Stainless Steel Coil Tube — Fan Coil Unit Application Series
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed for integration into fan coil unit (FCU) air conditioning systems and related hydronic heating and cooling applications. This product series is specifically engineered to meet the demanding operational requirements of modern building energy management systems, including participation in Demand Response (DR) programs that optimize load shifting and peak shaving in commercial and industrial HVAC infrastructure.
Coil tubes are formed by continuous bending of seamless or welded stainless steel tubes into helical or serpentine geometries, providing high surface-area-to-volume ratios essential for efficient heat exchange. The coiltube configuration allows for compact heat exchanger designs that minimize footprint while maximizing thermal transfer performance — a critical requirement for fan coil units operating within confined ceiling plenums and mechanical chases.
Material Composition and Properties
The coil tube series is fabricated from austenitic and duplex stainless steel grades selected for their superior corrosion resistance, mechanical integrity, and thermal conductivity characteristics.
- Primary Grades: AISI 304 (UNS S30400), AISI 316 (UNS S31600), and AISI 316L (UNS S31603)
- Alternative Grades: 2205 Duplex (UNS S32205) for high-chloride environments
- Chemical Composition (316L): C ≤ 0.03%, Si ≤ 1.00%, Mn ≤ 2.00%, P ≤ 0.045%, S ≤ 0.030%, Cr 16.0–18.0%, Ni 10.0–14.0%, Mo 2.0–3.0%
- Mechanical Properties: Tensile Strength (UTS) ≥ 515 MPa; Yield Strength (0.2% offset) ≥ 205 MPa; Elongation ≥ 40% (as per ASTM A213/A269)
- Corrosion Resistance: Excellent resistance to pitting and crevice corrosion in aqueous environments; pitting resistance equivalent number (PREN) ≥ 24 for 316L
- Thermal Conductivity: 14–16 W/(m·K) at 20°C
- Operating Temperature Range: −196°C to +870°C (continuous service)
Technical Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 6.35 mm – 25.4 mm (¼" – 1") |
| Wall Thickness (WT) | 0.5 mm – 2.0 mm (0.020" – 0.079") |
| Coil Pitch | 3 mm – 15 mm (adjustable per heat exchanger design) |
| Coil Height | 15 mm – 150 mm |
| Tube Length (as coiled) | Custom; standard reels 100 m – 500 m |
| Surface Finish | 2B, No. 4 Brushed, or Electropolished (Ra ≤ 0.4 μm) |
| Heat Exchanger Configuration | Tube-and-fin; serpentine; helical coil |
| Maximum Operating Pressure | 1.6 MPa (232 psi) at 25°C |
| Water Side Flow Rate | 0.2 – 5.0 L/min (typical FCU application) |
| Applicable Standards | ASTM A213, ASTM A269, EN 10217, GB/T 14976 |
| Demagnetization | Optional; residual magnetism ≤ 0.5 mT |
Manufacturing Process
The production of stainless steel coil tubes follows a rigorous multi-stage process to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Wire/Tube Drawing: Cold-rolled stainless steel wire is drawn through precision tungsten carbide dies to achieve the specified OD and wall thickness tolerances (±0.02 mm).
- Heat Treatment (Solution Annealing): Tubes are solution-annealed at 1050–1150°C followed by rapid water quenching to achieve full austenitic microstructure and maximum corrosion resistance.
- Pickling and Passivation: Surface oxide scales are removed via nitric-hydrofluoric acid pickling, followed by passivation treatment to form a stable chromium oxide protective layer.
- Coil Forming: Tubes are fed through a CNC-controlled coil bending machine at controlled temperatures (ambient to 150°C for warm forming) to produce the required helical or serpentine geometry without inducing work hardening or cracking.
- Fin Attachment: Aluminum or stainless steel fins are mechanically or brazed onto the coil tube to create the complete heat exchanger assembly.
- Final Inspection: Each coil tube undergoes dimensional verification, pressure testing, and visual/eddy current inspection.
Applications
The stainless steel coil tube series is engineered for demanding thermal management applications:
- Fan Coil Units (FCUs): Primary application in commercial HVAC systems for precise temperature and humidity control in offices, hospitals, hotels, and laboratories. The coil tube serves as the water-side heat exchanger core.
- Demand Response (DR) Systems: As studied in academic research on FCU system adaptability to demand response programs, coil tubes fabricated from high-performance stainless steel exhibit superior thermal inertia characteristics, enabling effective load shifting strategies during peak demand periods. The material's thermal stability allows FCUs to maintain comfort setpoints while cycling off during DR events.
- Industrial Process Cooling/Heating: Chemical processing, pharmaceutical manufacturing, and food-grade applications requiring hygienic heat transfer surfaces.
- Marine and Coastal Environments: 316L and duplex grades provide exceptional resistance to chloride-induced corrosion in coastal HVAC installations.
- Chilled Water Distribution: Integration into primary/secondary chilled water loops for large-scale building energy systems.
Quality Certifications and Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management systems and product certifications:
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- EN 10204 3.1 — Material Test Certificates
- ASTM A213/A269 — Seamless and welded stainless steel tube standards
- GB/T 14976 — Chinese national standard for seamless stainless steel tubes
- SMS/DIN 11866 — Hygienic design compliance (food and pharmaceutical grade)
- Pressure Testing: Hydrostatic testing at 1.5× maximum working pressure with zero leakage acceptance criteria
- Third-Party Inspection: Available upon request (SGS, BV, TUV)
Unique Selling Points
- Superior Thermal Performance: The austenitic microstructure provides consistent thermal conductivity across wide temperature ranges, ensuring stable heat exchange efficiency in FCU applications.
- Demand Response Compatibility: Engineered with thermal mass characteristics that support adaptive control strategies, enabling the coil tube–FCU system to participate effectively in grid demand response programs without compromising occupant comfort.
- Extended Service Life: Corrosion resistance eliminates the need for replacement within typical building HVAC lifecycles (20–30 years), reducing lifecycle costs.
- Hygienic Surface Quality: Electropolished finish (Ra ≤ 0.4 μm) prevents biofilm accumulation, critical for hospital and pharmaceutical applications.
- Custom Geometric Configuration: CNC-controlled coil forming allows tailored pitch, diameter, and length specifications to match specific heat exchanger thermal design requirements.
Note: All specifications are subject to confirmation based on final order requirements. Custom material grades, dimensions, and surface finishes are available upon request. Wenzhou Jixing Metal Materials Co., Ltd. provides full traceability documentation including mill test certificates, heat numbers, and dimensional inspection reports for every production lot.