Stainless Steel Coil Tube for HVAC Fan Coil Units — Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Product No. 1057), manufactured by Wenzhou Jixing Metal Materials Co., Ltd, is a precision-engineered tubular component designed primarily for use in Heating, Ventilation, and Air Conditioning (HVAC) systems, particularly within Fan Coil Units (FCU). This coil tube serves as the primary heat exchanger medium, facilitating thermal transfer between refrigerant or chilled water circuits and the ambient air stream.
Research and field performance studies — notably investigations into the Impact of Large Temperature Differences in Air Conditioning Chilled Water on Fan Coil Unit Performance — have demonstrated that the material integrity, thermal conductivity, and corrosion resistance of the coil tube are critical determinants of system efficiency, longevity, and operational reliability. Under conditions of significant supply water temperature differentials (ΔT) between inlet and outlet, the coil tube is subjected to repeated thermal cycling, mechanical fatigue, and potential microstructural stress. The stainless steel coil tube is specifically engineered to mitigate these degradation mechanisms while maintaining optimal heat exchange performance.
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from high-grade austenitic stainless steel, conforming to international standards including ASTM A213 (Standard Specification for Seamless Austenitic Stainless Steel Tube for Heat-Exchanger and Heat-Sink Service), EN 10216-5, and GB/T 14976. The primary alloy grades utilized are:
- 304 / 06Cr19Ni10 — General-purpose austenitic stainless steel offering excellent corrosion resistance, formability, and weldability.
- 316L / 022Cr17Ni12Mo2 — Molybdenum-enhanced grade with superior resistance to pitting and crevice corrosion, particularly advantageous in high-humidity or chlorinated environments.
- 321 / 06Cr18Ni11Ti — Titanium-stabilized grade suitable for elevated temperature applications, providing enhanced resistance to intergranular corrosion.
2.2 Key Physical and Mechanical Properties
- Thermal Conductivity: 14.6–16.3 W/(m·K) at 20°C, ensuring efficient heat transfer across the tube wall.
- Thermal Expansion Coefficient: 16–18 × 10⁻⁶ /°C, providing dimensional stability under thermal cycling.
- Tensile Strength: ≥ 520 MPa (minimum, annealed condition).
- Yield Strength: ≥ 205 MPa.
- Operating Temperature Range: −196°C to +870°C (304 grade); −273°C to +870°C (316L grade).
- Corrosion Resistance: Exceptional resistance to oxidation, acid environments, and atmospheric corrosion; pitting resistance equivalent number (PREN) ≥ 19 for 316L grade.
- Surface Finish: 2B cold-rolled finish (standard) or electropolished finish (optional), with surface roughness Ra ≤ 0.8 μm.
3. Technical Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (盘管 / Coil Tube) |
| Product No. | 1057 |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd |
| Material Grade | ASTM 304 / 316L / 321 (or equivalent) |
| Outer Diameter (OD) | 6.0 mm – 12.7 mm (standard range); customizable |
| Wall Thickness | 0.5 mm – 1.5 mm (±0.05 mm tolerance) |
| Coil Pitch | 10 mm – 50 mm (adjustable per design requirements) |
| Tube Length per Coil | Up to 10,000 mm (continuous coil) |
| Manufacturing Standard | ASTM A213 / EN 10216-5 / GB/T 14976 |
| Heat Treatment | Solution annealing at 1010–1150°C followed by controlled cooling |
| Surface Treatment | 2B finish (standard); Electropolished or passivated (optional) |
| Maximum Operating Pressure | 1.6 MPa (standard); up to 4.0 MPa (thick-wall variant) |
| Maximum Operating Temperature | 870°C (304); 870°C (316L); 900°C (321) |
| Minimum Bend Radius | 1.5 × OD (cold bending); 1.0 × OD (hot forming) |
| Welding Compatibility | TIG (GTAW), MIG (GMAW), resistance welding |
| Package Form | Coiled on wooden spools or custom crating |
4. Manufacturing Process
The production of the stainless steel coil tube follows a rigorous, multi-stage process ensuring dimensional accuracy, metallurgical integrity, and performance reliability:
- Raw Material Selection & Verification: Virgin stainless steel ingots or hot-rolled coils are sourced from certified mills. Incoming material undergoes spectroscopic analysis (OES) and mechanical testing to verify chemical composition and mechanical properties against the specified grade.
- Hot Rolling & Annealing: The base material is hot-rolled to approximate dimensions, followed by solution annealing at 1010–1150°C in a controlled atmosphere furnace to homogenize the microstructure, relieve residual stresses, and achieve the desired austenitic grain structure.
- Cold Drawing / Cold Reduction: The hot-rolled tube is cold-drawn through precision tungsten carbide dies to achieve the target outer diameter and wall thickness. This process imparts work hardening, enhancing mechanical strength while maintaining surface quality.
- Precision Coiling / Bending: Using CNC-controlled coiling machines, the straight tube is formed into the specified coil geometry. The bending process is carefully controlled to avoid wall thinning, ovality, or kinking, ensuring uniform cross-sectional integrity throughout the coil.
- Intermediate Annealing: Where required, the formed coil undergoes a stress-relief annealing cycle (typically at 800–1050°C) to eliminate residual stresses introduced during cold forming, thereby improving long-term fatigue resistance under thermal cycling conditions.
- Surface Finishing & Passivation: The coil tube is cleaned, passivated using nitric or citric acid solutions to remove surface contamination and form a protective chromium oxide layer. Electropolishing may be applied for critical applications requiring superior surface smoothness and corrosion resistance.
- Quality Inspection & Testing: Each production lot undergoes comprehensive inspection, including dimensional measurement, hydrostatic pressure testing, visual examination (including internal bore inspection), and sampling for mechanical and chemical analysis.
- Coil Assembly & Packaging: The finished coil tubes are wound onto protective wooden spools, secured with strapping, and packaged for shipment in accordance with export or domestic logistics requirements.
5. Applications
5.1 Primary Application: HVAC Fan Coil Units
The stainless steel coil tube is the core heat exchange element in Fan Coil Units (FCU), which are widely deployed in commercial, industrial, and residential building HVAC systems. The coil tube facilitates the transfer of thermal energy between the chilled water or hot water circulating through the tube and the air blown across the coil by a fan. Research into the effects of large supply water temperature differences (e.g., ΔT between 5°C and 20°C) on FCU performance has highlighted the importance of coil tube material selection in maintaining heat transfer efficiency, preventing condensation-related corrosion, and ensuring structural integrity under thermal cycling loads.
5.2 Additional Applications
- Chilled Water Heat Exchangers: Primary and secondary loop heat exchangers in central air conditioning plants.
- Refrigeration Systems: Evaporator and condenser coils in commercial refrigeration and cold storage equipment.
- Industrial Process Cooling: Heat exchangers in chemical processing, pharmaceutical manufacturing, and food processing industries where corrosion resistance is paramount.
- Domestic Water Heaters: Immersion coils and heat exchange elements in high-end residential and commercial water heating systems.
- Marine HVAC Systems: Corrosion-resistant coil tubes for shipboard air conditioning and ventilation systems exposed to salt-laden environments.
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework to ensure product conformity and traceability:
- ISO 9001:2015 — Quality Management System certification, demonstrating adherence to international standards for consistent product quality and continuous improvement.
- ISO 14001:2015 — Environmental Management System certification, reflecting commitment to environmentally responsible manufacturing practices.
- CE Marking — Conformity with European Union directives for machinery, pressure equipment, and safety standards applicable to HVAC components.
- ASTM / ASME Compliance — Materials and fabrication conform to American Society for Testing and Materials (ASTM) and American Society of Mechanical Engineers (ASME) standards.
- Third-Party Inspection: Available upon request — SGS, BV (Bureau Veritas), or TÜV inspection and certification services.
- Mill Test Reports (MTR): Each batch is accompanied by a full material test report including chemical composition, mechanical properties, and heat treatment records.
7. Unique Selling Points
The stainless steel coil tube from Wenzhou Jixing Metal Materials Co., Ltd distinguishes itself through the following key advantages:
- Superior Thermal Cycling Resilience: Engineered to withstand repeated thermal cycling under large ΔT conditions without degradation of mechanical properties or heat transfer efficiency, as validated by performance studies on FCU systems with high-temperature-differential chilled water circuits.
- Exceptional Corrosion Resistance: Austenitic stainless steel construction provides outstanding resistance to oxidation, condensation-induced corrosion, and chemical attack, significantly extending service life compared to carbon steel alternatives.
- Precision Coiling Technology: CNC-controlled coiling ensures uniform pitch, minimal ovality, and consistent wall thickness, guaranteeing optimal airflow distribution and heat exchange performance.
- Full Traceability: Complete material traceability from raw steel ingot to finished coil tube, supported by mill test reports and batch identification.
- Customization Capability: Flexible manufacturing parameters (OD, wall thickness, pitch, coil length, material grade) to meet specific design and application requirements.
- Comprehensive Quality Assurance: Multi-stage inspection protocol including dimensional, mechanical, hydrostatic, and visual testing at every critical process stage.
8. Conclusion
The stainless steel coil tube (Product No. 1057) represents a high-performance, reliable, and durable solution for HVAC heat exchange applications. Its proven ability to maintain structural integrity and thermal efficiency under demanding operating conditions — particularly in systems experiencing large chilled water temperature differentials — makes it the preferred choice for engineers and system designers seeking long-term reliability and energy efficiency. Wenzhou Jixing Metal Materials Co., Ltd is committed to delivering world-class coil tube products supported by rigorous quality standards, technical expertise, and responsive customer service.