Stainless Steel Coil Tube (盘管 Coiltube) for Fan Coil Unit Systems
1. Product Overview
The Stainless Steel Coil Tube (盘管 Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered heat exchanger component designed primarily for Fan Coil Unit (FCU) systems in commercial and industrial HVAC (Heating, Ventilation, and Air Conditioning) applications. This coiltube product integrates structural integrity, superior thermal conductivity, and exceptional resistance to water corrosion, making it a critical component in the air-side heat exchange process within fan coil units.
The product is categorized under technical literature and study materials (文献学习), encompassing comprehensive knowledge regarding the structure, installation methodology, and hydraulic resistance (水阻力) characteristics of fan coil unit systems. This coiltube is engineered to meet the stringent demands of modern building climate control systems, ensuring long-term operational reliability and energy efficiency.
2. Material Composition & Properties
2.1 Base Material
- Primary Alloy: Austenitic Stainless Steel (奥氏体不锈钢) — Grade 304 (UNS S30408) or Grade 316 (UNS S31603) as specified for application requirements.
- Alternative Grades: 304L (UNS S30403) for lower carbon content applications; 316L (UNS S31603) for enhanced chloride ion resistance in marine or coastal environments.
- Compliance Standards: ASTM A269 / ASME SA269 (Welded Austenitic Stainless Steel Tubing); GB/T 12771 (Chinese National Standard for Stainless Steel Seamless and Welded Tubes).
2.2 Key Mechanical Properties
- Tensile Strength: ≥ 520 MPa (Grade 304); ≥ 485 MPa (Grade 316)
- Yield Strength: ≥ 205 MPa (Grade 304); ≥ 170 MPa (Grade 316)
- Elongation: ≥ 40% (minimum)
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (Grade 304); 14.6 W/(m·K) at 20°C (Grade 316)
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, water-based cooling media, and mild chemical environments; Grade 316 offers superior resistance to chlorides and pitting corrosion.
2.3 Surface Finish
- Interior Surface: Electropolished or passivated finish to minimize fouling and biofilm accumulation within the coil circuit.
- Exterior Surface: Pickled and passivated (酸洗钝化) to ensure uniform oxide layer formation and enhanced corrosion protection.
- Surface Roughness: Ra ≤ 0.5 μm (electropolished); Ra ≤ 1.6 μm (pickled and passivated).
3. Technical Specifications
| Parameter | Specification | Unit | Standard Reference |
|---|---|---|---|
| Product Category | Stainless Steel Coil Tube (盘管 Coiltube) | — | Internal Catalog No. 1508 |
| Tube Outer Diameter (OD) | 6.0 / 8.0 / 9.52 / 12.0 (customizable) | mm | ASTM A269 |
| Wall Thickness | 0.5 / 0.8 / 1.0 / 1.2 (customizable) | mm | ASTM A269 / GB/T 12771 |
| Coil Diameter | 200 – 600 (configurable per FCU design) | mm | Manufacturer Specification |
| Coil Height | 100 – 400 (configurable) | mm | Manufacturer Specification |
| Number of Rows | 1 / 2 / 3 / 4 rows | — | Application-dependent |
| Tube Pitch (Lateral) | 16 / 19 / 22 / 25 | mm | Manufacturer Specification |
| Fin Spacing | 1.5 / 2.0 / 2.5 (customizable) | mm | ASHRAE Standard |
| Maximum Operating Pressure | 1.0 – 1.6 | MPa | GB/T 12771 |
| Hydrostatic Test Pressure | 2.4 – 3.2 | MPa | ASTM A269 |
| Operating Temperature Range | -40 to +250 | °C | Material Specification |
| Water Resistance (Pressure Drop) | 0.5 – 3.0 (depends on flow rate and configuration) | kPa | ASHRAE Handbook |
| Heat Transfer Coefficient | 2000 – 4000 | W/(m²·K) | ASHRAE Standard |
| Fin Material | Aluminum (Al) or Stainless Steel (304) | — | Application-dependent |
| Connection Type | Threaded (NPT/BSP), Flanged, or Brazed | — | ASME B1.20.1 |
| Surface Treatment | Pickled & Passivated / Electropolished | — | ASTM A380 |
| Manufacturing Standard | ASTM A269 / GB/T 12771 / ISO 7780 | — | Multi-standard compliance |
4. Manufacturing Process
4.1 Raw Material Preparation
High-purity stainless steel strip or seamless tubing conforming to ASTM A269 and GB/T 12771 specifications is procured from certified mill suppliers. Incoming material undergoes 100% spectroscopic analysis (光谱分析) to verify chemical composition, including carbon (C), chromium (Cr), nickel (Ni), molybdenum (Mo), and other trace elements within specified tolerance limits.
4.2 Tube Forming & Coiling
- Rolling & Forming: Stainless steel strip is cold-rolled to precise wall thickness tolerances (±0.05 mm) using high-precision rolling mills.
- Coil Winding: The formed tubing is wound into the specified coil geometry using CNC-controlled coiling machines, ensuring uniform spacing between turns and consistent coil diameter.
- Dimensional Control: Laser scanning systems monitor coil diameter, height, and turn spacing in real-time during the manufacturing process.
4.3 Welding & Brazing
- Tube-to-Header Welding: TIG (Tungsten Inert Gas) welding is employed for joining tube ends to headers (集管), utilizing argon gas shielding to prevent oxidation and ensure penetration quality.
- Fin Attachment: Aluminum fins are mechanically expanded onto the tube surface using hydraulic fin-expanders, creating tight thermal contact between the fin and tube walls.
- Header Assembly: Inlet and outlet headers are fabricated from stainless steel plate or pipe, welded to the coil tube ends with full-penetration welds.
4.4 Surface Treatment
- Pickling (酸洗): The assembled coil is immersed in a hydrofluoric-nitric acid bath to remove weld scale and oxide contamination.
- Passivation (钝化): A citric acid or nitric acid passivation treatment is applied to restore the protective chromium oxide layer on the surface.
- Electropolishing (电解抛光) [Optional]: For high-purity applications, electropolishing is performed to achieve a mirror-like interior surface with Ra ≤ 0.5 μm.
4.5 Quality Inspection & Testing
- Hydrostatic Testing (水压试验): Each coil unit is pressure-tested at 1.5× the maximum operating pressure for a minimum of 30 minutes to verify leak-tightness.
- Dimensional Inspection: Coordinate Measuring Machine (CMM) or laser scanning verifies OD, wall thickness, coil diameter, height, and fin spacing.
- Non-Destructive Testing (NDT): Dye Penetrant Inspection (DPI) or Magnetic Particle Inspection (MPI) is performed on all weld joints.
- Corrosion Testing: Salt spray testing (盐雾试验) per ASTM B117 for minimum 500 hours without pitting or significant corrosion.
- Performance Testing: Selected units undergo heat transfer and water resistance (水阻力) testing in calibrated test chambers to verify thermal performance and hydraulic pressure drop characteristics.
5. Applications
5.1 Primary Applications
- Fan Coil Units (FCU, 风机盘管): The primary application domain — serving as the core heat exchange element in air-handling units for commercial buildings, hotels, hospitals, and residential complexes.
- Air Conditioning Heat Exchangers: Used as evaporators and condensers in chilled water and hot water air conditioning systems.
- Industrial Process Cooling/Heating: Applied in food processing, pharmaceutical manufacturing, and chemical production facilities requiring corrosion-resistant heat exchange.
- Clean Room Systems: Suitable for HVAC applications in semiconductor fabrication, biotechnology, and pharmaceutical clean rooms where particulate control and corrosion resistance are critical.
5.2 System Integration
The coiltube is designed to integrate seamlessly with standard FCU configurations including ceiling-mounted, wall-mounted, and floor-concealed units. Its water resistance (水阻力) characteristics are engineered to balance thermal performance with acceptable pump head requirements, typically maintaining a pressure drop of 0.5–3.0 kPa at nominal flow rates, ensuring compatibility with standard variable-speed and constant-volume pump systems.
6. Quality Certifications & Compliance
6.1 Certifications
- ISO 9001:2015 — Quality Management System certification ensuring consistent manufacturing quality and process control.
- ISO 14001:2015 — Environmental Management System certification for sustainable manufacturing practices.
- CE Marking — Conformity with European health, safety, and environmental protection standards.
- UL Listed — Underwriters Laboratories certification for safety compliance in North American markets.
- SGS Testing Report — Independent third-party verification of material composition, mechanical properties, and dimensional accuracy.
- RoHS Compliance — Restriction of Hazardous Substances directive compliance for all material components.
6.2 Standards Compliance
- ASTM A269 / ASME SA269 — Specification for welded, austenitic stainless steel tubing for chemical and similar severe service.
- GB/T 12771 — Chinese National Standard for stainless steel seamless and welded tubes for general purposes.
- ISO 7780 — International standard for stainless steel tubing and pipe.
- ASHRAE Standard 34 — Refrigerant properties and safety classification (applicable to refrigerant-side applications).
- EN 10217-7 — European standard for heat exchanger tubes made of stainless steel.
- GB 50242 — Chinese standard for installation engineering quality acceptance of building water supply and drainage systems.
6.3 Traceability & Documentation
Each coil tube unit is accompanied by a comprehensive Quality Assurance (QA) documentation package including: Mill Test Certificates (MTC) for raw material, Certificate of Conformance (CoC), dimensional inspection reports, hydrostatic test records, NDT reports, and a unique batch/lot traceability number enabling full supply chain traceability from raw material mill to final installation.
7. Unique Selling Points (USPs)
7.1 Superior Corrosion Resistance
Unlike conventional copper or carbon steel coil tubes, the stainless steel coiltube offers exceptional resistance to water corrosion, biofilm formation, and chemical degradation. This translates to significantly extended service life — typically 15–25 years — compared to 5–10 years for copper alternatives, particularly in environments with aggressive water chemistry or high humidity.
7.2 Optimized Water Resistance (水阻力) Performance
Through precise engineering of tube diameter, coil geometry, and internal surface finish, the coiltube achieves an optimal balance between heat transfer efficiency and hydraulic pressure drop. The electropolished interior surface minimizes frictional losses, reducing pump energy consumption by up to 15–20% compared to standard finish alternatives.
7.3 Enhanced Thermal Performance
The combination of high thermal conductivity stainless steel and precision-engineered fin spacing delivers heat transfer coefficients of 2000–4000 W/(m²·K), ensuring efficient thermal exchange in both heating and cooling modes. This performance is maintained consistently over the product lifecycle without degradation.
7.4 Hygienic Design for Sensitive Applications
The smooth, non-porous stainless steel surface with electropolished interior prevents bacterial colonization and biofilm accumulation, making this coiltube ideal for pharmaceutical, food processing, and healthcare applications where hygiene standards are critical.
7.5 Customizable Configurations
Wenzhou Jixing Metal Materials Co., Ltd. offers flexible customization options including tube diameter, wall thickness, coil dimensions, number of rows, fin spacing, and connection types to accommodate specific FCU design requirements and system integration needs.
7.6 Energy Efficiency Contribution
By minimizing pressure drop and maximizing heat transfer efficiency, this coiltube contributes to overall system energy savings. When paired with variable-speed fans and pumps in modern FCU systems, the coiltube's hydraulic characteristics enable optimal operation across a wide range of part-load conditions, reducing total system energy consumption.
8. Installation Guidelines
Note: Proper installation is critical to achieving optimal performance and longevity. The following guidelines should be observed:
- Pre-Installation Inspection: Verify coil dimensions, connection types, and integrity of protective packaging before installation.
- Orientation: Install with headers oriented horizontally; ensure adequate clearance (minimum 150 mm) on all sides for airflow and maintenance access.
- Water Side Connection: Connect inlet and outlet