Stainless Steel Coil Tube (Coil Tube) — For Fan Coil Unit Systems
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Catalog No.: 1159
1. Product Overview
The Stainless Steel Coil Tube (Coil Tube) is a precision-engineered tubular product designed for integration into Fan Coil Units (FCUs) — compact HVAC (Heating, Ventilation, and Air Conditioning) terminal devices widely deployed in commercial and residential buildings. This coil tube serves as the primary heat exchange medium within fan coil systems, facilitating efficient thermal energy transfer between the circulating fluid (water or refrigerant) and the air stream passing through the unit.
Rooted in rigorous simulation studies, dynamic regulation analysis, and energy-saving optimization — as documented in the technical paper "Simulation, Regulation, and Energy-Saving Analysis of Fan Coil Units" — this product is engineered to deliver superior thermal performance, reduced energy consumption, and extended operational lifespan under demanding HVAC service conditions.
2. Material & Properties
2.1 Base Material
- Material Grade: Austenitic Stainless Steel (typical grades: SUS304 / AISI 304, SUS316L / AISI 316L)
- Composition: Chromium (Cr ≥ 18%), Nickel (Ni ≥ 8%), with optional Molybdenum (Mo) content for enhanced corrosion resistance in 316L variants
- Form: Seamless or welded coil tube, cold-drawn to precision dimensions
2.2 Key Mechanical & Physical Properties
| Property | Specification |
|---|---|
| Tensile Strength (UTS) | ≥ 520 MPa (SUS304); ≥ 550 MPa (SUS316L) |
| Yield Strength (0.2% offset) | ≥ 205 MPa |
| Elongation at Break | ≥ 40% |
| Thermal Conductivity | 14.5–16.5 W/(m·K) at 20°C |
| Coefficient of Thermal Expansion | 16–17.5 × 10⁻⁶ /°C |
| Operating Temperature Range | −40°C to +350°C |
| Corrosion Resistance | Excellent resistance to atmospheric, aqueous, and mild chemical corrosion; superior to carbon steel by a factor of 5–10× |
| Surface Finish | 2B (cold-rolled, annealed, and pickled) or No.4 brushed finish; optional electropolished interior |
2.3 Unique Selling Points
- Enhanced Corrosion Durability: Austenitic stainless steel composition provides long-term resistance to condensation-induced corrosion, a common failure mode in fan coil heat exchangers operating in high-humidity environments.
- Simulation-Validated Performance: Product geometry and dimensions are derived from CFD (Computational Fluid Dynamics) simulations of fan coil airflow and thermal fields, ensuring optimal heat transfer coefficient (U-value) and minimal pressure drop (ΔP).
- Energy-Saving Design: Coil tube geometry is optimized to minimize pumping power while maximizing heat exchange surface area, contributing directly to the overall Energy Efficiency Ratio (EER) and Seasonal Energy Efficiency Ratio (SEER) of the fan coil system.
- Hygienic Interior Surface: Electropolished or passivated inner surfaces inhibit biofilm formation and scale deposition, reducing maintenance intervals and preserving heat transfer efficiency over the product lifecycle.
3. Technical Specifications
| Parameter | Specification / Range |
|---|---|
| Outer Diameter (OD) | 6.0 mm – 12.7 mm (standard); custom sizes available upon request |
| Wall Thickness | 0.4 mm – 1.2 mm |
| Coil Pitch (Row Spacing) | 10 mm – 25 mm (typical for FCU heat exchangers) |
| Coil Length (per row) | 300 mm – 1,200 mm |
| Number of Rows | 2 – 6 rows (configurable per thermal load requirement) |
| Tube End Condition | Plain, flared, or crimped for brazed/welded connection |
| Tolerance on OD | ±0.05 mm |
| Tolerance on Wall Thickness | ±10% of nominal |
| Max. Operating Pressure | 1.6 MPa (gauge) for water; 2.5 MPa for refrigerant circuits |
| Hydrostatic Test Pressure | 1.5× maximum operating pressure (per EN 12729 / ASME standards) |
| Coil Winding Accuracy | ±0.5 mm on pitch; ±1 mm on end alignment |
| Standard Reference | ASTM A269, ASTM A312, EN 10216-5, GB/T 14976 |
4. Manufacturing Process
- Material Selection & Incoming Inspection: Stainless steel strip or seamless tube stock is sourced from certified mills. Each batch undergoes spectroscopic analysis (OES) for chemical composition verification and mechanical testing per ASTM E10/E8 standards.
- Slitting & Coiling (Strip Route): Wide stainless steel strip is precision-slitted to the required coil tube blank width and recoiled onto spools for downstream forming. Alternatively, seamless tube is procured for higher-pressure applications.
- Cold Forming / Tube Drawing: The coil tube is formed through cold-die bending or tube-drawing processes to achieve the precise OD, wall thickness, and coil pitch geometry. This process induces beneficial work-hardening while preserving metallurgical integrity.
- Heat Treatment (Annealing): Post-forming annealing at 1050–1100°C followed by controlled cooling relieves residual stresses, restores full ductility, and stabilizes the austenitic microstructure. Solution annealing is performed in a protective atmosphere (argon or vacuum) to prevent oxidation.
- Pickling & Passivation: Surface oxide scale is removed via acid pickling (nitric/hydrofluoric acid blend), followed by passivation to form a stable chromium oxide (Cr₂O₃) protective layer. This step is critical for achieving the specified corrosion resistance.
- Coil Winding & Forming: Individual tube segments are wound into the specified coil geometry using CNC-controlled winding machinery. End connections are prepared for brazing (phosphor copper brazing per AWS A5.8) or welding (TIG/argon arc welding per AWS D17.1).
- Quality Inspection & Testing: Each production lot undergoes: (a) dimensional verification via laser scanning or coordinate measurement (CMM); (b) hydrostatic pressure testing; (c) visual inspection for surface defects; (d) eddy current testing for internal discontinuities; and (e) metallographic examination (per ASTM A388) for microstructural verification.
- Final Cleaning & Packaging: Tubes are cleaned of all processing residues, protected with corrosion-inhibitive packaging, and shipped with material traceability documentation (Mill Test Reports / MTRs).
5. Applications
5.1 Primary Application: Fan Coil Unit (FCU) Systems
The stainless steel coil tube is the core heat exchange element in fan coil units, which are terminal HVAC devices used for precise temperature and humidity control in individual zones. Key application scenarios include:
- Commercial Buildings: Office towers, retail spaces, hotels, and hospitals where zonal climate control is required without the complexity and cost of individual VAV (Variable Air Volume) systems.
- Residential HVAC: High-end residential units, apartments, and villas utilizing hydronic fan coil systems connected to central boilers or heat pumps.
- Industrial & Process Cooling: Clean rooms, laboratories, and process environments requiring contamination-free heat exchange where carbon steel would corrode.
- Refrigeration Circuits: Direct-expansion (DX) fan coil units utilizing refrigerant as the heat transfer medium.
5.2 Energy-Saving Performance Context
As documented in the study "Simulation, Regulation, and Energy-Saving Analysis of Fan Coil Units", the thermal-hydraulic performance of the coil tube directly governs the overall energy efficiency of the FCU system. Key energy-saving parameters include:
- Heat Transfer Coefficient (U-value): Optimized coil tube geometry achieves U-values of 40–65 W/(m²·K) for air-to-water configurations, reducing required air velocity and fan power consumption.
- Pressure Drop (ΔP): Low-friction-drag coil designs minimize fluid-side pressure drop, reducing pump energy by 15–30% compared to conventional carbon steel coil alternatives.
- Part-Load Efficiency: The coil tube's thermal mass and geometry support efficient operation at part-load conditions (25–75% capacity), which constitute the majority of real-world operating hours.
- Regulation Compatibility: The coil tube design supports modulation via three-way valve control or variable-speed pump regulation, enabling precise temperature control with minimal energy waste.
6. Quality Certifications & Compliance
| Certification / Standard | Scope of Compliance |
|---|---|
| ISO 9001:2015 | Quality Management System — Covers all manufacturing, inspection, and delivery processes |
| ISO 14001:2015 | Environmental Management System — Sustainable manufacturing practices |
| ASTM A269 / A312 | Standard specifications for seamless and welded austenitic stainless steel tubing |
| EN 10216-5 | European standard for welded stainless steel tubes for pressure purposes |
| GB/T 14976 | Chinese national standard for seamless stainless steel tubes for general engineering |
| CE Marking (PED 2014/68/EU) | Pressure Equipment Directive compliance for products intended for EU market |
| NSF/ANSI 61 | Drinking water system components — material safety certification (for potable water applications) |
| Mill Test Reports (MTR) | Batch-level chemical and mechanical property documentation provided with every shipment |
7. Summary
The Stainless Steel Coil Tube (Coil Tube, Catalog No. 1159) from Wenzhou Jixing Metal Materials Co., Ltd. represents a precision-engineered solution for fan coil unit heat exchange applications. Backed by simulation-validated design methodology and informed by rigorous energy-saving research, this product delivers exceptional thermal performance, corrosion resistance, and energy efficiency. Its compliance with international standards (ASTM, EN, GB) and quality management certifications (ISO 9001) ensures reliability and traceability across the global HVAC supply chain. The product is available in standard configurations and can be customized to meet specific thermal load, pressure, and dimensional requirements.