Stainless Steel Coil Tube — HVAC Fan Coil Unit Series
Product Overview
The Stainless Steel Coil Tube (盘管 / Coil Tube) is a precision-engineered tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd (Product Reference No. 1520). Designed primarily for integration into Fan Coil Units (FCU) and broader HVAC (Heating, Ventilation, and Air Conditioning) systems, this coil tube serves as the core heat exchange medium responsible for thermal energy transfer between the circulating refrigerant/water and the ambient air stream. The product is engineered to meet rigorous performance evaluation indicators including thermal efficiency (COP — Coefficient of Performance), pressure drop, flow uniformity, and long-term corrosion resistance under variable operating conditions.
As a critical component in modern air-handling systems, the coil tube must satisfy stringent criteria regarding heat transfer coefficient, frost resistance, and mechanical durability. Wenzhou Jixing Metal Materials delivers coil tubes that align with industry-standard performance benchmarks for fan coil unit operation, ensuring optimal seasonal energy efficiency ratios (SEER — Seasonal Energy Efficiency Ratio) and heating seasonal performance factors (HSPF — Heating Seasonal Performance Factor).
Material & Properties
Base Material
- Primary Alloy: Austenitic Stainless Steel (奥氏体不锈钢) — Grade 304 (UNS S30400) / Grade 316L (UNS S31603)
- Composition (304): Chromium (Cr) 18–20%, Nickel (Ni) 8–10.5%, Manganese (Mn) ≤2.0%, Carbon (C) ≤0.08%
- Composition (316L): Chromium (Cr) 16–18%, Nickel (Ni) 10–14%, Molybdenum (Mo) 2–3%, Carbon (C) ≤0.03%
Key Physical & Mechanical Properties
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (Grade 304); 14.6 W/(m·K) at 20°C (Grade 316L)
- Density: 8.00 g/cm³
- Tensile Strength: ≥515 MPa (Grade 304); ≥485 MPa (Grade 316L)
- Yield Strength: ≥205 MPa
- Elongation: ≥40% (minimum)
- Operating Temperature Range: −196°C to +870°C
- Corrosion Resistance: Superior resistance to atmospheric, aqueous, and chemical corrosion; 316L grade offers enhanced pitting and crevice corrosion resistance via molybdenum alloying
- Surface Finish: 2B (cold-rolled and annealed) or No. 4 brushed finish; available in electropolished condition for sanitary applications
Technical Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 25.4 mm (customizable) | ISO 3506 / ASTM A269 |
| Wall Thickness | 0.4 mm – 2.0 mm | ISO 3506 / ASTM A213 |
| Coil Pitch (Helical Spacing) | 3.0 mm – 15.0 mm (adjustable per thermal load) | Manufacturer Specification |
| Coil Diameter | 80 mm – 500 mm (spiral winding diameter) | Custom / Application-Specific |
| Number of Rows | 1 – 6 rows (multi-row configurations available) | ASHRAE 15 / ANSI/ASHRAE 36 |
| Fins per Inch (FPI) | 8 – 14 fins/inch (aluminum or stainless steel fins) | Industry Standard |
| Tube Material Grade | 304 / 316L / 321 (per application requirements) | AISI / ASTM / EN 10216 |
| End Connection Type | Flared, brazed, threaded, or welded | ISO 228 / ASME B1.20.1 |
| Maximum Operating Pressure | 1.6 MPa – 4.0 MPa (depending on wall thickness) | ASME BPVC Section VIII |
| Pressure Drop (ΔP) | ≤ 15 kPa (at nominal flow rate) | Manufacturer Test Data |
| Heat Transfer Efficiency | ≥ 92% (based on NTU — Number of Transfer Units) | ASHRAE Handbook — HVAC Systems |
| Surface Treatment | PASSIVATE (acid pickling) / Anti-scalant coating available | ASTM A380 |
| Length per Coil | 5 m – 50 m (continuous coil supply) | Manufacturer Specification |
| Tolerance (OD) | ±0.05 mm | ISO 3506 |
| Tolerance (Wall Thickness) | ±10% of nominal | ASTM A269 |
Manufacturing Process
Step-by-Step Production Workflow
- Raw Material Procurement & Inspection: Cold-rolled stainless steel strip or seamless pipe stock is sourced from certified mills. Incoming material undergoes spectroscopic analysis (OES — Optical Emission Spectroscopy) and mechanical property verification per ASTM E1246.
- Forming & Cold Drawing: The stainless steel strip is precision-formed into tubular cross-sections via rotary draw bending or seamless cold-drawing processes. This ensures uniform wall thickness and dimensional accuracy critical for consistent heat transfer performance.
- Heli-coiling / Spiral Winding: The formed tube is wound into a helical coil configuration using CNC-controlled coiling machines. Coil pitch, diameter, and row arrangement are programmed according to the thermal load requirements of the target fan coil unit application.
- Fin Attachment (if finned): Aluminum or stainless steel fins are mechanically or hydro-drawn onto the coil tube surface to maximize the effective heat transfer area. Fin-to-tube bonding integrity is verified through pull-off testing.
- End Connection Fabrication: Tube ends are formed into flare, thread, or weld-prep configurations. Brazing joints (if applicable) use phosphorus-copper filler alloys (BCuP-2 per AWS A5.8) for high-temperature integrity.
- PASSIVATE Treatment: The coil tube undergoes acid pickling and passivation (ASTM A380) to remove surface contaminants and establish a protective chromium oxide layer, enhancing long-term corrosion resistance.
- Hydrostatic Pressure Testing: Each coil assembly is subjected to hydrostatic pressure testing at 1.5× the maximum operating pressure to verify structural integrity and absence of leaks.
- Performance Verification: Selected samples undergo thermal performance testing in accordance with ASHRAE Standard 15 and ISO 13373, measuring heat transfer rate, air-side and water-side pressure drops, and frost formation characteristics.
- Final Inspection & Packaging: Coils pass through a comprehensive quality assurance inspection including dimensional verification, visual surface inspection, and material traceability documentation before packaging for shipment.
Applications
Primary Application: Fan Coil Units (FCU)
The stainless steel coil tube is the central heat exchange element in Fan Coil Units — self-contained air-handling devices used in commercial and residential HVAC systems. The coil tube facilitates convective and conductive heat transfer between the chilled/hot water circuit and the air stream generated by the integrated fan motor. Performance evaluation indicators for FCUs — including cooling capacity, heating capacity, sensible heat ratio (SHR), airflow rate, and static pressure — are directly influenced by the coil tube's geometry, material properties, and manufacturing precision.
Expanded Application Domains
- Commercial HVAC Systems: Office buildings, hotels, hospitals, and retail facilities requiring zone-by-zone temperature control
- Residential Air Conditioning: Concealed and cassette-type indoor units for premium residential installations
- Industrial Process Cooling: Precision temperature control in manufacturing environments, data centers, and laboratory facilities
- Marine & Offshore HVAC: 316L-grade coil tubes for saltwater-exposed environments requiring superior pitting corrosion resistance
- Food & Pharmaceutical Processing: Hygienic-grade (electropolished) coil tubes for cold storage chambers and cleanroom air handling
- Refrigeration Systems: Evaporator and condenser coil assemblies in walk-in coolers and freezers
Quality Certifications & Compliance
| Certification / Standard | Description | Scope |
|---|---|---|
| ISO 9001:2015 | Quality Management System Certification | Manufacturing & Quality Assurance |
| ISO 14001:2015 | Environmental Management System Certification | Sustainable Manufacturing Practices |
| CE Marking (EU) | Conformity with European Machinery & Pressure Equipment Directives | European Market Compliance |
| EN 10216-5 | Welded Stainless Steel Tubes for Heat Exchangers | Product Material & Performance |
| ASTM A269 / A213 | Austenitic Stainless Steel Tubing Standards | Material Specification Compliance |
| ASME BPVC Section VIII | Pressure Vessel Code — Division 1 | Pressure Containment Verification |
| RoHS 2011/65/EU | Restriction of Hazardous Substances | Environmental Compliance |
| REACH (EC) 1907/2006 | Registration, Evaluation, Authorisation & Restriction of Chemicals | Chemical Safety Compliance |
Unique Selling Points
- Superior Corrosion Longevity: Austenitic stainless steel construction provides 2–3× the service life of conventional carbon steel coil tubes, significantly reducing maintenance frequency and total cost of ownership (TCO) in demanding HVAC environments.
- Optimized Thermal Performance: Precision helical coil geometry, engineered per ASHRAE performance evaluation methodologies, ensures maximum heat transfer efficiency with minimal pressure drop — directly contributing to improved COP and SEER ratings of the integrated fan coil unit.
- Customizable Configuration: Flexible manufacturing capabilities allow coil pitch, row count, fin density, and dimensional parameters to be tailored to specific thermal load requirements, enabling optimal performance matching for diverse installation scenarios.
- Hygienic & Food-Grade Option: Electropolished 316L coil tubes meet FDA and 3-A sanitary standards, making them suitable for food processing, pharmaceutical, and laboratory air-handling applications.
- Environmental Sustainability: Stainless steel is 100% recyclable with no loss of material properties, aligning with global sustainability mandates and reducing lifecycle carbon footprint compared to disposable coil alternatives.
Performance Evaluation Alignment
In accordance with the performance evaluation framework for Fan Coil Units (as referenced in industry literature — 《风机盘管空调器的现状及性能评价指标》), the coil tube parameters directly influence the following key performance indicators:
- Cooling/Heating Capacity (kW): Determined by coil surface area, fin density, and fluid-side heat transfer coefficient
- Sensible Heat Ratio (SHR): Governed by coil surface temperature and air-side heat transfer characteristics
- Air-Side Pressure Drop (Pa): Minimized through optimized coil pitch and fin geometry
- Water-Side Pressure Drop (kPa): Controlled by tube inner diameter and flow path length
- Frost Resistance: Enhanced by stainless steel's thermal conductivity uniformity and coil geometry optimization
- Acoustic Performance: Influenced by flow turbulence characteristics within the coil assembly
Note: All specifications are subject to engineering verification based on specific application requirements. Wenzhou Jixing Metal Materials Co., Ltd offers custom engineering support and performance simulation services to ensure optimal coil tube selection for each fan coil unit installation.