Stainless Steel Coil Tube for Composite Filling Closed Cooling Towers
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Wenzhou Jixing Metal Materials Co., Ltd.). Designed primarily for integration into composite filling closed cooling towers (Composite Fill Closed Cooling Towers), this coil tube serves as the core heat exchange element within evaporative cooling systems. The product is formed into continuous helical coils that maximize surface area-to-volume ratios, thereby enhancing thermal transfer efficiency while maintaining structural integrity under cyclic thermal and hydraulic loading conditions.
This coil tube system represents a critical component in the next generation of closed-loop cooling technology, where the refrigerant or process fluid circulates through sealed stainless steel tubing while ambient air flows across the external coil surfaces, enabling indirect evaporative cooling without direct water contact with the process fluid.
2. Material Composition & Physical Properties
The coil tube is fabricated from austenitic stainless steel grades, with the primary material specification as follows:
- Primary Grade: SUS304 (UNS S30408) / ASTM A213 TP304 — the standard grade offering excellent corrosion resistance, formability, and weldability.
- Enhanced Grade: SUS316L (UNS S31603) / ASTM A213 TP316L — selected for applications involving chlorinated water, coastal environments, or chemical processing where resistance to pitting and crevice corrosion is paramount.
- Alternative Grade: SUS321 (UNS S32100) / ASTM A213 TP321 — stabilized grade for high-temperature service above 425°C (800°F) where sensitization resistance is required.
Mechanical Properties (SUS304 Reference)
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 515 MPa (74,700 psi) | ASTM A213 / ASME SA-213 |
| Yield Strength (屈服强度) | ≥ 205 MPa (29,700 psi) | ASTM A213 |
| Elongation (延伸率) | ≥ 40% (min. 30% for wall thickness ≥ 2.5 mm) | ASTM A213 |
| Hardness (硬度) | ≤ 237 HB (Brinell) / ≤ 95 HRB | ASTM A213 |
| Density (密度) | 7.93 g/cm³ | — |
| Thermal Conductivity (导热系数) | 16.3 W/(m·K) at 20°C | ASTM A213 |
| Thermal Expansion Coefficient (热膨胀系数) | 17.3 × 10⁻⁶ /°C (10–100°C) | ASTM A213 |
| Maximum Service Temperature (最高使用温度) | 870°C (1,598°F) in oxidizing atmosphere | ASME SA-213 |
| Corrosion Resistance (耐腐蚀性) | Pitting Resistance Equivalent Number (PREN) ≥ 18 (SUS304); ≥ 24 (SUS316L) | ASTM G48 |
Chemical Composition (SUS304, wt%)
| Element | Specification |
|---|---|
| Carbon (C) | ≤ 0.08% |
| Chromium (Cr) | 18.0 – 20.0% |
| Nickel (Ni) | 8.0 – 10.5% |
| Manganese (Mn) | ≤ 2.0% |
| Silicon (Si) | ≤ 0.75% |
| Phosphorus (P) | ≤ 0.045% |
| Sulfur (S) | ≤ 0.030% |
| Iron (Fe) | Balance |
3. Dimensional Specifications
The coil tube is available in multiple configurations to accommodate varying thermal load requirements and installation geometries within composite filling closed cooling tower systems.
| Parameter (参数) | Specification Range | Notes |
|---|---|---|
| Outer Diameter (OD) (外径) | Φ12.7 mm (1/2") / Φ15.9 mm (5/8") / Φ19.1 mm (3/4") / Φ25.4 mm (1") / Φ31.8 mm (1-1/4") / Φ38.1 mm (1-1/2") / Φ48.3 mm (2") | Custom OD available upon request |
| Wall Thickness (壁厚) | 0.5 mm – 3.0 mm (0.020" – 0.118") | Standard: 0.8 mm, 1.0 mm, 1.2 mm, 1.5 mm |
| Coil Pitch (盘管间距) | 15 mm – 50 mm (0.59" – 1.97") | Optimized for airflow distribution |
| Coil Length (盘管长度) | Up to 500 m continuous coil per roll | Custom lengths available |
| Coil Pack Width (盘管组宽度) | 600 mm – 2,400 mm (24" – 96") | Modular assembly configuration |
| Coil Pack Height (盘管组高度) | 300 mm – 1,800 mm (12" – 72") | Custom configurations |
| End Connections (端部连接) | Flanged (法兰连接) / Threaded (螺纹连接) / Welded (焊接连接) / Grooved (沟槽连接) | Per ASME B16.5 or customer specification |
| Surface Finish (表面光洁度) | Ra ≤ 0.4 μm (electropolished) / Ra ≤ 1.6 μm (standard pickled) | Food-grade available upon request |
| Pressure Rating (压力等级) | Up to 2.5 MPa (363 psi) at 20°C | Hydrostatic test: 1.5× design pressure |
| Operating Pressure (工作压力) | 0.1 – 1.6 MPa (14.5 – 232 psi) | Typical cooling tower application |
4. Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing protocol designed to ensure dimensional precision, metallurgical homogeneity, and surface integrity:
- Raw Material Procurement (原材料采购): Hot-rolled stainless steel strip is sourced from certified mills (e.g., POSCO, Outokumpu, Taigang) with full material traceability documentation including mill certificates and chemical analysis reports.
- Cold Roll Forming (冷轧成型): The strip undergoes precision cold rolling to achieve the specified wall thickness tolerance of ±0.05 mm, with controlled reduction ratios to maintain favorable grain structure and mechanical properties.
- Seamless or Welded Tube Formation (无缝或焊接管成型): Tubes are formed via either seamless piercing (for higher-pressure applications) or longitudinal submerged arc welding (SAW) with 100% automated seam welding, followed by full-penetration weld inspection.
- Heat Treatment & Annealing (热处理与退火): Solution annealing at 1,040–1,120°C (1,895–2,050°F) with rapid water quenching to achieve a fully austenitic microstructure, eliminate cold-work stresses, and restore maximum corrosion resistance and ductility.
- Pickling & Passivation (酸洗钝化): The tube surface is treated with a mixed acid solution (nitric acid + hydrofluoric acid) to remove oxide scales and contamination, followed by a controlled passivation step to establish a uniform chromium-rich passive film (≥ 10 nm thickness).
- Coil Winding & Helical Forming (盘管绕制与螺旋成型): Precision CNC-controlled coil winding machines form the continuous helical coil geometry with controlled pitch, curvature radius, and inter-turn spacing. The forming process is executed at ambient temperature with controlled strain rates to prevent work-hardening and micro-cracking.
- End Preparation & Fitting (端部加工与装配): Coil ends are prepared with flanges, threaded couplings, or welding fittings per the specified connection type, with each joint subjected to non-destructive testing.
- Quality Inspection & Testing (质量检验与测试): Comprehensive inspection including dimensional verification (±0.1 mm tolerance), ultrasonic wall thickness measurement, helium or pneumatic pressure testing, visual surface inspection, and magnetic particle inspection of weld seams.
- Protective Packaging & Dispatch (防护包装与发货): Finished coil packs are protected with VCI (Vapor Corrosion Inhibitor) wrap, foam padding, and wooden or steel crating for safe transportation.
5. Performance Characteristics in Closed Cooling Tower Applications
Based on the referenced study "Performance Analysis of Coil Tube Composite Filling Closed Cooling Tower" (《盘管复合填料型闭式冷却塔性能分析》), the stainless steel coil tube integrated within a composite filling closed cooling tower demonstrates the following performance characteristics:
- Heat Transfer Coefficient (换热系数): Enhanced overall heat transfer coefficient (U-value) of 2,800–3,500 W/(m²·K) compared to conventional bare-tube configurations, achieved through the synergistic interaction between the coil tube's high surface-area geometry and the adjacent composite fill media.
- Cooling Efficiency (冷却效率): Approach temperatures as low as 2–3°C (3.6–5.4°F) between the leaving process fluid and the wet-bulb temperature of the ambient air, representing a significant improvement over open cooling tower configurations.
- Water Conservation (节水性能): Reduction of 70–90% in water consumption compared to open cooling towers, as the closed-loop design eliminates water loss through evaporation, drift, and blowdown of the process fluid.
- Scaling & Foulant Mitigation (防垢与防污): The sealed stainless steel coil tube prevents direct contact between the circulating process fluid and ambient air, thereby eliminating scale formation, biological growth, and chemical contamination on the heat exchange surfaces.
- Thermal Performance Degradation (热性能衰减): Annual degradation rate of less than 2% in heat transfer performance, attributable to the inherent anti-corrosion and anti-scaling properties of the stainless steel material.
6. Applications
The stainless steel coil tube is deployed across a broad spectrum of industrial and commercial applications where closed-loop cooling is required:
- Process Cooling (工艺冷却): Chemical processing, pharmaceutical manufacturing, food and beverage production, and semiconductor fabrication where fluid purity and contamination prevention are critical.
- HVAC Systems (暖通空调系统): Commercial and industrial air conditioning systems requiring efficient chiller condenser and evaporator heat exchange.
- Power Generation (发电): Condenser tubes in thermal and nuclear power plants, as well as heat recovery steam generators (HRSG) in combined cycle power plants.
- Marine & Offshore (海洋与海上): Heat exchangers in marine propulsion systems, offshore oil and gas platforms, and desalination plants where resistance to chloride-induced corrosion is essential.
- Renewable Energy (可再生能源): Concentrated solar power (CSP) plants and geothermal energy conversion systems requiring durable heat exchange components in aggressive thermal environments.
- Textile & Dyeing Industry (纺织与印染行业): Dyeing and finishing equipment where the coil tube provides reliable cooling of process fluids containing dyes, mordants, and chemical auxiliaries.
- Waste Heat Recovery (余热回收): Industrial waste heat recovery systems for energy efficiency improvement and carbon footprint reduction.
7. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management and product certification frameworks to ensure compliance with international standards:
- ISO 9001:2015 — Quality Management System (质量管理体系认证)
- ISO 14001:2015 — Environmental Management System (环境管理体系认证)
- ISO 45001:2018 — Occupational Health and Safety Management System (职业健康安全管理体系认证)
- ASME "S" Stamp — Authorized National Board Registration for pressure vessel and pressure piping components
- ASTM A213 / ASME SA-213 — Seamless austenitic stainless steel tubing for high-temperature service
- EN 10216-5 / EN 10217-7 — European standard for seamless and welded stainless steel tubes for heat exchangers
- GB/T 14976 — Chinese national standard for cold-rolled seamless stainless steel tubes
- GB/T 13296 — Chinese national standard for cold- and hot-rolled stainless steel seamless tubes
- PED 2014/68/EU — European Pressure Equipment Directive compliance for pressure-containing equipment
- NACE MR0175 / ISO 15156 — Compliance for sour service environments (hydrogen sulfide resistance)
- Third-Party Inspection: Available upon request (e.g., Bureau Veritas, DNV, Lloyd's Register, SGS)
8. Unique Selling Points
The stainless steel coil tube offered by Wenzhou Jixing Metal Materials Co., Ltd. distinguishes itself in the global market through several key differentiators:
- Integrated Coil-Pack Assembly: