Stainless Steel Coil Tube (Coiltube) — HVAC Fan Coil Unit Series
Product Code: 917 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular component designed primarily for integration into Fan Coil Unit (FCU) plus Fresh Air System (FCAS) architectures. This product serves as the core heat exchange medium within distributed air conditioning systems, facilitating efficient thermal transfer between circulating coolant (water or refrigerant) and ambient air. The coil tube's serpentine geometry maximizes surface area within a compact footprint, enabling high-capacity heat exchange while maintaining low pressure drop across the circuit.
Derived from extensive research into noise control measures for fan coil unit plus fresh air conditioning systems, this product incorporates design features that address acoustic performance alongside thermal efficiency — a critical consideration in modern HVAC engineering where indoor environmental quality (IEQ) demands both thermal comfort and acoustic comfort.
2. Material & Properties
2.1 Base Material
- Primary Alloy: Austenitic Stainless Steel conforming to ASTM A213/A213M (Standard Specification for Seamless Austenitic Stainless Steel Tubing for Heat-Transfer and General Engineering Service)
- Designation: Type 304 (UNS S30400) or Type 316L (UNS S31603), selected based on application corrosivity requirements
- Chemical Composition (Type 304): Cr 18.0–20.0%, Ni 8.0–10.5%, C ≤ 0.08%, Mn ≤ 2.0%, Si ≤ 1.0%, S ≤ 0.030%
- Chemical Composition (Type 316L): Cr 16.0–18.0%, Ni 10.0–14.0%, Mo 2.0–3.0%, C ≤ 0.030%
2.2 Mechanical Properties
- Tensile Strength: ≥ 515 MPa (75,000 psi)
- Yield Strength (0.2% Offset): ≥ 205 MPa (29,750 psi)
- Elongation (50 mm gauge length): ≥ 40%
- Density: 8.0 g/cm³ (Type 304)
- Thermal Conductivity: 16.3 W/(m·K) at 20°C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (20–100°C)
2.3 Corrosion Resistance
- Excellent resistance to atmospheric corrosion and oxidizing environments
- Resistance to pitting and crevice corrosion (Type 316L with molybdenum addition)
- Non-toxic surface finish suitable for potable water and food-grade applications
- Resistance to stress corrosion cracking under normal HVAC operating conditions
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm (1/4"), 9.53 mm (3/8"), 12.70 mm (1/2") | ASTM A213 |
| Wall Thickness | 0.50 mm – 1.20 mm (selectable) | ASTM A213 |
| Coil Pitch (Row Spacing) | 12.7 mm – 25.4 mm (adjustable per design) | ASHRAE 15 |
| Fin Pitch | 8 – 14 fins per inch (FPI) | — |
| Fin Material | Aluminum (Al 1100) or Stainless Steel (304) | ASTM B209 |
| Tube Rows | 2 to 8 rows (configurable) | — |
| Operating Temperature Range | −40°C to +150°C (−40°F to +302°F) | — |
| Maximum Operating Pressure | 1.6 MPa (232 psi) | — |
| Hydrostatic Test Pressure | 2.4 MPa (348 psi) | ASTM A213 |
| Surface Finish | Electropolished (Ra ≤ 0.4 μm) or Brushed | ASTM A967 |
| Connection Type | Flanged, Soldered, Brazed, or Welded (TIG) | ASME B31.9 |
| Coil Length (Standard) | 300 mm – 1200 mm (custom lengths available) | — |
| Acoustic Performance | ≤ 35 dBA at 1 meter (optimized for FCU integration) | ASHRAE 84 |
4. Manufacturing Process
4.1 Seamless Tube Production
- Hot Rolling: Billet heating to 1150–1250°C followed by piercing and rolling to produce seamless tube blanks meeting ASTM A213 dimensional tolerances.
- Cold Drawing / Cold Reduction: Multi-pass cold drawing through calibrated dies to achieve precise OD and wall thickness specifications with ±0.05 mm tolerance.
- Solution Annealing: Heating to 1050–1100°C in a protective atmosphere (argon or vacuum) followed by controlled cooling to restore full austenitic microstructure and maximize corrosion resistance.
4.2 Coil Forming
- Coil Bending: Precision CNC-controlled bending of the seamless tube into serpentine coil geometry with controlled bend radius (minimum 3D) to prevent ovality and wall thinning.
- Fin Attachment: Aluminum or stainless steel fins pressed or welded onto the coil tubes at specified fin pitch using automated finning machinery.
- Hydroforming (Optional): For enhanced structural rigidity, internal hydroforming may be applied to create oval or flattened tube profiles that increase heat transfer surface area while reducing airflow resistance.
4.3 Surface Treatment & Finishing
- Pickling & Passivation: Acid bath treatment to remove oxide scale followed by passivation per ASTM A967 to form a stable chromium oxide protective layer.
- Electropolishing: Electrochemical removal of surface imperfections achieving Ra ≤ 0.4 μm for hygienic and low-friction flow characteristics.
- Anti-Corrosion Coating (Optional): Application of fluoropolymer (PTFE) or ceramic-based coating on fin surfaces to enhance condensate drainage and reduce noise from water film vibration.
4.4 Quality Inspection
- Dimensional Verification: CMM (Coordinate Measuring Machine) inspection of coil geometry, pitch accuracy, and dimensional conformance.
- Leak Testing: 100% hydrostatic pressure testing at 2.4 MPa for minimum 5 minutes with zero pressure drop acceptance criteria.
- Non-Destructive Testing (NDT): Eddy current testing per ASTM E709 for detection of surface and near-surface defects.
- Acoustic Testing: Sound power level measurement in anechoic chamber per ASHRAE 84 to validate noise performance specifications.
5. Applications
5.1 Primary Application — Fan Coil Unit Plus Fresh Air Systems
This coil tube product is specifically engineered for integration into Fan Coil Unit (FCU) Plus Fresh Air System (FCAS) architectures. The following application-specific design considerations are incorporated:
- Low-Vibration Design: Optimized coil geometry and fin spacing to minimize aerodynamic noise generation, addressing the primary noise sources identified in FCU systems (airflow noise, water hammer, and structural vibration).
- Condensate Management: Surface-treated fin geometry promotes uniform condensate film formation and drainage, reducing the noise associated with intermittent water dripping and gurgling within the coil section.
- Pressure Drop Optimization: Balanced design between thermal performance and hydraulic pressure drop to minimize pump noise and system vibration.
- Acoustic Damping: Material selection and structural design minimize resonance frequencies that coincide with typical fan operating speeds (800–2800 RPM).
5.2 Additional Applications
- Commercial and residential HVAC systems (VRF, chiller-based systems)
- Industrial process cooling and heating circuits
- Food processing and pharmaceutical cleanroom systems
- Marine and offshore HVAC installations (corrosion-resistant Type 316L)
- Automotive thermal management systems
- Refrigeration evaporator and condenser coils
6. Quality Certifications & Standards Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification covering design, manufacturing, and quality assurance processes |
| ISO 14001:2015 | Environmental Management System certification |
| ASTM A213/A213M | Material specification compliance for seamless austenitic stainless steel tubing |
| ASME B31.9 | Pressure Piping — Refrigeration and Air-Conditioning, design and construction compliance |
| ASHRAE 15 | Standard for the Safety of Refrigeration Systems (safety compliance) |
| ASHRAE 84 | Methods for Measurement of Sound Power Levels of Fluid Machinery (acoustic testing compliance) |
| EN 10216-5 | European standard for welded and seamless steel tubes for pressure purposes |
| GB/T 14976 | Chinese national standard for cold-rolled seamless stainless steel tubes |
| RoHS 2.0 | Restriction of Hazardous Substances compliance for environmentally conscious manufacturing |
| SGS / Bureau Veritas | Third-party inspection and material verification reports available upon request |
7. Unique Selling Points
- Acoustic-Optimized Design: Unlike conventional coil tubes, this product incorporates noise-reduction engineering derived from FCU system noise control research, delivering ≤ 35 dBA operation — critical for sensitive environments such as hospitals, hotels, and office spaces.
- Full Austenitic Stainless Steel Construction: Superior corrosion resistance eliminates the need for internal coatings or linings, ensuring long-term reliability and low maintenance costs over a design life exceeding 25 years.
- Customizable Geometry: Flexible coil pitch, row count, fin density, and tube dimensions allow precise thermal performance matching to specific system design requirements.
- Integrated Noise Mitigation: Condensate-managed fin surface treatment and vibration-damped structural design address multiple noise sources simultaneously — airflow turbulence, water film instability, and mechanical resonance.
- Seamless Construction: Eliminates weld-induced corrosion initiation points, ensuring uniform flow characteristics and extended service life even in aggressive chemical environments.
- Complete Traceability: Each coil tube batch is accompanied by a full material traceability record, including mill certificates, heat number, and third-party test reports.
8. Technical Notes
Note on Noise Control Integration: This coil tube product is designed as a component within a holistic noise control strategy for FCU + Fresh Air systems. For optimal acoustic performance, it should be installed with appropriate vibration isolation mounts, acoustic lining on fan housings, and properly sized air ducts with diffusers. The coil tube's low-pressure-drop design contributes to reduced fan energy consumption and lower fan speed requirements, indirectly reducing aerodynamic noise at the source.
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. — Specialized in precision stainless steel tube and coil products for HVAC, industrial, and engineering applications.