Stainless Steel Coil Tube (Coil Tube) — Fan Coil Unit Condensate Management Series
Product Catalog No.: 1148 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd
1. Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coil Tube") is a precision-engineered tubular component designed primarily for integration into Fan Coil Units (FCUs) and hydronic air distribution systems. Wenzhou Jixing Metal Materials Co., Ltd manufactures these coil tubes to exacting metallurgical standards, ensuring long-term reliability in HVAC (Heating, Ventilation, and Air Conditioning) applications where condensate management is critical.
This product addresses the persistent industry challenge of condensate overflow and leakage in fan coil unit installations — a problem that can lead to structural water damage, mold growth, and compromised indoor air quality (IAQ). The coil tube is engineered with specific geometric, material, and surface characteristics that minimize condensate accumulation and facilitate controlled drainage.
Key Industry Context: According to the principle outlined in the technical literature "Prevention and Control of Condensate Overflow in Fan Coil Units," the root causes of condensate overflow include uneven heat exchange surface temperatures, improper slope design of condensate drain pans, and material-induced surface tension effects. The Coil Tube product is designed to mitigate each of these factors.
2. Material & Properties
The Coil Tube is fabricated from high-grade austenitic stainless steel, selected for its superior corrosion resistance, thermal conductivity, and long service life in humid HVAC environments.
2.1 Base Material Composition
| Element | Symbol | Minimum Content (%) | Maximum Content (%) |
|---|---|---|---|
| Chromium | Cr | 18.0 | — |
| Nickel | Ni | 8.0 | — |
| Molybdenum | Mo | 2.0 | — |
| Carbon | C | — | 0.08 |
| Manganese | Mn | — | 2.0 |
| Silicon | Si | — | 1.0 |
| Sulfur | S | — | 0.03 |
2.2 Mechanical & Physical Properties
- Tensile Strength (Rm): ≥ 520 MPa
- Yield Strength (Rp0.2): ≥ 205 MPa
- Elongation (A50): ≥ 40%
- Thermal Conductivity (at 20°C): 16.3 W/(m·K)
- Thermal Expansion Coefficient: 16.0 × 10⁻⁶ /°C
- Density: 8.0 g/cm³
- Operating Temperature Range: −40°C to +150°C
2.3 Surface Treatment & Coating
The outer surface of the Coil Tube receives a specialized hydrophilic or super-hydrophilic coating (available in two variants) to reduce the contact angle of condensate droplets to below 10°, thereby promoting rapid and uniform condensate drainage. This surface engineering directly addresses the condensate overflow problem documented in fan coil unit service literature.
- Coating Type A — Standard Hydrophilic: Contact angle < 30°, suitable for moderate humidity environments (RH 40–70%)
- Coating Type B — Super-Hydrophilic: Contact angle < 10°, recommended for high-humidity applications (RH > 70%) and coastal installations
3. Technical Specifications
| Parameter | Specification | Standard / Tolerance |
|---|---|---|
| Outer Diameter (OD) | 7.94 mm (⅝") / 9.53 mm (⅜") / 12.70 mm (½") | ±0.10 mm per GB/T 14976 |
| Wall Thickness | 0.60 mm / 0.80 mm / 1.00 mm | ±0.05 mm |
| Fins per Inch (FPI) | 10 FPI / 12 FPI / 14 FPI | ±0.5 FPI |
| Fin Material | Aluminum (Al 1100) or Copper-Aluminum bonded | GB/T 3190 |
| Fin Thickness | 0.10 mm – 0.15 mm | ±0.02 mm |
| Tube Passes | 2-row / 4-row / 6-row / 8-row | Customizable |
| Coil Length | Up to 3000 mm (continuous coil) | ±10 mm |
| Coil Diameter (Winding) | Φ200 mm – Φ500 mm | ±5 mm |
| End Connection | Flared / Soldered / Brazed / Threaded (G1/2", G3/4") | ASME B1.20.1 |
| Pressure Rating | 1.6 MPa (PN16) / 2.5 MPa (PN25) | GB/T 15607 |
| Flow Rate Range | 0.5 – 15.0 L/min (per row) | — |
| Heat Transfer Coefficient (U-value) | 45 – 65 W/(m²·K) | Dependent on configuration |
| Condensate Drain Slope | ≥ 1:100 (built-in) | Prevents pooling per AHRI 410 |
4. Manufacturing Process
The production of the Stainless Steel Coil Tube at Wenzhou Jixing Metal Materials Co., Ltd follows a rigorously controlled multi-stage manufacturing sequence:
- Raw Material Selection & Inspection: Stainless steel strip (Grade 316L or equivalent) undergoes incoming quality inspection including spectrometric analysis (OES), mechanical testing, and surface defect evaluation per GB/T 4237.
- Tube Forming (Cold Roll & Seam Welding): Precision cold-rolled strip is formed into seamless or single-seam tubes via high-frequency induction welding (HF welding), achieving weld strength ≥ 95% of base metal.
- Surface Finishing: The tube surface is polished to a mirror finish (Ra ≤ 0.4 μm) using electropolishing or mechanical polishing, reducing surface roughness to minimize condensate adhesion.
- Fin Stamping & Attachment: Aluminum fins are stamped to precise geometry and attached to the tube via mechanical crimping or brazing (soft solder at 210°C), ensuring intimate thermal contact with a joint resistance < 5 mΩ·cm².
- Coil Winding: The finned tube is wound into a helical coil using CNC-controlled winding machines, maintaining consistent pitch and alignment tolerances.
- Hydrophilic Coating Application: A nanostructured hydrophilic or super-hydrophilic coating is applied via chemical vapor deposition (CVD) or sol-gel dip-coating, followed by thermal curing at 150°C for 2 hours.
- Hydrostatic Pressure Testing: Each coil assembly is subjected to a hydrostatic pressure test at 1.5× working pressure (2.4 MPa for PN16) for a minimum of 30 seconds to verify structural integrity and weld soundness.
- Final Quality Inspection: Includes dimensional verification (CMM), coating adhesion testing (cross-cut per ASTM D3359), condensate flow rate measurement, and visual inspection under magnification.
5. Applications
The Stainless Steel Coil Tube is engineered for a broad spectrum of HVAC and fluid management applications where condensate control and corrosion resistance are paramount:
- Fan Coil Units (FCUs): Primary application — the coil tube serves as the heat exchanger element in commercial and residential FCUs, where the hydrophilic surface ensures rapid condensate shedding into the drain pan, preventing overflow.
- Chilled Water Air Handling Units (AHUs): Used in large-scale commercial HVAC systems for precise temperature and humidity control.
- VRF (Variable Refrigerant Flow) Systems: Integrated into indoor units of multi-split air conditioning systems.
- Industrial Process Cooling: Heat exchange applications in food processing, pharmaceutical manufacturing, and chemical plants requiring hygienic-grade materials.
- Marine HVAC Systems: The 316L-grade stainless steel provides superior resistance to chloride-induced pitting corrosion in coastal and marine environments.
- Condensate Drain Systems: The coil tube's design incorporates a minimum 1:100 slope, directly addressing the condensate overflow issues described in the technical literature on FCU maintenance.
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework to ensure product reliability and regulatory compliance:
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System — covers entire production lifecycle |
| ISO 14001:2015 | Environmental Management System — sustainable manufacturing practices |
| GB/T 14976 | Seamless and welded stainless steel tubes for general engineering |
| GB/T 4237 | Stainless steel plates, sheets, and strips — material specifications |
| GB/T 15607 | Stainless steel tubes and fittings for pressure applications |
| AHRI 410 / 430 | Air-Conditioning and Refrigeration Institute — commercial unitary equipment standards |
| EN 10217 | European standard for stainless steel tubes for pressure purposes |
| ASME B1.20.1 | Threaded pipe fitting standards for end connections |
| NSF/ANSI 61 | Drinking water system components — health effects certification (optional) |
7. Unique Selling Points (USPs)
- Super-Hydrophilic Surface Technology: Proprietary nano-coating reduces condensate contact angle to below 10°, enabling condensate droplets to shed at significantly lower surface temperatures — directly preventing the condensate overflow failures documented in FCU service literature.
- Grade 316L Stainless Steel Construction: Superior to standard 304 stainless steel in chloride-rich environments, providing a projected service life exceeding 25 years even in coastal or industrial settings.
- Integrated Drainage Geometry: Built-in 1:100 minimum slope and optimized coil pitch ensure positive condensate drainage without reliance on external drain pan modifications.
- High-Frequency Induction Welding: Achieves weld integrity ≥ 95% of base metal strength with minimal heat-affected zone (HAZ), preserving the corrosion resistance of the 316L alloy.
- Customizable Configuration: Available in multiple tube diameters, fin densities, row configurations, and coating types to match specific thermal load and environmental requirements.
- Full Traceability: Each coil tube batch is accompanied by a Material Test Certificate (MTC) per EN 10204 Type 3.1, providing complete chemical and mechanical analysis documentation.
8. Technical Literature Reference
The design philosophy of this Coil Tube product is informed by the technical paper "Prevention and Control of Condensate Overflow in Fan Coil Units" (《风机盘管凝结水外溢的防治》), which identifies three primary failure modes: (1) insufficient sub