Stainless Steel Coil Tube for Fan Coil Unit Heat Exchange Systems
Product Overview
The Stainless Steel Coil Tube (产品编号: 1106) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered heat exchange component specifically designed for Fan Coil Unit (FCU) applications in commercial and residential HVAC (Heating, Ventilation, and Air Conditioning) systems. This coiled tube configuration maximizes the surface-area-to-volume ratio, enabling superior thermal transfer efficiency in both heating and cooling cycles. The product represents a critical component in the thermal management architecture of modern building climate control systems, where consistent performance, corrosion resistance, and long service life are paramount.
Unlike conventional straight-tube heat exchangers, the coil tube geometry allows for compact installation within fan coil units while maintaining high heat exchange capacity. The stainless steel construction provides inherent resistance to chemical attack from refrigerants, condensate, and ambient moisture, making it suitable for aggressive operating environments including coastal installations, industrial facilities, and food processing plants.
Material Composition and Properties
The coil tube is fabricated from austenitic stainless steel grades that meet or exceed international standards for mechanical strength, corrosion resistance, and thermal conductivity. The primary alloying elements and their functional contributions are detailed below:
- Chromium (Cr): 18–20% — Provides the passive oxide layer essential for corrosion resistance and chemical stability across a wide pH range.
- Nickel (Ni): 8–10% — Stabilizes the austenitic crystal structure, enhancing ductility and resistance to intergranular corrosion.
- Carbon (C): ≤ 0.03% — Minimally controlled to prevent chromium carbide precipitation during welding and heat treatment.
- Molybdenum (Mo): 2–3% (in 316-grade variants) — Confers superior resistance to pitting and crevice corrosion in chloride-containing environments.
- Iron (Fe): Balance — Structural base element providing bulk mechanical integrity.
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 520 MPa | ASTM A270 / EN 10216-5 |
| Yield Strength (屈服强度) | ≥ 205 MPa | ASTM A270 / EN 10216-5 |
| Thermal Conductivity (导热系数) | 14–16 W/(m·K) at 20°C | ASTM E153 |
| Corrosion Resistance (耐蚀性) | Equivalent to Grade 304/316 | ASTM G48 / ISO 3659 |
| Operating Temperature Range (工作温度范围) | −196°C to +870°C | ASTM A270 |
| Surface Roughness (表面粗糙度) | ≤ Ra 0.8 μm (inner surface) | ISO 4287 |
| Density (密度) | 7.90–8.00 g/cm³ | ASTM A967 |
Technical Specifications
The following dimensional and performance parameters define the standard product configuration. Custom specifications are available upon request through the manufacturer's engineering team:
| Parameter | Standard Value | Tolerance |
|---|---|---|
| Outer Diameter (OD, 外径) | Φ9.52 mm / Φ12.7 mm / Φ15.88 mm | ±0.10 mm |
| Wall Thickness (壁厚) | 0.50 mm / 0.80 mm / 1.00 mm | ±0.05 mm |
| Coil Diameter (盘管直径) | Φ100 mm – Φ500 mm | ±1.0 mm |
| Coil Height (盘管高度) | 50 mm – 300 mm | ±1.5 mm |
| Tube Length per Coil (每圈管长) | Custom, typically 2.0 – 15.0 m | ±0.1 m |
| Number of Turns (圈数) | 6 – 48 turns | ±1 turn |
| Turn Spacing (圈间距) | 1.5 – 5.0 mm | ±0.2 mm |
| End Connection Type (端部连接方式) | Flared / Threaded / Brazed / Welded | Per ASME B31.9 |
| Maximum Working Pressure (最大工作压力) | 1.6 MPa (standard) / 2.5 MPa (reinforced) | Per ASME B31.9 |
| Hydrostatic Test Pressure (水压试验压力) | 3.0 MPa (standard) / 4.0 MPa (reinforced) | ASME B31.9 |
| Fin Configuration (翅片配置) | Aluminum fins, 0.15 mm thick, 2.0 mm pitch | Per manufacturer spec |
| Weight (重量) | 0.8 – 12.0 kg (depending on configuration) | — |
Manufacturing Process
The production of stainless steel coil tubes for fan coil unit applications follows a rigorous multi-stage manufacturing sequence designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection and Inspection: Stainless steel strip (typically Grade 304 or 316L) is sourced from certified mills. Incoming material undergoes spectroscopic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition and visual inspection for surface defects.
- Slitting and Leveling: The coil strip is slit to precise width dimensions using high-speed slitting lines. The slit strip is then passed through a leveling machine to eliminate coil set and ensure flatness within ±0.05 mm/m.
- Tubular Forming (Roll Forming): Multi-stand roll forming machines progressively shape the flat strip into a seamless tube. The forming stations are precision-ground to maintain consistent wall thickness and roundness throughout the tube length.
- Welding (if applicable): For welded tube configurations, a high-frequency induction welding (HF-W) process is employed. The weld seam is subsequently ground flush and inspected via eddy current testing (ECT) to detect subsurface discontinuities.
- Coiling and Spooling: The formed tube is coiled onto a mandrel using a computer-controlled coiling head that ensures uniform turn spacing and concentricity. The coiling process is monitored via laser displacement sensors to maintain dimensional tolerances.
- Fin Attachment: Aluminum fins are mechanically attached to the coil tube using a hydraulic fin-rolling process that creates a tight mechanical bond without damaging the tube surface. Fin density and pitch are controlled to optimize the heat transfer coefficient while minimizing airflow resistance.
- Surface Treatment: The finished coil tube undergoes electropolishing or mechanical polishing to achieve the specified surface roughness (Ra ≤ 0.8 μm). This treatment enhances corrosion resistance, reduces fouling potential, and improves aesthetic appearance.
- Quality Inspection and Testing: Each unit undergoes hydrostatic pressure testing, dimensional verification using coordinate measuring machines (CMM), visual inspection, and (where applicable) radiographic testing (RT) or ultrasonic testing (UT) of critical joints.
- Packaging and Dispatch: Approved units are wrapped in protective film, secured on wooden pallets, and packed in export-grade cartons with desiccant packs to prevent moisture ingress during transit.
Applications
The stainless steel coil tube is a versatile component with applications spanning multiple sectors. Its primary deployment is within fan coil units, but its performance characteristics extend its utility to adjacent thermal management systems:
- Commercial HVAC Systems: Fan coil units installed in office buildings, hotels, hospitals, and shopping centers for individual zone temperature control. The stainless steel coil tube serves as the primary heat exchange element, transferring thermal energy between the refrigerant/water circuit and the circulated air stream.
- Residential Climate Control: Concealed and exposed fan coil units in high-end residential applications where noise performance, corrosion resistance, and long service life are critical selection criteria.
- Industrial Process Cooling: Heat recovery and process cooling applications in manufacturing facilities, including chemical processing, pharmaceutical production, and food and beverage processing where sanitary-grade materials are mandated.
- Marine and Coastal Installations: HVAC systems in maritime vessels, offshore platforms, and coastal buildings where elevated chloride exposure demands superior corrosion resistance inherent to 316-grade stainless steel.
- Food Processing and Dairy Industry: Refrigeration and pasteurization systems requiring compliance with FDA, 3-A Sanitary Standards, and EHEDG (European Hygienic Engineering Design Group) guidelines.
- Pharmaceutical Clean Rooms: Temperature and humidity control systems in GMP (Good Manufacturing Practice) environments where particulate generation must be minimized and surface contamination is strictly controlled.
- Data Center Cooling: Precision cooling units for server rooms and telecommunications facilities requiring reliable, low-maintenance thermal management solutions.
Quality Certifications and Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring that every coil tube product meets international standards for safety, performance, and reliability:
| Certification / Standard | Scope of Compliance |
|---|---|
| ISO 9001:2015 | Quality Management System — Covers all manufacturing processes from raw material intake to final dispatch. |
| ISO 14001:2015 | Environmental Management System — Ensures environmentally responsible manufacturing practices. |
| ASME B31.9 | Pressure Piping — Refrigeration and Air-Conditioning — Governs design, fabrication, and testing of pressure-containing components. |
| EN 10216-5 | European Standard for Heat Exchanger Tubes — Specifies requirements for seamless and welded tubes used in heat exchangers. |
| ASTM A270 | Standard Specification for Stainless Steel Tubular Products (Seamless, Welded, and Heavy-Welded) for Boilers, Heat Exchangers, and Similar Applications. |
| CE Marking | Conformity with European Machinery Directive (2006/42/EC) and Pressure Equipment Directive (PED 2014/68/EU) where applicable. |
| RoHS Compliance | Restriction of Hazardous Substances Directive (2011/65/EU) — Ensures absence of lead, mercury, cadmium, and other restricted materials. |
| REACH Compliance | Registration, Evaluation, Authorisation and Restriction of Chemicals — Confirms material safety for end-user exposure. |
Unique Selling Points
- Superior Corrosion Resistance: The austenitic stainless steel construction provides exceptional resistance to corrosion from condensate, refrigerants, and atmospheric contaminants. This translates to a significantly extended service life compared to carbon steel or copper alternatives, reducing total cost of ownership (TCO) over the system's operational lifetime.
- Precision Coiling Geometry: Computer-controlled coiling ensures uniform turn spacing and concentricity, which optimizes airflow distribution across the coil face and prevents localized hot spots or bypassing — common failure modes in poorly manufactured coil assemblies.
- Sanitary-Grade Surface Finish: The electropolished inner surface (Ra ≤ 0.8 μm) minimizes biofilm formation and fouling accumulation, maintaining heat transfer efficiency over extended operating periods without requiring chemical cleaning interventions.
- Modular and Configurable Design: Available in multiple OD, wall thickness, and coil diameter configurations, the product can be tailored to specific fan coil unit capacities ranging from 0.5 kW to 25 kW cooling/heating loads.
- Environmental Sustainability: Stainless steel is 100% recyclable with no loss of material properties, aligning with circular economy principles and green building certification requirements (LEED, BREEAM, WELL).
- Manufacturing Heritage: Leveraging the metallurgical expertise and manufacturing infrastructure of Wenzhou Jixing Metal Materials Co., Ltd., the product benefits from vertically integrated production, reducing supply chain risk and ensuring consistent quality across production batches.
Technical Note: The thermal performance of the coil tube assembly is governed by the