Stainless Steel Coil Tube (盘管) — HVAC Fan Coil Unit Application Grade
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd
Product Catalog No.: 1409
Classification: Literature & Technical Reference — Product Knowledge Series
1. Product Overview
The Stainless Steel Coil Tube (盘管) is a precision-engineered tubular product formed into continuous helical or serpentine coil configurations, primarily designed for use in Fan Coil Units (FCUs) and other HVAC (Heating, Ventilation, and Air Conditioning) terminal equipment. Unlike conventional straight pipe segments, coil tubes are manufactured as a single continuous length wound into a compact coil form, which eliminates the need for field welding or brazing joints — significantly reducing potential leak points and improving long-term system reliability.
This product line is developed with particular attention to the critical selection parameters identified in HVAC equipment engineering literature, including heat transfer efficiency, pressure drop characteristics, corrosion resistance under humid indoor air conditions, and dimensional compatibility with standard FCU chassis configurations. The coil tube serves as the primary heat exchange medium within the FCU, transferring thermal energy between the circulating refrigerant or hot water and the ambient air drawn across the coil face by the fan assembly.
2. Material & Properties
2.1 Base Alloy Composition
The coil tube is fabricated from austenitic stainless steel conforming to internationally recognized standards. The primary grades offered include:
- SUS304 (ASTM A269 TP304 / UNS S30400): The standard grade offering excellent general-purpose corrosion resistance, formability, and weldability. Contains 18% Chromium (Cr) and 8% Nickel (Ni) as minimum composition.
- SUS316 (ASTM A269 TP316 / UNS S31600): Enhanced grade with 2–3% Molybdenum (Mo) addition, providing superior resistance to chlorided environments and condensate corrosion common in HVAC applications.
- SUS321 (ASTM A269 TP321 / UNS S32100): Titanium-stabilized grade suitable for elevated temperature applications where intergranular corrosion resistance is critical.
2.2 Mechanical Properties (Typical Values for SUS304)
| Property | Specification | Standard Reference |
|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 520 MPa (75,400 psi) | ASTM A269 / EN 10217-7 |
| Yield Strength (屈服强度) | ≥ 205 MPa (29,700 psi) | ASTM A269 |
| Elongation (延伸率) | ≥ 40% (at 50 mm gauge length) | ASTM A269 |
| Hardness (硬度) | ≤ 217 HB (annealed condition) | ASTM E10 |
| Density (密度) | 8.0 g/cm³ | — |
| Thermal Conductivity (导热系数) | 16.3 W/(m·K) at 100°C | ASTM A269 |
| Thermal Expansion Coefficient (热膨胀系数) | 17.3 × 10⁻⁶ /K (20–100°C) | ASTM A269 |
2.3 Corrosion Resistance
The austenitic stainless steel matrix provides inherent resistance to atmospheric corrosion, condensate water, and mildly acidic environments encountered in indoor air handling systems. The passive chromium oxide layer (Cr₂O₃) self-heals upon exposure to oxygen, maintaining long-term protection. SUS316 grade additionally resists pitting and crevice corrosion in the presence of chlorides (Cl⁻), making it particularly suitable for coastal installations or applications involving treated water additives.
3. Technical Specifications
| Parameter | Specification | Notes |
|---|---|---|
| Outer Diameter (OD) (外径) | φ6.35 mm, φ8.00 mm, φ9.53 mm, φ10.00 mm, φ12.00 mm, φ15.88 mm | Standard sizes per FCU industry norms |
| Wall Thickness (壁厚) | 0.30 mm – 1.20 mm | Customizable per application pressure rating |
| Coil Pitch (螺距) | 6.0 mm – 15.0 mm | Determines heat transfer surface density |
| Coil Diameter (盘管直径) | φ100 mm – φ500 mm | Dependent on FCU chassis dimensions |
| Coil Length (盘管长度) | 5 m – 50 m (continuous) | Single-piece, joint-free construction |
| Number of Rows (排数) | 2-row, 3-row, 4-row, 6-row configurations | Row count affects thermal capacity |
| Surface Finish (表面光洁度) | Ra ≤ 0.8 μm (BA finish) or Ra ≤ 1.6 μm (2B finish) | BA = Bright Annealed; 2B = Cold Rolled |
| Operating Pressure (工作压力) | ≤ 1.6 MPa (water circuit); ≤ 2.5 MPa (refrigerant circuit) | Hydrostatic test at 1.5× working pressure |
| Operating Temperature (工作温度) | −40°C to +150°C (water); −60°C to +120°C (refrigerant) | Based on SUS304 grade |
| Tolerance — OD (外径公差) | ± 0.05 mm (for OD ≤ 10 mm); ± 0.08 mm (for OD > 10 mm) | Per ASTM A269 |
| Tolerance — Wall Thickness (壁厚公差) | ± 10% of nominal | Per ASTM A269 |
| End Connection Type (端部连接形式) | Flared, threaded (M14×1.5, G1/2"), brazed, or compression fitting | Customizable per OEM requirements |
4. Manufacturing Process
The production of stainless steel coil tubes involves a multi-stage precision manufacturing sequence:
- Material Selection & Incoming Inspection: Cold-rolled stainless steel strip or seamless pipe stock is sourced from certified mills. Incoming material undergoes chemical composition verification (OES spectroscopy), mechanical property testing, and surface quality inspection per ASTM A269 / EN 10217-7 requirements.
- Coiling / Winding (盘绕成型): The pipe or formed tube is wound into the required helical or serpentine configuration using precision CNC-controlled coiling equipment. The winding process maintains controlled tension to prevent ovalization or deformation of the tube cross-section. Coil pitch and diameter are maintained within tight tolerances to ensure uniform heat transfer performance across the entire coil assembly.
- Heat Treatment (热处理): For cold-worked configurations, a solution annealing cycle at 1050°C – 1150°C followed by rapid quenching is performed to restore full austenitic microstructure and eliminate work-hardening effects. This ensures optimal corrosion resistance and ductility.
- Surface Treatment (表面处理): Bright annealing (BA) in a controlled reducing atmosphere (H₂/N₂ mixture) produces a smooth, bright surface finish with no scale formation. Alternatively, pickling and passivation (酸洗钝化) may be applied to remove any residual scale and establish the protective chromium oxide passive film.
- End Forming & Connection Preparation (端部加工): Tube ends are machined, flared, threaded, or prepared for compression fittings per the specific FCU OEM specification. End preparation is performed with precision tooling to ensure leak-tight connections.
- Hydrostatic Pressure Testing (水压试验): Each coil tube assembly undergoes 100% hydrostatic pressure testing at 1.5 times the maximum design working pressure, held for a minimum of 5 minutes with zero pressure drop and no visible leakage. This ensures structural integrity and weld/joint quality.
- Final Inspection & Dimensional Verification (最终检验): Coil diameter, pitch, total length, OD, and wall thickness are verified using calibrated measuring instruments. Surface defects are inspected visually and, where applicable, by eddy current testing (ECT) for subsurface discontinuities.
- Packaging & Marking (包装与标识): Coils are wrapped in protective plastic film and packed in wooden crates or export-grade cartons. Each unit is marked with product identification, material grade, heat number, dimensions, and manufacturing date.
5. Applications
The stainless steel coil tube is the core heat exchange element in a broad spectrum of HVAC and thermal management systems. Key application domains include:
- Fan Coil Units (风机盘管): The primary application. Coil tubes serve as the evaporator (cooling mode) or condenser (heating mode) in FCUs used for precise temperature and humidity control in commercial buildings, hospitals, laboratories, and cleanrooms.
- Chilled Water Air Handling Units (CHW-AHU): Coil tubes integrated into larger air handling units for central air conditioning systems in office towers, hotels, and industrial facilities.
- VRF/VAV Terminal Units (变制冷剂流量/变风量末端设备): Variable Refrigerant Flow (VRF) and Variable Air Volume (VAV) systems where coil tubes provide terminal heat exchange with modulating capacity control.
- Cleanroom HVAC Systems (洁净室空调系统): SUS316 grade coil tubes used in pharmaceutical, semiconductor, and biotechnology facilities where ultra-low particulate emission and chemical resistance are mandated.
- Marine & Coastal HVAC (海洋及沿海空调): SUS316 coil tubes deployed in marine vessel HVAC systems and coastal installations where chloride-induced corrosion is a primary concern.
- Refrigeration Evaporators (制冷蒸发器): Low-temperature coil tubes operating with R410A, R32, R134a, or CO₂ (R744) refrigerants in commercial refrigeration and cold chain applications.
5.1 Selection Considerations for Fan Coil Unit Integration
Based on engineering literature review (《对风机盘管设备选型问题的探讨》), the following critical parameters govern coil tube selection for FCU applications:
- Heat Transfer Capacity (换热能力): The coil tube's effective heat transfer surface area, determined by OD, wall thickness, coil pitch, and number of rows, must match the FCU's design cooling/heating load. Undersized coils lead to inadequate temperature control; oversized coils increase capital cost and pressure drop.
- Pressure Drop (压降): The internal flow resistance of the coil tube directly impacts pump energy consumption and system flow rate stability. Smooth internal surfaces (BA finish) and appropriate wall thickness minimize frictional losses.
- Condensate Management (冷凝水管理): In cooling mode, condensate forms on the coil tube outer surface. The coil tube's surface finish and hydrophilic coating (if applied) influence condensate drainage efficiency, preventing water accumulation and microbial growth.
- Material Compatibility (材料兼容性): The coil tube material must be compatible with the circulating fluid (water, glycol-water mixtures, or refrigerant) and any treatment chemicals used in the system. SUS304 is suitable for most applications; SUS316 is recommended where chlorides or aggressive additives are present.
- Dimensional Compatibility (尺寸兼容性): Coil tube dimensions (coil diameter, pitch, total length) must fit within the FCU chassis envelope while maintaining adequate air flow across the coil face. Custom coil configurations are available to match specific OEM chassis designs.
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains rigorous quality management systems and holds the following certifications and complies with the following standards:
| Standard / Certification | Scope of Application |
|---|---|
| ISO 9001:2015 (质量管理体系) | Quality Management System — full manufacturing process |
| ISO 14001:2015 (环境管理体系) | Environmental Management System — sustainable manufacturing |
| ASTM A269 / A269M | Standard Specification for Seamless and Welded Austenitic Stainless Steel Pipe, Tube, and Hollow Shapes |
| EN 10217-7 | Non-alloy and alloy steel tubes — Technical delivery conditions — Part 7: Seamless and welded tubes of austenitic stainless steel for special purposes |
| GB/T 14976 (中国国家标准) | Chinese National Standard for seamless stainless steel tubes for general engineering purposes |
| GB/T 12771 (中国国家标准) | Chinese National Standard for welded stainless steel tubes for general engineering purposes |