Stainless Steel Coil Tube for Thermal Energy Storage Systems
Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular component designed primarily for thermal energy storage (TES) applications, particularly in ice-melting and ice-harvesting systems. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd, this product is constructed from high-grade austenitic stainless steel and is wound into a continuous helical coil configuration to maximize heat transfer surface area within a compact volumetric footprint.
The design and performance characteristics of this coil tube are informed by advanced research into the dynamic characteristics of ice melting in external coil tube configurations for thermal energy storage (外融冰盘管蓄冷动态特性研究). This foundational study addresses the transient heat transfer behavior, ice accretion dynamics, and melt-down kinetics that govern the efficiency and reliability of coil-based thermal storage systems. The resulting product is optimized for both charge (freezing) and discharge (melting) cycles, ensuring consistent thermal performance over thousands of operational cycles.
Coil tubes of this type serve as the core heat exchange element in latent heat thermal energy storage (LHTES) systems, where phase-change materials (PCMs)—most commonly water/ice—are used to store and release thermal energy. The helical winding geometry promotes turbulent flow on the fluid side, enhancing convective heat transfer coefficients and reducing the overall thermal resistance of the system.
Material & Properties
Base Material Composition
The coil tube is fabricated from austenitic stainless steel, with the primary grade being SUS304 (ASTM A269 TP304), supplemented by SUS316L (ASTM A269 TP316L) for applications requiring enhanced corrosion resistance. The material selection is driven by the demanding operational environment of thermal energy storage systems, which may involve repeated freeze-thaw cycles, exposure to glycol-based heat transfer fluids, and long-term immersion in aqueous environments.
- SUS304 / ASTM TP304: Contains approximately 18% Chromium (Cr) and 8% Nickel (Ni), providing excellent general corrosion resistance, formability, and weldability. Suitable for potable water systems and standard thermal storage applications.
- SUS316L / ASTM TP316L: Contains 16–18% Cr, 10–14% Ni, and 2–3% Molybdenum (Mo), with ultra-low carbon content (≤0.03%). The addition of Molybdenum provides superior resistance to pitting and crevice corrosion, making it ideal for applications involving chlorinated water or aggressive chemical environments.
Key Mechanical and Physical Properties
| Property | SUS304 | SUS316L |
|---|---|---|
| Tensile Strength (抗拉强度) | ≥515 MPa | ≥485 MPa |
| Yield Strength (屈服强度) | ≥205 MPa | ≥170 MPa |
| Elongation (延伸率) | ≥40% | ≥45% |
| Density (密度) | 7.93 g/cm³ | 8.00 g/cm³ |
| Thermal Conductivity at 20°C (热导率) | 16.3 W/(m·K) | 14.6 W/(m·K) |
| Thermal Conductivity at 100°C (热导率) | 21.6 W/(m·K) | 19.8 W/(m·K) |
| Thermal Conductivity at 200°C (热导率) | 25.1 W/(m·K) | 24.2 W/(m·K) |
| Specific Heat Capacity (比热容) | 500 J/(kg·K) | 500 J/(kg·K) |
| Thermal Expansion Coefficient (热膨胀系数) | 16.0 × 10⁻⁶ /K | 16.0 × 10⁻⁶ /K |
| Operating Temperature Range (工作温度范围) | −196°C to +870°C | −196°C to +870°C |
Corrosion Resistance Performance
The austenitic microstructure of these stainless steel grades provides inherent resistance to oxidation and corrosion across a wide range of environments. In the context of thermal energy storage systems, the following corrosion resistance characteristics are particularly significant:
- Freeze-thaw resistance: The material maintains structural integrity and surface finish through repeated freeze-thaw cycles, with no degradation in mechanical properties down to −196°C (Liquid Nitrogen Temperature).
- Glycol compatibility: Full compatibility with ethylene glycol (EG) and propylene glycol (PG) heat transfer fluids at concentrations up to 60% by volume.
- Pitting resistance: SUS316L achieves a PREN (Pitting Resistance Equivalent Number, 点蚀当量值) of ≥24, providing robust protection against chloride-induced pitting.
Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD, 外径) | 6.0 mm – 25.4 mm (1/4" – 1") |
| Wall Thickness (壁厚) | 0.5 mm – 2.0 mm |
| Coil Diameter (盘管直径) | 150 mm – 1,200 mm (configurable) |
| Coil Length (盘管长度) | Up to 2,000 meters per continuous coil |
| Winding Pitch (绕距) | 1.2 × OD – 2.5 × OD (adjustable based on heat transfer requirements) |
| Surface Finish (表面光洁度) | Ra ≤ 0.8 μm (polished); Ra ≤ 1.6 μm (pickled) |
| End Configuration (端部形式) | Plain, threaded (NPT/BSP), flanged, or soldered |
| Maximum Working Pressure (最大工作压力) | Up to 4.0 MPa (dependent on OD and wall thickness) |
| Hydrostatic Test Pressure (水压试验压力) | 1.5 × Maximum Working Pressure |
| Heat Transfer Fluid (传热流体) | Water, Glycol-Water Mixtures, Brine Solutions |
| Phase Change Medium (相变介质) | Water/Ice (Standard); Custom PCM configurations available |
| Applicable Standards (适用标准) | ASTM A269, ASTM A270, GB/T 12771, GB/T 14976 |
Manufacturing Process
The manufacturing of stainless steel coil tubes for thermal energy storage applications follows a rigorous multi-stage process designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
-
Material Selection and Incoming Inspection (选材与来料检验):
Stainless steel seamless tubes conforming to ASTM A269 or ASTM A270 are procured from certified mills. Each batch undergoes spectrographic analysis (光谱分析) to verify chemical composition, along with mechanical testing including tensile testing, hardness testing, and Charpy impact testing. -
Heat Treatment (热处理):
The tube stock is solution-annealed (固溶退火) at temperatures between 1040°C and 1150°C, followed by rapid quenching in water or air. This process dissolves carbide precipitates, restores full austenitic structure, and ensures maximum corrosion resistance and ductility. -
Precision Forming and Coil Winding (精密成型与盘绕):
Computer Numerically Controlled (CNC) winding equipment is used to form the straight tube into the specified helical coil geometry. The winding parameters—including coil diameter, pitch, and winding angle—are precisely controlled to ensure uniform spacing and consistent heat transfer characteristics throughout the coil length. Special attention is given to maintaining the tube's cross-sectional geometry during bending to avoid ovality (椭圆度) exceeding 1% of the nominal OD. -
Welding (焊接):
Where coil sections require joining, orbital automatic welding (自动轨道焊接) is employed using argon gas shielding. Weld parameters are optimized to minimize heat-affected zone (HAZ, 热影响区) sensitization. Post-weld annealing (焊后退火) may be applied to restore corrosion resistance in the HAZ. -
Pickling and Passivation (酸洗钝化):
The finished coil undergoes chemical pickling to remove scale, discoloration, and surface contaminants. Subsequent passivation treatment forms a stable chromium oxide (Cr₂O₃) passive film on the surface, enhancing long-term corrosion resistance. -
Surface Finishing (表面处理):
For applications requiring enhanced heat transfer performance or hygienic standards, the coil surface may be mechanically polished to achieve a Ra ≤ 0.8 μm finish. Electropolishing (电解抛光) is available upon request for critical applications. -
Quality Inspection and Testing (质量检测):
Each coil undergoes comprehensive final inspection including:- Dimensional verification (尺寸检测) using laser scanning or coordinate measuring machines (CMM)
- Hydrostatic pressure testing (水压试验) at 1.5× working pressure for a minimum of 5 minutes
- Visual inspection (目视检查) for surface defects, weld integrity, and coating uniformity
- Non-Destructive Testing (NDT, 无损检测) including dye penetrant testing (PT, 渗透检测) or eddy current testing (ECT, 涡流检测) for internal and external defect detection
Applications
The stainless steel coil tube is designed for a broad spectrum of thermal energy storage and heat exchange applications:
Primary Applications
-
Ice-Harvesting Thermal Energy Storage (蓄冷系统):
The primary application domain. The coil tube is immersed in a tank containing water, through which a refrigerant or chilled brine circulates. During the charging phase, the water surrounding the coil freezes, forming an ice layer. During discharge, the ice melts as warm fluid circulates through the coil, releasing stored thermal energy. The dynamic characteristics of this process—including ice growth kinetics, melt-down rates, and thermal stratification—are optimized through careful coil geometry design. -
Ice-Melting Thermal Energy Storage (外融冰盘管蓄冷):
In external ice-melting configurations, the coil tube is positioned within a structured ice matrix. Research into the dynamic characteristics of this configuration (外融冰盘管蓄冷动态特性研究) has informed the design parameters—particularly coil pitch, tube diameter, and flow velocity—to maximize the rate of heat extraction during the melting phase while minimizing thermal losses. -
Cold Chain and Refrigeration Systems (冷链与制冷系统):
Used as evaporator coils in walk-in cold rooms, blast freezers, and refrigerated transport containers. The stainless steel construction ensures hygiene compliance and resistance to the corrosive effects of low-temperature refrigerants. -
Process Heat Recovery (工艺余热回收):
Deployed in industrial processes where waste heat needs to be captured and stored for later use, contributing to energy efficiency and carbon reduction goals.
Industry Segments
- Commercial HVAC (Building Energy Management, 建筑能源管理)
- Industrial Process Cooling (工业过程冷却)
- Food and Beverage Processing (食品加工)
- Pharmaceutical Manufacturing (制药生产)
- Renewable Energy Integration — Solar Thermal Storage (可再生能源集成 — 太阳能蓄热)
Quality Certifications and Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management system and holds the following certifications:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System (质量管理体系) |
| ISO 14001:2015 | Environmental Management System (环境管理体系) |
| ISO 45001:2018 | Occupational Health and Safety Management System (职业健康安全管理体系) |
| CE Marking (欧盟CE认证) | Compliance with European Union directives for pressure equipment (PED 2014/68/EU) |
| TUV Certification (TUV认证) | Independent third-party quality and safety assessment |
| GB/T 19001-2016 | Chinese National Standard for Quality Management Systems |
Product-Specific Compliance
- Material Compliance: ASTM A269 (Welded Austenitic Stainless Steel Tubes for Chemical Service), ASTM A270 (Welded Austenitic Chromium and Chromium-Nickel Stainless Steel Tubing for General Applications)
- Pressure Vessel Standards: GB/T 150 (Pressure Vessels), ASME Section VIII Division 1 (where applicable for integrated system components)