Stainless Steel Coiltube (盘管) — Internal-Melting Ice Coil Tube System
1. Product Overview
The Stainless Steel Coiltube (盘管 / Coil Tube), as manufactured by Wenzhou Jixing Metal Materials Co., Ltd, is a precision-engineered tubular product designed for thermal energy storage (TES) systems, particularly those utilizing ice-based latent heat storage technology. This product line encompasses both fully frozen (complete freezing) and partially frozen (incomplete freezing) internal-melting ice coil configurations, offering versatile solutions for energy-efficient cooling applications.
The coil tube architecture is specifically optimized for internal melting ice storage (Internal-Melting Ice Storage, IMIS) systems, where the stainless steel coil serves as the structural and thermal exchange medium within a frozen ice matrix. The design ensures superior heat transfer efficiency during both the freezing (charging) and melting (discharging) cycles, addressing the critical comparison between complete freezing and incomplete freezing operational modes.
Key performance differentiators of this product include:
- Enhanced thermal conductivity through optimized coil geometry and wall thickness
- Resistance to freeze-thaw cycling degradation, ensuring long-term structural integrity
- Adaptability to both full-freeze and partial-freeze operational regimes
- Corrosion-resistant stainless steel construction suitable for aqueous and brine environments
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from Stainless Steel (奥氏体不锈钢), predominantly utilizing the following grades:
- SUS304 / AISI 304 (06Cr19Ni10): General-purpose grade offering excellent corrosion resistance and formability
- SUS316 / AISI 316 (06Cr17Ni12Mo2): Enhanced molybdenum content for superior resistance to chloride-induced pitting corrosion
- SUS321 / AISI 321 (06Cr18Ni11Ti): Titanium-stabilized grade suitable for elevated temperature applications
2.2 Mechanical Properties
| Property | Specification (SUS304 Grade) | Test Standard |
|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 520 MPa | ASTM A270 / GB/T 12771 |
| Yield Strength (屈服强度) | ≥ 205 MPa | ASTM A270 / GB/T 12771 |
| Elongation (延伸率) | ≥ 40% | ASTM A270 / GB/T 12771 |
| Hardness (硬度) | ≤ 92 HRB | ASTM A270 / GB/T 12771 |
| Cold Bend (冷弯试验) | 180° bend, no cracking at 3D | GB/T 12451 |
2.3 Thermal Properties
| Property | Value | Relevance to Ice Coil Application |
|---|---|---|
| Thermal Conductivity (热导率) | 16.3 W/(m·K) at 20°C | Ensures efficient heat transfer between coil fluid and ice matrix |
| Thermal Expansion Coefficient (热膨胀系数) | 17.3 × 10⁻⁶ /°C | Compatible with volumetric expansion of water/ice (9% volume increase) |
| Specific Heat Capacity (比热容) | 500 J/(kg·K) | Contributes to thermal mass during freeze-thaw cycles |
2.4 Corrosion Resistance
The stainless steel coil tube demonstrates exceptional resistance to:
- Freeze-thaw cycling: Maintains mechanical integrity over 10,000+ cycles without microcrack initiation
- Aqueous corrosion: Suitable for direct contact with water, brine solutions (NaCl, CaCl₂), and glycol-based coolants
- Chloride pitting: SUS316 grade achieves > 1,000 hours without pitting in 3.5% NaCl solution at 60°C
- Stress corrosion cracking (SCC): Austenitic microstructure provides inherent resistance to chloride-induced SCC
3. Specifications
3.1 Geometric Specifications
| Parameter | Standard Range | Custom Range | Unit |
|---|---|---|---|
| Outer Diameter (外径, OD) | 12 – 108 | 6 – 219 | mm |
| Wall Thickness (壁厚) | 0.5 – 4.0 | 0.3 – 8.0 | mm |
| Coil Diameter (盘管外径) | 300 – 3,000 | 200 – 6,000 | mm |
| Coil Length / Spool Length (盘长) | 50 – 500 | 30 – 1,000 | m |
| Coil Pitch (螺距) | 15 – 80 | 10 – 150 | mm |
| Surface Finish (表面光洁度) | Ra ≤ 1.6 μm (BA) | Ra ≤ 0.4 μm (Electropolished) | μm |
3.2 Performance Specifications for Ice Coil Application
| Performance Parameter | Complete Freezing Mode (完全冻结) | Incomplete Freezing Mode (不完全冻结) |
|---|---|---|
| Freezing Temperature Range (冻结温度范围) | −2°C to −10°C | −2°C to −5°C |
| Ice Formation Degree (结冰率) | ≥ 95% | 60% – 85% |
| Heat Transfer Coefficient (传热系数) | 800 – 1,200 W/(m²·K) | 1,000 – 1,500 W/(m²·K) |
| Freezing Time (冻结时间) | 4 – 6 hours | 2 – 3 hours |
| Melting Time (融化时间) | 6 – 8 hours | 3 – 5 hours |
| Cycle Efficiency (循环效率) | 90% – 95% | 85% – 92% |
4. Manufacturing Process
4.1 Process Flow
- Material Selection & Inspection (原材料选择与检验): Incoming stainless steel strip/sheet is verified for chemical composition (via OES spectroscopy), mechanical properties, and surface quality per ASTM A240 or GB/T 4237.
- Slitting & Edge Trimming (分条与修边): Strip is slit to precise coil tube width with edge burr removal to ensure uniform weld quality.
- Cold Forming / Roll Forming (冷成型/辊压成型): Precision roll-forming machines shape the strip into seamless or welded tube profiles with controlled dimensional tolerances (±0.1 mm).
- Welding (焊接) (if applicable): Automatic orbital or helical welding with argon shielding (TIG/Orbital welding per ASME B31.3) produces full-penetration welds with controlled heat input to minimize sensitization.
- Coiling / Spiral Winding (盘绕成型): The straight tube is coiled onto precision mandrels to achieve specified coil diameter and pitch. Uniform tension control prevents ovality and deformation.
- Pickling & Passivation (酸洗钝化): Hydrochloric or citric acid pickling removes heat-affected zones; subsequent passivation with nitric or citric acid forms a stable chromium oxide protective layer.
- Surface Treatment (表面处理): Optional electropolishing (电解抛光) achieves Ra ≤ 0.4 μm finish, critical for reducing fouling in ice storage applications.
- Quality Inspection (质量检验): Multi-stage inspection including dimensional verification, hydrostatic testing (hydro test at 1.5× working pressure), eddy current testing for weld integrity, and surface defect detection.
- Packaging & Marking (包装与标识): Coils are wrapped in protective film, wooden pallets, or custom crates with moisture-absorbing desiccants. Each coil is marked with product identification, heat number, and traceability codes.
4.2 Special Considerations for Ice Coil Tubes
The manufacturing process for ice coil tubes incorporates additional controls not required for standard coil tube production:
- Controlled deformation rates during coiling to prevent residual stress concentrations that could initiate cracking under thermal cycling
- Enhanced weld quality — full radiographic testing (RT) or ultrasonic testing (UT) of all welds to ensure zero-defect integrity under freeze-thaw conditions
- Post-coil stress relief annealing (optional) at 1050°C followed by rapid water quenching to restore full solution-annealed microstructure
- Dimensional consistency — tight tolerance control on coil pitch and diameter to ensure uniform ice contact and predictable thermal performance
5. Applications
5.1 Primary Applications
- Ice Thermal Energy Storage (Ice TES) Systems: The primary application domain, where the coil tube serves as the heat exchange medium within frozen ice tanks. Complete freezing mode is employed for maximum energy density, while incomplete freezing mode provides faster response times for peak-shaving applications.
- Commercial Refrigeration (商业制冷): Supermarket cold chain systems, walk-in freezers, and cold storage warehouses utilizing ice storage for load shifting.
- Building HVAC Systems (建筑暖通空调): District cooling networks and large commercial buildings using ice storage for nighttime charging and daytime cooling delivery.
- Industrial Process Cooling (工业过程冷却): Metalworking, food processing, and chemical industries requiring stable cold supply with reduced peak electrical demand.
- Emergency Cooling Systems (应急冷却系统): Data centers, hospitals, and critical infrastructure requiring reliable backup cooling independent of grid stability.
5.2 Operational Modes Comparison
| Criteria | Complete Freezing (完全冻结) | Incomplete Freezing (不完全冻结) |
|---|---|---|
| Energy Density (能量密度) | High (maximum ice formation) | Medium (partial ice formation) |
| System Response Speed (系统响应速度) | Slower (full melting required) | Faster (ice slurry circulation) |
| Equipment Complexity (设备复杂度) | Lower | Higher (ice slurry pump required) |
| Applicable Cooling Load (适用冷负荷) | Steady-state base load | Peak-shaving / transient load |
| Long-term Reliability (长期可靠性) | Excellent (stable solid-ice interface) | Good (requires pump maintenance) |
6. Quality Certifications & Standards Compliance
6.1 Applicable Standards
- GB/T 12771 — Stainless steel seamless tubes for general purposes (中国国家标准)
- GB/T 14976 — Cold-rolled stainless steel seamless tubes
- GB/T 14975 — Cold-rolled stainless steel welded tubes
- ASTM A270 — Standard specification for austenitic stainless steel seamless, welded and heavy-wall welded tubes
- ASTM A312 — Standard specification for austenitic stainless steel seamless, welded and heavy-wall welded pipe, tubes and fittings
- EN 10217-7 — Stainless steel cold-drawn seamless tubes for pressure purposes
- JIS G3459 — Stainless steel seamless tubes for general use
6.2 Quality Certifications
- ISO 9001:2015 — Quality Management System certification
- ISO 14001:2015 — Environmental Management System certification
- CE Marking — Conformity with European directives for pressure equipment (PED 2014/68/EU)
- Material Test Reports (MTR) — Full chemical composition and mechanical property documentation for each heat lot
- Mill Test Reports (MTR) — Traceability from raw material through final product
6.3 Inspection & Testing Protocols
- Hydrostatic Testing (水压试验): 100% of coils tested at 1.5× maximum working pressure, minimum 10 seconds hold time
- Dimensional Inspection (尺寸检验): OD, wall thickness, coil diameter, pitch — verified per GB/T 12451 sampling protocols
- Surface Quality Inspection (表面质量检验): Visual and dye penetrant testing (PT) for surface defects
- Weld Integrity Testing (焊缝完整性检验): Eddy current testing (ET) or ultrasonic testing (UT) for welded products
- Chemical Analysis (化学成分分析): OES or ICP verification of Cr, Ni, Mo