Stainless Steel Coil Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered seamless or welded stainless steel tube supplied in coiled form, designed for applications requiring continuous length without butt joints. The product is available in a wide range of grades, including austenitic (e.g., AISI 304, 316, 316L), duplex (e.g., 2205), and ferritic stainless steels, offering superior corrosion resistance, mechanical integrity, and formability. Coiltube configurations eliminate the need for field welding, reducing installation time and failure points in complex piping systems. This product is particularly suited for heat exchanger coil assemblies, including fan coil units (FCU) and other HVAC (Heating, Ventilation, and Air Conditioning) applications, where thermal efficiency and measurement accuracy are critical.
From a metallurgical standpoint, the coil form factor presents unique challenges in residual stress distribution and dimensional tolerance control. Wenzhou Jixing addresses these through optimized cold-drawing and controlled coiling processes, ensuring uniform wall thickness and consistent geometric accuracy across the entire coil length. The product is manufactured to comply with international standards including ASTM A213, ASTM A269, ASTM A554, ISO 13905, and EN 10216-5.
2. Material & Properties
2.1 Available Grades and Chemical Composition
The primary alloy grades offered are detailed below. Chemical compositions conform to ASTM A240 and EN 10088 specifications.
| Grade (ASTM / EN) | Cr (%) | Ni (%) | Mo (%) | C (%) Max | Key Characteristics |
|---|---|---|---|---|---|
| 304 / 1.4301 | 18.0–20.0 | 8.0–10.5 | — | 0.08 | General-purpose corrosion resistance; excellent weldability |
| 316 / 1.4401 | 16.0–18.0 | 10.0–14.0 | 2.0–3.0 | 0.08 | Enhanced pitting and crevice corrosion resistance (Mo addition) |
| 316L / 1.4404 | 16.0–18.0 | 10.0–14.0 | 2.0–3.0 | 0.03 | Low-carbon variant; superior weldability without sensitization |
| 321 / 1.4541 | 17.0–19.0 | 9.0–12.0 | — | 0.08 | Ti-stabilized; resistant to intergranular corrosion at elevated temperatures |
| 304L / 1.4307 | 18.0–20.0 | 8.0–10.5 | — | 0.03 | Low-carbon 304; preferred for welded heat exchanger assemblies |
| 2205 / 1.4462 | 22.0–23.0 | 4.5–6.5 | 2.5–3.5 | 0.03 | Duplex phase; high strength (~2× austenitic); excellent chloride resistance |
2.2 Mechanical Properties (Annealed Condition)
| Property | 304 / 304L | 316 / 316L | 321 | 2205 | Test Standard |
|---|---|---|---|---|---|
| Tensile Strength (MPa) Min | 515 | 515 | 515 | 450 | ASTM A213 |
| Yield Strength (MPa) Min | 205 | 205 | 205 | 255 | ASTM A213 |
| Elongation (%) Min | 40 | 40 | 40 | 35 | ASTM A213 |
| Property | 304 / 304L | 316 / 316L | 321 | 2205 | Test Standard |
| Thermal Conductivity (W/m·K) at 100°C | 16.3 | 16.3 | 16.3 | 17.0 | ASTM E153 |
| Specific Heat (J/kg·K) at 100°C | 500 | 500 | 500 | 500 | ASTM E1225 |
| Coefficient of Thermal Expansion (×10⁻⁶/°C, 20–100°C) | 17.3 | 17.3 | 17.3 | 15.0 | ASTM E228 |
| Maximum Service Temperature (°C) | 870 | 870 | 900 | 300 | Material-specific |
2.3 Surface Finish Options
- No. 1 (Cold-Rolled and Annealed): Matte, scaled-free finish; suitable for general industrial use.
- 2B (Cold-Rolled, Annealed, Pickled, and Passivated): Smooth, slightly reflective surface; standard for food-grade and pharmaceutical applications.
- Ba / Bright Annealed: High-luster finish with minimal surface roughness; ideal for optical and decorative applications.
- Electropolished (EP): Ra ≤ 0.4 μm; removes surface contaminants and work-hardened layer; required for sanitary and bioprocessing systems.
- Pickled and Passivated (PP): Removes mill scale and forms a protective chromium oxide film; standard for atmospheric and mild chemical service.
3. Specifications
3.1 Dimensional Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 3.0 mm – 219.1 mm (1/8" – 8") | ASTM A554 / ISO 13905 |
| Wall Thickness (WT) | 0.3 mm – 12.7 mm (0.012" – 0.5") | ASTM A554 / ISO 13905 |
| OD Tolerance | ±0.15 mm (OD ≤ 10 mm); ±0.5% (OD > 10 mm) | ASTM A554 |
| WT Tolerance | ±10% (WT ≤ 3 mm); ±12.5% (WT > 3 mm) | ASTM A554 |
| Coil Length | Standard: 15 m – 120 m; Custom lengths available | Customer specification |
| Coil Inner Diameter (ID) | 150 mm – 600 mm (standard); up to 1,200 mm (custom) | Customer specification |
| Coil Weight | Up to 5,000 kg per coil (standard); up to 8,000 kg (special) | Customer specification |
| Straightness (per 1,000 mm) | ≤ 1.5 mm | ASTM A554 |
| Roundness | ≤ 0.5% of OD | ISO 13905 |
| Surface Roughness (Ra) | ≤ 0.8 μm (standard); ≤ 0.4 μm (electropolished) | ASTM A269 |
3.2 Pressure Rating and Design Parameters
| OD (mm) | WT (mm) | Grade | Allowable Stress (MPa) at 20°C | Design Pressure (MPa) | Applicable Code |
|---|---|---|---|---|---|
| 9.53 | 1.65 | 316L | 138 | 4.75 | ASME B31.3 |
| 12.70 | 2.11 | 316L | 138 | 6.28 | ASME B31.3 |
| 19.05 | 2.77 | 316L | 138 | 8.75 | ASME B31.3 |
| 25.40 | 3.05 | 316L | 138 | 11.20 | ASME B31.3 |
| 38.10 | 3.40 | 316L | 138 | 13.85 | ASME B31.3 |
| 50.80 | 4.57 | 316L | 138 | 17.50 | ASME B31.3 |
Note: Design pressure values are calculated per ASME B31.3 Process Piping Code using the Barlow formula: P = (2 × S × E × t) / D_o, where S = allowable stress, E = joint efficiency (1.0 for seamless), t = wall thickness, and D_o = outer diameter. Values are provided for informational purposes; actual design must be verified by a licensed engineer.
3.3 Heat Exchanger and Fan Coil Unit (FCU) Coil Applications
When employed in fan coil unit (FCU) assemblies, the stainless steel coil tube serves as the primary heat transfer surface. The following parameters are critical for thermal performance and measurement accuracy:
| Parameter | Typical Specification | Relevance to FCU Performance |
|---|---|---|
| Tube OD × WT | 9.53 × 0.4 mm (3/8" × 0.016") | Optimizes heat transfer area-to-flow resistance ratio |
| Fin Type | Aluminum or copper fin, 2–4 FPI (fins per inch) | Enhances external heat transfer coefficient |
| Row Configuration | 2-row, 4-row, or 6-row | Determines capacity and pressure drop |
| Design Heat Transfer Coefficient (U-value) | 60–100 W/m²·K (air-side limited) | Overall effectiveness of the coil assembly |
| Operating Pressure Range | 0.5–1.5 MPa (typical HVAC) | Ensures structural integrity under pump head |
| Operating Temperature Range | 5°C to 90°C (chilled/hot water) | Compatible with standard HVAC refrigerant/water loops |
3.4 Humidity Effects on Heat Measurement Accuracy — Technical Considerations
An important aspect of coil tube performance in fan coil units is the influence of ambient humidity on the accuracy of heat transfer measurements. In a fan coil unit, the coil surface temperature often falls below the dew point of the surrounding air, causing condensation on the tube and fin surfaces. This condensation introduces several measurement uncertainties:
- Enthalpy-based measurement error: The latent heat released during condensation (approximately 2,450 kJ/kg of water at standard conditions) adds to the sensible heat transfer, causing total heat capacity to exceed the sensible heat capacity measured by inlet/outlet temperature differentials alone. If humidity is not accounted for, capacity ratings can be overestimated by 5–15%.
- Thermal resistance modification: The condensate film on the coil surface acts as an additional thermal resistance layer, reducing the effective overall heat transfer coefficient (U-value). This effect is more pronounced at low air velocities and high humidity ratios.
- Water carryover: Inadequate condensate drainage can lead to water carryover downstream, affecting