Stainless Steel Coil Tube for High-Density Data Center Dry Cooling Systems
1. Product Overview
The stainless steel coil tube (also known as coiltube or dry coil tube) is a precision-engineered heat exchange component specifically designed for evaporative and dry cooling systems in high-density data center infrastructure. Unlike conventional straight-pipe heat exchangers, coil tubes leverage the helical geometry to maximize surface-area-to-volume ratios, thereby achieving superior thermal transfer efficiency under compact spatial constraints typical of modern hyperscale data centers.
Developed by Wenzhou Jixing Metal Materials Co., Ltd., this product line addresses the critical challenge of thermal management in data centers where rack power densities routinely exceed 50 kW/m². The coil tube serves as the primary heat exchange medium in dry cooling (also referred to as free-cooling or indirect evaporative cooling) systems, enabling efficient rejection of server waste heat while minimizing water consumption and energy overhead.
2. Material & Properties
2.1 Base Material
- Primary Alloy Grade: AISI 304 / 304L Stainless Steel (UNS S30400 / S30403)
- Alternative Grade: AISI 316L Stainless Steel (UNS S31603) for high-chloride or coastal environments
- Composition (304L typical): C ≤ 0.03%, Cr 18.0–20.0%, Ni 8.0–11.0%, Mn ≤ 2.0%, Si ≤ 1.0%, S ≤ 0.03%
- Surface Finish: Electro-polished (Ra ≤ 0.4 μm) or No. 4 brushed finish
2.2 Mechanical Properties
- Tensile Strength (UTS): ≥ 515 MPa (75 ksi)
- Yield Strength (0.2% offset): ≥ 205 MPa (30 ksi)
- Elongation: ≥ 40% (ASTM A270)
- Hardness: ≤ 92 HRB (annealed condition)
- Operating Temperature Range: −196 °C to +870 °C (cryogenic to elevated)
2.3 Thermal Properties
- Thermal Conductivity: 16.3 W/(m·K) at 25 °C
- Specific Heat Capacity: 500 J/(kg·K) at 25 °C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (20–100 °C)
2.4 Corrosion Resistance
- Excellent resistance to atmospheric, freshwater, and mild chemical environments
- Passive chromium oxide film (Cr₂O₃) self-healing capability
- Suitable for indirect evaporative cooling with recirculated water (TDS ≤ 500 ppm)
- 316L variant provides additional molybdenum (Mo 2.0–3.0%) for chloride stress corrosion resistance
3. Specifications
| Parameter | Specification | Standard / Tolerance |
|---|---|---|
| Outer Diameter (OD) | 12.7 mm / 16.0 mm / 19.05 mm / 25.4 mm (1/2", 5/8", 3/4", 1") | ASTM A270 / ±0.05 mm |
| Wall Thickness (WT) | 0.8 mm – 3.0 mm | ASTM A270 / ±10% |
| Coil Pitch (Helix Spacing) | 15 mm – 50 mm (configurable) | ±0.5 mm |
| Coil Diameter (Mean) | 100 mm – 500 mm | ±1.0 mm |
| Effective Length per Spool | 5 m – 50 m | Custom order |
| Maximum Operating Pressure | 1.6 MPa (232 psi) standard; 4.0 MPa upon request | ASME B31.3 |
| End Connections | Flanged (ANSI 150#), Threaded (NPT/BSP), Socket-weld, or Buttweld | ASME B16.5 / B16.11 |
| Heat Exchange Efficiency | U-value: 180 – 320 W/(m²·K) (air-side, dry cooling) | Manufacturer test report |
| Weight per Meter | 0.25 – 1.8 kg/m (depending on OD and WT) | Calculated per ISO 4380 |
| Surface Area per Meter | 39 – 79 dm²/m (external surface) | Geometric calculation |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Inspection: Ingot certification verification, spectroscopic analysis (OES), and visual surface inspection per ASTM A270 Grade 2 requirements.
- Hot Rolling & Annealing: Billet rolling to approximate OD, followed by solution annealing at 1050–1100 °C with rapid air cooling to achieve fully austenitic microstructure.
- Cold Drawing & Sizing: Multi-pass cold reduction through hardened tungsten carbide (WC) dies to achieve final OD and WT dimensions with tight tolerances.
- Intermediate Annealing: Periodic annealing at 1050 °C to relieve cold-work stresses and restore ductility for continued forming.
- Coil Forming (Helical Bending): Precision CNC-controlled spiral bending using a rotary mandrel and bending die set. The bending radius is maintained at R ≥ 3D (D = outer diameter) to prevent wall thinning below 5% of nominal thickness.
- Final Annealing & Pickling: Post-forming annealing to eliminate residual stresses from bending, followed by acid pickling (nitric-hydrofluoric acid blend) to restore the passive chromium oxide surface layer.
- Surface Finishing: Electro-polishing or mechanical polishing to achieve specified surface roughness (Ra ≤ 0.4 μm for high-flow applications).
- End Preparation: Flange welding (GTAW/Orbital welding), threading, or bevel preparation for field welding.
- Hydrostatic Pressure Testing: 100% leak testing at 1.5× maximum operating pressure for a minimum dwell time of 5 minutes.
- Non-Destructive Testing (NDT): Eddy current (EC) inspection for internal/external surface defects; visual inspection (VT) of welds per ASME BPVC Section V.
4.2 Key Manufacturing Considerations
- Wall Thinning Control: During helical bending, the outer fiber of the coil experiences tensile strain. Wall thinning must be controlled to ≤ 5% of nominal wall thickness to maintain structural integrity and pressure rating.
- Springback Compensation: The CNC bending system incorporates springback compensation algorithms based on material stress-strain curves to ensure dimensional accuracy of the coil pitch and mean diameter.
- Weld Quality: Orbital TIG (GTAW) welding is employed for flange attachments to ensure full penetration, uniform weld beads, and minimal heat-affected zone (HAZ) sensitization.
5. Applications in High-Density Data Centers
5.1 Dry Cooling System Architecture
In high-density data center cooling architectures, the stainless steel coil tube functions as the core heat exchange element within dry coolers (also known as air-side economizers or indirect evaporative coolers). The system operates on the following principle:
- Hot water (typically 30–45 °C) from the data hall chiller loop circulates through the stainless steel coil tubes.
- Ambient air is drawn across the coil bundle by high-efficiency axial fans, creating cross-flow or counter-flow heat exchange.
- When ambient dry-bulb temperature is below the supply water temperature, sensible heat is rejected to the atmosphere — achieving "free cooling" with zero water consumption.
- In indirect evaporative configurations, a secondary water circuit (sacrificial water) evaporates over the coil, lowering the effective air-side temperature below dry-bulb toward wet-bulb conditions, enabling cooling even at higher ambient temperatures.
5.2 Performance Advantages in Data Center Applications
- High Surface-to-Volume Ratio: The helical geometry provides 3–5× more heat transfer surface per unit volume compared to straight-pipe designs, enabling compact heat exchanger cabinets suitable for constrained rooftop or mechanical room installations.
- Enhanced Turbulence: Flow through helical tubes generates secondary Dean vortex flows, increasing the internal heat transfer coefficient by 20–40% compared to straight tubes at equivalent Reynolds numbers.
- Corrosion Durability: Stainless steel eliminates the risk of internal corrosion scaling that plagues copper and carbon steel alternatives, ensuring long-term U-value stability and reduced maintenance intervals.
- Low Fouling Tendency: The smooth electro-polished surface (Ra ≤ 0.4 μm) minimizes biofilm and mineral deposit adhesion, extending cleaning cycles to 12–24 months.
- Compact Footprint: Coil tubes can be arranged in serpentine or multi-pass configurations within modular heat exchanger cabinets, achieving high thermal capacity in minimal floor space — critical for data center density optimization.
5.3 System Integration
- Compatible with variable-speed chiller plants and precision air handling units (AHUs)
- Integrates with Building Management Systems (BMS) via temperature and flow sensors for demand-controlled ventilation
- Suitable for hybrid cooling architectures combining dry cooling, evaporative cooling, and mechanical refrigeration
- Designed for modular scalability — additional coil modules can be added in parallel as data center capacity expands
6. Unique Selling Points
1. Precision Helical Geometry: CNC-controlled coil forming with ±0.5 mm pitch accuracy ensures uniform flow distribution and predictable thermal performance across the entire heat exchanger bundle.
2. Full-Length Hydrostatic Testing: Every coil tube spool undergoes 100% pressure testing, guaranteeing zero-defect delivery and eliminating in-service failure risk in critical data center cooling infrastructure.
3. Cryogenic-to-Elevated Temperature Capability: The austenitic stainless steel matrix provides reliable operation from −196 °C (liquid nitrogen) to +870 °C, far exceeding the operating envelope of data center cooling applications and enabling future-proofing for advanced liquid immersion cooling systems.
4. Zero-Water Free Cooling Mode: Enables up to 80% of annual cooling hours to operate in zero-water-consumption dry cooling mode, significantly reducing Total Cost of Ownership (TCO) and environmental footprint (PUE optimization).
5. Customizable Configuration: Coil diameter, pitch, length, and end connections are fully customizable to match specific heat exchanger cabinet dimensions and process water flow requirements.
7. Quality Certifications & Standards Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification for manufacturing processes |
| ISO 14001:2015 | Environmental Management System certification |
| ASTM A270 / A270M | Standard specification for seamless austenitic stainless steel tubing |
| ASME B31.3 | Process piping design and pressure rating compliance |
| EN 10217-7 | European standard for stainless steel tubes for heat exchangers |
| GB/T 14976 | Chinese national standard for cold-rolled seamless stainless steel tubing |
| CE Marking | European Conformity for pressure equipment (PED 2014/68/EU) |
| Mill Test Reports (MTR) | Chemical composition and mechanical property verification per heat lot |
| NDT Reports | Eddy current and visual inspection reports per ASME BPVC Section V |
8. Conclusion
The stainless steel coil tube manufactured by Wenzhou Jixing Metal Materials Co., Ltd. represents a state-of-the-art thermal management solution purpose-built for the demanding thermal loads of modern high-density data centers. By combining the inherent corrosion resistance and mechanical robustness of austenitic stainless steel with the geometric efficiency of helical coil design, this product delivers superior heat transfer performance, minimal maintenance requirements, and long service life — all within a compact footprint that aligns with the space-constrained realities of data center infrastructure. As the industry continues to push toward higher rack densities and more stringent Power Usage Effectiveness (PUE) targets, the dry coil tube emerges as an indispensable component in sustainable, high-efficiency data center cooling architectures.