Stainless Steel Coil Tube (Coiltube) — HVAC & Industrial Grade
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered, continuously coiled tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is specifically designed for demanding thermal exchange, fluid conveyance, and structural applications, with particular emphasis on its deployment within Fan Coil Units (FCUs) in commercial hospitality and building services sectors.
Unlike conventional straight-length tubing, the coiltube configuration offers a compact heat transfer surface area within minimal spatial footprints, making it an ideal solution for Fan Coil Units operating in tourist hotels, residential complexes, and commercial facilities. The continuous coil geometry ensures uniform flow distribution, reduced pressure drop, and enhanced thermal efficiency compared to bent or segmented alternatives.
Unique Selling Points
- Low Noise Profile: Optimized coil geometry minimizes aerodynamic turbulence and fluid-induced vibration, addressing critical noise concerns in hospitality environments where acoustic comfort is paramount.
- Continuous Coiling: Factory-coiled configuration eliminates field welding and brazing joints, reducing leak risk and improving long-term reliability.
- Corrosion Resistance: Austenitic stainless steel composition provides superior resistance to condensation-induced pitting and chloride attack common in HVAC condensate environments.
- Thermal Efficiency: High surface-area-to-volume ratio delivers superior heat transfer coefficients (U-values) for both heating and cooling cycles.
2. Material & Properties
The Coiltube is fabricated from high-grade austenitic stainless steel conforming to international material standards. The primary material grades available are detailed below:
| Property | Grade 304 (UNS S30400) | Grade 316 (UNS S31600) | Grade 316L (UNS S31603) |
|---|---|---|---|
| Chromium (Cr) | 18.0–20.0% | 16.0–18.0% | 16.0–18.0% |
| Nickel (Ni) | 8.0–10.5% | 10.0–14.0% | 10.0–14.0% |
| Molybdenum (Mo) | — | 2.0–3.0% | 2.0–3.0% |
| Carbon (C) Max | 0.08% | 0.08% | 0.03% |
| Tensile Strength (MPa) | ≥515 | ≥515 | ≥485 |
| Yield Strength (MPa) | ≥205 | ≥205 | ≥170 |
| Thermal Conductivity (W/m·K) at 20°C | 16.3 | 16.3 | 16.3 |
| Operating Temperature Range | -196°C to +870°C | -196°C to +870°C | -196°C to +870°C |
| Corrosion Resistance | General atmospheric, mild chemical | Enhanced chloride resistance | Superior chloride resistance, weld-sensitive |
| Recommended Application | Standard HVAC, general service | Marine HVAC, coastal environments | High-purity systems, post-weld service |
3. Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) |
| Product Code / Serial No. | 1575 |
| Outer Diameter (OD) | 6.35 mm (1/4") to 25.4 mm (1") |
| Wall Thickness (WT) | 0.3 mm to 1.5 mm |
| Coil Diameter (CD) | 100 mm to 800 mm (customizable) |
| Coil Length | Continuous coil up to 200 m per spool |
| Surface Finish | Bright Annealed (BA) / Polished / Passivated |
| Surface Roughness (Ra) | ≤ 0.4 μm (BA finish) |
| Tolerance on OD | ± 0.05 mm |
| Tolerance on WT | ± 0.02 mm |
| Pressure Test | 1.5× working pressure, helium leak test optional |
| Standard References | ASTM A213, ASTM A269, ASME B36.19M, EN 10216-5 |
| Packaging | Wooden pallet with protective wrapping, moisture-barrier film |
4. Manufacturing Process
- Raw Material Inspection: Ingot or coil stock is received and subjected to spectroscopic analysis (OES) to verify chemical composition against ASTM specifications. Certificates of Analysis (CoA) are documented for each heat lot.
- Hot Rolling & Cold Reduction: Billet material is hot-rolled into seamless tube blanks, followed by cold-drawing or cold-rolling to achieve precise dimensional tolerances and improved surface finish.
- Solid Solution Annealing: Tubes are heat-treated at 1050°C–1150°C followed by controlled water or air quenching to achieve full austenitic microstructure, relieve residual stresses, and maximize corrosion resistance.
- Precision Coiling: Annealed tubes are fed through a CNC-controlled coiling head that forms the tube into a consistent helical spiral. The coiling process employs a mandrel-die system to prevent wall-thinning, ovality, or kinking at bend radii. Minimum bend radius is maintained at ≥ 2× OD to preserve structural integrity.
- Surface Passivation & Cleaning: Coiled tubes undergo electrochemical passivation using nitric or citric acid baths to remove free iron and establish a stable chromium oxide passive layer. Subsequent ultrasonic cleaning removes all chemical residues.
- Hydrostatic & Helium Leak Testing: Each coil is pressure-tested at 1.5× the maximum design pressure. For critical HVAC applications, helium mass spectrometer leak testing is performed to verify integrity at sensitivities below 1×10⁻⁹ Pa·m³/s.
- Final Inspection & Packaging: Dimensional verification, visual surface inspection, and mechanical property sampling are conducted. Approved coils are wrapped in protective film, secured on wooden pallets, and prepared for shipment.
5. Applications
Primary Applications
- HVAC Fan Coil Units (FCUs): The primary application domain. Coiltube serves as the core heat exchanger element in fan coil units installed in tourist hotels, resorts, hospitals, and commercial buildings. The continuous coil design provides uniform heat exchange across the entire coil surface while minimizing air-side pressure drop and operational noise.
- Air Conditioner Evaporators & Condensers: Used in split-system and packaged air conditioning units where compact heat exchange surfaces are required.
- Refrigeration Systems: Employed in evaporator coils for commercial refrigeration and cold storage facilities.
- Heat Exchanger Cores: Integral components in shell-and-tube and plate-and-fin heat exchangers for industrial process cooling and heating.
Hospitality-Specific Considerations
Based on engineering studies regarding noise conditions in fan coil units within tourist hotel environments, the Coiltube product has been optimized to address the following acoustic challenges:
- Flow-Induced Vibration: The continuous coil geometry distributes fluid momentum evenly, reducing localized turbulence that generates broadband noise at frequencies perceptible to human hearing (20 Hz – 20 kHz).
- Resonance Mitigation: Coil pitch and diameter are engineered to avoid natural frequency resonance with typical HVAC fan blade pass-by frequencies.
- Condensate Drainage: The coil configuration facilitates gravity-assisted condensate collection, preventing water hammer and drip noise that are common sources of guest complaints in hospitality settings.
Recommended noise mitigation measures in conjunction with Coiltube installation include the use of flexible connector hoses, vibration-isolating mounting brackets, and acoustic baffles within the FCU housing.
Secondary Applications
- Medical equipment fluid circuits requiring sterilizable tubing
- Food and beverage processing systems (dairy, beverage, pharmaceutical)
- Marine and coastal HVAC systems requiring chloride-resistant tubing
- Solar thermal collector systems
- Industrial process heating and cooling loops
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system ensuring that all Coiltube products meet or exceed international standards. The following certifications and compliance documents are available:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification covering all manufacturing and quality assurance processes |
| ISO 14001:2015 | Environmental Management System certification for sustainable manufacturing practices |
| ISO 45001:2018 | Occupational Health and Safety Management System |
| CE Marking | Conformity with European Union safety, health, and environmental protection standards |
| EN 10204 3.1 | Inspection Certificate — material and product test data verified by qualified inspection personnel |
| ASTM A213 / A269 | Material specification compliance for seamless austenitic stainless steel tubing |
| ASME B36.19M | Dimensional and tolerance compliance for stainless steel tubing |
| NACE MR0175 / ISO 15156 | Resistance to sulfide stress cracking (for applicable grades) |
| NSF/ANSI 61 | Drinking water system components certification (for potable water applications) |
7. Technical Notes & Recommendations
- Installation: Install Coiltube with minimum bend radius of 2× OD to prevent collapse or wall thinning. Use appropriate expansion joints and flexible connectors to isolate vibration from the building structure.
- Welding: If field welding is required, use TIG (GTAW) welding with argon gas shielding. Post-weld annealing and passivation are recommended for Grade 316 and 316L to restore corrosion resistance at weld zones.
- Storage: Store in a dry, well-ventilated environment. Avoid contact with carbon steel to prevent galvanic contamination. Protect from UV exposure and mechanical abrasion.
- Maintenance: For HVAC applications, periodic inspection of coil surface for fouling, scaling, or corrosion is recommended. Chemical cleaning should use pH-neutral solutions compatible with austenitic stainless steel.
- Noise Control: In hospitality installations, supplement Coiltube performance with acoustic enclosures, silencers, and variable-speed fan motors to achieve ambient noise levels below 35 dBA at 1 meter, in compliance with hotel industry acoustic standards.