Stainless Steel Coil Tube for District Cooling Ice-Storage Systems
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Series: No. 285 — Coil Tube (Coiltube)
Category: Literature-Based Engineering Reference Product
1. Product Overview
The Stainless Steel Coil Tube is a precision-engineered heat-exchange component designed primarily for District Cooling Systems (区域供冷系统), particularly within ice-storage thermal energy systems. In these applications, coil tubes are submerged within a water pool or tank to facilitate the storage and controlled release of cooling energy through a process known as External Ice-Melting Cooling Release (外融冰释冷). The coil tube serves as the critical interface between the refrigerant or chilled water circuit and the thermal storage medium, enabling efficient thermal transfer during both the charging (freezing) and discharging (ice-melting) phases of the system cycle.
This product line is developed based on extensive experimental research into the cooling-release characteristics of external ice-melting water pools, incorporating validated performance parameters to ensure optimal thermal efficiency, structural integrity, and long-term reliability under cyclic thermal stress conditions.
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from high-grade Stainless Steel (不锈钢), with the following material options available:
- Grade 304 (UNS S30408): The standard austenitic stainless steel offering excellent general corrosion resistance, formability, and weldability. Suitable for most district cooling applications where chloride exposure is minimal.
- Grade 316 (UNS S31603): Enhanced austenitic stainless steel with added molybdenum (2.0–3.0% Mo), providing superior resistance to pitting and crevice corrosion in chloride-containing environments. Recommended for coastal or industrial applications.
- Grade 316L (UNS S31603L): Low-carbon variant of Grade 316 with carbon content ≤0.03%, optimized for welded applications to prevent intergranular corrosion sensitization during welding processes.
2.2 Key Physical and Mechanical Properties
| Property | Grade 304 | Grade 316 / 316L |
|---|---|---|
| Chromium Content (Cr) | 18.0–20.0% | 16.0–18.0% |
| Nickel Content (Ni) | 8.0–10.5% | 10.0–14.0% |
| Molybdenum Content (Mo) | — | 2.0–3.0% | Carbon Content (C) | ≤0.08% | ≤0.03% (316L) / ≤0.08% (316) |
| Tensile Strength (Rm) | ≥515 MPa | ≥485 MPa |
| Yield Strength (Rp0.2) | ≥205 MPa | ≥170 MPa |
| Elongation (A) | ≥40% | ≥35% |
| Density | ~7.93 g/cm³ | ~8.00 g/cm³ |
| Thermal Conductivity (25°C) | ~16.3 W/(m·K) | ~14.6 W/(m·K) |
| Operating Temperature Range | −196°C to +870°C | −196°C to +870°C |
2.3 Corrosion Resistance
The austenitic stainless steel microstructure, stabilized by the chromium oxide passive film (Cr2O3), provides outstanding resistance to:
- General aqueous corrosion in freshwater and brackish water environments
- Pitting and crevice corrosion in chloride-bearing solutions (particularly for Grade 316/316L)
- Intergranular corrosion following appropriate heat treatment or use of low-carbon grades
- Scaling and fouling under thermal cycling conditions in ice-storage applications
3. Specifications
3.1 Geometric and Dimensional Specifications
| Parameter | Specification |
|---|---|
| Tube Outer Diameter (OD) | 12 mm – 50 mm (customizable) |
| Tube Wall Thickness | 0.5 mm – 3.0 mm |
| Coil Pitch (Spacing Between Turns) | 15 mm – 80 mm (design-dependent) |
| Coil Overall Diameter | 200 mm – 2000 mm (customizable) |
| Coil Length / Number of Turns | Custom-engineered per system requirements |
| Surface Finish (Roughness) | Ra ≤ 0.8 μm (standard); Ra ≤ 0.4 μm (polished) |
| End Connection Types | Threaded (BSP/NPT), Flanged (ANSI/GB), Welded, Grooved |
| Dimensional Tolerance | ±0.05 mm (OD), ±0.02 mm (wall thickness) |
3.2 Performance Specifications
| Parameter | Specification |
|---|---|
| Design Pressure | 0.6 MPa – 2.5 MPa (configurable) |
| Design Temperature | −10°C to +60°C (standard district cooling) |
| Thermal Transfer Coefficient | 800 – 1500 W/(m²·K) (depending on flow regime) |
| Flow Velocity (Inside Tube) | 1.5 – 3.5 m/s (recommended range) |
| Reynolds Number Range | Re > 10,000 (turbulent flow ensured) |
| Design Service Life | ≥ 25 years under normal operating conditions |
| Ice-Melting Cooling Efficiency | ≥ 90% thermal release efficiency (validated experimentally) |
3.3 Compliance Standards
| Standard | Scope |
|---|---|
| ASTM A213 / A269 | Seamless and welded austenitic stainless steel tubing |
| EN 10216-5 | Welded stainless steel tubes for heat exchangers |
| GB/T 12771 | Chinese national standard for welded stainless steel tubes |
| GB/T 14976 | Seamless stainless steel tubes for general engineering |
| ASME B31.5 | Pressure piping for refrigeration and air-conditioning |
| ISO 1127 | Dimensions and tolerances for stainless steel tubes |
4. Manufacturing Process
4.1 Raw Material Procurement
Stainless steel strip or seamless tube blanks are procured from certified mills with full chemical composition analysis and mechanical property documentation. Each batch undergoes incoming inspection including spectroscopic analysis to verify elemental composition within specified limits.
4.2 Tube Forming
- Coil Winding: The stainless steel tube is precision-wound using CNC-controlled coil winding machines to achieve exact pitch, diameter, and number of turns as specified in the engineering design. The winding process maintains uniform tension to prevent ovality and distortion.
- Support Structure Integration: Internal support rings or wire-form supports are installed at calculated intervals to prevent tube collapse or vibration under differential pressure conditions during operation.
- End Fitting Installation: Inlet and outlet connections are welded or threaded onto the coil ends using precision fixtures to ensure alignment and minimize stress concentrations.
4.3 Welding
Welding operations are performed using one of the following methods:
- TIG Welding (GTAW): Tungsten Inert Gas welding with argon shielding for all stainless steel joints, ensuring clean, high-quality welds with minimal oxidation.
- Orbital Welding: Automated orbital welding for critical connections, providing consistent weld quality and traceability.
All welds are performed with appropriate pre- and post-weld heat treatment protocols to prevent sensitization and ensure mechanical integrity.
4.4 Post-Processing
- Pickling and Passivation: Removal of weld scale and formation of a uniform chromium oxide passive layer to maximize corrosion resistance.
- Surface Cleaning: Mechanical or chemical cleaning to achieve the specified surface roughness (Ra value).
- Hydrostatic Pressure Testing: Each coil tube is pressure-tested at 1.5× the design pressure for a minimum of 30 minutes to verify integrity and absence of leaks.
- Dimensional Inspection: Final verification of coil geometry, pitch accuracy, and overall dimensions against design drawings.
5. Applications
5.1 Primary Application: District Cooling Ice-Storage Systems
The core application of this coil tube product is in District Cooling Systems utilizing ice-storage thermal energy technology. The system operates on the principle of External Ice-Melting Cooling Release (外融冰释冷), where:
- Charging Phase: The coil tube circulates refrigerant or sub-zero brine, causing ice to form on the external surface of the tube within the storage pool.
- Discharging Phase: Chilled water is circulated through the coil tube, absorbing heat from the surrounding ice as it melts, thereby releasing stored cooling energy to the building or district cooling network.
Experimental research has validated that the cooling-release efficiency of external ice-melting water pool systems reaches or exceeds 90%, with the coil tube geometry and material properties being critical determinants of overall system performance.
5.2 Additional Applications
- Chilled Water Heat Exchangers: Indirect heat exchange in commercial and industrial HVAC systems.
- Thermal Energy Storage Tanks: Hot water or cold water storage systems requiring high corrosion resistance.
- Process Cooling Systems: Industrial applications in food processing, pharmaceutical manufacturing, and chemical processing where hygienic, corrosion-resistant heat transfer is required.
- Marine and Offshore Cooling: Applications exposed to saline or brackish water environments where Grade 316/316L is specified.
- Geothermal Heat Pump Systems: Submerged coil configurations for ground-source or water-source heat exchange.
6. Quality Certifications
6.1 Manufacturing Certifications
| Certification | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent product quality and continuous improvement |
| ISO 14001:2015 | Environmental Management System certification |
| CE Marking | Conformity with European Union directives for machinery and pressure equipment |
| PED (2014/68/EU) | Pressure Equipment Directive compliance for pressure-rated applications |
| GB/T 19001 | Chinese national quality management system standard |
6.2 Product Testing and Verification
- Chemical Composition Analysis: Spectroscopic verification of all alloying elements per ASTM/EN/GB standards
- Mechanical Testing: Tensile testing, hardness testing, and impact testing on material samples
- Hydrostatic Pressure Testing: 100% inspection at 1.5× design pressure
- Visual and Dye Penetrant Testing (PT): Surface inspection of all welds and critical areas
- Dimensional Inspection: Precision measurement of coil geometry, pitch, and connection dimensions
- Thermal Performance Testing: Laboratory validation of heat transfer coefficients and cooling-release efficiency
- Cyclic Fatigue Testing: Verification of structural integrity over 25+ year design life under thermal cycling
6.3 Traceability and Documentation
Each coil tube product is accompanied by a comprehensive Material Test Certificate (MTC) and Product Data Sheet providing full traceability from raw material mill certification through manufacturing, testing, and final inspection. This documentation ensures compliance with international project requirements and facilitates owner's engineering review and approval.
7. Unique Selling Points
- Experimentally Validated Performance: Product design is informed by rigorous experimental research on external ice-melting water pool cooling-release characteristics, ensuring that the coil tube geometry and material selection deliver proven thermal efficiency in real-world district cooling applications.
- Superior Corrosion Resistance: Grade 316L stainless steel construction provides exceptional longevity in water-based thermal storage environments, significantly reducing maintenance requirements and extending service life beyond 25 years.
- Precision Engineering: CNC-controlled coil winding ensures exact geometric accuracy, which is critical for achieving uniform ice formation and melting patterns around the tube surface, directly impacting cooling-release efficiency.
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