Stainless Steel Coil Tube (Coiltube) — Fan Coil Unit Application Series
Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product designed primarily for heat exchanger applications within Fan Coil Units (FCUs) and other hydronic HVAC (Heating, Ventilation, and Air Conditioning) systems. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd, this product series is engineered to deliver superior thermal conductivity, exceptional corrosion resistance, and long-term structural integrity under continuous thermal cycling conditions.
Coil tubes are formed by cold-bending continuous lengths of stainless steel pipe into uniform helical or serpentine configurations. The resulting geometry maximizes heat transfer surface area within a compact envelope, making them ideal for compact heat exchanger cores used in fan coil units, air handlers, and industrial process cooling/heating systems.
Material & Properties
The coil tube product line utilizes premium-grade austenitic stainless steel, selected for its optimal combination of mechanical strength, corrosion resistance, and thermal performance in HVAC environments.
- Primary Alloy Grades: AISI 304 (UNS S30400), AISI 316L (UNS S31603), and AISI 321 (UNS S32100)
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, condensate water, and mild chemical environments; Grade 316L provides enhanced pitting resistance due to 2.0–3.0% Mo (Molybdenum) content
- Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C, ensuring efficient heat exchange between the working fluid and ambient air
- Operating Temperature Range: −196°C to +870°C (Grade 304); −196°C to +925°C (Grade 321)
- Non-magnetic (in the annealed condition): Suitable for applications where electromagnetic interference is a concern
- Surface Finish: No. 4 brushed finish or 2B cold-rolled finish; available upon request in electropolished condition for hygienic applications
Technical Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 8.0 mm – 16.0 mm (custom sizes available) | ASTM A213 / EN 10216-5 |
| Wall Thickness (WT) | 0.6 mm – 1.5 mm | ASTM A269 / GB/T 14976 |
| Bend Radius | ≥ 2.5 × OD (minimum) | ISO 4427 |
| Coil Length (per unit) | 3.0 m – 15.0 m (configurable) | Manufacturer specification |
| Number of Turns | 5 – 50 turns (application-dependent) | — |
| Pressure Rating | Up to 1.6 MPa (16 bar) at 20°C; derated at elevated temperatures | EN 12261 / ASME B31.9 |
| Surface Roughness (Ra) | ≤ 0.8 μm (standard); ≤ 0.4 μm (electropolished) | ISO 4287 |
| End Preparation | Plain end, beveled end, or pre-soldered connection fittings | ASTM A774 |
| Dimensional Tolerance | OD: ±0.1 mm; WT: ±0.05 mm | ASTM A213 |
| Coil Pitch | 12.0 mm – 25.0 mm (adjustable per heat exchanger design) | — |
Manufacturing Process
The production of high-quality stainless steel coil tubes involves a multi-stage precision manufacturing process designed to maintain material integrity, dimensional accuracy, and surface quality throughout fabrication:
- Raw Material Selection & Incoming Inspection: Cold-rolled stainless steel seamless or welded pipe is sourced from certified mills. Each lot undergoes spectroscopic composition analysis (PMI — Positive Material Identification) and mechanical property verification prior to processing.
- Stress Relief Annealing: Incoming pipe is solution-annealed at 1050–1100°C followed by controlled cooling to eliminate residual stresses from prior forming operations, ensuring consistent bendability and minimizing the risk of stress corrosion cracking (SCC).
- Coil Forming / Cold Bending: The straight pipe is fed through a CNC-controlled coil winding machine. Precision tooling ensures uniform bend radii and consistent coil pitch. The bending process is performed at controlled speeds to prevent work-hardening, material thinning, or ovalization of the tube cross-section.
- Dimensional Inspection: Post-forming coils are inspected for OD, wall thickness, bend radius, pitch uniformity, and total coil length using optical and laser-based measurement systems.
- Surface Treatment (Optional): Electropolishing or passivation treatment may be applied to remove surface contaminants, enhance corrosion resistance, and achieve a hygienic-grade finish (Ra ≤ 0.4 μm).
- End Preparation & Assembly: Coil ends are cut to length, beveled, and prepared for brazing or mechanical connection to header manifolds in the final heat exchanger assembly.
- Pressure Testing: Each coil assembly undergoes hydrostatic pressure testing at 1.5× the maximum working pressure to verify leak-tightness and structural soundness.
- Final Inspection & Packaging: Products are visually inspected, documented with traceable heat numbers, and packaged in protective sleeves with moisture-absorbing desiccants for shipment.
Applications
Primary Applications
- Fan Coil Units (FCUs): The coil tube serves as the core heat exchange element in FCUs, transferring thermal energy between chilled/hot water and room air via forced convection. This is the primary design application referenced in performance test system studies.
- Air Handling Units (AHUs): Used in both supply and return air conditioning coils for commercial and industrial ventilation systems.
- Process Cooling & Heating: Applied in food processing, pharmaceutical manufacturing, and chemical plant heat recovery systems where corrosion resistance is critical.
- Refrigeration Systems: Employed as evaporator and condenser coils in commercial refrigeration equipment.
Secondary Applications
- Industrial HVAC systems in hospitals, cleanrooms, and laboratories
- Marine and offshore HVAC installations (Grade 316L for chloride resistance)
- Heat recovery ventilators (HRVs) and energy recovery ventilators (ERVs)
- Solar thermal collector loops
- Process water heating in semiconductor and electronics manufacturing
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework ensuring product traceability and conformance to international standards:
- ISO 9001:2015 — Quality Management Systems
- ISO 14001:2015 — Environmental Management Systems
- ISO 45001:2018 — Occupational Health and Safety Management
- EN 10204 — Type 3.1 Material Test Certificates provided with each shipment
- ASTM A213 — Seamless and Welded Austenitic Stainless Steel Tubing for High-Temperature Service
- EN 10216-5 — Technical Delivery Conditions for Seamless Tubes of Stainless Steels for Pressure Purposes
- GB/T 14976 — Chinese National Standard for Cold-Rolled or Cold-Drawn Stainless Steel Seamless Tubes
- ASME BPV Code — Compliance for pressure vessel applications (where applicable)
Unique Selling Points
- Optimized Thermal Performance: Precision coil geometry with controlled pitch and bend radius maximizes heat transfer coefficient (U-value) while minimizing pressure drop across the coil circuit.
- Extended Service Life: Austenitic stainless steel construction provides resistance to pitting, crevice corrosion, and stress corrosion cracking in condensate-rich HVAC environments — significantly outperforming carbon steel alternatives.
- Custom Configurability: OD, wall thickness, coil length, pitch, and number of turns are all customizable to meet specific Fan Coil Unit performance test requirements and thermal load calculations.
- Full Traceability: Each production batch is traceable to mill heat numbers with complete material test reports, ensuring compliance with procurement and regulatory requirements.
- Energy Efficiency Contribution: The high thermal conductivity and smooth internal surface of stainless steel coil tubes reduce pumping energy requirements and support compliance with energy efficiency regulations (e.g., EU ErP Directive, DOE standards).
- Hygienic Compatibility: Available in electropolished finish suitable for pharmaceutical, food-grade, and laboratory HVAC applications where condensate purity is critical.
Engineering Note: When integrating coil tubes into Fan Coil Unit performance test systems, factors such as coil pitch uniformity, header-to-coil connection integrity, and flow distribution across parallel coil circuits significantly influence measured performance parameters including air-side and water-side heat transfer coefficients, overall heat exchange capacity, and pressure drop characteristics. Wenzhou Jixing Metal Materials Co., Ltd provides technical support and test data to facilitate accurate performance validation and system commissioning.