Stainless Steel Coil Tube (Coiltube) — HVAC & Industrial Heat Exchange Application Series
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered, continuously wound tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd., designed for use in heat exchange assemblies, particularly within Fan Coil Units (FCUs) and Hydronic Air Handling Systems in commercial, industrial, and transit infrastructure environments. The coil tube is formed into helical or serpentine configurations that maximize surface-area-to-volume ratios, thereby enhancing convective and radiative heat transfer efficiency in air conditioning, refrigeration, and process cooling applications.
This product line has been validated through field deployment in critical infrastructure projects, including the Guangzhou Metro Line 2 Fan Coil Unit Monitoring Technology, where stainless steel coil tubes demonstrated superior performance in high-humidity, corrosive, and continuous-duty operating environments. The coiltube geometry enables compact integration into ceiling-mounted, wall-mounted, and concealed FCU enclosures while maintaining structural integrity under cyclic thermal loading.
1.1 Unique Selling Points
- Corrosion Resistance: Stainless steel construction provides exceptional resistance to chloride-induced pitting, acid condensate corrosion, and microbial attack (Legionella compliance), significantly extending service life compared to carbon steel alternatives.
- Thermal Stability: Maintains mechanical properties across a wide operating temperature range of −40 °C to +250 °C, suitable for both heating and cooling cycles.
- Hygienic Surface Finish: Available in electropolished (Ra ≤ 0.4 μm) or passivated finishes, ensuring compliance with potable water and pharmaceutical-grade standards.
- Compact Geometry: The coiled configuration delivers up to 3.5× the heat exchange surface area per unit footprint compared to straight-pipe configurations, enabling space-optimized FCU designs.
- Weld-Free Assembly: Precision coil winding eliminates longitudinal weld seams, reducing stress-corrosion crack (SCC) initiation sites and improving pressure-vessel reliability.
- Monitoring Compatibility: Designed with standardized port geometries for seamless integration with Building Management System (BMS) sensors, enabling real-time monitoring of supply/return water temperatures, flow rates, and coil fouling factors.
2. Material & Properties
2.1 Material Grades
The coil tube is manufactured from austenitic and super-austenitic stainless steel grades conforming to international standards. The primary grades offered are:
- ASTM A213 TP304 / UNS S30408: General-purpose austenitic stainless steel with balanced corrosion resistance and formability. Ideal for standard HVAC and hydronic applications.
- ASTM A213 TP316L / UNS S31603: Low-carbon variant with added molybdenum (2.0–3.0%), providing superior resistance to pitting and crevice corrosion in chloride-rich environments (e.g., coastal metro stations, marine HVAC systems).
- ASTM A213 TP321 / UNS S32100: Titanium-stabilized grade offering enhanced resistance to intergranular corrosion during high-temperature operation (>450 °C), suitable for industrial process heating loops.
- ASTM A213 TP316Ti / UNS S31635: Titanium-stabilized 316 variant combining molybdenum and titanium benefits for demanding chemical processing and pharmaceutical applications.
2.2 Mechanical Properties (Typical, Cold-Wound Condition)
| Property | Grade 304 | Grade 316L | Grade 321 | Grade 316Ti |
|---|---|---|---|---|
| Tensile Strength (Rm) | ≥ 515 MPa | ≥ 485 MPa | ≥ 515 MPa | ≥ 515 MPa |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ≥ 170 MPa | ≥ 205 MPa | ≥ 205 MPa |
| Elongation (A50) | ≥ 40 % | ≥ 40 % | ≥ 40 % | ≥ 40 % |
| Hardness (HBW) | ≤ 210 | ≤ 210 | ≤ 210 | ≤ 210 |
| Thermal Conductivity (20 °C) | 16.3 W/(m·K) | 16.3 W/(m·K) | 16.3 W/(m·K) | 16.3 W/(m·K) |
| Coefficient of Thermal Expansion (20–100 °C) | 17.3 × 10⁻⁶ /°C | 17.3 × 10⁻⁶ /°C | 17.3 × 10⁻⁶ /°C | 17.3 × 10⁻⁶ /°C |
| Density (20 °C) | 8.00 g/cm³ | 8.03 g/cm³ | 8.00 g/cm³ | 8.03 g/cm³ |
| Maximum Operating Temperature | 870 °C | 870 °C | 900 °C | 870 °C |
2.3 Chemical Composition (wt%)
| Element | Grade 304 | Grade 316L | Grade 321 | Grade 316Ti |
|---|---|---|---|---|
| Carbon (C) max | 0.08 | 0.03 | 0.08 | 0.08 |
| Chromium (Cr) | 18.0–20.0 | 16.0–18.0 | 18.0–20.0 | 16.0–18.0 |
| Nickel (Ni) | 8.0–10.5 | 10.0–14.0 | 9.0–12.0 | 12.0–15.0 |
| Molybdenum (Mo) | — | 2.0–3.0 | — | 2.0–3.0 |
| Titanium (Ti) | — | — | 5 × (C + 0.02)–0.70 | 5 × (C + 0.02)–0.70 |
| Sulfur (S) max | 0.03 | 0.03 | 0.03 | 0.03 |
| Phosphorus (P) max | 0.045 | 0.045 | 0.045 | 0.045 |
3. Specifications
3.1 Geometric Dimensions
| Parameter | Specification Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 3.0 mm – 25.4 mm (1/8" – 1") | ASTM A213 / EN 10216-5 |
| Wall Thickness | 0.3 mm – 1.5 mm | ASTM A213 / GB/T 12771 |
| Coil Inner Diameter (CID) | 25 mm – 200 mm | Custom / Project-Specific |
| Coil Outer Diameter (COD) | 50 mm – 500 mm | Custom / Project-Specific |
| Coil Height / Length | 50 mm – 3,000 mm | Custom / Project-Specific |
| Turn Spacing (Pitch) | 1.5 mm – 10.0 mm | Custom / Project-Specific |
| Number of Turns | 3 – 500 turns | Custom / Project-Specific |
| End Connection Type | Flared, Grooved, Threaded, Brazed, or Welded (TIG) | ASME B1.20.1 / EN 10226 |
| Surface Finish | Mirror Polished (Ra ≤ 0.2 μm), Electropolished (Ra ≤ 0.4 μm), Passivated, or 2B Mill Finish | ASTM A240 / ISO 11400 |
| Maximum Working Pressure | 1.6 MPa – 6.3 MPa (depending on OD and wall thickness) | ASME B31.9 / EN 12828 |
| Design Pressure (at 20 °C) | Up to 10.0 MPa (burst pressure ≥ 4 × working pressure) | GB/T 12771 / EN 10216-5 |
| Tolerance on OD | ±0.05 mm (precision grade) | ISO 4287 |
| Tolerance on Wall Thickness | ±0.03 mm | ISO 4287 |
| Concentricity | ≤ 0.05 mm | ISO 1101 |
| Roundness | ≤ 0.5 % of OD | ISO 1101 |
| Coil Straightness | ≤ 1.0 mm/m (when uncoiled) | GB/T 14977 |
| Operating Temperature Range | −40 °C to +250 °C (continuous) | ASTM A213 |
| Delivery Condition | Solution Annealed (SA), Cold Worked (CW), or Stress Relieved (SR) | ASTM A213 |
| Applicable Standards | ASTM A213, EN 10216-5, GB/T 12771, JIS G3459, ISO 11400 | Multi-standard compliance |
3.2 Heat Transfer Performance (Typical FCU Application)
| Parameter | Value |
|---|---|
| Overall Heat Transfer Coefficient (U-value, air/water) | 40 – 90 W/(m²·K) (depending on fin geometry and airflow velocity) |
| Water Side Heat Transfer Coefficient | 2,500 – 5,000 W/(m²·K) |
| Air Side Heat Transfer Coefficient (with aluminum fins) | 25 – 70 W/(m²·K) |
| Recommended Water Flow Velocity | 0.5 – 2.0 m/s |
| Recommended Air Velocity (face velocity) | 1.5 – |