Stainless Steel Coil Tube (Coiltube) — Fan Coil Unit Condensate Drainage Application
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product No. 1292). This product is specifically designed for HVAC (Heating, Ventilation, and Air Conditioning) systems, with a primary application in condensate drainage piping for Fan Coil Units (FCUs). The coil tube offers superior corrosion resistance, mechanical durability, and thermal stability, making it an ideal solution for environments where moisture, condensation, and temperature fluctuations are prevalent.
Unlike conventional carbon steel or copper tubing, the stainless steel coil tube eliminates the risk of internal corrosion, mineral scaling, and microbial growth, thereby ensuring long-term hydraulic efficiency and hygienic performance in condensate handling systems.
2. Material & Properties
2.1 Base Material
- Material Grade: SUS 304 / SUS 316L Stainless Steel (ASTM A269 / ASTM A213)
- Composition (SUS 304): Fe (balance), Cr 18–20%, Ni 8–10.5%, Mn ≤2%, Si ≤0.75%, C ≤0.08%
- Composition (SUS 316L): Fe (balance), Cr 16–18%, Ni 10–14%, Mo 2–3%, C ≤0.03%
2.2 Mechanical Properties
- Tensile Strength (UTS): ≥ 515 MPa (SUS 304); ≥ 485 MPa (SUS 316L)
- Yield Strength (0.2% Proof Stress): ≥ 205 MPa
- Elongation at Break: ≥ 40%
- Hardness: ≤ 92 HRB (annealed condition)
2.3 Physical & Chemical Properties
- Density: 7.93 g/cm³
- Thermal Conductivity: 16.3 W/(m·K) at 20°C
- Specific Heat: 0.50 J/(g·°C)
- Corrosion Resistance: Excellent resistance to acidic condensate (pH 4–7), chlorides (up to 1000 ppm in 316L), and atmospheric moisture
- Operating Temperature Range: −196°C to +870°C
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | Φ8 mm – Φ32 mm (customizable) | ASTM A269 / GB/T 12771 |
| Wall Thickness | 0.5 mm – 2.0 mm (±0.1 mm tolerance) | ISO 3506 |
| Coil Inner Diameter (CID) | Φ500 mm – Φ2000 mm | Manufacturer specification |
| Surface Finish | Ba < 0.4 μm (electropolished); Ra ≤ 1.6 μm (standard) | ASTM A967 |
| End Condition | Plain cut, beveled, or formed (threaded / flanged) | Per customer drawing |
| Pressure Rating | Up to 1.6 MPa (PN16) at 20°C | EN 10217 |
| Hydrostatic Test Pressure | 1.5× working pressure (minimum 2.5 MPa) | ISO 1127 |
| Coil Length per Reel | 50 m – 500 m (standard); up to 1000 m (special order) | — |
| Dimensional Tolerance | OD: ±0.15 mm; Wall thickness: ±10% | ASTM A269 |
| Packaging | Wooden reel / steel drum with moisture-proof wrapping | ISO 4180 |
4. Manufacturing Process
- Raw Material Procurement: High-purity stainless steel strip (coil) sourced from certified mills, with full mill test certificates (MTC) per EN 10204 3.1.
- Coil Forming / Cold Bending: Precision CNC-controlled coil bending machines form the strip into continuous helical tubes with uniform curvature radius, ensuring consistent wall thickness throughout.
- Welding (if applicable): Automatic TIG (Tungsten Inert Gas) welding with argon gas shielding (99.99% Ar) to produce seamless or welded coil tubes with smooth internal weld profiles.
- Heat Treatment: Solution annealing at 1050°C–1100°C followed by water quenching to restore full austenitic structure and maximum corrosion resistance.
- Pickling & Passivation: Acid pickling (HNO₃/HF mixture) removes mill scale and heat tint; passivation treatment forms a protective chromium oxide layer (≥100 nm thickness).
- Electropolishing (optional): Electrochemical polishing reduces surface roughness to Ra < 0.25 μm, critical for sanitary and condensate applications to prevent biofilm accumulation.
- Quality Inspection: 100% visual inspection, dimensional verification via laser measurement, hydrostatic pressure testing, and random sample destructive testing (tensile, hardness, intergranular corrosion per ASTM A262 Practice E).
- Packaging & Dispatch: Coils wound onto protective reels, wrapped in PE film and kraft paper, secured with steel strapping, and labeled with batch traceability codes.
5. Applications
5.1 Primary Application: Fan Coil Unit (FCU) Condensate Drainage
The coil tube serves as the condensate drain piping in commercial and industrial fan coil unit systems. Key design considerations include:
- Pipe Diameter Selection: Based on condensate flow rate (typically 0.5–3 L/min per FCU unit), pipe diameter is selected per the Darcy-Weisbach equation with a minimum slope of 1:100 to ensure gravity-driven drainage without stagnation.
- Corrosion Environment: Condensate in HVAC systems typically has a pH of 4.5–6.5 due to dissolved CO₂ and organic acids; SUS 316L grade is recommended for aggressive environments with chloride exposure.
- Hygienic Design: Smooth internal surface (Ra ≤ 0.5 μm) prevents biofilm formation and Legionella proliferation, complying with ASHRAE 188 and EN 12845 standards.
5.2 Secondary Applications
- Industrial process piping for chemical, pharmaceutical, and food-grade applications
- Automotive exhaust system components (heat-resistant grades)
- Heat exchanger tubing for HVAC chiller and boiler systems
- Medical equipment fluid transport lines
- Decorative and architectural railing systems
6. Quality Certifications & Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification for manufacturing processes |
| ISO 14001:2015 | Environmental Management System compliance |
| CE Marking (EN 10217) | European conformity for pressure equipment components |
| ASTM A269 / A213 | American material and dimensional standard compliance |
| GB/T 12771 (Chinese National Standard) | Seamless stainless steel tubes for fluid transport |
| EN 12845 / ASHRAE 188 | Legionella control and hygienic water system compliance |
| NSF/ANSI 61 | Drinking water system components safety certification |
| Mill Test Certificate (MTC) | EN 10204 Type 3.1 with full chemical and mechanical data |
7. Unique Selling Points
Expert-Engineered Condensate Management: Wenzhou Jixing Metal Materials Co., Ltd. provides coil tubes specifically optimized for Fan Coil Unit condensate drainage systems, incorporating industry best practices for pipe diameter selection, slope design, and material grade matching to condensate chemistry.
- Superior Corrosion Resistance: 3–5× longer service life compared to galvanized steel alternatives in acidic condensate environments; eliminates internal rust and iron ion contamination.
- Hygienic & Food-Safe: Electropolished surfaces compliant with 3-A Sanitary Standards, preventing bacterial colonization in moisture-rich HVAC applications.
- Precision Manufacturing: CNC coil forming with ±0.15 mm dimensional accuracy ensures perfect fit with standard HVAC fittings, reducing installation time and leak risk.
- Full Traceability: Each coil batch is traceable to raw material mill certificates, ensuring complete supply chain transparency and regulatory compliance.
- Custom Engineering Support: Technical consultation available for condensate pipe diameter calculation, system hydraulic design, and material selection based on specific application parameters (flow rate, temperature, pH, chloride content).
- Sustainability: Stainless steel is 100% recyclable with no loss of material properties; product lifecycle carbon footprint is 60% lower than copper alternatives.
8. Technical Notes for Condensate Pipe Diameter Selection
Based on industry literature and engineering practice, the following guidelines apply to condensate drain piping design using stainless steel coil tubes:
- Flow Rate Estimation: Condensate production per FCU unit = 0.8 × sensible cooling load (kW) × 0.01 L/(kW·min), adjusted for relative humidity.
- Pipe Sizing: Minimum pipe diameter shall ensure velocity ≤ 1.5 m/s to prevent erosion and noise; typical condensate drain sizes range from DN15 (Φ16 mm) to DN40 (Φ40 mm).
- Slope Requirement: Minimum longitudinal slope of 1:100 (1%) is mandatory; steeper slopes (1:50) are recommended for pipes < DN25 to prevent air pocket formation.
- Trapping: P-traps with seal depth ≥ 50 mm must be installed at each FCU unit to prevent air infiltration from drainage systems.
- Material Selection: SUS 304 for standard indoor applications; SUS 316L for coastal environments or systems with chlorinated water treatment.
Wenzhou Jixing Metal Materials Co., Ltd. — Precision Stainless Steel Coil Tubes for Demanding Industrial Applications.