Stainless Steel Coil Tube for Ice Thermal Energy Storage Systems
Product Code: 1430 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Category: Industrial Tubing & Heat Exchange Components
1. Product Overview
The Stainless Steel Coil Tube (盘管 / Coiltube) is a precision-engineered tubular component designed specifically for use in ice thermal energy storage (TES) systems, particularly coil-type ice storage tanks. These coil tubes serve as the primary heat exchange medium, facilitating the transfer of thermal energy between a refrigerant fluid (typically brine or glycol solution) and the surrounding ice mass within the storage vessel. The helical coil geometry maximizes the surface-area-to-volume ratio, enabling efficient freezing and melting cycles essential for peak-shaving and load-management applications in commercial and industrial HVAC systems.
Based on extensive experimental research into the ice storage mechanism of coil-type tanks, this product has been optimized to address critical performance challenges including uneven ice formation, thermal stratification, and reduced heat transfer efficiency during discharge cycles. The coil tube design incorporates careful consideration of flow velocity, thermal conductivity, and mechanical integrity under repeated freeze-thaw cycles.
2. Material & Properties
2.1 Base Material
- Primary Alloy: Austenitic Stainless Steel — Grade 304 (UNS S30400) or Grade 316L (UNS S31603), selected based on application-specific corrosion resistance requirements.
- Alternative Grades: Grade 321 (UNS S32100) for elevated-temperature service; Grade 316Ti for enhanced strength and corrosion resistance in chlorinated environments.
- Composition (Grade 304): Cr: 18.0–20.0%, Ni: 8.0–10.5%, C: ≤0.08%, Mn: ≤2.0%, Si: ≤0.75%, P: ≤0.045%, S: ≤0.030%, Fe: Balance.
- Composition (Grade 316L): Cr: 16.0–18.0%, Ni: 10.0–14.0%, Mo: 2.0–3.0%, C: ≤0.030%, Mn: ≤2.0%, Si: ≤0.75%, Fe: Balance.
2.2 Mechanical Properties
| Property | Grade 304 | Grade 316L | Test Standard |
|---|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 515 MPa | ≥ 485 MPa | ASTM A240 / GB/T 12771 |
| Yield Strength (屈服强度) | ≥ 205 MPa | ≥ 170 MPa | ASTM A240 / GB/T 12771 |
| Elongation (延伸率) | ≥ 40% | ≥ 40% | ASTM A240 / GB/T 12771 |
| Hardness (硬度, HBW) | ≤ 210 | ≤ 210 | ASTM A240 |
| Thermal Conductivity (热导率, 20°C) | 16.3 W/(m·K) | 14.6 W/(m·K) | ASTM E153 |
| Linear Expansion Coefficient (线膨胀系数) | 16.0 × 10⁻⁶ /°C | 16.5 × 10⁻⁶ /°C | ASTM E228 |
2.3 Corrosion Resistance
- Excellent resistance to atmospheric corrosion, dilute acids, and alkaline solutions.
- Grade 316L offers superior resistance to chloride-induced pitting and crevice corrosion (氯化物点蚀与缝隙腐蚀), critical for brine-based ice storage systems using calcium chloride (CaCl₂) or sodium chloride (NaCl) solutions.
- Passivation treatment per ASTM A967 ensures a stable chromium oxide (Cr₂O₃) film for long-term corrosion protection.
3. Specifications
| Parameter | Specification |
|---|---|
| Tube Outer Diameter (OD) | Φ 12 mm, Φ 16 mm, Φ 19 mm, Φ 25 mm, Φ 32 mm (custom sizes available) |
| Wall Thickness | 0.8 mm – 2.0 mm (typical: 1.0 mm – 1.5 mm) |
| Coil Diameter (螺旋直径) | Φ 200 mm – Φ 800 mm (customizable per tank geometry) |
| Coil Pitch (螺距) | 25 mm – 60 mm (optimized for ice formation uniformity) |
| Coil Turns (圈数) | 10 – 150 turns (determined by storage capacity requirement) |
| Total Tube Length | 5 m – 500 m (per coil assembly) |
| Surface Finish | No. 4 Brushed Finish (Ra ≤ 0.8 μm) or Passivated Finish |
| Connection Type | Flanged (ASME B16.5), Threaded (NPT/BSP), or Welded Ends |
| Operating Temperature | −40 °C to +150 °C |
| Maximum Operating Pressure | 1.6 MPa (standard); 2.5 MPa (reinforced) |
| Design Life | ≥ 20 years (100,000+ freeze-thaw cycles) |
| Standards Compliance | ASTM A269, ASTM A270, GB/T 12771, EN 10216-5, JIS G3459 |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection & Inspection: Cold-rolled stainless steel strip is sourced from certified mills and subjected to spectroscopic analysis (光谱分析) to verify chemical composition. Incoming material undergoes visual inspection, dimensional check, and mechanical property testing.
- Cutting & Preparation: Strip is cut to the required length using precision shearing or laser cutting equipment, with edge quality inspected to prevent defects in downstream forming.
- Forming (Seam Welding): The flat strip is formed into a circular tube using a seam welding machine. The weld seam is ground and polished to achieve a smooth internal surface, minimizing flow resistance and turbulence.
- Helical Coiling (螺旋成型): The straight tube is wound into a helical coil using a CNC-controlled coiling machine. The coil diameter, pitch, and number of turns are precisely controlled to meet design specifications. Spring-back compensation algorithms ensure dimensional accuracy.
- Welding & Assembly: Inlet and outlet connections are welded using TIG (Tungsten Inert Gas) welding with filler metal matched to the base alloy. Weld joints undergo radiographic testing (RT) or dye penetrant inspection (PT) for integrity verification.
- Heat Treatment (if applicable): Stress-relief annealing at 300–400 °C for coiled assemblies to eliminate residual stresses introduced during forming, ensuring dimensional stability during thermal cycling.
- Passivation & Surface Treatment: The completed coil tube is cleaned and passivated using a nitric acid or citric acid-based solution per ASTM A967. A passivation test (ferric sulfate test) confirms the effectiveness of the passive film.
- Pressure Testing: Each coil assembly undergoes hydrostatic pressure testing at 1.5× the maximum operating pressure for a minimum of 30 minutes, with zero leakage tolerance.
- Final Inspection & Packaging: Dimensional verification, visual inspection, and documentation compilation. Coils are packaged with protective end caps and moisture-absorbing desiccants.
4.2 Key Manufacturing Considerations
- Weld Quality: The seam weld and end connections must maintain full penetration without porosity, undercut, or cold laps. Welded joints shall exhibit mechanical properties equivalent to the base material.
- Coil Geometry Precision: Uniform pitch and consistent coil diameter are critical for even ice formation distribution. Deviations exceeding ±2 mm in coil diameter may result in localized ice bridging (冰桥效应), reducing effective heat transfer area.
- Internal Surface Smoothness: The internal surface roughness (Ra) shall not exceed 0.8 μm to minimize pressure drop and fouling potential during prolonged operation with brine solutions.
5. Applications
5.1 Primary Application: Ice Thermal Energy Storage (冰蓄冷系统)
The coil tube is the core heat exchange component in coil-type ice storage tanks (盘管式冰蓄冷箱), which are integral to thermal energy storage systems used for:
- Peak Load Shaving (削峰填谷): Ice is produced during off-peak hours (low electricity tariff periods) and melted during peak demand hours, reducing building cooling load and electricity costs by 20–40%.
- Emergency Backup Cooling: Ice storage provides thermal inertia for continued cooling during power outages or chiller failures, typically sustaining 4–12 hours of cooling capacity.
- Grid Load Management: Reduces peak electrical demand on the grid, supporting utility demand-response programs.
5.2 Experimental Research Context
Research on the ice storage mechanism of coil-type tanks (盘管式冰蓄冷箱蓄冷机理实验研究) has identified several key performance factors that inform the design and optimization of coil tubes:
- Ice Formation Pattern: Ice grows radially outward from the tube surface, forming a layered structure. The coil pitch and flow velocity determine whether uniform ice blankets form or localized ice fingers develop.
- Heat Transfer Degradation: As ice thickness increases, thermal resistance rises, reducing the heat transfer rate. Optimal coil design balances ice storage capacity with acceptable discharge rates.
- Flow Distribution: Uniform flow distribution across all coil turns is essential. Design features such as manifold configurations and inlet/outlet positioning are critical.
- Freeze-Thaw Cycle Fatigue: The cyclic thermal stress imposed by repeated freeze-thaw operations must be accommodated by the tube material and weld joints without fatigue failure.
5.3 Other Applications
- Industrial process heat exchange (chemical, pharmaceutical, food processing)
- Cooling systems for commercial refrigeration and cold storage facilities
- Heat recovery systems in waste-to-energy plants
- Geothermal energy extraction systems
- Cryogenic applications (liquid nitrogen, liquid oxygen storage and transfer)
6. Quality Certifications & Standards
6.1 Manufacturing Certifications
- 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 — European Conformity (European Union compliance)
- PED (Pressure Equipment Directive 2014/68/EU) — For pressure-containing coil assemblies
6.2 Product Standards
- ASTM A269/A269M — Standard Specification for Welded Austenitic Stainless Steel Seamless and Welded Tubes for Chemical and Similar Severe Service
- ASTM A270/A270M — Standard Specification for Austenitic Stainless Steel and Heat-Resisting Chromium-Chromium-Nickel Stainless Steel Seamless, Welded, and Heavy-Walled Tubes
- GB/T 12771-2019 — Stainless Steel Seamless Tubes for General Purposes (中国国家标准)
- EN 10216-5 — Non-Heat-Resisting and Heat-Resisting Stainless Steel Tubes for Mechanical and Technical Uses
- JIS G3459 — Specification for Seamless Stainless Steel Tubes for General Use
6.3 Testing & Inspection Protocols
| Test Type | Method | Acceptance Criteria |
|---|---|---|
| Chemical Composition | OES Spectroscopy (ASTM E415) | Within specified grade limits |
| Mechanical Properties | Tensile Test (ASTM E8) | Meets minimum values per ASTM A240 |
| Weld Integrity |