Stainless Steel Coil Tube for HVAC Fan Coil Units
Product Overview
The stainless steel coil tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular component specifically designed for two-pipe fan coil unit (FCU) systems and broader HVAC (Heating, Ventilation, and Air Conditioning) heat exchange applications. This product represents a critical thermal transfer medium within closed-loop hydronic systems, where efficient heat dissipation or absorption between a circulating fluid and ambient air is paramount. The coil tube is engineered to withstand prolonged exposure to thermal cycling, pressure differentials, and corrosive media, ensuring long-term operational reliability in both commercial and industrial environments.
The design philosophy of this coil tube aligns with the principles outlined in the analysis of two-pipe fan coil unit selection methods, emphasizing optimal heat transfer efficiency, minimal pressure drop, and compatibility with standard fan coil unit geometries. As a key component in the selection and specification of FCU systems, the coil tube's dimensional accuracy, material grade, and surface finish directly influence the overall thermal performance and service life of the installed unit.
Material & Properties
The coil tube is fabricated from high-quality austenitic stainless steel, primarily conforming to the following material grades:
- SUS304 / ASTM A213 TP304 (18/8 Stainless Steel) — General-purpose grade offering excellent corrosion resistance, weldability, and formability. Suitable for most HVAC applications involving water-based heat transfer fluids.
- SUS316L / ASTM A213 TP316L (Low-Carbon 18/10/2.5 Stainless Steel) — Enhanced corrosion resistance due to molybdenum addition. Recommended for applications involving chlorinated water, glycol-based antifreeze solutions, or marine-adjacent installations.
- SUS321 / ASTM A213 TP321 (Titanium-Stabilized Stainless Steel) — Superior resistance to intergranular corrosion at elevated temperatures, suitable for high-temperature heating loops.
Key material properties include:
- Thermal Conductivity: 14.2–16.3 W/(m·K) at 20°C, providing efficient heat transfer between the working fluid and the surrounding air stream.
- Coefficient of Thermal Expansion: 17.3 × 10⁻⁶ /°C, ensuring dimensional stability under thermal cycling conditions.
- Maximum Service Temperature: Up to 870°C (SUS304) / 870°C (SUS316L) in continuous air service.
- Corrosion Resistance: Excellent resistance to atmospheric, aqueous, and mild chemical environments; pitting resistance number (PREN) of 18–26 depending on grade.
- Mechanical Properties: Tensile strength ≥ 515 MPa (SUS304 annealed); yield strength ≥ 205 MPa; elongation ≥ 40%.
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) |
| Material Grade | SUS304 / SUS316L / SUS321 (Customizable) |
| Outer Diameter (OD) | Ø6.0 mm, Ø8.0 mm, Ø10.0 mm, Ø12.0 mm, Ø14.0 mm, Ø16.0 mm (±0.1 mm tolerance) |
| Wall Thickness | 0.5 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.5 mm, 2.0 mm (±0.05 mm tolerance) |
| Tube Length (Coiled) | 5 m – 200 m per coil (custom lengths available) |
| Coil Inner Diameter | Ø300 mm – Ø1000 mm (configurable) |
| Surface Finish | No.1 Annealed, 2B, BA (Bright Annealed), or Custom |
| Working Pressure | Up to 1.6 MPa (standard); up to 4.0 MPa (reinforced configurations) |
| Temperature Range | −40°C to +250°C (continuous service) |
| Standards Compliance | ASTM A213, ASTM A778, GB/T 14976, EN 10216-5, JIS G3459 |
| Welding Compatibility | TIG (GTAW), Orbital, Laser welding — all grades |
| Finish Options | Passivated, Pickled, Electropolished (Ra ≤ 0.4 μm) |
| Order Quantity | Minimum 50 kg; bulk orders preferred |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing protocol designed to ensure dimensional precision, metallurgical integrity, and surface quality:
- Raw Material Procurement: Virgin stainless steel billets or continuous casting slabs are sourced from certified mills. Incoming material undergoes spectroscopic analysis (OES) to verify chemical composition compliance with specified grades.
- Hot Rolling & Annealing: The initial hot-rolled tube is solution-annealed at 1050–1100°C followed by controlled air or water quenching to achieve a fully austenitic microstructure with optimal mechanical properties.
- Cold Drawing / Cold Rolling: The tube is cold-worked through precision dies to achieve the target outer diameter and wall thickness with tight dimensional tolerances (±0.1 mm OD). This process enhances surface finish and mechanical strength through strain hardening.
- Intermediate Annealing: Where cold work exceeds 30% reduction, intermediate annealing is performed to prevent cracking and restore ductility.
- Coiling: The finished tube is wound onto precision-guided reels using tension-controlled coiling equipment to prevent deformation, kinking, or surface damage. Coil diameter and layer count are optimized based on tube stiffness and handling requirements.
- Pickling & Passivation: The coiled tube is subjected to acid pickling (HNO₃/HF blend or citric acid solution) to remove oxide scales and surface contaminants, followed by passivation treatment to form a protective chromium oxide layer (Cr₂O₃), enhancing corrosion resistance.
- Quality Inspection: Each batch undergoes hydrostatic pressure testing, dimensional measurement (caliper, micrometer, bore gauge), visual inspection, and optional eddy current testing for internal defect detection.
Applications
The stainless steel coil tube from Wenzhou Jixing Metal Materials Co., Ltd. serves a diverse range of industrial and commercial applications:
- Two-Pipe Fan Coil Units (FCUs): Primary application as the heat exchange coil in HVAC systems for commercial buildings, hotels, hospitals, and office complexes. The coil tube facilitates efficient heat transfer between water/steam (heating) and refrigerant-chilled water (cooling) within the FCU air handler.
- Chilled Water Cooling Systems: Used in evaporator coils for central air conditioning and process cooling applications.
- Steam Heating Systems: Deployed in radiator coils and steam-to-water heat exchangers for space heating.
- Industrial Heat Exchangers: Suitable for shell-and-tube heat exchangers, plate-fin coils, and custom thermal management systems in food processing, pharmaceutical, and chemical industries.
- Refrigeration & Air Conditioning: Employed in evaporator and condenser coils for medium-temperature refrigeration systems where corrosion resistance is critical.
- Solar Water Heating Systems: Utilized in evacuated tube collectors and flat plate collectors for solar thermal energy conversion.
- Automotive & Transportation: Applied in heat exchanger components for electric vehicle battery thermal management and HVAC systems.
Quality Certifications & Standards
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring product conformity with international standards:
- ISO 9001:2015 — Quality Management System certification covering all manufacturing and quality assurance processes.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices.
- CE Marking (EU Directive 2014/68/EU — PED) — Compliance with European Pressure Equipment Directive for pressure-rated applications.
- ASTM International Compliance — Full compliance with ASTM A213 (welded austenitic stainless steel tubes), ASTM A778 (welded austenitic stainless steel tubes for boiler and heat exchanger service).
- GB/T 14976 — Chinese National Standard for seamless stainless steel tubes.
- JIS G3459 — Japanese Industrial Standard for seamless and welded austenitic stainless steel tubes.
- EN 10216-5 — European Standard for welded austenitic stainless steel tubes for general engineering.
Unique Selling Points
- Precision Dimensional Control: Tight tolerances (±0.1 mm OD, ±0.05 mm wall thickness) ensure seamless integration into fan coil unit assemblies and heat exchanger manufacturing, reducing installation waste and improving system efficiency.
- Superior Corrosion Resistance: The austenitic stainless steel composition provides exceptional resistance to pitting, crevice corrosion, and stress corrosion cracking, extending service life beyond 25 years in typical HVAC applications.
- Optimized Thermal Performance: The combination of high thermal conductivity and precise wall thickness control maximizes the heat transfer coefficient (U-value), directly contributing to energy-efficient FCU operation and reduced operational costs.
- Customizability: Flexible configuration options including tube diameter, wall thickness, coil length, surface finish, and material grade allow tailored solutions for specific FCU selection requirements.
- Hygienic & Food-Grade Compliance: Electropolished finish options (Ra ≤ 0.4 μm) meet FDA and EHEDG standards for food and pharmaceutical processing applications.
- Environmental Sustainability: Stainless steel is 100% recyclable with minimal loss of material properties, supporting green building certifications (LEED, BREEAM) and circular economy objectives.
Technical Note: When selecting coil tubes for two-pipe fan coil unit applications, engineers should consider the interaction between tube diameter, wall thickness, fin spacing, and flow velocity to optimize the balance between heat transfer capacity and pressure drop. The coil tube specifications provided by Wenzhou Jixing Metal Materials Co., Ltd. are designed to complement standard FCU selection methodologies, enabling accurate thermal performance prediction and energy consumption estimation during the design phase.