Stainless Steel Coil Tube for HVAC Fan Coil Unit Systems
1. Product Overview
The Stainless Steel Coil Tube (Product No. 719) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered tubular component designed specifically for integration into Fresh Air + Fan Coil Unit (FCU) Air Conditioning Systems. This coil tube serves as the primary heat exchange medium within fan coil units, facilitating efficient thermal transfer between circulating refrigerant/water and ambient air in both heating and cooling modes.
Unlike conventional copper coil assemblies, the stainless steel coil tube offers superior corrosion resistance, extended service life, and compatibility with modern high-efficiency HVAC commissioning protocols. The product is manufactured in accordance with international standards for building services engineering and is suitable for residential, commercial, and industrial air conditioning applications.
2. Material & Properties
2.1 Material Composition
The coil tube is fabricated from Stainless Steel (奥氏体不锈钢), with the following grade options available:
- Grade 304 (UNS S30400) — Standard austenitic stainless steel with excellent general corrosion resistance, suitable for most indoor HVAC applications.
- Grade 316 (UNS S31600) — Enhanced austenitic stainless steel with molybdenum addition, offering superior resistance to chloride-induced pitting corrosion, ideal for coastal or high-humidity environments.
- Grade 316L (UNS S31603) — Low-carbon variant of 316L, recommended for applications requiring welding without sensitization concerns.
2.2 Mechanical Properties
| Property | Specification | Test Method |
|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 520 MPa (Grade 304) / ≥ 570 MPa (Grade 316) | ASTM A370 / GB/T 228.1 |
| Yield Strength (屈服强度) | ≥ 205 MPa (Grade 304) / ≥ 240 MPa (Grade 316) | ASTM A370 / GB/T 228.1 |
| Elongation (延伸率) | ≥ 40% (Grade 304) / ≥ 35% (Grade 316) | ASTM A370 / GB/T 228.1 |
| Hardness (硬度) | ≤ 210 HB (annealed condition) | ASTM E10 / GB/T 231.1 |
| Thermal Conductivity (导热系数) | 16.3 W/(m·K) at 25°C | ASTM E1461 |
2.3 Corrosion Resistance
- Pitting Resistance (耐点蚀性): PREN (Pitting Resistance Equivalent Number) ≥ 19 for Grade 316, ensuring resistance to condensate and refrigerant-induced pitting.
- Intergranular Corrosion Resistance (抗晶间腐蚀): Verified per ASTM A262 Practice No. 1A.
- Chloride Resistance (耐氯离子腐蚀): Suitable for environments with chloride concentrations up to 500 ppm.
3. Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (盘管) |
| Product Number | 719 |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd (温州吉兴金属材料有限公司) |
| Outer Diameter (OD) | 6.35 mm (1/4") / 9.52 mm (3/8") / 12.7 mm (1/2") / 15.88 mm (5/8") |
| Wall Thickness | 0.5 mm / 0.6 mm / 0.8 mm / 1.0 mm |
| Coil Pitch (螺旋间距) | 10 mm – 25 mm (adjustable per application) |
| Coil Diameter (盘管直径) | 150 mm – 500 mm (customizable) |
| Tube Length per Coil | 2 m – 12 m (standard); up to 20 m (custom) |
| Number of Rows | 2-row / 3-row / 4-row configurations |
| Surface Finish | Bright Annealed (BA) / Pickled & Passivated |
| Working Pressure | ≤ 1.6 MPa (standard); ≤ 2.5 MPa (reinforced) |
| Operating Temperature Range | -40°C to +180°C |
| Refrigerant Compatibility | R410A, R32, R134a, R22, Water/Glycol Solutions |
| Standards Compliance | ASTM A213 / ASTM A269 / GB/T 12771 / EN 10216-5 |
| Fin Configuration | Plain tube / External finned (aluminum fins, 12-16 fins/inch) |
| Connection Type | Flared / Compression / Brazed / Soldered |
4. Manufacturing Process
4.1 Raw Material Selection & Inspection
Stainless steel seamless tubes are sourced from certified mills with full Mill Test Certificates (MTC) per EN 10204 3.1. Incoming material undergoes spectroscopic analysis (OES) to verify chemical composition within ASTM A213/A269 tolerances. Each batch is subjected to hydrostatic pressure testing at 1.5× the maximum working pressure.
4.2 Coil Forming
- Tube Straightening & Cutting: Raw seamless tubes are straightened and cut to precise lengths using high-precision plasma or cold-cutting equipment.
- Coil Winding: Tubes are mechanically wound onto precision mandrels using CNC-controlled coiling machines to achieve uniform pitch and consistent coil diameter. The winding process ensures no kinking, flattening, or stress concentration at the coil bends.
- Row Assembly: Single coils are assembled into 2-row, 3-row, or 4-row configurations with U-bend connections, ensuring minimum bend radius of 3× tube OD to prevent wall thinning.
4.3 Surface Treatment
- Pickling & Passivation: The coil tube assembly undergoes pickling to remove scale and oxide layers, followed by passivation treatment to form a protective chromium oxide film (Cr₂O₃), enhancing corrosion resistance.
- Finning (if applicable): Aluminum fins are mechanically or hydraulically expanded onto the tube OD to increase heat transfer surface area by 3–5×.
4.4 Quality Control & Testing
- Dimensional Inspection: OD, wall thickness, coil pitch, and overall dimensions verified using calipers, micrometers, and laser measurement systems.
- Pressure Testing: Each coil tube assembly undergoes pneumatic or hydrostatic pressure testing at 1.5× the rated working pressure for a minimum of 3 minutes with no leakage permitted.
- Visual Inspection: 100% visual inspection for surface defects, weld quality, fin integrity, and dimensional conformity.
- Leak Detection: Helium leak detection or nitrogen bubble testing for critical applications requiring zero-leakage assurance.
5. Applications
5.1 Fan Coil Unit (FCU) Systems
The primary application of this coil tube is within Fan Coil Units, where it functions as the core heat exchanger in Fresh Air + FCU Air Conditioning Systems (新风加风机盘管空调系统). The coil tube transfers thermal energy between the circulating chilled/hot water and the air stream forced by the unit's fan, enabling precise temperature and humidity control.
5.2 System Commissioning Context
In accordance with 《新风加风机盘管空调系统调试技术》 (Commissioning Technology for Fresh Air + Fan Coil Unit Air Conditioning Systems), the coil tube must meet specific performance criteria during system commissioning:
- Cooling Capacity Verification: The coil tube's heat transfer coefficient must achieve ≥95% of the manufacturer's rated capacity under design conditions (7°C/12°C chilled water supply, 27°C/60% RH indoor air).
- Flow Balance: Uniform water flow distribution across all coil rows is verified to prevent thermal stratification and ensure balanced air discharge temperatures.
- Condensate Management: The coil tube's surface temperature must remain above the dew point during heating mode to prevent condensate formation and subsequent microbial growth.
5.3 Industry Applications
- Commercial Buildings: Office towers, hotels, shopping malls, hospitals, and educational institutions requiring zoned climate control.
- Residential Buildings: High-end apartments and residential complexes with centralized HVAC systems.
- Industrial Facilities: Clean rooms, laboratories, data centers, and pharmaceutical manufacturing requiring precise temperature and humidity control.
- Special Environments: Coastal facilities, marine applications, and high-chloride environments where Grade 316/316L coil tubes provide essential corrosion protection.
6. Quality Certifications & Standards Compliance
6.1 International Standards
- ASTM A213: Standard Specification for Seamless Austenitic Stainless Steel Tubing for High-temperature Service
- ASTM A269: Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Other Severely Corrosive Environments
- EN 10216-5: Tubes for Heat Exchangers and Heat Sinks — Technical Delivery Conditions — Part 5: Nickel-Chromium-Iron-Cr-Ni Austenitic Stainless Steel Tubes
- ISO 11114-1: Refrigerants — General Safety and Environmental Information — Part 1: Classification and Basic Safety and Environmental Requirements
6.2 Chinese National Standards
- GB/T 12771: Non-alloy and alloy seamless steel tubes for heat exchangers and heat sinks
- GB/T 4237: Cold-rolled stainless steel sheets and strips
- GB 50736: Code for Construction and Acceptance of Air Conditioning Engineering
6.3 Manufacturer Certifications
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- CE Marking — European Conformity for construction products
- CNCA — China National Certification and Accreditation Administration
7. Unique Selling Points
Why Choose Wenzhou Jixing Metal Materials Co., Ltd Stainless Steel Coil Tubes?
- Superior Corrosion Resistance: Unlike copper coil tubes, stainless steel coil tubes are immune to dezincification, ammonia corrosion, and refrigerant-induced degradation, ensuring a service life exceeding 20 years in HVAC applications.
- Enhanced Hygienic Performance: The smooth, non-porous surface of stainless steel prevents bacterial adhesion and biofilm formation, making it ideal for hospital, pharmaceutical, and food-grade HVAC systems.
- Commissioning-Ready Design: The coil tube's precise dimensional tolerances and uniform coil geometry ensure predictable and consistent heat transfer performance, simplifying system commissioning procedures per 《新风加风机盘管空调系统调试技术》 guidelines.
- Customizable Configurations: Available in multiple tube diameters, coil pitches, row configurations, and surface finishes to meet specific design requirements for diverse HVAC system architectures.
- Energy Efficiency: Optimized coil geometry and optional fin configurations maximize heat transfer efficiency, contributing to lower energy consumption and reduced operational costs in fan coil unit systems.
- Full Traceability: Every coil tube batch is accompanied by complete material traceability documentation, including mill certificates, heat numbers, and test reports, ensuring compliance with project quality assurance requirements.
8. Technical Reference: Commissioning Integration
During the commissioning phase of a Fresh Air + Fan Coil Unit Air Conditioning System, the stainless steel coil tube must be validated through the following key performance indicators:
| Commissioning Parameter | Acceptance Criteria | Verification Method |
|---|---|---|
| Cooling Capacity | ≥ 95% of rated capacity | Water flow metering + air-side temperature/humidity measurement |
| Water Flow Rate | Within ±10% of design value | Calibrated flow meter at coil inlet/outlet |
| Pressure Drop (ΔP) | Within manufacturer's specified range | Differential pressure gauge across coil |
| Air Discharge Temperature | Within ±1.0°C of setpoint | Thermocouple at coil outlet |
| Leakage | Zero leakage | Visual inspection + pressure decay test |
| Condensate Drainage | Free-flowing, no accumulation | Visual inspection + flow test |
This comprehensive technical specification ensures that the Stainless Steel Coil Tube (Product No. 719) from Wenzhou Jixing Metal Materials Co., Ltd meets the highest standards of quality, performance,