Stainless Steel Coil Tube for Fan Coil Air Conditioning Systems
Product Code: 1483 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd
1. Product Overview
The stainless steel coil tube (盘管) is a precision-engineered tubular component specifically designed for integration into humidifying fan coil air conditioning systems (Humidifying Fan Coil Air Conditioning System). Unlike conventional copper or carbon steel coil tubes, stainless steel coil tubes offer superior corrosion resistance, extended service life, and enhanced hygienic performance—making them an ideal choice for HVAC (Heating, Ventilation, and Air Conditioning) applications where moisture exposure is continuous and air quality standards are stringent.
This product represents a specialized category of stainless steel tubing formed into serpentine or spiral coil configurations, optimized for maximum heat transfer efficiency within compact fan coil units. The coil geometry facilitates efficient thermal exchange between the refrigerant or chilled water flowing through the tube and the ambient air drawn across the finned surface by the fan assembly.
2. Material & Properties
The coil tubes are manufactured from austenitic stainless steel grades conforming to international metallurgical standards. The primary alloy compositions and their corresponding properties are detailed below:
2.1 Commonly Used Grades
- AISI 304 (UNS S30408): The most widely specified grade for coil tube applications, offering excellent general corrosion resistance with 18% Chromium (Cr) and 8% Nickel (Ni) content. Suitable for most indoor HVAC environments.
- AISI 316 (UNS S31608): Enhanced grade containing 2–3% Molybdenum (Mo), providing superior resistance to chloride-induced pitting and crevice corrosion. Recommended for humidifying systems with high moisture content or coastal installations.
- AISI 321 (UNS S32108): Titanium-stabilized grade with added Titanium (Ti) to prevent intergranular corrosion during welding operations, ensuring structural integrity at welded joints.
2.2 Key Mechanical and Physical Properties
| Property | AISI 304 | AISI 316 |
|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 515 |
| Yield Strength (MPa) | ≥ 205 | ≥ 205 |
| Elongation (%) | ≥ 40 | ≥ 40 |
| Density (kg/m³) | 7930 | 8000 |
| Thermal Conductivity at 100°C (W/m·K) | 16.3 | 14.6 |
| Operating Temperature Range (°C) | −196 to +870 | −196 to +870 |
| Corrosion Resistance (ASTM G48) | Excellent (general) | Superior (chloride environments) |
2.3 Surface Finish
The interior and exterior surfaces of the coil tube are finished to achieve a Ra (Roughness Average) value of ≤ 0.4 μm, ensuring minimal flow resistance and preventing biofilm accumulation—a critical consideration in humidifying air conditioning applications where microbial growth must be inhibited.
3. Technical Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 – 12.7 mm (1/4" – 1/2") | ASTM A213 / GB/T 14976 |
| Wall Thickness | 0.5 – 1.2 mm | ASTM A269 / EN 10217 |
| Coil Pitch (Center-to-Center Spacing) | 15 – 30 mm | Manufacturer Specification |
| Tube Passes (Rows) | 2 – 8 passes | Application-dependent |
| Coil Length (per unit) | 0.5 – 3.0 m | Custom fabrication available |
| Fin Material | Aluminum (Al) or Stainless Steel (SS) | ASTM B209 / ASTM A240 |
| Fin Spacing | 1.5 – 2.5 mm | Design-specific |
| Working Pressure | 1.6 – 2.5 MPa (232 – 363 psi) | ASME BPV Code Section I |
| Hydrostatic Test Pressure | 3.0 MPa (435 psi) | 1.5 × Working Pressure |
| End Connection Type | Flared, Brazed, or Welded (Orbital) | ASME B31.5 |
| Surface Treatment | Passivated / Electropolished (optional) | ASTM A967 / A380 |
| Maximum Flow Velocity | ≤ 3.0 m/s (chilled water) | ASHRAE Handbook |
4. Manufacturing Process
The fabrication of stainless steel coil tubes for fan coil applications follows a rigorous multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical integrity, and functional performance:
4.1 Seamless Tube Production
- Hot Rolling & Piercing: Steel billets are heated to approximately 1200–1250°C and pierced through a mandrel to produce seamless hollow blanks.
- Cold Drawing: The hot-rolled blanks undergo cold drawing through precision dies to achieve the final outer diameter and wall thickness tolerances (±0.05 mm).
- Annealing: Solution annealing at 1050–1100°C followed by rapid water quenching restores full austenitic microstructure and eliminates work-hardening effects.
4.2 Coil Forming
- Coil Bending: The straight tube is formed into serpentine or spiral coil configurations using CNC-controlled coil forming machines. Bending radii are maintained at ≥ 3× tube OD to prevent wall thinning and ovality.
- Stress Relief: Post-forming stress relief annealing at 850–900°C eliminates residual stresses introduced during cold bending, preventing dimensional drift during service.
- Fin Attachment: Aluminum or stainless steel fins are applied to the coil via fin-tube bonding (mechanical crimping, brazing, or expansion crimping) to maximize the heat transfer surface area.
4.3 End Processing & Quality Assurance
- End Preparation: Tube ends are deburred, chamfered, and flared or threaded to specified connection geometries.
- Passivation: Chemical passivation treatment (ASTM A967) removes free iron contamination from the surface, forming a protective chromium oxide layer.
- Hydrostatic Testing: Each coil unit is pressure-tested at 3.0 MPa for a minimum dwell time of 30 seconds to verify weld integrity and tube wall soundness.
- Dimensional Inspection: Coordinate Measuring Machine (CMM) or laser scanning verifies coil pitch, row alignment, and overall envelope dimensions.
5. Applications
Stainless steel coil tubes manufactured by Wenzhou Jixing Metal Materials Co., Ltd are designed for the following primary applications within humidifying fan coil air conditioning systems:
5.1 Commercial HVAC Systems
- Chilled water coil assemblies in commercial building air handling units (AHUs)
- Humidifying fan coil units for hospital operating rooms, cleanrooms, and pharmaceutical facilities
- Precision temperature and humidity control systems in data centers and server rooms
5.2 Industrial Applications
- Food processing and beverage manufacturing facilities requiring hygienic air conditioning
- Electronics manufacturing cleanroom environments (ISO Class 5–7)
- Textile mills requiring precise humidity control during production processes
5.3 Residential & Light Commercial
- High-end residential HVAC systems with humidification/dehumidification capability
- Hotel and hospitality industry fan coil units
- Commercial kitchen ventilation and spot cooling systems
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains comprehensive quality management systems and product certifications to ensure international market compliance:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification covering all manufacturing and quality assurance processes |
| ISO 14001:2015 | Environmental Management System certification demonstrating sustainable manufacturing practices |
| ASTM A213 / A269 | Conformance to American Society for Testing and Materials specifications for seamless stainless steel tubes |
| EN 10217-7 | European standard for stainless steel tubes and heat exchangers |
| GB/T 14976 | Chinese national standard for seamless stainless steel tubes for general engineering |
| NSF/ANSI 61 | National Sanitation Foundation certification for potable water contact applications |
| CE Marking | European Conformity marking for products placed on the European Economic Area market |
| ASME BPV Code | American Society of Mechanical Engineers Boiler and Pressure Vessel Code compliance for pressure-containing components |
7. Unique Selling Points
Corrosion Resistance Superiority: Unlike carbon steel alternatives that require internal coatings or cathodic protection, stainless steel coil tubes provide inherent resistance to the corrosive effects of humidified air, condensate water, and chemical additives—eliminating maintenance-related downtime and reducing total cost of ownership (TCO) by an estimated 40–60% over a 15-year service life.
- Hygienic Performance: The austenitic microstructure and passivated surface resist biofilm formation, meeting FDA 21 CFR Part 117 requirements for food-grade air conditioning systems.
- Thermal Efficiency: Precision coil geometry with optimized pitch and row configurations achieves a heat transfer coefficient (U-value) of 85–120 W/m²·K, outperforming standard carbon steel coils by 15–25%.
- Weld Integrity: Orbital TIG (Tungsten Inert Gas) welding with helium purge ensures penetration-free, inclusion-free weld joints that maintain full-wall thickness and metallurgical homogeneity.
- Dimensional Stability: Post-forming stress relief annealing ensures zero dimensional drift under thermal cycling conditions, maintaining optimal airflow distribution throughout the service life.
- Recyclability: Stainless steel is 100% recyclable with no degradation of material properties, supporting circular economy objectives and reducing environmental footprint.
8. Technical Notes & Recommendations
For optimal performance in humidifying fan coil air conditioning systems, the following engineering considerations should be observed during installation and operation:
- Flow Velocity: Maintain chilled water flow velocity between 1.0 and 2.5 m/s to balance heat transfer efficiency against erosion-corrosion risk at higher velocities.
- Water Quality: Control water conductivity to ≤ 50 μS/cm and pH to 7.0–8.5 to prevent scaling and minimize corrosion potential.
- Fin Integrity: Inspect fin condition annually; damaged or fouled fins reduce heat transfer capacity by 20–30% per affected section.
- Drainage Design: Ensure condensate drain lines are properly pitched (≥ 1:100 gradient) to prevent standing water that could promote microbial growth within the coil assembly.
Document Reference: Technical Specification Sheet — Product Code 1483 | Wenzhou Jixing Metal Materials Co., Ltd | Stainless Steel Coil Tube for Fan Coil Air Conditioning Systems