Stainless Steel Coil Tube for Fan Coil Unit Systems (FCU)
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Code: JX-CT-373
Classification: Precision Formed Tubular Products — Coil Tube Series
1. Product Overview
The JX-CT-373 Stainless Steel Coil Tube is a precision-engineered continuous tube product specifically designed for use in Fan Coil Unit (FCU) systems within building HVAC (Heating, Ventilation, and Air Conditioning) applications. The coil tube serves as the primary heat exchange element in FCU systems, facilitating efficient thermal transfer between the circulating fluid (water or refrigerant) and the ambient air stream.
Unlike conventional straight or bent tube configurations, the coil tube is formed into a continuous helical or serpentine geometry that maximizes the heat transfer surface area within a compact envelope. This geometry is critical for achieving optimal thermal performance in space conditioning applications, where high coefficient of performance (COP) and energy efficiency are paramount.
Recent advancements in intelligent building control systems — particularly those employing Deep Reinforcement Learning (DRL) algorithms — have further elevated the importance of coil tube design parameters. The geometric regularity, thermal consistency, and material uniformity of the JX-CT-373 coil tube enable predictable thermal response characteristics, which are essential for AI-driven adaptive control strategies in modern building energy management systems.
2. Material & Properties
2.1 Base Material
The coil tube is manufactured from high-grade austenitic stainless steel, selected for its superior corrosion resistance, thermal conductivity, and mechanical stability under repeated thermal cycling conditions.
- Primary Alloy: AISI 304 (UNS S30400) — Chromium-Nickel Austenitic Stainless Steel
- Alternative Grade: AISI 316L (UNS S31603) — Molybdenum-bearing variant for aggressive chemical environments
- Supplemental Option: AISI 321 (UNS S32100) — Titanium-stabilized grade for elevated-temperature applications
2.2 Mechanical Properties
| Property | Specification (AISI 304) | Test Standard |
|---|---|---|
| Tensile Strength (UTS) | ≥ 515 MPa | ASTM A270 / EN 10216-5 |
| Yield Strength (0.2% Offset) | ≥ 205 MPa | ASTM A270 |
| Elongation at Break | ≥ 40% | ASTM A270 |
| Hardness (HBW) | ≤ 200 | ISO 6506 |
| Thermal Conductivity (20°C) | 16.3 W/(m·K) | ASTM E1225 |
| Thermal Expansion Coefficient (20–100°C) | 17.3 × 10⁻⁶ /K | ASTM E228 |
| Corrosion Resistance (3.5% NaCl, 60°C) | ≥ 1000 hours without pitting | ASTM G48 |
2.3 Chemical Composition (AISI 304, wt%)
| Element | C | S | P | Cr | Ni | Mn | Si | N |
|---|---|---|---|---|---|---|---|---|
| Max / Range | ≤ 0.08 | ≤ 0.03 | ≤ 0.045 | 18.0–20.0 | 8.0–10.5 | ≤ 2.0 | ≤ 0.75 | ≤ 0.10 |
3. Technical Specifications
| Parameter | Specification | Tolerance |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm / 9.53 mm / 12.70 mm / 15.88 mm | ± 0.10 mm |
| Wall Thickness (WT) | 0.50 mm / 0.70 mm / 1.00 mm | ± 0.05 mm |
| Coil Pitch (Helical Spacing) | 15.0 – 25.0 mm (adjustable per application) | ± 0.3 mm |
| Coil Diameter (Helix Diameter) | 200 – 800 mm | ± 2.0 mm |
| Tube Length (Continuous) | 3.0 – 50.0 m (spooled) | ± 0.5% |
| Surface Finish | Mirror polish (Ra ≤ 0.4 μm) / Brushed (Ra ≤ 1.6 μm) | — |
| Operating Pressure | Up to 1.6 MPa (gauge) | — |
| Operating Temperature Range | −40°C to +200°C | — |
| Fluid Compatibility | Water, glycol solutions, refrigerants (R-134a, R-410A) | — |
| End Preparation | Plain end / Threaded (G½, G¾) / Flanged | — |
| Coating (Optional) | PVD (Physical Vapor Deposition) TiN / TiAlN | — |
| Package | Spooled on wooden reel, moisture-proof wrapped | — |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Inspection: Incoming stainless steel strip or seamless tube is verified for chemical composition (via XRF spectrometry), mechanical properties, and surface quality per ASTM A270 / EN 10216-5.
- Slitting & Leveling: Wide strip is slit to required coil tube blank width and cold-rolled to achieve precise thickness tolerance (± 0.05 mm).
- Precision Coiling (Forming): Multi-roller forming stations progressively bend the flat strip into a continuous helical coil geometry. Roller profiles are CNC-calibrated to maintain constant pitch, helix diameter, and wall thickness throughout the coil length.
- Welding (if welded tube): TIG (Tungsten Inert Gas) welding along the longitudinal seam using high-purity argon shielding (99.999% Ar). Weld penetration is verified by ultrasonic testing (UT) per ASTM E747.
- Heat Treatment: Solution annealing at 1040–1120°C followed by rapid water quenching to restore full austenitic microstructure and maximize corrosion resistance.
- Pickling & Passivation: Immersion in mixed acid bath (HNO₃ + HF) to remove scale and oxide films, followed by passivation treatment to establish a protective chromium oxide layer.
- Surface Finishing: Electropolishing or mechanical polishing to achieve specified surface roughness (Ra ≤ 0.4 μm for mirror finish).
- Dimensional Inspection: Laser micrometer measurement of OD, wall thickness, pitch, and helix diameter at intervals of ≤ 1 m throughout the coil length.
- Pressure Testing: Hydrostatic pressure test at 2.4× operating pressure (3.84 MPa) for a minimum dwell time of 30 seconds per ASTM D1599 equivalent.
- Final Inspection & Packaging: Visual inspection, spooling onto wooden reel, moisture-barrier wrapping, and labeling with batch traceability information.
4.2 Key Process Parameters
| Process Stage | Critical Parameter | Control Value |
|---|---|---|
| Cold Rolling | Roll gap / Reduction ratio | ≤ 15% per pass |
| Coil Forming | Roller speed / Feed rate | 0.5 – 3.0 m/min |
| TIG Welding | Welding current / Shielding gas | 80–150 A / 99.999% Ar |
| Solution Annealing | Temperature / Dwell time | 1080 ± 15°C / 20 min |
| Electropolishing | Voltage / Temperature | 12–18 V / 45–55°C |
5. Applications
5.1 Primary Applications
- Commercial Building HVAC Systems: Fan Coil Units (FCUs) for office buildings, hotels, hospitals, and retail spaces. The coil tube functions as the core heat exchanger element, transferring thermal energy between chilled/heated water and the air stream generated by the FCU fan.
- Residential Air Conditioning: Concealed and ceiling-mounted FCU systems in high-end residential developments requiring quiet operation and compact heat exchange surfaces.
- Industrial Process Cooling: Precision temperature control for manufacturing equipment, electronics cooling, and laboratory climate control systems.
- Medical Facility HVAC: Operating theaters, clean rooms, and pharmacy environments where corrosion resistance and hygienic surface finish are critical.
5.2 Integration with Intelligent Control Systems
The JX-CT-373 coil tube is designed for compatibility with advanced building automation systems (BAS) that employ Deep Reinforcement Learning (DRL) for adaptive thermal management. Key design considerations include:
- Thermal Uniformity: Consistent wall thickness and pitch geometry ensure predictable and uniform heat transfer coefficients across the entire coil length, enabling accurate modeling in DRL-based control algorithms.
- Low Thermal Mass Variance: Tight dimensional tolerances minimize thermal inertia variations between individual coils, facilitating rapid system response to control signals.
- Flow Characterization: The helical geometry produces a well-defined pressure drop vs. flow rate relationship, which is essential for accurate CFD (Computational Fluid Dynamics) modeling in intelligent control system design.
- Scalability: Modular coil tube lengths and diameters allow system designers to configure FCU units across a wide range of cooling/heating capacities (2.0 – 25.0 kW), supporting the scalability required for multi-zone DRL control architectures.
6. Quality Certifications & Compliance
6.1 International Certifications
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- ISO 45001:2018 — Occupational Health and Safety Management System
- CE Marking — European Conformity for construction products (EN 14470)
- EN 10204 3.1 — Material Test Certificate (third-party verified)
6.2 Product-Specific Standards
- ASTM A270 / A270M — Standard Specification for Seamless and Welded Austenitic Stainless Steel Pipes and Tubes
- EN 10216-5 — Non-ferrous metallic products — Tubes and pipes for pressure purposes — Part 5: Technical delivery conditions for seamless austenitic stainless steel tubes
- JIS G3459 — Japanese Industrial Standard for seamless and welded austenitic stainless steel tubes
- GB/T 12771 — Chinese National Standard for seamless stainless steel tubes for general purposes
6.3 Testing & Verification Protocols
| Test Method | Standard | Frequency | Acceptance Criteria |
|---|---|---|---|
| Hydrostatic Pressure Test | ASTM D1599 | 100% of production | No leakage at 2.4× operating pressure for 30 s |
| Ultrasonic Weld Inspection | ASTM E747 | 100% of welded coils | Full penetration, no voids or cracks |
| Intergranular Corrosion Test | ASTM A262 Practice E | Batch sampling (1% min.) | No intergranular attack after 48 h in 65% HNO₃ at 65°C |
| Pitting Corrosion Resistance | ASTM G48 | Quarterly type test | PIT ≥ 1000 hours in 3.5% NaCl at 60°C |
| Dimensional Verification | ISO 4287 | 100% of production (online) | OD, WT, pitch within specified tolerances |
| Surface Roughness | ISO 4287 | Per batch | Ra ≤ 0.4 μm (mirror) / ≤ |