Stainless Steel Coil Tube for Fan Coil Unit Water Systems
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular component designed for integration into fan coil unit (FCU) water-based heating, ventilation, and air conditioning (HVAC) systems. This product serves as the core heat exchange medium within closed-loop hydronic circuits, facilitating efficient thermal energy transfer between the circulating water medium and the ambient air stream. The coil tube is specifically engineered to operate under dynamic operating conditions characterized by fluctuating pressure differentials, variable flow rates, and cyclic thermal loading — conditions commonly encountered in modern energy-efficient building HVAC infrastructure.
This product line is distinguished by its compatibility with advanced control architectures incorporating Proportional-Integral-Derivative (PID) pressure differential regulation and Variable Frequency Drive (VFD) modulation, enabling dynamic energy consumption optimization in real-time operational scenarios.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its superior corrosion resistance, mechanical integrity, and thermal conductivity characteristics essential for long-term service in hydronic environments.
- Base Material: Austenitic stainless steel (SS304 / SS316L conforming to ASTM A269 / ASME SA-269)
- Corrosion Resistance: Excellent resistance to pitting, crevice corrosion, and general aqueous corrosion; SS316L grade provides enhanced chloride resistance
- Thermal Conductivity: 16.3 W/(m·K) (SS304) / 14.6 W/(m·K) (SS316L) at 20°C
- Operating Temperature Range: −196°C to +400°C continuous service
- Mechanical Strength: Minimum yield strength of 205 MPa (SS304) / 170 MPa (SS316L); tensile strength ≥ 515 MPa
- Surface Finish: Mill finish (No. 1) or polished (2B/BA) depending on application requirements
- Sanitary Grade Compliance: Available in electropolished finish for pharmaceutical and food-grade HVAC applications
Specifications
| Parameter | Specification |
|---|---|
| Product Designation | Coil Tube — SS Coil Tube for FCU Hydronic Systems (Catalog No. 254) |
| Material Grade | ASTM A269 TP304 / TP316L |
| Outer Diameter (OD) | 6.35 mm (1/4") — 12.7 mm (1/2") standard; custom available |
| Wall Thickness | 0.5 mm — 1.5 mm (tolerance ±0.1 mm) |
| Coil Winding Diameter | 50 mm — 200 mm (customizable per OEM requirements) |
| Tube Length per Coil | 1.0 m — 15.0 m (continuous coil form) |
| Maximum Working Pressure | 1.6 MPa (standard) / 2.5 MPa (reinforced) |
| Hydrostatic Test Pressure | 3.2 MPa (2× working pressure) |
| Maximum Flow Velocity | 3.0 m/s (optimized for PID pressure differential control) |
| Heat Transfer Coefficient | ≥ 2,500 W/(m²·K) (internal convective) |
| Pressure Differential Range | 5 kPa — 50 kPa (compatible with VFD modulation) |
| Surface Roughness (Ra) | ≤ 0.8 μm (standard) / ≤ 0.2 μm (electropolished) |
| End Preparation | Deburred, chamfered, or formed to OEM specification |
| Packaging | Coiled on protective spools with moisture barrier wrapping |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorously controlled multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical homogeneity, and surface integrity:
- Raw Material Selection: Certified austenitic stainless steel seamless tube (ERW or cold-drawn) sourced from accredited mills with full mill test certificates (MTC) per EN 10204 Type 3.1.
- Cold Drawing & Sizing: Precision cold drawing through calibrated dies to achieve specified OD and wall thickness within ±0.1 mm tolerance, ensuring uniform cross-sectional geometry.
- Intermediate Annealing: Solution annealing at 1,050°C — 1,100°C in a controlled atmosphere (hydrogen or vacuum) to relieve cold-work stresses and restore full austenitic microstructure.
- Coil Winding: Continuous spiral coiling on CNC-controlled winding machines with precise diameter control (±1 mm), maintaining consistent pitch and avoiding kinking or flattening of the tube cross-section.
- Surface Treatment: Pickling and passivation (citric acid or nitric acid based) to remove mill scale and establish a protective chromium oxide passive film; optional electropolishing for ultra-low Ra finishes.
- Quality Inspection: 100% hydrostatic pressure testing, dimensional verification via ultrasonic thickness gauging, visual surface inspection, and spectral analysis (PMI — Positive Material Identification) for chemical composition confirmation.
- Final Assembly & Packaging: Coil tubes are spooled, labeled with traceability markings (heat number, batch code, specification), and packaged with desiccant protection for shipment.
Applications
The stainless steel coil tube is engineered for deployment in high-performance hydronic HVAC systems where dynamic energy optimization is critical:
- Fan Coil Units (FCU): Primary application — serves as the internal heat exchange coil within fan coil water systems, enabling precise thermal modulation through PID-controlled pressure differential regulation and variable frequency pump/fan coordination.
- Commercial HVAC Systems: Office buildings, hotels, hospitals, and retail facilities requiring zoned temperature control with energy efficiency optimization.
- Industrial Process Cooling: Precision temperature control in manufacturing environments where stainless steel corrosion resistance is mandated (chemical plants, semiconductor fabrication).
- Pharmaceutical & Cleanroom HVAC: Electropolished variants for GMP-compliant facilities requiring sanitary-grade heat exchange components.
- Data Center Cooling: High-density cooling loops where reliable thermal management under continuous variable load conditions is essential.
- Marine & Offshore HVAC: Saltwater-resistant SS316L variants for marine vessel climate control systems.
Unique Selling Points
- Dynamic Energy Optimization Compatibility: Specifically designed with hydraulic characteristics (pressure drop curves, flow-turbulence profiles) optimized for integration with PID pressure differential controllers and VFD-driven pumping systems, enabling up to 30–40% energy consumption reduction in dynamic operating scenarios.
- Precision Dimensional Control: Tight tolerances on coil winding diameter and tube geometry ensure consistent heat transfer performance across the entire product lifecycle, minimizing performance drift under cyclic thermal loading.
- Full Traceability: Each coil tube batch carries complete traceability documentation including mill certificates, heat treatment records, and inspection reports — supporting OEM qualification and regulatory compliance.
- Extended Service Life: Superior corrosion resistance and fatigue performance under dynamic pressure conditions ensure service life exceeding 20 years under normal hydronic operating conditions.
- Custom Engineering Capability: Flexible manufacturing parameters (OD, wall thickness, coil diameter, length, surface finish) enable tailored solutions for specific OEM system designs.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management and product certification systems:
- ISO 9001:2015 — Quality Management System certification
- ISO 14001:2015 — Environmental Management System certification
- ISO 45001:2018 — Occupational Health and Safety Management System certification
- CE Marking — Conformity with European directives for construction products (EN 10217, EN 10216)
- EN 10204 Type 3.1 — Full material certification documentation
- ASME BPV Code — Compliance for pressure-containing applications (where applicable)
- RoHS / REACH Compliance — Restriction of Hazardous Substances and chemical registration compliance
- Mill Test Certificate (MTC) — Provided with every batch shipment confirming chemical composition and mechanical properties
Technical Note: The hydraulic characteristics of this coil tube product have been specifically characterized for compatibility with dynamic energy optimization control strategies. The pressure drop versus flow rate relationship follows a predictable quadratic profile (ΔP ∝ Q²) within the design operating range, facilitating accurate PID controller tuning and enabling stable closed-loop pressure differential regulation across the full modulation range of VFD-driven system components. Field validation studies demonstrate that systems incorporating this coil tube geometry achieve measurable energy savings of 25–40% compared to conventional coil designs under variable-load operating conditions.