Stainless Steel Coil Tube — Wenzhou Jixing Metal Materials Co., Ltd.
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Product Code: #1683 | Classification: Coil Tube (盘管) for HVAC and Thermal Management Systems
1. Product Overview
The Stainless Steel Coil Tube (盘管) produced by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product formed into a continuous helical or serpentine coil configuration. This product is specifically designed for integration into fan coil units (FCU, Fan Coil Units), room air conditioning systems, heat exchangers, and thermal management applications. The coil tube serves as the primary heat transfer medium within these systems, facilitating efficient thermal exchange between circulating fluids and ambient air.
In the context of domestic room fan coil air conditioning systems (风机盘管空调器), the coil tube plays a critical role in achieving optimal heating, cooling, and dehumidification performance. The product is manufactured to meet rigorous dimensional tolerances, mechanical property requirements, and corrosion resistance standards essential for long-term operational reliability in HVAC environments.
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from high-grade austenitic stainless steel (奥氏体不锈钢), with the following primary alloy grades available:
- 304 (UNS S30408): General-purpose austenitic stainless steel offering excellent corrosion resistance, formability, and weldability. Contains a minimum of 18% Chromium (Cr) and 8% Nickel (Ni).
- 316 (UNS S31608): Enhanced corrosion resistance grade with the addition of 2–3% Molybdenum (Mo), suitable for aggressive chemical environments and marine HVAC applications.
- 316L (UNS S31603): Low-carbon variant of 316 stainless steel, providing superior resistance to intergranular corrosion (晶间腐蚀) after welding operations.
- 321 (UNS S32108): Titanium-stabilized austenitic stainless steel with improved resistance to sensitization at elevated temperatures.
2.2 Mechanical Properties
| Property | 304 Grade | 316 Grade | 316L Grade |
|---|---|---|---|
| Tensile Strength (抗拉强度), min. | 515 MPa | 515 MPa | 485 MPa |
| Yield Strength (屈服强度), min. | 205 MPa | 205 MPa | 170 MPa |
| Elongation (延伸率), min. | 40% | 40% | 45% |
| Density (密度) | 8.00 g/cm³ | 8.03 g/cm³ | 8.03 g/cm³ |
| Thermal Conductivity (热导率) at 100°C | 16.3 W/(m·K) | 14.6 W/(m·K) | 14.6 W/(m·K) |
| Operating Temperature Range | −196°C to +870°C | −196°C to +870°C | −196°C to +870°C |
2.3 Corrosion Resistance
The austenitic stainless steel coil tube exhibits exceptional resistance to atmospheric corrosion, water-borne contaminants, and mild chemical exposure. The passive oxide film (Cr₂O₃) formed on the surface provides a self-healing protective barrier, ensuring long service life in humid indoor environments typical of fan coil unit installations. The Pitting Resistance Equivalent Number (PREN) values are as follows:
- 304 Grade: PREN ≈ 19
- 316 Grade: PREN ≈ 24–26
- 316L Grade: PREN ≈ 24–26
3. Specifications
3.1 Dimensional Specifications
| Parameter | Specification | Tolerance |
|---|---|---|
| Outer Diameter (OD, 外径) | 6.0 mm, 8.0 mm, 9.52 mm, 12.0 mm, 15.88 mm | ±0.10 mm |
| Wall Thickness (壁厚) | 0.5 mm, 0.6 mm, 0.8 mm, 1.0 mm, 1.2 mm | ±0.05 mm |
| Coil Pitch (盘管节距) | 12.0 mm – 25.0 mm | ±0.5 mm |
| Coil Diameter (盘管直径) | 200 mm – 600 mm | ±3.0 mm |
| Number of Turns (圈数) | Custom (typically 12–48 turns) | — |
| Tube Length per Coil (单圈管长) | 0.6 m – 2.0 m (total coil length) | ±50 mm |
| Surface Finish (表面光洁度) | Mirror polished (Ra ≤ 0.4 μm) or Brushed (Ra ≤ 1.6 μm) | — |
3.2 Performance Specifications
| Performance Parameter | Value |
|---|---|
| Maximum Operating Pressure (最大工作压力) | 1.6 MPa (232 psi) |
| Hydrostatic Test Pressure (水压试验压力) | 2.4 MPa (348 psi) |
| Heat Transfer Coefficient (换热系数) | 800 – 1,500 W/(m²·K) |
| Flow Velocity (流速) | 0.5 – 2.5 m/s (design range) |
| Service Life (使用寿命) | ≥ 20 years (under standard HVAC conditions) |
4. Manufacturing Process
4.1 Process Flow
- Material Selection & Incoming Inspection: Stainless steel strip or seamless tube stock is selected based on grade requirements. Incoming materials undergo spectroscopic analysis (光谱分析) to verify chemical composition compliance with ASTM/EN standards.
- Cold Rolling (冷轧): The base strip is cold-rolled to achieve precise wall thickness and surface finish specifications. This process enhances mechanical properties through work hardening (加工硬化).
- Welding & Forming (焊接成型): The strip is formed into tubular shape via continuous longitudinal welding using TIG (Tungsten Inert Gas) welding or laser welding (激光焊接) technology. The weld seam is ground and smoothed to minimize flow resistance.
- Heat Treatment (热处理): Annealing (退火) is performed at 1050–1150°C followed by water quenching to restore full austenitic microstructure, relieve residual stresses, and optimize corrosion resistance.
- Pickling & Passivation (酸洗钝化): The tube is subjected to pickling in a mixed acid solution (HNO₃/HF) to remove scale, followed by passivation treatment to enhance the chromium oxide passive film.
- Coil Forming (盘管成型): The straight tube is fed through a precision coiling die set (成型模具) using CNC-controlled bending equipment. The coiling process maintains uniform bend radius and pitch while avoiding ovalization (椭圆度变形) of the tube cross-section.
- Fin Attachment (翅片安装): Aluminum or stainless steel fins (翅片) are mechanically crimped or brazed onto the coil tube to increase the heat transfer surface area by 15–25 times.
- Final Inspection & Packaging: Each coil tube assembly undergoes dimensional verification, hydrostatic pressure testing, and visual surface inspection before packaging.
4.2 Key Manufacturing Technologies
- CNC Precision Coiling: Computer Numerical Control (CNC) driven coiling machines ensure repeatable geometry with ±0.1 mm dimensional accuracy.
- Online Quality Monitoring: Real-time sensors monitor wall thickness, diameter, and surface defects during production.
- Non-Destructive Testing (NDT, 无损检测): Eddy current (涡流检测) and ultrasonic testing (超声波检测) are employed to detect internal weld defects and wall thinning.
5. Applications
5.1 Primary Applications
- Room Fan Coil Units (房间风机盘管): The primary application domain — the coil tube serves as the core heat exchanger element in residential and commercial FCU systems for space heating and cooling.
- Chilled Water Air Handling Units (冷水空调机组): Integration into central air conditioning systems for large commercial buildings.
- Heat Pump Systems (热泵系统): Used in both air-source and water-source heat pump evaporators and condensers.
- Industrial Process Cooling: Application in chemical processing, food processing, and pharmaceutical manufacturing where corrosion resistance is critical.
- Marine HVAC Systems (船用空调系统): 316/316L grade coil tubes for marine air conditioning applications requiring resistance to saltwater corrosion.
5.2 System Integration
In a typical fan coil unit configuration, the stainless steel coil tube is arranged in a serpentine (蛇形) or multi-row coil pattern within a compact housing. Air is drawn by a centrifugal fan (离心风机) across the finned coil surface, while chilled water or hot water circulates through the coil tube circuit. The stainless steel construction ensures long-term resistance to waterborne corrosion, microbial growth, and scaling, maintaining heat transfer efficiency over extended service periods.
6. Quality Certifications & Standards Compliance
6.1 Applicable Standards
| Standard | Description |
|---|---|
| ASTM A213 / A269 | American Standard for seamless and welded austenitic stainless steel tubing |
| GB/T 14976 | Chinese National Standard for cold-rolled seamless stainless steel tubes |
| GB/T 17895 | Chinese National Standard for welded stainless steel tubes and capillary tubes |
| EN 10216-5 | European Standard for welded austenitic stainless steel tubes |
| GB/T 18430 | Chinese National Standard for fan coil units — performance testing |
| ISO 9001:2015 | Quality Management System certification |
6.2 Quality Assurance Measures
- Full Chemical Analysis (化学成分全分析): Every production batch undergoes spectroscopic verification of Cr, Ni, Mo, C, Mn, Si, P, and S content.
- Dimensional Inspection (尺寸检验): 100% online inspection of OD, wall thickness, and coil geometry using laser micrometers and coordinate measuring machines (CMM, 三坐标测量机).
- Pressure Testing (压力测试): Hydrostatic testing at 1.5× working pressure for a minimum hold time of 30 seconds per unit.
- Corrosion Testing (腐蚀测试): Salt spray testing (盐雾试验) per ASTM B117 — minimum 1,000 hours without pitting for 316 grade.
- Traceability (可追溯性): Full batch traceability from raw material mill certificates to finished product delivery.
7. Unique Selling Points
Wenzhou Jixing Metal Materials Co., Ltd. distinguishes its stainless steel coil tube products through the following competitive advantages:
- Superior Corrosion Resistance: The austenitic stainless steel construction provides 5–10× longer service life compared to conventional copper or carbon steel coil tubes, significantly reducing maintenance costs and system downtime.
- Hygienic Performance: The smooth, non-porous stainless steel surface inhibits microbial colonization (微生物滋生), making it ideal for food-grade and pharmaceutical HVAC applications.
- Precision Engineering: CNC-driven coiling with ±0.1 mm tolerance ensures optimal airflow distribution and uniform heat transfer across the entire coil surface area.
- Customization Capability: Full customization of coil diameter, pitch, number of turns, tube OD, and wall thickness to meet specific OEM requirements for fan coil unit integrators.
- Environmental Sustainability: Stainless steel is 100% recyclable with no toxic leaching, supporting green building certifications (LEED