Stainless Steel Coil Tube for Fan Coil Unit Systems
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 Units (FCUs) and hydronic air-handling systems. This product serves as the core heat exchange element within chilled water and hot water distribution circuits, facilitating efficient thermal transfer between the circulating fluid and ambient air. The coil tube is engineered with optimized geometric parameters and material selection to support advanced inlet water temperature control strategies, enabling significant improvements in system energy efficiency, thermal comfort, and operational reliability.
As a critical component in commercial HVAC (Heating, Ventilation, and Air Conditioning) infrastructure, the coil tube must withstand prolonged exposure to varying thermal loads, pressure fluctuations, and potential corrosion from water treatment chemicals. Wenzhou Jixing's stainless steel coil tubes are designed to meet these demanding requirements while maintaining dimensional accuracy and surface integrity throughout their service life.
Material and Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its exceptional combination of corrosion resistance, mechanical strength, and thermal conductivity. The material specification ensures long-term durability in both potable and non-potable water applications.
Primary Material Grade
- AISI 304 (SAE 304 / 1.4301): The standard grade for general-purpose coil tube applications, offering excellent corrosion resistance in most water-based environments. Contains a minimum of 18% Chromium (Cr) and 8% Nickel (Ni).
- AISI 316L (SAE 316L / 1.4404): An enhanced grade incorporating Molybdenum (Mo, 2–3%) for superior resistance to chloride-induced pitting corrosion, recommended for coastal or high-chloride water treatment systems.
- AISI 316 (SAE 316 / 1.4401): A non-low-carbon variant of 316, suitable for applications requiring higher yield strength at moderate temperatures.
Mechanical and Thermal Properties
- Yield Strength: ≥ 205 MPa (AISI 304); ≥ 170 MPa (AISI 316L)
- Tensile Strength: ≥ 515 MPa (AISI 304); ≥ 485 MPa (AISI 316L)
- Elongation at Break: ≥ 40% (AISI 304); ≥ 35% (AISI 316L)
- Thermal Conductivity (at 20°C): 16.3 W/(m·K) (AISI 304); 14.6 W/(m·K) (AISI 316L)
- Operating Temperature Range: −196°C to +870°C (oxidizing atmosphere)
- Maximum Operating Pressure: Up to 1.6 MPa (standard); 2.5 MPa (reinforced configurations)
- Surface Finish: 2B (cold-rolled and annealed) or No. 4 brushed finish; interior Ra ≤ 0.8 μm for fluid flow optimization
Technical Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Tube Outer Diameter (OD) | 6.35 mm, 9.53 mm, 12.70 mm, 15.88 mm | ASTM A213 / EN 10216-5 |
| Tube Wall Thickness | 0.50 mm – 1.20 mm (standard); up to 1.60 mm (heavy-duty) | ASTM A269 |
| Coil Pitch (Spacing Between Turns) | 12 mm – 25 mm (adjustable per application) | Manufacturer's design specification |
| Coil Diameter (Bundled) | 200 mm – 600 mm (custom configurations available) | EN 12235 |
| Number of Rows (Passes) | 2, 3, 4, or 6 rows (multi-pass configurations) | ASHRAE Standard 90.1 |
| Fin Type | Aluminum (Al) flat fins, corrugated fins, or enhanced micro-fins | Fin thickness: 0.10 mm – 0.20 mm |
| Fin Pitch | 1.5 mm – 3.0 mm (measured in fins per 25.4 mm) | ASHRAE Guideline 34 |
| Connection Type | Threaded (M22×1.5, G¾), Flanged (DN15–DN50), or Brazed | EN 1092-1 / ASME B16.5 |
| Design Pressure Rating | 1.6 MPa (standard); 2.5 MPa (high-pressure variant) | EN 12235 / PED 2014/68/EU |
| Recommended Inlet Water Temperature (Chilled) | 7°C – 12°C (optimized range for energy efficiency) | ASHRAE Handbook — HVAC Systems |
| Recommended Inlet Water Temperature (Heating) | 45°C – 60°C (optimized range for comfort and efficiency) | ASHRAE Handbook — HVAC Systems |
| Maximum Recommended Flow Velocity | 1.5 m/s (chilled water); 2.0 m/s (heating water) | Hydronic Engineering Standards |
| Surface Treatment | Passivation (citric acid or nitric acid); optional chromate-free conversion coating | ASTM A967 |
| Compliance Standards | EN 12235, ASHRAE 90.1, ISO 9001, PED 2014/68/EU | — |
Manufacturing Process
The production of Wenzhou Jixing's stainless steel coil tubes follows a rigorous multi-stage manufacturing protocol designed to ensure dimensional precision, metallurgical integrity, and consistent performance.
- Material Procurement and Mill Certification: Stainless steel tubing is sourced from certified mills with full material traceability. Each batch is accompanied by a Mill Test Certificate (MTC) documenting chemical composition (via optical emission spectrometry) and mechanical properties.
- Tube Cutting and Preparation: Raw tubing is cut to specified lengths using precision plasma or laser cutting systems. Cut ends are deburred and chamfered to prevent fluid turbulence and edge damage during subsequent forming operations.
- Tube Forming and Coiling: Tubes are formed into the required coil geometry using CNC-controlled mandrel bending machines. The bending process is executed at controlled temperatures to prevent work hardening and maintain the annealed microstructure. Bend radius is maintained at a minimum of 3× tube OD to avoid wall thinning or ovality exceeding 5%.
- Fin Insertion and Crimping: Aluminum fins are precisely punched to fit between tube passes and secured via mechanical crimping or high-frequency resistance welding (HF welding). Fin-to-tube contact resistance is minimized to ensure optimal heat transfer.
- Header Assembly and Brazing: Individual tube passes are connected to stainless steel or copper headers using vacuum brazing at temperatures between 620°C and 650°C. The vacuum environment (≤ 10⁻³ mbar) ensures oxide-free joints with full penetration and leak-tight integrity.
- Passivation and Surface Treatment: The assembled coil undergoes acid passivation to remove surface contaminants and restore the chromium oxide passive layer. This process follows ASTM A967 procedures using citric acid (preferred for environmental compliance) or nitric acid solutions.
- Pressure Testing and Leak Detection: Each unit undergoes hydrostatic pressure testing at 1.5× the maximum design pressure (typically 2.4 MPa for standard units) for a minimum hold time of 30 minutes. Electronic leak detection systems monitor for any pressure drop exceeding 0.01 MPa.
- Dimensional Inspection and Quality Assurance: Final inspection includes verification of coil diameter, pitch, row count, connection dimensions, and surface finish quality using coordinate measuring machines (CMM) and automated optical inspection systems.
Applications
The stainless steel coil tube is integral to a wide range of commercial, industrial, and institutional HVAC systems, particularly in applications where water quality variability, corrosion resistance, and long-term reliability are paramount.
Primary Application Areas
- Commercial Building HVAC: Fan coil units installed in office buildings, retail spaces, hotels, and hospitals for localized temperature control and air quality management. The optimized inlet water temperature range (7–12°C for cooling; 45–60°C for heating) ensures efficient operation within the coil's designed thermal envelope.
- Industrial Process Cooling and Heating: Precision temperature control in pharmaceutical manufacturing, food processing, semiconductor fabrication, and laboratory environments where contamination resistance is critical.
- Data Center Thermal Management: High-density cooling applications where stainless steel's corrosion resistance ensures long service life in humid environments with aggressive water treatment chemicals.
- Marine and Coastal Applications: HVAC systems on vessels, offshore platforms, and coastal facilities where elevated chloride levels in ambient air and water necessitate AISI 316L-grade materials.
- Renewable Energy Integration: Coil tubes integrated with solar thermal systems, heat pumps, and district energy networks for low-carbon heating and cooling solutions.
Performance Optimization Note
Based on thermodynamic analysis of fan coil unit systems, optimal performance is achieved when the inlet water temperature is maintained within a carefully calibrated range. For cooling operation, an inlet temperature of 7–12°C provides the best balance between dehumidification capacity, sensible heat transfer rate, and compressor efficiency. Excessively low inlet temperatures (below 7°C) risk coil frosting and reduced dehumidification effectiveness, while excessively high temperatures (above 12°C) diminish the temperature differential driving heat transfer. Similarly, for heating operation, inlet temperatures of 45–60°C maximize thermal output without causing discomfort from excessive surface temperatures or triggering condensation on coil surfaces during transitional weather conditions.
Quality Certifications and Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring that every coil tube product meets or exceeds international standards for safety, performance, and environmental responsibility.
Certifications and Standards
- ISO 9001:2015: Quality Management Systems certification ensuring consistent product quality through documented processes, continuous improvement, and customer satisfaction monitoring.
- EN 12235: European standard for air-conditioning and heat pump equipment — air/water heat exchangers, covering design, manufacture, and testing requirements.
- CE Marking (PED 2014/68/EU): Conformity with the European Pressure Equipment Directive for pressure-containing components, validated by a Notified Body.
- ASTM A213 / A269: American standards for seamless and welded stainless steel tubing, verifying chemical composition, dimensions, and mechanical properties.
- ASHRAE 90.1: Compliance with American Society of Heating, Refrigerating and Air-Conditioning Engineers energy efficiency standards for commercial buildings.
- RoHS 2011/65/EU: Restriction of Hazardous Substances compliance, confirming the absence of lead, mercury, cadmium, and other restricted materials in excess of permitted thresholds.
- REACH (EC 1907/2006): Registration, Evaluation, Authorisation and Restriction of Chemicals compliance for all raw materials and manufacturing processes.
- SGS / Intertek Third-Party Testing: Independent verification of material composition, pressure integrity, thermal performance, and corrosion resistance through accredited laboratory testing.
Warranty and Reliability
Wenzhou Jixing provides a minimum 5-year warranty on coil tube products against manufacturing defects, with a demonstrated field service life exceeding 15 years under normal operating conditions. Comprehensive traceability documentation, including heat number references, test certificates, and installation records, is maintained for each production batch to support lifecycle management and predictive maintenance programs.
Unique Selling Points
- Thermally Optimized Design: Coil geometry engineered to maximize heat transfer efficiency at recommended inlet water temperatures, reducing energy consumption by up to 18% compared to conventional designs.
- Premium Material Selection: Full-range availability of AISI 304 and 316L grades with complete mill certification traceability, ensuring corrosion resistance tailored to specific water chemistry conditions.
- Precision Manufacturing: CNC-controlled forming and vacuum brazing processes guarantee dimensional accuracy (±0.5 mm tolerance on coil geometry) and leak-tight joints validated by 100% pressure testing.
- Customization Capability: Flexible configuration options for tube diameter, fin density, row count, and connection types to accommodate specific system design requirements and spatial constraints.
- Environmental Compliance: Chromate-free surface treatments, RoHS and REACH compliance, and recyclable material composition supporting sustainable building practices and green certification programs (LEED, BREEAM).