Stainless Steel Coil Tube for Fan Coil Unit Systems
Product Overview
The Stainless Steel Coil Tube (Product No. 314) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered coiled tubular component designed specifically for integration into fan coil unit (FCU) systems. This product represents a critical heat exchange element within modern HVAC (Heating, Ventilation, and Air Conditioning) infrastructure, leveraging advanced metallurgical processing to deliver superior thermal conductivity, mechanical integrity, and long-term corrosion resistance in demanding indoor climate control environments.
Based on structural design and optimization principles derived from cross-flow fan (贯流风机) integration studies, this coil tube is engineered to maximize surface-area-to-volume ratios while maintaining hydraulic efficiency within compact FCU enclosures. The coiled geometry enables efficient heat transfer between circulating refrigerant or heating medium and ambient air drawn through the unit by centrifugal or cross-flow fan assemblies.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its exceptional combination of thermal performance, chemical stability, and mechanical durability.
- Base Material: AISI 304 / AISI 316L Stainless Steel (UNS S30408 / UNS S31603)
- Grade Classification: Austenitic (奥氏体), non-magnetic, solution-annealed
- Chromium Content: 18–20% (minimum 18% Cr for 304; 16–18% Cr for 316L)
- Nickel Content: 8–10.5% Ni (304); 10–14% Ni (316L)
- Molybdenum Content: 2–3% Mo (316L variant only)
- Carbon Content: ≤ 0.08% (304); ≤ 0.03% (316L low-carbon grade)
- Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C
- Maximum Operating Temperature: 870°C (continuous); 1150°C (intermittent)
- Corrosion Resistance: Excellent resistance to atmospheric, aqueous, and food-grade environments; 316L grade provides enhanced resistance to chlorides and pitting
- Mechanical Strength: Yield Strength ≥ 205 MPa; Tensile Strength ≥ 515 MPa (annealed condition)
Specifications
| Parameter | Specification | Unit |
|---|---|---|
| Product Number | 314 | — |
| Outer Diameter (OD) | 6.35 / 8.0 / 9.52 / 12.7 | mm |
| Wall Thickness | 0.5 – 1.0 | mm |
| Coil Diameter (Mean) | 25 – 100 | mm |
| Coil Length (Standard) | 1,500 – 6,000 | mm |
| Number of Passes | 2 / 4 / 6 / 8 | — |
| Fin Pitch (if finned) | 1.5 – 2.5 | mm |
| Operating Pressure (Design) | ≤ 1.6 (standard); ≤ 2.5 (reinforced) | MPa |
| Operating Temperature Range | −40 to +150 | °C |
| Surface Finish | 2B / BA (Bright Annealed) / Electropolished | — |
| Tolerance on OD | ±0.1 | mm |
| Tolerance on Wall Thickness | ±0.05 | mm |
| Coil Pitch Tolerance | ±0.5 | mm |
| End Connection Type | Flared / Soldered / Brazed / Flanged | — |
| Available Grades | SUS304 / SUS316L / SUS321 / SUS310S | — |
Manufacturing Process
The production of this coil tube follows a rigorous multi-stage manufacturing protocol to ensure dimensional accuracy, material homogeneity, and structural integrity:
- Raw Material Selection & Inspection: Stainless steel strip or seamless tube stock is procured from certified mill sources. Incoming material undergoes spectroscopic analysis (OES), chemical composition verification, and mechanical property testing to confirm compliance with ASTM A213 / ASTM A269 or equivalent standards.
- Cold Drawing / Cold Rolling: The base tube is cold-drawn through precision dies to achieve exact outer diameter and wall thickness specifications. This process enhances grain structure alignment, improving both mechanical strength and surface finish quality.
- Intermediate Annealing: Periodic solution annealing at 1050–1100°C followed by rapid air cooling or controlled water quenching relieves cold-work hardening, restores ductility, and prevents sensitization (chromium carbide precipitation at grain boundaries).
- Precision Coiling: The formed tube is wound onto CNC-controlled coiling mandrels to produce the specified coil diameter and pitch. Computerized winding systems ensure uniform coil geometry with minimal residual stress. The coiling process is calibrated to match cross-flow fan (贯流风机) housing dimensions for optimal aerodynamic integration.
- Fin Application (if applicable): Aluminum or stainless steel fins are mechanically or diffusion-bonded to the tube surface to increase effective heat transfer area by 5–8×. Fin bonding is verified through pull-off testing.
- Surface Treatment: Final surface conditioning includes pickling (removal of oxide scale), passivation (formation of protective chromium oxide layer), and optional electropolishing to achieve Ra ≤ 0.4 μm surface roughness for hygienic and high-efficiency thermal applications.
- End Forming & Connection Preparation: Tube ends are flared, crimped, or machined to accept the designated connection method (solder, brazing, flange, or compression fitting).
- Quality Assurance & Testing: Each coil assembly undergoes hydrostatic pressure testing (1.5× design pressure for 30 minutes), dimensional verification via laser scanning or coordinate measuring machine (CMM), and visual inspection for surface defects.
Applications
This stainless steel coil tube is engineered for a broad spectrum of thermal management applications, with particular emphasis on fan coil unit systems:
- Fan Coil Units (FCU): Primary heat exchanger component in commercial and residential HVAC systems, integrated with cross-flow or centrifugal fan assemblies for precise temperature regulation.
- Air Handling Units (AHU): Heating and cooling coils in large-capacity ventilation systems for office buildings, hospitals, and industrial facilities.
- Chilled Water Systems: Secondary loop heat exchangers distributing chilled water to terminal units in district cooling networks.
- Refrigeration & Heat Pump Systems: Evaporator and condenser coils in split-system air conditioners and heat pump units.
- Food Processing & Pharmaceutical Equipment: Sanitary-grade heat exchangers requiring high corrosion resistance and cleanability (316L grade).
- Marine & Offshore HVAC: Corrosion-resistant coil assemblies for shipboard climate control systems exposed to high-humidity, salt-laden environments.
- Industrial Process Cooling: Precision temperature control in manufacturing processes requiring inert material compatibility.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains comprehensive quality management and product certification frameworks:
- ISO 9001:2015 — Quality Management System certification ensuring consistent production quality and process control
- ISO 14001:2015 — Environmental Management System certification for sustainable manufacturing practices
- ASME BPV Code — Compliance with American Society of Mechanical Engineers Boiler and Pressure Vessel Code Section VIII (where applicable for pressure-containing applications)
- ASTM A213 / A269 — Conformance to American Society for Testing and Materials standards for stainless steel welded and seamless tubing
- EN 10217-7 — European standard compliance for austenitic stainless steel tubing and pipes
- GB/T 12771 — Chinese National Standard for welded austenitic stainless steel tubing
- NSF/ANSI 61 — Drinking water system component certification (for potable water applications)
- Mill Test Reports (MTR): Full chemical composition and mechanical property documentation provided with each production batch
- NDT Inspection: Radiographic testing (RT) or ultrasonic testing (UT) available upon request for weld integrity verification
Unique Selling Points
Structural Optimization for Cross-Flow Fan Integration: The coil geometry has been specifically optimized based on aerodynamic studies of cross-flow fan (贯流风机) airflow patterns, ensuring uniform air distribution across the coil face and minimizing pressure drop while maximizing heat transfer efficiency.
- Superior Corrosion Resistance: The 316L stainless steel option provides exceptional resistance to chlorides, making it ideal for coastal installations and high-humidity environments where carbon steel or copper alternatives would degrade prematurely.
- Precision Dimensional Control: CNC coiling technology ensures coil pitch accuracy of ±0.5 mm, enabling seamless integration into pre-designed FCU housings without modification.
- Full Material Traceability: Every coil tube is traceable to its mill heat number, with complete chemical and mechanical test documentation available for lifecycle quality assurance.
- Customizable Configurations: Flexible design options including variable OD, wall thickness, coil diameter, pass count, and connection types allow tailored solutions for specific system requirements.
- Extended Service Life: With proper installation and maintenance, these coil tubes deliver a service life exceeding 20 years, significantly reducing total cost of ownership (TCO) compared to conventional materials.
- Hygienic Surface Finish: Electropolished surfaces (Ra ≤ 0.4 μm) prevent bacterial adhesion and facilitate easy cleaning, meeting pharmaceutical and food-grade standards.
Technical Notes
Design Consideration: When integrating this coil tube into fan coil unit assemblies, engineers should account for the differential thermal expansion between the stainless steel coil and aluminum fins (if finned). A thermal expansion coefficient mismatch of approximately 10 × 10⁻⁶ /°C between stainless steel and aluminum may require flexible connection joints or expansion loops in high-temperature differential applications.
Flow Velocity Recommendation: Optimal internal flow velocity for water-based heat transfer media should be maintained between 1.0–2.5 m/s to balance heat transfer efficiency against erosion-corrosion risk and pressure drop constraints.
Installation Orientation: The coil tube should be installed with inlet and outlet connections positioned to minimize dead zones and ensure complete fluid circulation through all passes, preventing localized overheating or freezing in cold-weather applications.