Stainless Steel Coil Tube for Fan Coil Units — Technical Specification
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Product No.: 460 | Classification: HVAC Coil Components
1. Product Overview
The Stainless Steel Coil Tube (盘管 / Coiltube) is a precision-engineered heat exchanger component designed for integration into Fan Coil Units (FCUs) used in commercial and industrial HVAC (Heating, Ventilation, and Air Conditioning) systems. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coil tube serves as the primary heat transfer medium, facilitating the exchange of thermal energy between circulating refrigerant or hot water and the ambient air stream.
The design and performance of this coil tube are governed by internationally recognized metrological standards, including the simplified calculation methodology for measurement uncertainty in cooling and heating capacity of Fan Coil Units. This ensures that every unit delivered meets stringent accuracy and reliability requirements for thermal performance characterization.
2. Material & Properties
2.1 Base Material
- Primary Alloy: Austenitic Stainless Steel, conforming to AISI 304 (UNS S30400) or AISI 316L (UNS S31603) grades
- Chromium Content: ≥ 18% (provides primary corrosion resistance)
- Nickel Content: ≥ 8% (stabilizes austenitic microstructure)
- Molybdenum Content (316L): 2.0%–3.0% (enhanced pitting and crevice corrosion resistance)
- Carbon Content (L-grade): ≤ 0.03% (prevents sensitization during welding)
2.2 Mechanical Properties
| Property | AISI 304 | AISI 316L | Test Standard |
|---|---|---|---|
| Tensile Strength (Rm) | 515–730 MPa | 485–720 MPa | ASTM A270 / EN 10216-5 |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ≥ 170 MPa | ASTM A270 / EN 10216-5 |
| Elongation at Break (A50) | ≥ 40% | ≥ 35% | ASTM A270 / EN 10216-5 |
| Hardness (HV10) | ≤ 210 HV | ≤ 210 HV | ISO 6507 |
| Corrosion Potential (MPP) | ≥ 250 mV | ≥ 270 mV | ISO 15559 |
2.3 Thermal Properties
- Thermal Conductivity: 16.3 W/(m·K) at 20°C
- Specific Heat Capacity: 498 J/(kg·K) at 20°C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (20–100°C)
- Operating Temperature Range: −196°C to +870°C
3. Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Tube Outer Diameter (OD) | 9.52 mm / 12.70 mm / 15.88 mm (3/8", 1/2", 5/8") | ASTM A270 |
| Tube Wall Thickness | 0.81 mm – 1.65 mm (0.032" – 0.065") | ASTM A270 / EN 10216-5 |
| Fin Type | Continuous L-fin / Discrete Plate-fin / Microchannel | — |
| Fin Material | Aluminum (1100 / 3003) or Stainless Steel | ASTM B209 / ASTM B209M |
| Fin Density | 8–14 fins per inch (FPI) | — |
| Coil Row Count | 2 / 3 / 4 / 6 rows (configurable) | ASHRAE 15 |
| Circuit Count | 1–16 circuits (application-dependent) | — |
| Connection Type | Flare / Solder / Brazed / Threaded / Flanged | ASME B31.5 |
| Maximum Working Pressure | 2.5 MPa (362.6 psi) — refrigerant side | ASME BPV Code |
| Hydrostatic Test Pressure | 3.75 MPa (543.9 psi) — 1.5× working pressure | ASME BPV Code |
| Refrigerant Compatibility | R-410A, R-32, R-134a, R-407C, R-404A, Ammonia (NH₃) | ASHRAE 34 |
| Surface Treatment | Pickling & Passivation / Electropolishing / PVD Coating | ASTM A967 |
| Weight Tolerance | ± 5% of nominal | — |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Procurement: Cold-rolled stainless steel strip or seamless tube from certified mills, with full material traceability documentation (Mill Test Report / MTR).
- Coil Winding & Forming: High-precision CNC-guided coiling machines wind the tube into the required serpentine or spiral geometry. Bending radii are controlled to ≥ 3D (three times the tube diameter) to prevent wall thinning and ovality.
- Fin Insertion / Finning: Aluminum or stainless steel fins are inserted or bonded to the coil tubes using either the continuous L-fin insertion method or discrete fin stacking, followed by crimping or brazing to ensure thermal and mechanical bonding.
- Brazing / Soldering: Circuit headers and connections are brazed using phosphorus-copper brazing alloys (BCuP-1) in a nitrogen-protected furnace at 600–700°C to ensure leak-tight joints without oxidation.
- Pickling & Passivation: Post-brazing pickling removes oxide scale using a controlled acid bath (HNO₃/HF mixture), followed by passivation treatment to restore the chromium oxide protective layer (ASTM A967).
- Pressure Testing: Each coil undergoes 100% hydrostatic pressure testing at 1.5× the maximum working pressure, held for a minimum of 15 minutes, with zero leakage permitted.
- Performance Testing: Sample coils are tested on a calibrated capacity test bench in accordance with ASHRAE Standard 15 (formerly AHRI 430), measuring cooling capacity, heating capacity, and associated parameters (air flow, temperature rise, pressure drop).
- Final Inspection & Packaging: Visual inspection, dimensional verification, and protective packaging (VCI wrapping, wooden crates) prior to shipment.
4.2 Metrological Uncertainty Framework
Wenzhou Jixing Metal Materials Co., Ltd. adopts the simplified calculation methodology for measurement uncertainty in cooling and heating capacity of Fan Coil Units, aligned with the principles of the GUM (Guide to the Expression of Uncertainty in Measurement, JCGM 100:2008) and ASHRAE Standard 15. This framework ensures that:
- All capacity measurements are accompanied by a documented Expanded Uncertainty (U) at a coverage factor of k = 2 (95% confidence level).
- Contributing uncertainty sources — including air mass flow rate, air temperature, refrigerant/water flow rate, and temperature difference — are individually quantified and combined using the law of propagation of uncertainty.
- The simplified method reduces computational complexity while maintaining metrological traceability to national standards.
"The simplified calculation method enables rapid and reliable determination of measurement uncertainty for fan coil unit capacity, ensuring compliance with international trade and quality assurance requirements without necessitating full GUM-compliant measurement models for routine production testing."
5. Applications
- Commercial HVAC Systems: Office buildings, hotels, hospitals, shopping malls, and educational facilities utilizing packaged Fan Coil Units for space conditioning.
- Industrial Process Cooling: Precision temperature control in pharmaceutical manufacturing, food processing, and semiconductor fabrication facilities.
- Refrigeration Systems: Condenser and evaporator coils in commercial refrigeration units, walk-in coolers, and cold storage applications.
- Marine & Offshore HVAC: Corrosion-resistant coil tubes for shipboard and offshore platform ventilation systems (AISI 316L grade recommended).
- Heat Recovery Systems: Energy-efficient heat exchangers in district heating networks and waste heat recovery installations.
- Solar Thermal Systems: Absorber tubes in solar water heating collectors requiring long-term durability under cyclic thermal loading.
6. Quality Certifications & Standards Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System — certified for design, manufacturing, and supply of metal coil products |
| ISO 14001:2015 | Environmental Management System — sustainable manufacturing practices |
| ISO 45001:2018 | Occupational Health & Safety Management System |
| CE Marking | Compliance with EU Machinery Directive (2006/42/EC) and Pressure Equipment Directive (PED 2014/68/EU) |
| RoHS Compliance | Restriction of Hazardous Substances — compliant with EU Directive 2011/65/EU |
| REACH Compliance | Registration, Evaluation, Authorisation and Restriction of Chemicals — EU Regulation (EC) No 1907/2006 |
| EN 10204 3.1 | Inspection Certificate — material conformity documentation per European standard |
| ASHRAE Standard 15 | Method of Testing Air-Curtains, Air-Fans, and Fan Coil Units for Rating Purposes |
| ANSI/ASHRAE 34 | Designation and Safety Classification of Refrigerants — refrigerant compatibility verification |
| ASME BPV Code | Boiler and Pressure Vessel Code — Section I, pressure containment compliance |
7. Unique Selling Points
- Metrologically Rigorous Capacity Verification: Industry-leading application of simplified uncertainty calculation methodology ensures that every coil tube's thermal performance data is traceable, repeatable, and internationally recognized — providing customers with confidence in specified cooling and heating capacities.
- Superior Corrosion Resistance: AISI 316L grade availability with molybdenum enhancement delivers exceptional resistance to chlorides, acidic condensate, and aggressive industrial atmospheres, significantly extending service life over conventional carbon steel coils.
- Full Material Traceability: Each production batch is accompanied by a complete Mill Test Report (MTR) and certificate of conformity, enabling end-to-end supply chain transparency.
- Customizable Geometric Configurations: Flexible row count, circuit arrangement, fin density, and connection types accommodate a wide range of OEM and ODM requirements.
- Comprehensive Quality Assurance: 100% hydrostatic pressure testing, sample-based thermal performance testing, and multi-stage visual and dimensional inspection ensure zero-defect delivery.
- Global Standards Compliance: Simultaneous adherence to ASME, ASHRAE, EN, and ISO standards facilitates seamless integration into international HVAC projects without re-certification.
8. Technical Notes & Recommendations
Note: When specifying coil tubes for Fan Coil Unit applications, the measurement uncertainty of the unit's cooling and heating capacity should be considered as a critical selection parameter. Wenzhou Jixing Metal Materials Co., Ltd. recommends that end-users and system integrators request the Expanded Uncertainty (U, k=2) value alongside nominal capacity ratings to ensure system performance predictions account for measurement variability. The simplified calculation method provides a practical and efficient pathway to this critical data.
Company: Wenzhou Jixing Metal Materials Co., Ltd. | Product Catalog No.: 460 | Document Revision: Technical Specification v1.0