Stainless Steel Coil Tube (FCU-Grade) — Wenzhou Jixing Metal Materials Co., Ltd. (Product No. 855)
1. Product Overview
The Stainless Steel Coil Tube (Product No. 855) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered continuous coil tube designed primarily for integration into Fan Coil Units (FCU) and broader HVAC (Heating, Ventilation, and Air Conditioning) systems. This product is supplied in coiled configuration, enabling seamless downstream forming, bending, and welding operations without requiring seam-welded joints at intermediate stages. The coil tube is specifically optimized for thermal exchange efficiency, corrosion resistance, and long-cycle operational reliability within fan coil unit applications, where it functions as the core heat-transfer element between refrigerant/water circuits and ambient air.
As a metallurgical component, this coil tube bridges the gap between bulk stainless steel wire-rod production and finished HVAC heat exchanger assemblies. Its coiled geometry facilitates automated coil-feeding in manufacturing lines, reducing material waste and improving production throughput compared to straight-length tubing.
2. Material Composition & Properties
2.1 Base Alloy
The coil tube is fabricated from austenitic stainless steel grades, predominantly SAE 304 (UNS S30400) and SAE 316 (UNS S31600), selected for their superior corrosion resistance, formability, and thermal conductivity characteristics suitable for HVAC service environments.
- SAE 304: Contains approximately 18–20% Chromium (Cr) and 8–10% Nickel (Ni). Offers excellent resistance to atmospheric and mild chemical corrosion. Ideal for standard indoor fan coil unit applications.
- SAE 316: Contains approximately 16–18% Cr, 10–14% Ni, and 2–3% Molybdenum (Mo). The addition of Molybdenum significantly enhances resistance to chloride-induced pitting corrosion, making it suitable for coastal or high-humidity environments.
2.2 Key Mechanical & Physical Properties
- Tensile Strength (UTS): 515–720 MPa (depending on grade and cold-work condition)
- Yield Strength: ≥205 MPa (0.2% offset)
- Elongation: ≥40% (as-rolled condition)
- Thermal Conductivity: 14.6–16.3 W/(m·K) at 20°C
- Coefficient of Thermal Expansion: 17.3 × 10⁻⁶ /K (20–100°C)
- Density: 7.93 g/cm³
- Operating Temperature Range: −196°C to +870°C (SAE 304); −270°C to +870°C (SAE 316)
2.3 Surface Condition
The outer surface of the coil tube is typically supplied in a 2B finish (cold-rolled, annealed, and pickled), providing a smooth, non-directional matte surface with excellent formability. A No. 4 brushed finish or BA (Bright Annealed) finish is available upon request for applications requiring enhanced aesthetic or hygienic properties.
3. Technical Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Designation | Stainless Steel Coil Tube (FCU-Grade) | Internal — Wenzhou Jixing No. 855 |
| Material Grade | SAE 304 / SAE 316 (Austenitic Stainless Steel) | ASTM A213 / ASTM A269 |
| Outer Diameter (OD) | 6.00 mm – 25.00 mm (customizable) | ISO 3506 / GB/T 12771 |
| Wall Thickness | 0.30 mm – 1.50 mm (typical: 0.50 mm – 0.80 mm) | ASTM B619 / GB/T 14976 |
| Coil Inner Diameter | 300 mm – 600 mm | Manufacturer standard |
| Coil Length per Spool | 100 m – 500 m (typical: 200 m – 300 m) | Customer-specified |
| Roundness Tolerance | ±0.05 mm | ISO 12833 |
| OD Tolerance | ±0.02 mm – ±0.05 mm | ASTM A213 |
| Wall Thickness Tolerance | ±0.02 mm – ±0.03 mm | ASTM A213 |
| Surface Roughness (Ra) | ≤ 0.8 μm (inner); ≤ 1.6 μm (outer) | ISO 13567 |
| Weld Seam (if applicable) | Automatic Argon Arc Welded (TIG); Seam strength ≥ 90% of base metal | ISO 15493 |
| Packing | Export-grade wooden pallet with moisture-proof wrapping and steel strapping | ISO 4180 |
| Applicable Standards | ASTM A213, ASTM A269, GB/T 12771, GB/T 14976, EN 10216-5, JIS G3447 | — |
4. Manufacturing Process
The production of the Stainless Steel Coil Tube follows a rigorous multi-stage metallurgical and forming process to ensure dimensional accuracy, mechanical integrity, and surface quality:
- Raw Material Selection: High-purity austenitic stainless steel wire rod (hot-rolled and annealed) is sourced from certified mills. Incoming material undergoes spectroscopic analysis (OES) and chemical composition verification to confirm compliance with the specified grade.
- Wire Rod Annealing & Pickling: The wire rod is solution-annealed at 1050–1150°C followed by acid pickling and descaling to remove oxide scales and ensure a clean, corrosion-resistant base surface.
- Forming & Sizing: The wire rod is passed through a series of precision cold-drawing dies to achieve the target outer diameter and wall thickness. This cold-working process introduces controlled strain hardening, enhancing mechanical properties while maintaining formability.
- Welding (if welded tube): For welded coil tube, the formed strip is continuously welded using Automatic Tungsten Inert Gas (TIG) welding with high-purity Argon (Ar, ≥99.99%) as shielding gas. The welding parameters are computer-controlled to ensure consistent bead geometry and penetration.
- Intermediate Annealing: Post-welding or post-drawing annealing is performed at 1020–1100°C in a protective atmosphere (H₂/N₂ mixture) to relieve residual stresses, restore ductility, and stabilize the austenitic microstructure.
- Coil Winding: The continuous tube is wound onto steel cores to form coils of the specified inner diameter. Tension control systems ensure uniform coil packing without kinking or deformation.
- Quality Inspection: Each coil undergoes 100% ultrasonic testing (UT) for internal defects, hydrostatic pressure testing (typically 1.5–2.0 MPa) for leak integrity, dimensional measurement (OD, wall thickness, roundness), and surface inspection.
- Final Treatment & Packing: The coil is passivated (acid immersion) to enhance passive film formation, then wrapped in moisture-proof polyethylene film, placed on wooden pallets, and strapped for export-grade shipping.
5. Applications
The Stainless Steel Coil Tube (Product No. 855) is designed for critical use in the following domains:
- Fan Coil Units (FCU): The primary application — the coil tube serves as the heat exchange circuit within fan coil units used in commercial buildings, hospitals, hotels, and residential HVAC systems. The tube's thermal conductivity and corrosion resistance ensure efficient heat transfer between chilled/hot water and air over extended service life.
- Air Handling Units (AHU) & Chilled Beam Systems: Used in large-scale commercial and industrial HVAC installations where high-performance heat exchange coils are required.
- Heat Exchanger Manufacturing: The coiled configuration enables direct integration into shell-and-tube heat exchangers, plate-fin coil assemblies, and air-cooled condensers.
- Refrigeration & Cryogenic Systems: SAE 316 grade coil tube is suitable for refrigerant circuits in commercial refrigeration, cold storage, and low-temperature process equipment.
- Food & Pharmaceutical Processing: The hygienic surface finish and corrosion resistance make this coil tube suitable for heat exchange applications in food-grade and pharmaceutical processing equipment.
- Marine & Coastal HVAC Systems: SAE 316 grade provides superior resistance to chloride-laden marine atmospheres, ensuring longevity in coastal installations.
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework to ensure product conformity and traceability:
- ISO 9001:2015 — Quality Management System certification covering the full manufacturing and supply chain process.
- ISO 14001:2015 — Environmental Management System certification, demonstrating commitment to sustainable manufacturing practices.
- Material Test Reports (MTR): Each batch is accompanied by a mill test certificate documenting chemical composition, mechanical properties, and heat treatment records.
- Third-Party Inspection: Products are available for third-party inspection by agencies such as SGS, BV (Bureau Veritas), or TUV upon customer request.
- Compliance with International Standards: ASTM A213 (seamless), ASTM A269 (welded), EN 10216-5 (austenitic stainless steel tubes), GB/T 12771, GB/T 14976, and JIS G3447.
- Non-Destructive Testing (NDT): Ultrasonic testing (UT) and eddy current testing (ECT) are performed to detect internal and surface defects.
- Hydrostatic Testing: 100% of coils pass hydrostatic pressure testing to verify weld integrity and wall thickness uniformity.
7. Unique Selling Points
- Coiled Delivery Advantage: Continuous coil format eliminates butt-weld joints inherent in straight-length tubing, providing superior leak resistance and mechanical integrity for heat exchanger applications. This also enables automated coil-feeding in downstream manufacturing, reducing labor costs and material waste by up to 15%.
- FCU-Specific Optimization: The dimensional tolerances (±0.02–0.05 mm on OD and wall thickness) and surface quality are specifically calibrated for Fan Coil Unit heat exchanger requirements, ensuring optimal fin-tube contact and airflow characteristics.
- Dual-Grade Availability: Both SAE 304 and SAE 316 grades are offered, providing customers with flexibility to match material selection to environmental severity — from standard indoor installations to aggressive coastal or industrial settings.
- Full Traceability: Every coil is heat-number marked and accompanied by a complete material test report, ensuring full supply chain traceability from raw material to finished product.
- Energy Efficiency Contribution: The high thermal conductivity and low fouling tendency of austenitic stainless steel contribute to improved COP (Coefficient of Performance) in fan coil units, directly supporting energy conservation objectives in building HVAC systems — a critical consideration in the context of 《风机盘管的运行调节与节能》(Operation Regulation and Energy Saving of Fan Coil Units).
- Customization Capability: Non-standard OD, wall thickness, and coil dimensions are available upon request, allowing tailored solutions for specialized heat exchanger designs.
8. Technical Note on Energy Efficiency in FCU Applications
In the context of fan coil unit operation and energy conservation, the selection of coil tube material and geometry directly influences system performance. The stainless steel coil tube's smooth internal surface (Ra ≤ 0.8 μm) minimizes flow friction losses within the water circuit, reducing pumping power requirements. Furthermore, the material's resistance to corrosion and scale formation maintains heat transfer efficiency over the service life, preventing the progressive degradation of thermal performance that is commonly observed with carbon steel alternatives. This makes the stainless steel coil tube a technically superior choice for energy-efficient FCU designs, aligning with global trends toward green building standards and HVAC energy optimization.