Stainless Steel Evaporative Cooling Coil Tube for Closed Cooling Towers
Product Overview
The Stainless Steel Evaporative Cooling Coil Tube (Product Code: 348) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered heat exchange component designed specifically for closed-loop cooling tower systems. This coil tube is fabricated from high-grade austenitic stainless steel and is integral to the evaporative cooling process, where it facilitates efficient heat transfer and mass transfer between the process fluid and the surrounding air-water vapor environment.
Unlike conventional open cooling tower designs, the coil tube employed in closed cooling towers operates as a sealed heat exchanger, preventing direct contact between the process fluid and the external atmosphere. This design eliminates concerns related to fluid contamination, evaporation losses, and scaling, making it an indispensable component in applications demanding ultra-high fluid purity and thermal efficiency.
Key Principle: The coil tube functions as the primary heat transfer surface in a closed cooling tower. Process fluid flows through the interior of the coil tube while water droplets are sprayed over the exterior surface. Heat is transferred from the process fluid through the tube wall to the water film, and subsequently dissipated into the atmosphere via evaporation and convection — a coupled heat and mass transfer mechanism governed by the Penetration Theory and Two-Resistance Theory.
Material & Properties
Base Material Specification
The coil tube is manufactured from 304 (UNS S30400) or 316L (UNS S31603) austenitic stainless steel, selected for their superior corrosion resistance, thermal conductivity, and mechanical integrity under cyclic thermal loading conditions typical of cooling tower operations.
Mechanical Properties
- Tensile Strength (UTS): ≥ 520 MPa (304) / ≥ 485 MPa (316L)
- Yield Strength (0.2% offset): ≥ 205 MPa (304) / ≥ 170 MPa (316L)
- Elongation at Break: ≥ 40% (304) / ≥ 35% (316L)
- Hardness (HB): ≤ 217 (304) / ≤ 210 (316L)
- Thermal Conductivity (at 20°C): 16.3 W/(m·K) (304) / 14.6 W/(m·K) (316L)
- Thermal Expansion Coefficient (20–100°C): 17.3 × 10⁻⁶ /°C (304) / 16.0 × 10⁻⁶ /°C (316L)
Corrosion Resistance
- Chloride Pitting Resistance (CPT): 304 — 20–30°C; 316L — 40–60°C
- Intergranular Corrosion Resistance: Verified per ASTM A467, 316L grade with ≤ 0.03% carbon
- Crevice Corrosion: 316L grade exhibits superior resistance in chloride-rich cooling tower water environments
- Stress Corrosion Cracking (SCC): Austenitic structure inherently resistant to chloride-induced SCC
Chemical Composition (Typical, wt%)
| Element | 304 (UNS S30400) | 316L (UNS S31603) |
|---|---|---|
| C (Carbon) | ≤ 0.08 | ≤ 0.03 |
| Mn (Manganese) | ≤ 2.00 | ≤ 2.00 |
| P (Phosphorus) | ≤ 0.045 | ≤ 0.045 |
| S (Sulfur) | ≤ 0.030 | ≤ 0.030 |
| Si (Silicon) | ≤ 1.00 | ≤ 1.00 |
| Cr (Chromium) | 18.00 – 20.00 | 16.00 – 18.00 |
| Ni (Nickel) | 8.00 – 10.50 | 10.00 – 14.00 |
| Mo (Molybdenum) | — | 2.00 – 3.00 |
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Evaporative Cooling Coil Tube (盘管 Coiltube) |
| Product Code | 348 |
| Material Grade | 304 / 316L / 321 / Duplex 2205 (customizable) |
| Outer Diameter (OD) | 12 mm – 50 mm (standard range) |
| Wall Thickness | 0.5 mm – 3.0 mm |
| Tube Length (per Coil) | 5 m – 50 m (configurable per system design) |
| Coil Pitch | 15 mm – 40 mm (adjustable for heat transfer optimization) |
| Coil Diameter | 200 mm – 1200 mm |
| Surface Finish | BA (Bright Annealed) Ra ≤ 0.4 μm / No. 4 Polish / Custom |
| Operating Temperature | −50°C to +450°C |
| Operating Pressure | ≤ 2.5 MPa (PN25) |
| End Connection | Threaded / Flanged / Welded / Brazed (per client requirement) |
| Tolerance (OD) | ±0.05 mm |
| Tolerance (Wall Thickness) | ±10% |
| Applicable Standards | ASTM A213, ASTM A269, GB/T 12771, EN 10216-5 |
Manufacturing Process
1. Raw Material Procurement & Inspection
Stainless steel seamless tubes are sourced from certified mills and subjected to incoming inspection including chemical composition verification (spectrometric analysis), mechanical testing, and dimensional measurement. Material traceability is maintained throughout the production chain via heat number documentation.
2. Straightening & Dimensional Preparation
The incoming straight tube is precisely measured and cut to the required coil length. A high-precision hydraulic straightening machine is employed to ensure the tube meets the specified straightness tolerance (≤ 1 mm/m) prior to coiling operations.
3. Precision Coiling (Forming)
The core manufacturing step involves cold coiling the stainless steel tube to the specified coil diameter and pitch using a CNC-controlled coiling machine. Critical process parameters include:
- Coiling radius — must exceed the minimum bending radius to prevent wall thinning and ovalization
- Forming speed — controlled to minimize work hardening and residual stress
- Post-form annealing — solution annealing at 1050–1100°C followed by rapid quenching to restore the austenitic microstructure and relieve cold-work-induced stresses
4. Surface Treatment & Cleaning
The coiled tube undergoes pickling and passivation treatment to remove surface oxides, mill scale, and any carbonaceous contamination. This process ensures the formation of a stable, protective chromium oxide film (Cr₂O₃) on the surface, which is critical for long-term corrosion resistance in the cooling tower environment. Surface roughness is verified to meet the specified Ra values.
5. Heat Transfer Enhancement (Optional)
For applications demanding enhanced thermal performance, the coil tube may be supplied with external fins (spiral or plate-type) mechanically bonded or welded to the tube outer surface. Alternatively, internal corrugations or twisted-tape inserts can be incorporated to increase the convective heat transfer coefficient on the process fluid side. The enhancement factor (h_enhanced / h_plain) typically ranges from 1.5 to 3.0 depending on the geometry and flow conditions.
6. Quality Assurance & Testing
- Dimensional Inspection: 100% verification of OD, wall thickness, coil pitch, and overall length using precision measuring instruments
- Hydrostatic Pressure Test: Each coil is pressure-tested at 1.5× the maximum operating pressure to verify weld integrity and absence of leaks
- Non-Destructive Testing (NDT): Eddy current testing (ECT) and/or penetrant testing (PT) for surface defect detection
- Microstructural Examination: Grain boundary analysis to confirm freedom from intergranular corrosion susceptibility
- Corrosion Testing: Salt spray testing (ASTM B117) for ≥ 500 hours for 316L grade
7. Packaging & Shipping
Completed coil tubes are wrapped in protective polyethylene film, placed in wooden crates with moisture-absorbing desiccant, and secured for transport. Each package is labeled with product identification, material certificate reference, and handling instructions.
Applications
The stainless steel evaporative cooling coil tube is a critical component in a wide range of industrial and commercial thermal management systems. Key application domains include:
1. Chemical & Petrochemical Industry
Cooling of corrosive process fluids (acids, alkalis, chloride-containing solutions) where open cooling tower designs are unsuitable due to contamination risk or fluid degradation.
2. Power Generation
Condenser cooling coils in power plants, particularly in water-scarce regions where closed-loop systems minimize water consumption and eliminate scaling-related fouling.
3. Pharmaceutical & Food Processing
Cooling of ultra-pure water (UPW), pharmaceutical intermediates, and food-grade fluids where cross-contamination must be strictly prevented. The 316L grade is preferred for compliance with FDA and GMP standards.
4. HVAC & Data Center Cooling
Indoor unit coils for closed-loop cooling systems in commercial buildings, data centers, and precision air conditioning installations where quiet operation, compact footprint, and high efficiency are paramount.
5. Electronics & Semiconductor Manufacturing
Chilled water cooling coils for lithography equipment, plasma etching tools, and other high-power-density semiconductor processing equipment requiring precise temperature control.
6. Marine & Offshore Applications
Cooling systems on ships, offshore platforms, and desalination plants where exposure to seawater and high humidity demands exceptional corrosion resistance. Duplex 2205 grade is recommended for these environments.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd maintains rigorous quality management systems and holds the following certifications:
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health & Safety Management System
- NADCAP — National Aerospace and Defense Contracting Authority Accreditation Program (for aerospace-grade applications)
- CE Marking — European Conformity per Pressure Equipment Directive (PED) 2014/68/EU
- ASME — American Society of Mechanical Engineers certification for pressure vessel components
- API Q1 — Quality Management System for Petroleum, Petrochemical, and Natural Gas Industries
All products are accompanied by a full Mill Test Certificate (MTC) conforming to EN 10204 3.1, detailing chemical composition, mechanical properties, heat treatment status, and dimensional verification data. Third-party inspection (TPI) by organizations such as SGS, BV, or Lloyd's Register is available upon customer request.
Unique Selling Points
- Superior Heat Transfer Performance: The coil geometry maximizes the heat transfer surface area per unit volume, achieving thermal efficiencies up to 95% in evaporative cooling applications. The coupled heat and mass transfer mechanism — leveraging both sensible heat exchange and latent heat of evaporation — provides cooling capacity 3–5× greater than conventional air-cooled heat exchangers.
- Exceptional Corrosion Resistance: The austenitic stainless steel construction with optional molybdenum enhancement (316L) provides outstanding resistance to the aggressive chloride-containing environments typical of cooling tower water, ensuring service life exceeding 20 years without significant degradation.
- Sealed System Integrity: As a closed-loop component, the coil tube completely isolates the process fluid from the external environment, eliminating evaporation losses, contamination ingress, and scaling — critical advantages in pharmaceutical, food, and semiconductor industries.
- Customizable Design: Available in a wide range of diameters, wall thicknesses, coil pitches, and configurations to meet specific thermal load requirements. Finned, corrugated, and insert-enhanced variants are available for high-performance applications.
- Full Traceability & Certification: End-to-end material traceability from mill to finished product, with comprehensive testing documentation and international certifications ensuring compliance with the most stringent global standards.
Design Note: When specifying the coil tube for a closed cooling tower system, the engineer must consider the Number of Transfer Units (NTU), the Approach Temperature between the process fluid outlet and the wet-bulb air temperature, and the Heat and Mass Transfer Coefficient (KLa) to ensure the system meets the required cooling duty. Wenzhou Jixing provides thermal simulation and CFD analysis services to optimize the coil geometry for specific operating conditions.