Stainless Steel Coil Tube for Fan Coil Unit Systems
Product Overview
The Stainless Steel Coil Tube (Model Reference: JX-1403) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered coiled tubing product designed specifically for integration into Fan Coil Unit (FCU) systems, hydronic heating and cooling loops, and HVAC (Heating, Ventilation, and Air Conditioning) distribution networks. This coil tube is formed into continuous helical or serpentine configurations that maximize heat exchange surface area within compact volumetric envelopes, making it an indispensable component in commercial and residential HVAC applications.
Unlike conventional straight pipe assemblies, the coil tube geometry provides superior thermal performance through enhanced fluid turbulence and reduced pressure drop, directly contributing to improved system efficiency (Coefficient of Performance, COP) and energy conservation in building services engineering.
Material & Properties
Base Material Composition
- Primary Alloy: Austenitic stainless steel conforming to ASTM A269/A269M and EN 10217-7 standards
- Grade Options: 304 (UNS S30400), 316 (UNS S31600), 316L (UNS S31603), and 321 (UNS S32100) available upon specification
- Chemical Composition (Typical 304): Carbon (C) ≤0.08%, Chromium (Cr) 18.0–20.0%, Nickel (Ni) 8.0–10.5%, Manganese (Mn) ≤2.0%, Silicon (Si) ≤0.75%, Phosphorus (P) ≤0.045%, Sulfur (S) ≤0.030%
- Chemical Composition (Typical 316L): Carbon (C) ≤0.03%, Chromium (Cr) 16.0–18.0%, Nickel (Ni) 10.0–14.0%, Molybdenum (Mo) 2.0–3.0%
Mechanical & Physical Properties
- Tensile Strength: ≥515 MPa (Grade 304), ≥485 MPa (Grade 316L)
- Yield Strength (0.2% offset): ≥205 MPa
- Elongation (at break): ≥40% (minimum)
- Hardness: ≤95 HRB (annealed condition)
- Density: 8.0 g/cm³
- Thermal Conductivity: 16.3 W/(m·K) at 20°C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (20–100°C)
- Operating Temperature Range: −196°C to +870°C (Grade 304); −273°C to +870°C (Grade 316L)
Corrosion Resistance
- Excellent resistance to atmospheric corrosion, fresh water, and mild industrial environments (Grade 304)
- Superior resistance to pitting and crevice corrosion in chloride-containing environments, seawater, and chemical processing applications (Grade 316L)
- Passive oxide film (Cr₂O₃) self-healing capability ensures long-term integrity in aggressive HVAC water treatment chemistries
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | φ9.52 mm, φ12.70 mm, φ15.88 mm, φ19.05 mm, φ22.23 mm, φ25.40 mm (custom sizes available) | ASTM A269 / EN 10217-7 |
| Wall Thickness (WT) | 0.5 mm – 3.0 mm (tolerance ±10%) | ASTM A269 |
| Coil Pitch (Center-to-Center) | 15 mm – 40 mm (configurable per thermal load requirements) | Manufacturer Specification |
| Coil Diameter | φ100 mm – φ500 mm | Manufacturer Specification |
| Number of Rows | 1 to 6 rows | ASHRAE Handbook – HVAC Systems and Equipment |
| Total Tube Length per Coil | 2.0 m – 15.0 m | Manufacturer Specification |
| Surface Finish | 2B (Cold Rolled and Annealed), No. 4 Brushed, or Mirror Polish (Ra ≤ 0.4 μm) | ASTM A480 |
| End Form | Plain cut, Threaded (BSP/NPT), Flanged, or Brazed connections | ASME B1.20.1 / B1.20.3 |
| Pressure Rating | Up to 2.5 MPa (working pressure), 6.3 MPa (hydrostatic test) | EN 12266 / ASME B31.9 |
| Tolerance on OD | ±0.05 mm (precision coiled) | ISO 1128 |
| Tolerance on Wall Thickness | ±10% of nominal | ASTM A269 |
| Heat Treatment | Solution Annealed (1050–1150°C) followed by rapid quench | ASTM A269 |
| Maximum Design Temperature | 150°C (hot water heating), 8°C (chilled water cooling) | ASHRAE 90.1 |
| Fluid Velocity (Recommended) | 0.5 – 2.0 m/s | ASHRAE Handbook |
Manufacturing Process
Process Flow
- Raw Material Preparation: Cold-rolled stainless steel strip (coil form) is received with mill test certificates (MTC) confirming chemical composition and mechanical properties. Incoming material undergoes visual inspection, dimensional verification, and spectral analysis (PMI – Positive Material Identification) to confirm alloy grade.
- Strip Annealing (if required): Cold-worked strip may undergo stress-relief annealing at 1050–1150°C in a controlled atmosphere (argon or vacuum) to restore full annealed condition and eliminate residual stresses from upstream forming operations.
- Tube Forming: Precision roll-forming or extrusion converts flat strip into seamless tubular stock with controlled wall thickness uniformity. The forming process is monitored via in-line laser measurement systems for real-time dimensional feedback.
- Heat Treatment: Solution annealing (solutionizing) at 1050–1150°C with water quench or forced-air quench ensures uniform austenitic microstructure, maximum corrosion resistance, and optimal mechanical properties. Intergranular corrosion sensitivity is eliminated through this process.
- Precision Coiling: The formed tube is fed through a CNC-controlled coiling machine that imparts the required helical geometry with exact pitch, coil diameter, and row configuration. The coiling process maintains tube roundness within ±0.05 mm OD tolerance and eliminates kinks or distortion.
- Fin Attachment (if applicable): For enhanced heat transfer configurations, aluminum or stainless steel fins are mechanically or diffusion-bonded to the coil tube surface at specified fin spacing (typically 2.0–3.5 mm).
- Surface Treatment: Final surface finishing (pickling and passivation per ASTM A380) removes scale, contaminants, and forms a protective chromium oxide passive layer. Optional electropolishing may be applied for critical hygiene applications.
- End Processing: Tube ends are machined to specified connection types (threading, flanging, or beveling) with concentricity tolerance of ±0.1 mm.
- Quality Inspection: Each coil assembly undergoes 100% visual inspection, hydrostatic pressure testing at 1.5× working pressure (minimum 3.75 MPa), dimensional verification, and leak testing. Sampling-based ultrasonic testing (UT) and radiographic testing (RT) may be performed per EN 10228-7.
- Packaging and Dispatch: Coils are wrapped in moisture-barrier packaging with desiccants and shipped in protective wooden crates or export-grade steel containers.
Applications
Primary Applications
- Fan Coil Units (FCU): The coil tube serves as the primary heat exchanger element in FCU systems, transferring thermal energy between the circulating fluid (hot or chilled water) and the air stream. Typical installations include commercial office buildings, hotels, hospitals, and residential apartments.
- HVAC Hydronic Distribution: Used in heating and cooling loops where compact, high-efficiency heat exchange surfaces are required within limited mechanical room or ceiling plenum space.
- Chilled Water Cooling Coils: Operates at supply temperatures of 6–12°C, providing sensible and latent cooling for air handling applications.
- Hot Water Heating Coils: Operates at supply temperatures of 40–85°C, delivering radiant and convective heating to occupied spaces.
- Industrial Process Cooling: Applicable in pharmaceutical manufacturing, food processing, and laboratory environments where hygiene-grade stainless steel (316L) is mandated.
System Integration
- Compatible with two-pipe, three-pipe, and four-pipe FCU configurations
- Integrates with variable flow control valves (thermostatic or motorized) for modulating thermal output
- Designed for low-pressure-drop operation to minimize pumping energy (fan energy and pump energy optimization per ASHRAE 90.1)
- Suitable for both open-loop and closed-loop water distribution systems
Quality Certifications & Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification covering design, manufacture, and testing of coil tube products |
| ISO 14001:2015 | Environmental Management System ensuring sustainable manufacturing practices and minimal environmental impact |
| EN 10217-7 | European standard for austenitic stainless steel tubes for heat exchangers and heating equipment |
| ASTM A269/A269M | American standard for seamless and welded austenitic stainless steel tubes for boiler, heat exchanger, and similar applications |
| EN 10204-3.1 | Inspection certificate (mill test certificate) type 3.1 confirming material conformity |
| CE Marking | Conformity with European Machinery Directive and Pressure Equipment Directive (PED 2014/68/EU) where applicable |
| NSF/ANSI 61 | Drinking Water System Components – Health Effects certification for potable water applications (Grade 316L) |
| ASME B31.9 | Code for Heating and Cooling Systems (hydronic piping system design reference) |
| ASHRAE 90.1 | Energy Standard for Buildings – compliance with minimum efficiency requirements for HVAC systems |
Unique Selling Points
- Superior Corrosion Durability: The austenitic stainless steel construction provides exceptional resistance to corrosion from HVAC water treatment chemicals (glycol, biocides, inhibitors), eliminating the need for copper-nickel alloys or protective coatings and extending service life beyond 25 years.
- Precision Coiling Geometry: CNC-controlled coiling ensures uniform pitch and tube roundness, directly translating to consistent thermal performance, reduced air-side pressure drop, and balanced airflow distribution across the coil face.
- Hygiene-Grade Options: Grade 316L with electropolished finish (Ra ≤ 0.4 μm) meets pharmaceutical and food-grade requirements, eliminating dead-leg contamination risks in critical environments.
- Energy Efficiency: Optimized coil geometry minimizes pumping energy while maximizing heat transfer coefficient (U-value), contributing to overall system COP improvement of 15–25% compared to conventional configurations.
- Design Flexibility: Customizable OD, wall thickness, pitch, row count, and coil diameter to precisely match thermal load calculations and spatial constraints of any FCU or AHU (Air Handling Unit) design.
- Full Traceability: Each production batch is accompanied by a complete quality dossier including MTC, dimensional inspection reports, pressure test records, and surface finish measurements, ensuring complete supply chain traceability per ISO 9001 requirements.
- Maintenance Advantage: The smooth internal surface of seamless stainless steel coil tubes minimizes fouling and scaling accumulation, reducing maintenance frequency and preserving heat transfer efficiency over the system lifecycle.
Installation & Maintenance Guidelines
- Ensure proper flow direction and adequate air-side velocity (1.5–2.5 m/s face velocity) for optimal heat transfer performance
- Maintain water quality per ASHRAE 95.1 (closed-loop) or ASHRAE 188 (potable water) standards to prevent scaling and biological growth
- Recommended annual inspection of coil surface for fouling; chemical cleaning with non-abrasive acid solutions (pH 3–5) if heat transfer degradation exceeds 10%
- Verify hydrostatic integrity annually at 1.5× design pressure; replace coil if any leak is detected
- Install isolation valves and air vents upstream of coil assembly to facilitate maintenance and prevent air binding