Stainless Steel Coil Tube — Energy-Saving Fan Coil Unit Series
1. Product Overview
The Stainless Steel Coil Tube (catalog No. 344) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product specifically designed for integration into energy-saving fan coil units (FCUs) within commercial and industrial HVAC (Heating, Ventilation, and Air Conditioning) systems. This coil tube serves as the primary heat exchange element, facilitating efficient thermal transfer between the circulating refrigerant or heating medium and the airstream passing over the coil assembly.
As a core component of the energy-efficient fan coil unit architecture, this coil tube is engineered to minimize thermal resistance, maximize surface contact area, and withstand prolonged exposure to aggressive working fluids including water-glycol mixtures, brine solutions, and low-temperature refrigerants. The product represents a convergence of metallurgical science, thermal-fluid engineering, and precision manufacturing to deliver superior energy performance, extended service life, and reliable operational integrity under demanding environmental conditions.
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from high-grade austenitic stainless steel conforming to international standards. The following material grades are available depending on application requirements:
- ASTM A213 TP304 / TP316 — Seamless stainless steel tubing for general and corrosion-resistant applications
- SUS304 / SUS316L — Japanese Industrial Standard (JIS) equivalent grades with low carbon content for enhanced weldability
- EN 10216-5 / 10217-7 — European Standard seamless stainless steel tubes for heat exchanger service
2.2 Mechanical Properties
| Property | Typical Value (304 Grade) | Typical Value (316L Grade) | Test Standard |
|---|---|---|---|
| Tensile Strength (Ultimate) | ≥ 515 MPa | ≥ 485 MPa | ASTM A370 |
| Yield Strength (0.2% Offset) | ≥ 205 MPa | ≥ 170 MPa | ASTM A370 |
| Elongation (at Rupture) | ≥ 40% | ≥ 40% | ASTM A370 |
| Hardness (HB) | ≤ 201 | ≤ 217 | ASTM E10 |
| Thermal Conductivity (at 20°C) | 16.3 W/(m·K) | 14.6 W/(m·K) | ASTM E153 |
| Thermal Expansion Coefficient (20–100°C) | 17.3 × 10⁻⁶ /°C | 17.1 × 10⁻⁶ /°C | ASTM E228 |
2.3 Chemical Composition (Typical)
| Element | 304 Grade (wt%) | 316L Grade (wt%) |
|---|---|---|
| Carbon (C) | ≤ 0.08 | ≤ 0.03 |
| Chromium (Cr) | 18.0 – 20.0 | 16.0 – 18.0 |
| Nickel (Ni) | 8.0 – 10.5 | 10.0 – 14.0 |
| Molybdenum (Mo) | — | 2.0 – 3.0 |
| Manganese (Mn) | ≤ 2.0 | ≤ 2.0 |
| Sulfur (S) | ≤ 0.03 | ≤ 0.03 |
| Phosphorus (P) | ≤ 0.045 | ≤ 0.045 |
2.4 Surface Finish
The internal and external surfaces of the coil tube are finished to a precision grade suitable for heat exchanger applications:
- Internal Surface Roughness (Ra): ≤ 0.8 μm (electropolished option available at ≤ 0.4 μm)
- External Surface Roughness (Ra): ≤ 1.6 μm (BA — Bright Annealed finish)
- Optional Passivation Treatment: Per ASTM A967 to enhance passive film integrity and corrosion resistance
3. Specifications
| Parameter | Specification |
|---|---|
| Product Designation | Stainless Steel Coil Tube — Catalog No. 344 |
| Outer Diameter (OD) | 6.35 mm (¼"), 9.52 mm (⅜"), 12.7 mm (½"), 15.88 mm (⅝"), 19.05 mm (¾") |
| Wall Thickness | 0.5 mm – 2.0 mm (selectable per application) |
| Coil Length | Up to 120 m per continuous coil (custom lengths available) |
| Coil Inner Diameter (Coil ID) | 300 mm – 800 mm (configurable) |
| Operating Temperature Range | −196°C to +870°C (continuous); cryogenic service capable |
| Maximum Operating Pressure | ≤ 2.5 MPa (design-dependent; verify per ASME BPVC Section VIII) |
| Refrigerant Compatibility | R-22, R-410A, R-407C, R-134a, R-32, R-1234yf, Ammonia (NH₃), CO₂ (R-744) |
| Working Fluid Compatibility | Water, Ethylene Glycol (EG), Propylene Glycol (PG), Brine Solutions, Distilled Water |
| Tolerance — OD | ±0.05 mm (per ASTM A213 / EN 10217-7) |
| Tolerance — Wall Thickness | ±10% of nominal |
| Helical Pitch (if finned) | 3.0 mm – 6.0 mm (customizable) |
| Material Certificate | EN 10204 Type 3.1 (Mill Test Certificate) |
| Compliance Standards | ASTM A213, EN 10216-5, EN 10217-7, JIS G3459, GB/T 12771 |
4. Manufacturing Process
The production of the stainless steel coil tube follows a rigorous, multi-stage manufacturing workflow to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection & Incoming Inspection — Stainless steel strip or seamless tube blanks are procured from certified mills. Incoming material undergoes chemical composition verification via Optical Emission Spectroscopy (OES) and mechanical property testing per ASTM A370.
- Coil Winding / Tube Forming — The tube is wound into a helical coil geometry using precision CNC-controlled winding equipment. The winding process maintains constant tension and controlled curvature radius to prevent microstructural deformation, work hardening, or surface damage. The coil geometry is optimized to maximize heat transfer surface area per unit volume within the fan coil unit housing.
- Heat Treatment & Stress Relief — Following coil forming, the product undergoes solution annealing at 1050°C – 1150°C with rapid water quenching to restore full austenitic microstructure, relieve residual stresses introduced during forming, and ensure maximum corrosion resistance and ductility.
- Surface Finishing — The tube surface is subjected to Bright Annealing (BA) in a controlled atmosphere furnace (H₂ or vacuum) to achieve a clean, smooth, oxide-free surface. Electropolishing may be applied to the internal bore to reduce surface roughness below 0.4 μm Ra, minimizing flow resistance and fouling potential.
- Passivation Treatment — A chemical passivation process per ASTM A967 is applied to establish a stable chromium oxide passive film, enhancing resistance to pitting and crevice corrosion in aggressive environments.
- Dimensional Inspection & Quality Control — Each coil is inspected using laser micrometers, ultrasonic thickness gauges, and visual examination systems. Internal bore inspection may include borescope examination to verify surface integrity and absence of defects.
- Pressure Testing / Leak Testing — The assembled coil tube undergoes hydrostatic pressure testing at 1.5× the maximum design pressure (per ASME BPVC Section VIII Div. 1) or pneumatic leak testing using nitrogen at the specified test pressure.
- Packaging & Shipping — The finished coil tube is wrapped in protective film, placed in moisture-absorbent packaging, and secured on wooden pallets for transport. Each shipment is accompanied by a Mill Test Certificate (MTC) per EN 10204 Type 3.1.
5. Applications
The stainless steel coil tube is designed for integration into energy-saving fan coil units and heat exchanger assemblies across a broad spectrum of HVAC and industrial applications:
- Commercial HVAC Systems — Energy-efficient fan coil units installed in office buildings, shopping centers, hotels, hospitals, and educational facilities. The coil tube enables efficient sensible and latent heat exchange, contributing to overall system COP (Coefficient of Performance) improvement.
- Industrial Process Cooling & Heating — Heat exchanger coils in pharmaceutical, food processing, semiconductor manufacturing, and chemical production facilities where sanitary-grade stainless steel and corrosion resistance are mandatory.
- Cleanroom Air Handling — Low-particulate coil tubes for controlled-environment systems in biotechnology, electronics fabrication, and medical device manufacturing. The electropolished internal surface minimizes particle generation and bacterial adhesion.
- Cold Storage & Refrigeration — Cryogenic-grade coil tubes for low-temperature air-cooled evaporators in cold storage warehouses, frozen food distribution centers, and industrial refrigeration plants.
- Marine & Offshore HVAC — Corrosion-resistant coil tubes (316L grade) for HVAC systems on naval vessels, offshore platforms, and coastal facilities exposed to saltwater environments.
- Data Center Cooling — High-efficiency coil tubes for precision air conditioning units in server rooms and data centers, where thermal management efficiency directly impacts energy consumption and operational cost.
6. Quality Certifications & Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent product quality and process control |
| ISO 14001:2015 | Environmental Management System certification for sustainable manufacturing practices |
| EN 10204 Type 3.1 | Mill Test Certificate providing full traceability of material composition, heat numbers, and test results |
| ASME BPVC Section VIII | Pressure Vessel Code compliance for pressure-containing applications |
| CE Marking (EU) | Conformity with European Machinery Directive and Pressure Equipment Directive (PED 2014/68/EU) |
| GB/T 12771 (China) | Chinese National Standard for stainless steel seamless tubes for heat exchangers |
| ASTM A213 | American standard specification for seamless austenitic stainless steel tubes for heat exchangers |
| EN 10217-7 | European standard for austenitic stainless steel tubes for heat exchangers |
7. Unique Selling Points
- Energy Efficiency Optimization — The coil geometry is engineered to maximize the heat transfer coefficient while minimizing pressure drop, directly contributing to reduced fan power consumption and improved overall system energy performance. This aligns with global energy efficiency regulations including EU Ecodesign Directive and ASHRAE 90.1.
- Exceptional Corrosion Resistance