Stainless Steel Coil Tube (盘管) — Wenzhou Jixing Metal Materials Co., Ltd.
1. Product Overview
The Stainless Steel Coil Tube (盘管 / Coil Tube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed primarily for heat exchange applications in Heating, Ventilation, and Air Conditioning (HVAC) systems, with particular emphasis on Fan Coil Unit (FCU) integration. The coil tube is formed into a helical or serpentine configuration to maximize surface area within a compact envelope, thereby optimizing thermal transfer efficiency between the working fluid and the ambient air stream.
This product line addresses the critical engineering challenge of achieving rational motor-to-coil matching in fan coil units — a topic extensively studied in the referenced technical literature 《风机盘管电机的合理匹配》 (Rational Matching of Fan Coil Unit Motors). The coil tube geometry, wall thickness, and material selection are all calibrated to ensure optimal pressure drop characteristics, which directly govern the motor power requirements and overall system energy efficiency.
2. Material & Properties
2.1 Base Material Grades
- Austenitic Stainless Steels: Grade 304 (UNS S30408 / 06Cr19Ni10) and Grade 316 (UNS S31603 / 022Cr17Ni12Mo2) are the primary material specifications for general and corrosion-critical applications respectively.
- Super-Austenitic Grades: Grade 904L (UNS N08904) and Grade 2205 Duplex (UNS S32205) are available for aggressive chemical environments and high-temperature service.
- Industrial Fe-Ni-Cr Alloys: Alloy 625 (UNS N06625) and Alloy C-276 (UNS N10276) are offered for extreme corrosion resistance and elevated temperature duty.
2.2 Mechanical Properties (Typical Values for Grade 304, Annealed Condition)
| Property | Specification | Standard Reference |
|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 520 MPa | ASTM A213 / EN 10217-7 |
| Yield Strength (屈服强度, 0.2% offset) | ≥ 205 MPa | ASTM A213 / EN 10217-7 |
| Elongation (延伸率) | ≥ 35% | ASTM A213 |
| Hardness (硬度) | ≤ 210 HB | ASTM E10 |
| Thermal Conductivity (导热系数, 300 °C) | ~ 16.3 W/(m·K) | ASM Handbook Vol. 6 |
| Coefficient of Thermal Expansion (热膨胀系数, 20–100 °C) | 17.3 × 10⁻⁶ /°C | ASTM A276 |
| Maximum Service Temperature (最高使用温度) | 870 °C (Grade 304) | ASME BPV Code VIII |
2.3 Chemical Composition (Grade 304, Typical %)
| Element | Specification |
|---|---|
| Carbon (C) | ≤ 0.08 |
| Manganese (Mn) | ≤ 2.00 |
| Chromium (Cr) | 18.00 – 20.00 |
| Nickel (Ni) | 8.00 – 10.50 |
| Nitrogen (N) | ≤ 0.10 |
| Sulfur (S) | ≤ 0.030 |
| Phosphorus (P) | ≤ 0.045 |
| Iron (Fe) | Balance |
3. Specifications
3.1 Dimensional Specifications
| Parameter | Range / Value | Tolerance | Standard |
|---|---|---|---|
| Outer Diameter (外径, OD) | Φ6.0 mm – Φ50.8 mm | ±0.15 mm | ASTM A213 |
| Wall Thickness (壁厚, WT) | 0.5 mm – 3.0 mm | ±10% | ASTM A213 |
| Coil Pitch (盘管节距) | 6 mm – 25 mm | ±0.5 mm | Custom / OEM |
| Coil Bend Radius (盘管弯曲半径) | ≥ 1.5 × OD | — | EN 10217-7 |
| Coil Length (盘管展开长度) | 0.5 m – 50.0 m | ±1% | Custom / OEM |
| Number of Turns (圈数) | 10 – 500 turns | ±2 turns | Custom / OEM |
| End Forming (端部成型) | Plain, Flanged, Threaded, or Socket Weld | Per drawing | ASME B16.11 |
| Surface Finish (表面光洁度) | Ra ≤ 0.8 μm (polished) / Ra ≤ 1.6 μm (pickled) | — | ASTM A276 |
3.2 Performance Specifications
| Parameter | Specification |
|---|---|
| Design Pressure (设计压力) | Up to 4.0 MPa (40 bar) |
| Hydrostatic Test Pressure (水压试验压力) | 1.5 × Design Pressure |
| Pressure Drop (压降, at rated flow) | ≤ 25 kPa per 10 m of coil |
| Heat Transfer Coefficient (传热系数) | ≥ 2,500 W/(m²·K) (water-to-air, turbulent flow) |
| Operating Temperature Range (工作温度范围) | −196 °C to +870 °C (Grade 304) |
| Corrosion Resistance (耐蚀性) | Potential Pit Initiation Temperature (PIT): ≥ 40 °C (Grade 316, 3.5% NaCl) |
4. Manufacturing Process
The production of the Stainless Steel Coil Tube follows a rigorous multi-stage manufacturing sequence compliant with international quality standards:
- Raw Material Selection (原材料选择): Virgin stainless steel strip or seamless tube stock is procured from certified mills (e.g., Outokumpu, Nippon Steel, POSCO, Taigang). Each batch is accompanied by a Mill Test Certificate (MTC) conforming to EN 10204 Type 3.1.
- Seamless Tube Manufacturing (无缝钢管制造): Tubes are produced via the Automatic Plug Piercing (APPLI) or Mannesmann piercing process, followed by hot rolling, cold drawing, and cold reduction to achieve the required dimensional accuracy and mechanical properties.
- Heat Treatment (热处理): Solution annealing (固溶处理) is performed at 1050–1100 °C with water or air quenching to restore full austenitic microstructure, ensuring maximum corrosion resistance and ductility.
- Coil Forming / Bending (盘管成型 / 弯曲): The straight tube is formed into a helical coil using CNC-controlled rotary bending machines (数控旋弯机). The bending process is performed at ambient temperature with internal mandrel support to prevent ovality exceeding 10% of the nominal OD. Multi-pass incremental bending is employed for tight-radius configurations.
- Welding (焊接, if applicable): For coil assemblies requiring inlet/outlet headers, TIG (Tungsten Inert Gas) welding per ASME Section IX is performed using matching filler metal (e.g., ER308L for Grade 304, ER316L for Grade 316) under argon shielding.
- Pickling and Passivation (酸洗钝化): The coil tube is subjected to pickling in a mixed acid solution (HNO₃ + HF or citric acid-based) to remove scale and discoloration, followed by passivation to establish a stable chromium oxide (Cr₂O₃) protective film on the surface.
-
Non-Destructive Testing (无损检测, NDT):
- Eddy Current Testing (涡流检测) per ASTM E309 for internal defect detection.
- Helium Leak Testing (氦检漏) per ASME PTC 25 for weld integrity verification.
- Visual Inspection (目视检测) per ASTM E165 for surface quality assessment.
- Hydrostatic Pressure Testing (水压试验): Each coil is pressure-tested at 1.5× the design pressure with demineralized water for a minimum hold time of 30 seconds. Zero leakage is the acceptance criterion.
- Dimensional Verification (尺寸验证): Coordinate Measuring Machine (CMM) inspection confirms coil pitch uniformity, turn-to-turn spacing, and overall envelope dimensions within specified tolerances.
- Packaging and Dispatch (包装发运): Finished coils are wrapped in moisture-barrier film, placed in wooden crates with desiccant packs, and shipped with full documentation including MTC, NDT reports, and dimensional certificates.
5. Applications
5.1 Primary Application: HVAC Fan Coil Units (风机盘管机组)
The coil tube is the core heat exchange element in Fan Coil Units (FCU), where the rational matching between the coil tube geometry and the fan motor power is critical for system efficiency. Key considerations include:
- Air-Side Heat Transfer: The coil tube arrangement determines the effective heat transfer surface area, which must be matched to the fan airflow capacity to avoid over- or under-sizing.
- Pressure Drop Balance: The hydraulic resistance of the coil tube must be compatible with the motor's pressure-capacity curve to ensure stable operation across all speed settings (high, medium, low).
- Condensate Management: In cooling mode, the coil tube surface temperature must remain above the dew point at the inlet air conditions to prevent excessive condensate formation, which can impair airflow and promote microbial growth.
5.2 Additional Applications
- Industrial Heat Exchangers (工业换热器): Shell-and-tube and plate-and-fin heat exchangers in chemical, petrochemical, and pharmaceutical processing.
- Refrigeration Systems (制冷系统): Evaporator and condenser coil tubes in commercial refrigeration and air conditioning systems.
- Geothermal Heat Pumps (地源热泵): U-tube ground heat exchangers for closed-loop geothermal systems.
- Food and Beverage Processing (食品饮料加工): Pasteurization heat exchangers and sanitary-grade cooling coils compliant with FDA and 3-A standards.
- Marine Applications (海洋应用): Seawater heat exchanger coils for shipboard HVAC and power generation systems, utilizing Grade 316 or Alloy C-276 for chloride resistance.
- Nuclear Industry (核工业): Intermediate heat exchanger (IHX) and steam generator (SG) tubes in advanced reactor designs (e.g., Gen-IV systems).
6. Quality Certifications & Standards Compliance
The Stainless Steel Coil Tube product line from Wenzhou Jixing Metal Materials Co., Ltd. is manufactured and tested in accordance with the following international standards and certifications:
| Certification / Standard | Description | Scope |
|---|---|---|
| ISO 9001:2015 | Quality Management System (质量管理体系) | Full manufacturing process |
| ISO 14001:2015 | Environmental Management System (环境管理体系) | Production facility operations |
| ISO 45001:2018 | Occupational Health & |