Stainless Steel Coil Tube for FP Fan Coil Unit Air Conditioners
Product Overview
The Stainless Steel Coil Tube (盘管 Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered heat exchange component specifically designed for FP (Fan Coil Unit) series air conditioning systems. This product represents a critical thermal transfer element within closed-loop HVAC (Heating, Ventilation, and Air Conditioning) systems, where fluid circulation through coiled tubing facilitates efficient heat absorption and dissipation. The coil tube is engineered to withstand prolonged exposure to water, refrigerant mixtures, and ambient atmospheric conditions while maintaining structural integrity and thermal conductivity over extended service life.
The FP Fan Coil Unit Air Conditioner system utilizes these coil tubes as the primary heat exchanger medium, enabling temperature regulation in commercial, industrial, and residential environments. Wenzhou Jixing Metal Materials Co., Ltd. produces these coil tubes adhering to rigorous metallurgical standards, ensuring optimal performance in demanding thermal cycling applications.
Material & Properties
The coil tube is fabricated from high-grade stainless steel, selected for its exceptional combination of corrosion resistance, mechanical strength, and thermal performance. The following table summarizes the key material properties:
| Property | Specification | Standard Reference |
|---|---|---|
| Base Material | Austenitic Stainless Steel (奥氏体不锈钢) | ASTM A269 / GB/T 14976 |
| Grade | SUS304 / SUS316L (304 / 316L) | ASTM A270 |
| Outer Diameter (OD) | 9.52 mm / 12.70 mm / 15.88 mm (3/8" / 1/2" / 5/8") | ASME B36.19M |
| Wall Thickness (WT) | 0.81 mm – 1.65 mm (0.032" – 0.065") | — |
| Coil Diameter | 200 mm – 800 mm (configurable) | — |
| Tensile Strength | ≥ 515 MPa (74,700 psi) | ASTM A270 |
| Yield Strength | ≥ 205 MPa (29,700 psi) | ASTM A270 |
| Thermal Conductivity | 16.3 W/(m·K) (at 100°C) | — |
| Operating Temperature Range | -196°C to +400°C (-320°F to +752°F) | — |
| Maximum Working Pressure | 1.6 MPa (232 psi) | — |
| Surface Finish | Pickled & Passivated (Ra ≤ 0.8 μm) | ASTM A380 |
| Chromium Content | 18% – 20% | — |
| Nickel Content | 8% – 10.5% | — |
| Molybdenum Content (316L) | 2% – 3% | — |
Key Metallurgical Advantages
- Corrosion Resistance: The chromium-rich passive oxide layer (Cr₂O₃) provides superior resistance to pitting corrosion, crevice corrosion, and intergranular corrosion, particularly in the presence of chlorides and de-icing salts common in HVAC condensate systems.
- Cryogenic and High-Temperature Stability: The austenitic crystal structure maintains ductility at cryogenic temperatures without martensitic transformation, making the material suitable for both heating and cooling duty cycles.
- Weldability: Low carbon variants (304L, 316L) exhibit excellent weldability with minimal sensitization risk, enabling reliable TIG (Tungsten Inert Gas) welded joints at coil-to-fin connections and header connections.
- Hygienic Surface: The smooth, non-porous surface finish minimizes biofilm accumulation and facilitates CIP (Clean-In-Place) cleaning procedures.
Specifications
| Parameter | Detail |
|---|---|
| Product Designation | FP Coil Tube – Wenzhou Jixing Series (Catalog No. 1715) |
| Tube Configuration | Spiral-wound coil with integrated headers (集管) |
| Number of Rows | 1-Row / 2-Row / 3-Row / 4-Row (per application) |
| Fin Material | Aluminum (铝翅片) or Stainless Steel (不锈钢翅片) |
| Fin Density | 10 FPI (Fins Per Inch) to 21 FPI |
| Tube Pitch (横向节距) | 25.4 mm / 31.75 mm (1" / 1.25") |
| Refrigerant Type Compatibility | R-22, R-407C, R-410A, R-134a, R-32, Water/Glycol Mixtures |
| Cooling Capacity Range | 2.0 kW – 35.0 kW (6,800 BTU/h – 119,000 BTU/h) |
| Heating Capacity Range | 2.0 kW – 30.0 kW (6,800 BTU/h – 102,000 BTU/h) |
| Flow Rate (Water Side) | 0.3 L/min – 8.0 L/min |
| Pressure Drop (Water Side) | ≤ 30 kPa (at nominal flow rate) |
| Overall Heat Transfer Coefficient (U-value) | 70 – 120 W/(m²·K) |
| Insulation Class | Integrated or optional polyurethane foam jacket (聚氨酯保温层) |
| Connection Type | Threaded (螺纹连接) / Flanged (法兰连接) / Compression Fitting (卡套连接) |
| Drain Pan | Integrated stainless steel condensate drain tray (冷凝水接水盘) |
| Mounting Options | Ceiling Concealed (嵌入式) / Wall Mounted (壁挂式) / Floor Standing (落地式) / Ducted (风管式) |
Manufacturing Process
The production of FP Coil Tubes at Wenzhou Jixing Metal Materials Co., Ltd. follows a multi-stage manufacturing sequence designed to ensure dimensional accuracy, metallurgical homogeneity, and surface integrity:
- Raw Material Procurement and Inspection: Cold-rolled stainless steel strip (冷轧不锈钢带材) is sourced from certified mills (e.g., POSCO, Outokumpu, Baosteel). Each batch undergoes spectroscopic analysis (光谱分析) via OES (Optical Emission Spectroscopy) to verify chemical composition compliance with ASTM/GB standards. Incoming material is inspected for surface defects, hardness uniformity, and dimensional tolerance.
- Tube Forming (制管): The cold-rolled strip is fed into a precision cold-drawing and forming line. The strip is slit to the required width, then rolled and seam-welded using high-frequency induction welding (高频感应焊接) or TIG welding to form seamless-appearing tubes. The welding process is monitored in real-time using capacitance sensing and ultrasonic weld inspection to detect porosity, lack of fusion, or undercut defects.
- Cold Drawing and Sizing (冷拔定径): Formed tubes pass through a series of cold-drawing dies (冷拔模具) to achieve precise outer diameter and wall thickness tolerances (±0.05 mm). This process simultaneously improves surface finish, enhances mechanical properties through strain hardening (加工硬化), and eliminates residual stresses from the forming stage.
- Heat Treatment (热处理): Tubes are solution-annealed (固溶处理) at 1050°C – 1100°C in a protective atmosphere furnace (inert gas or vacuum), followed by controlled cooling. This process dissolves carbide precipitates, restores full austenitic structure, and maximizes corrosion resistance. For 316L grade, a sub-solution anneal at 850°C – 900°C may be applied to prevent sensitization while maintaining mechanical properties.
- Pickling and Passivation (酸洗钝化): Post-welding oxide scale is removed through pickling with a mixed acid solution (nitric acid + hydrofluoric acid, 硝酸+氢氟酸). The surface is then passivated with a citric acid or nitric acid solution to re-establish the protective chromium oxide layer. Passivation effectiveness is verified using the Copper Sulfate Test (硫酸铜试验) per ASTM A395 or the Ferric Chloride Test (氯化铁试验).
- Coil Winding (盘绕): Treated tubes are precision-wound around a mandrel (芯轴) using a CNC-controlled winding machine. The winding process maintains consistent coil diameter, inter-turn spacing, and tube alignment. Spring-back compensation algorithms ensure dimensional accuracy after release from the mandrel. Bending radii are maintained at ≥ 3D (three times the tube outer diameter) to prevent kinking or ovality.
- Header Fabrication and Assembly (集管制造与组装): Inlet and outlet headers are fabricated from stainless steel pipe (不锈钢管) and assembled via TIG welding to the coil ends. Weld joints are inspected using dye penetrant testing (渗透探伤) or magnetic particle inspection (磁粉探伤) to ensure leak-tight integrity.
- Fin Insertion (翅片插入): Precision-cut aluminum or stainless steel fins are inserted between tube rows using a fin-insertion machine. Fin-tube contact is optimized to minimize thermal contact resistance (热接触电阻). Fin edges are deburred to prevent air turbulence and noise generation.
- Pressure Testing (压力测试): Each completed coil assembly undergoes hydrostatic pressure testing (水压试验) at 1.5× the maximum working pressure (1.5× 1.6 MPa = 2.4 MPa) for a minimum of 30 minutes. Pneumatic testing (气密性试验) at 0.6 MPa is also performed to verify zero leakage. All test results are documented and traceable to individual serial numbers.
- Final Inspection and Packaging: Completed units are visually inspected, dimensionally verified, and performance-tested on a calibration rig. Each unit is tagged with a unique serial number, material certificate reference, and test report number. Packaging includes protective foam wrapping, moisture-absorbing desiccants, and wooden or cardboard crating with appropriate shock and vibration protection.
Applications
The FP Fan Coil Unit Coil Tube finds extensive application across multiple sectors of the built environment and industrial processes:
- Commercial HVAC Systems: Office buildings, shopping malls, hotels, hospitals, and educational institutions utilize FP fan coil units for precise zone-level temperature control. The stainless steel coil tube provides reliable heat exchange in both cooling (制冷) and heating (制热) modes.
- Industrial Process Cooling: Electronic manufacturing facilities, pharmaceutical cleanrooms (洁净室), and food processing plants require coil tubes with hygienic surfaces and resistance to chemical cleaning agents. The 316L grade option provides additional molybdenum-enhanced resistance for aggressive environments.
- Residential Comfort Systems: High-end residential installations employ concealed FP units with stainless steel coil tubes for silent, efficient climate control. The corrosion-resistant construction ensures long service life without degradation of indoor air quality.
- Marine and Offshore Applications: The inherent corrosion resistance of austenitic stainless steel makes these coil tubes suitable for marine air conditioning systems where salt spray and high humidity pose significant challenges to conventional carbon steel or copper heat exchangers.
- Data Center Thermal Management: Server room cooling systems benefit from the high thermal efficiency and compact design of stainless steel coil tubes, enabling effective heat removal in high-density computing environments.
- Renewable Energy Integration: FP units equipped with these coil tubes can be integrated with heat pump systems (热泵系统), solar thermal collectors (太阳能集热器), and district heating/cooling networks (区域供冷供热网络) for energy-efficient building climate management.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring product reliability and regulatory compliance:
- ISO 9001:2015 – Quality Management System (质量管理体系) certification covering all manufacturing, inspection, and delivery processes.
- ISO 14001:2015 – Environmental Management System (环境管理体系) certification demonstrating commitment to sustainable manufacturing practices.
- ISO 45001:2018 – Occupational Health and Safety Management System (职业健康安全管理体系) certification.
- CE Marking – Conformity with European Union directives including the Machinery Directive (2006/42/EC) and Pressure Equipment Directive (PED 2014/68/EU) for pressure-containing components.
- EN 12828 / EN 12831 – Compliance with European standards for heating systems in buildings and component requirements.
- ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) – Product performance data validated against ASHRAE Handbook of Fundamentals thermal performance criteria.
- GB/T 14976 – Chinese national standard for seamless and welded stainless steel tubes for general engineering use.
- GB 50242 – Chinese national standard for acceptance of building water supply and drainage engineering, applicable to condensate drainage systems.
- Material Traceability: Each production batch is accompanied by a Mill Test Certificate (MTC, 材质证明书) conforming to EN 10204 Type 3.1, providing full chemical composition, mechanical property data, and heat treatment records.
- NDT (Non-Destructive Testing, 无损检测): Weld joints and critical areas are inspected using PT (Penetrant Testing, 渗透检测) and MT (Magnetic Particle Testing, 磁粉检测) per ASTM E709 and ASTM E1417.
- Third-Party Testing: Periodic verification of product performance by accredited laboratories including SGS, Bureau Veritas, and TÜV Rheinland.
Unique Selling Points
1. Superior Corrosion Resistance: Unlike traditional copper tube and fin (铜管铝翅片) heat exchangers, the all