Stainless Steel Coil Tube (Coiltube) — Fan Coil System Application
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular component designed for integration into fan coil air conditioning systems, particularly those incorporating wet film humidification technology. The coil tube serves as the primary heat exchange medium, facilitating efficient thermal transfer between the refrigerant or chilled water circuit and the surrounding air stream. Constructed from high-grade austenitic stainless steel, this product offers superior corrosion resistance, mechanical durability, and long-term thermal performance stability under demanding HVAC operating conditions.
The coil tube is supplied in continuous coiled form (Coiltube configuration), enabling flexible on-site installation and custom-length cutting to meet specific system layout requirements. This product is classified under the industrial reference designation Sequence No. 488 within the manufacturer's product catalog.
2. Material & Properties
2.1 Base Material
- Primary Grade: AISI 304 / ASTM A213 TP304 (18/8 Austenitic Stainless Steel)
- Alternative Grade: AISI 316 / ASTM A213 TP316 (Marine-Grade Stainless Steel, Mo-enhanced)
- Composition: Chromium (Cr) ≥ 18%, Nickel (Ni) ≥ 8%, Carbon (C) ≤ 0.08%, Molybdenum (Mo) 2.0–3.0% (for 316 grade)
2.2 Mechanical Properties
- Tensile Strength (UTS): ≥ 515 MPa (74,700 psi)
- Yield Strength (0.2% Offset): ≥ 205 MPa (29,700 psi)
- Elongation at Break: ≥ 40%
- Hardness (Rockwell B): 80–95 HRB
- Operating Temperature Range: −196°C to +870°C (−321°F to +1,598°F)
2.3 Thermal Properties
- Thermal Conductivity (at 20°C): 16.3 W/(m·K)
- Specific Heat Capacity: 500 J/(kg·K)
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C
2.4 Corrosion Resistance
- Excellent resistance to atmospheric corrosion, humid environments, and aqueous condensate
- Resistance to pitting and crevice corrosion in chloride-containing environments (316 grade)
- Non-reactive surface suitable for potable water and HVAC condensate drainage
3. Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm (1/4"), 9.53 mm (3/8"), 12.7 mm (1/2"), 15.88 mm (5/8"), 19.05 mm (3/4") | ASTM A213 / GB/T 14976 |
| Wall Thickness | 0.5 mm – 2.0 mm (customizable) | ASTM A213 |
| Coil Diameter | 150 mm – 600 mm | Manufacturer Specification |
| Coil Length | 5 m – 50 m (standard); up to 200 m (custom order) | Manufacturer Specification |
| Surface Finish | Mirror Polish (Ra ≤ 0.4 μm), Bright Annealed (BA), or Matte | ASTM A473 |
| End Condition | Plain, Beveled, or Flanged | ASME B16.25 |
| Pressure Rating | Up to 1.6 MPa (232 psi) at 20°C | GB/T 14976 |
| Tolerance (OD) | ±0.05 mm – ±0.10 mm | ISO 1307 |
| Tolerance (Wall Thickness) | ±10% of nominal | ASTM A213 |
| Welding Compatibility | TIG (GTAW), Orbital, Brazing compatible | ASME Section IX |
| Food/Hygiene Grade | Available per 3-A Sanitary Standards | 3-A Standard No. 14-18 |
4. Manufacturing Process
4.1 Material Preparation
High-purity austenitic stainless steel billets or strip stock are sourced from certified mills (e.g., Outokumpu, Kocks, POSCO) with full mill test certificates (MTC) conforming to EN 10204 Type 3.1. Incoming material undergoes spectroscopic verification (OES analysis) to confirm chemical composition within specified tolerances.
4.2 Seamless Tube Forming
- Piercing: Billets are heated to 1,150°C – 1,200°C and pierced to form hollow slabs.
- Rolling & Drawing: Continuous rolling reduces the cross-section to near-final dimensions; multi-stage cold drawing achieves precise OD and wall thickness tolerances.
- Pilot Drawing: Internal pilot rods ensure uniform wall thickness and roundness.
4.3 Heat Treatment
Following cold working, the tube undergoes solution annealing (Solution Heat Treatment) at 1,050°C – 1,100°C with rapid water quenching to dissolve carbide precipitates, restore full austenitic microstructure, and ensure maximum corrosion resistance and ductility.
4.4 Surface Finishing
- Pickle & Passivate: Acid immersion (HNO₃/HF blend) removes scale and forms a protective chromium oxide passive layer.
- Electropolishing: (Optional) Electrochemical polishing achieves mirror finish with Ra ≤ 0.4 μm surface roughness, critical for hygiene and flow efficiency applications.
- Precision Coiling: The tube is coiled on CNC-controlled winding equipment to achieve uniform coil geometry with controlled bend radius (minimum 3× OD) to prevent kinking or ovality.
4.5 Quality Inspection
- Visual inspection for surface defects, weld seams, and geometric deviations
- Hydrostatic pressure testing at 1.5× working pressure for minimum 10 seconds
- Eddy current (ET) testing for internal wall thickness verification and defect detection
- Spectroscopic (PMI) analysis for material grade confirmation
5. Applications
5.1 Fan Coil Air Conditioning Systems
The primary application domain is the integration of stainless steel coil tubes into fan coil units (FCU) for commercial and industrial HVAC systems. The coil tube functions as the heat exchanger core, transferring thermal energy between the circulating refrigerant/chilled water and the air stream driven by the fan assembly. In systems incorporating wet film humidification (as referenced in the associated technical study), the stainless steel coil tube provides critical resistance to continuous moisture exposure and condensate corrosion, ensuring extended service life compared to carbon steel or copper alternatives.
5.2 Additional Applications
- Chilled water distribution coils in commercial buildings
- Refrigeration evaporator coils in cold storage facilities
- Heat recovery coils in ventilation systems
- Industrial process heating/cooling loops
- Food and beverage processing equipment (sanitary grade)
- Pharmaceutical cleanroom HVAC systems
6. Quality Certifications
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification for manufacturing processes |
| ISO 14001:2015 | Environmental Management System compliance |
| CE Marking | Conformity with European health, safety, and environmental protection standards |
| EN 10204 3.1 | Mill Test Certificate providing full chemical and mechanical property data |
| ASTM A213 / A269 | Standard specifications for seamless austenitic stainless steel tube |
| GB/T 14976 | Chinese national standard for seamless stainless steel hydraulic fluid tubes |
| NACE MR0175 / ISO 15156 | Resistance to sulfide stress cracking (for 316 grade in H₂S environments) |
| 3-A Sanitary Standards | Food-grade surface finish and construction (optional) |
7. Unique Selling Points
- Superior Corrosion Resistance: Austenitic stainless steel construction provides exceptional resistance to condensate, humid air, and wet film humidification environments — significantly outperforming copper and carbon steel alternatives in wet HVAC applications.
- Long Service Life: Designed for 20–30 year operational lifespan without degradation of heat transfer efficiency or structural integrity.
- Hygienic Surface: Available in electropolished mirror finish (Ra ≤ 0.4 μm), preventing bacterial colonization and facilitating easy cleaning — ideal for food-grade and pharmaceutical HVAC applications.
- Customizable Configuration: Flexible coil diameters, tube lengths, and end conditions enable precise integration into diverse system architectures.
- Low Maintenance: Non-corrosive surface eliminates the need for protective coatings, reducing lifecycle maintenance costs.
- Thermal Efficiency: Smooth internal bore and precise wall thickness ensure optimal turbulent flow characteristics and high heat transfer coefficients.
- Full Traceability: Each coil batch is accompanied by complete material traceability documentation including heat number, chemical analysis, and mechanical test results.
Note: The technical study referenced (《湿膜加湿在风机盘管空调系统中的应用研究》 — "Research on the Application of Wet Film Humidification in Fan Coil Air Conditioning Systems") specifically validates the suitability of stainless steel coil tubes in high-moisture HVAC environments. The research demonstrates that stainless steel coil tubes maintain thermal efficiency and structural integrity over extended operational cycles in wet film humidification systems, where continuous condensation exposure would prematurely degrade conventional copper or aluminum coil materials.