P) | Ra ≤ 0.4 μm |
| End Condition | Plain / Beveled / Threaded / Flanged | Per customer drawing |
| Operating Pressure | ≤ 2.5 MPa (design) | Hydrostatic test at 3.75 MPa |
| Operating Temperature Range | −40°C to +120°C | — |
| Temperature Differential (ΔT) | Up to 25 K (supply vs. return) | — |
| Refrigerant Compatibility | R134a, R410A, R32, Water/Glycol mixtures | — |
| Applicable Standard | ASTM A269 / ASTM A778 / GB/T 12771 / JIS G3446 | — |
| Coating / Passivation | Chromate-free passivation (6% HNO₃ + 2% HF) | ISO 9409-1 |
4. Manufacturing Process
4.1 Raw Material Preparation
Manufacturing commences with the procurement of certified stainless steel seamless tubes or precision-welded tubes conforming to ASTM A269 or ASTM A778 specifications. Incoming material undergoes spectrographic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition and mechanical testing to confirm conformity with specified grades.
4.2 Coil Forming
- Uncoiling & Straightening: The straight tube stock is fed through a multi-roller straightener to achieve dimensional accuracy and eliminate residual curvature from prior processing.
- Coil Winding: A CNC-controlled coiling machine forms the tube into the specified helical geometry with precise control over pitch, coil diameter, and transition radii. The forming process is conducted at ambient temperature (cold coiling) to avoid sensitization of the austenitic microstructure.
- Transition Bend Control: Entry and exit transitions are formed with minimum bend radius of 3D (three times the outer diameter) to prevent wall thinning and ovalization exceeding 10%.
4.3 Surface Treatment
- Acid Pickling: Immersion in a hydrofluoric-nitric acid solution (HF:HNO₃, 1:4 ratio) to remove mill scale, oxide films, and surface contaminants.
- Passivation: Treatment with 6% nitric acid solution to restore the passive chromium oxide layer, enhancing long-term corrosion resistance. This step is critical for ensuring the tube maintains its protective oxide film after mechanical forming.
- Final Cleaning: Ultrasonic or high-pressure deionized water rinse to remove all chemical residues.
4.4 Quality Inspection
- Dimensional Verification: Laser-based dimensional measurement of OD, wall thickness, coil diameter, and pitch consistency.
- Hydrostatic Testing: Each coil is subjected to internal hydrostatic pressure testing at 1.5× the maximum design pressure for a minimum dwell time of 30 seconds to detect any through-wall defects.
- Visual & Eddy Current Inspection: Automated eddy current scanning identifies subsurface defects, weld seam discontinuities, and wall thickness variations.
- Corrosion Testing: Salt spray testing (ASTM B117) for a minimum of 1000 hours with no evidence of pitting or intergranular attack.
4.5 Packaging & Shipping
Completed coil tubes are packaged in moisture-absorbent desiccant-lined polyethylene wrapping, secured on wooden pallets with protective corner guards. Each unit is labeled with a unique traceability code linking to the manufacturing batch, heat number, and inspection records.
5. Applications
5.1 Primary Application: FPDW DC Brushless Fan Coil Units
The coil tube is specifically engineered for integration into the FPDW-type DC Brushless Large Temperature Difference Fan Coil Unit system. These units are characterized by:
- High temperature differential capability (ΔT up to 25 K) enabling compact ductwork and reduced air volume requirements
- DC brushless motor integration for variable speed control, energy efficiency, and silent operation
- Modular design permitting rapid installation in commercial and residential HVAC systems
- Compatibility with both heating and cooling modes using water or refrigerant as the heat transfer medium
5.2 Secondary Applications
- Commercial HVAC: Large-scale air handling units, chiller coils, and heat recovery systems in office buildings, hospitals, and hotels
- Industrial Process Cooling: Precision temperature control in semiconductor manufacturing, pharmaceutical processing, and food processing facilities
- Refrigeration Systems: Evaporator and condenser coils in commercial refrigeration equipment
- Heat Exchanger Manufacturing: Raw material for plate-fin and finned-tube heat exchanger fabrication
- Marine & Offshore: Corrosion-resistant heat exchange components in marine HVAC and ballast water systems
6. Unique Selling Points
Metallurgical Excellence: The austenitic stainless steel construction provides an inherently corrosion-resistant heat transfer medium that eliminates the need for internal coatings or cathodic protection, significantly extending service life beyond carbon steel alternatives (estimated 25–30 years vs. 8–12 years).
- Large Temperature Differential Capability: Optimized geometry enables ΔT values up to 25 K, reducing required airflow volume by up to 30% compared to conventional coil designs, thereby minimizing ductwork sizing and fan energy consumption.
- DC Brushless Motor Compatibility: Designed for seamless integration with DC brushless fan motors, enabling precise airflow modulation (20%–100% capacity), reduced vibration, and noise levels below 28 dB(A) at low speed.
- Superior Thermal Performance: The bright annealed surface finish minimizes thermal boundary layer resistance, enhancing convective heat transfer coefficients by approximately 15% compared to standard pickled finishes.
- Hygienic Design: The smooth internal bore (Ra ≤ 0.4 μm) prevents biofilm accumulation and facilitates easy cleaning, meeting NSF/ANSI 61 standards for potable water contact.
- Full Traceability: Each coil tube carries a unique identification code enabling complete traceability from raw material heat number through final inspection, ensuring compliance with ISO 9001 quality management requirements.
- Environmental Compliance: Chromate-free passivation process, recyclable stainless steel construction (100% recyclable), and RoHS/REACH compliant materials.
7. Quality Certifications & Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System — Certified for manufacturing of metal products and tubes |
| ISO 14001:2015 | Environmental Management System |
| ASTM A269 / A778 | Material and dimensional conformance for austenitic stainless steel tubes |
| EN 10216-5 | European standard for seamless and welded stainless steel tubes |
| GB/T 12771 | Chinese national standard for stainless steel welded tubes for general use |
| NSF/ANSI 61 | Drinking Water System Components — Health Effects (where applicable) |
| CE Marking | Compliance with EU Machinery Directive and Pressure Equipment Directive (PED 2014/68/EU) |
| RoHS / REACH | Restriction of Hazardous Substances and Registration, Evaluation, Authorization of Chemicals |
| Mill Test Certificate (MTC) | EN 10204 Type 3.1 — Full third-party verified material certification per batch |
8. Conclusion
The Stainless Steel Coil Tube (Product No. 479) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. represents a state-of-the-art thermal transfer component engineered for the demanding requirements of modern large temperature differential HVAC systems. Its combination of metallurgical integrity, precision manufacturing, and compliance with international standards positions it as a reliable, high-performance solution for commercial and industrial heating, cooling, and air conditioning applications worldwide.