Stainless Steel Coil Tube for Thermal Energy Storage Systems
Product Overview
The Stainless Steel Coil Tube (Coiltube), as manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered product designed for advanced thermal energy storage (TES) applications, particularly in ice-storage systems. These coil tubes serve as the primary heat exchange elements within coiled tube thermal storage containers, enabling efficient phase-change heat transfer between the working fluid and the ice/water medium. The product is engineered to withstand cyclic thermal stresses, cryogenic temperatures, and prolonged immersion in aqueous environments, making it an indispensable component in commercial and industrial cooling infrastructure.
Based on rigorous simulation and calculation studies of the ice-storage process in coiled tube thermal energy storage containers, the design parameters of these coil tubes are optimized for maximum volumetric heat transfer efficiency, minimal pressure drop, and long-term structural integrity under repeated freeze-thaw cycles.
Material & Properties
The coil tubes are fabricated from high-grade austenitic stainless steel, selected for superior corrosion resistance, cryogenic toughness, and dimensional stability under thermal cycling.
- Base Material: Austenitic Stainless Steel (奥氏体不锈钢)
- Standard Grades: AISI 304 (UNS S30400), AISI 316L (UNS S31603), or custom duplex grades upon request
- Cryogenic Performance: Maintains ductility and fracture toughness down to −196°C (liquid nitrogen temperature range)
- Corrosion Resistance: Excellent resistance to pitting, crevice corrosion, and chloride-induced stress corrosion cracking (SCC)
- Thermal Conductivity: Approximately 14–16 W/(m·K) for 304 grade, providing adequate heat transfer rates for ice-storage applications
- Surface Finish: Electropolished or mechanically polished to achieve Ra ≤ 0.4 μm, minimizing fouling and biofilm accumulation
- Chemical Composition (AISI 304): C ≤ 0.08%, Mn ≤ 2.0%, Si ≤ 1.0%, Cr 18.0–20.0%, Ni 8.0–10.5%, S ≤ 0.030%
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 12 mm – 60 mm (customizable) | ASME B36.19M |
| Wall Thickness (WT) | 0.8 mm – 3.0 mm | ASME B36.19M |
| Coil Pitch / Spacing | 15 mm – 80 mm (design-dependent) | Project-specific simulation |
| Coil Diameter | 300 mm – 3000 mm | Custom fabrication |
| Number of Coils per Unit | 1 – 200 (system-dependent) | Thermal design calculation |
| Operating Temperature Range | −40°C to +120°C | Material datasheet |
| Maximum Working Pressure | 1.6 MPa – 6.3 MPa | ASME BPV Code / PED |
| Ice Storage Capacity (per container) | 50 kWh – 50,000 kWh | Thermodynamic simulation |
| Heat Transfer Coefficient | 200 – 800 W/(m²·K) (tube-side) | Empirical correlation (Dittus-Boelter) |
| Design Service Life | ≥ 25 years | ISO 15649 |
| Welding Method | Orbital TIG (GTAW) / Laser welding | ASME Section IX |
| Surface Treatment | Passivation (ASTM A967), pickling | ASTM A380 |
Manufacturing Process
The production of stainless steel coil tubes for thermal storage applications follows a multi-stage, tightly controlled manufacturing workflow:
- Material Selection and Incoming Inspection: Stainless steel seamless tubes are procured from certified mills and subjected to spectrographic analysis, hydrostatic testing, and dimensional verification per ASTM A269/A270.
- Thermal Simulation and Design Optimization: Using computational fluid dynamics (CFD) and thermodynamic modeling, the coil geometry—including pitch, diameter, number of turns, and inlet/outlet configuration—is optimized to maximize ice formation efficiency while minimizing pumping power. The simulation accounts for natural convection effects in the water/ice medium and transient heat flux distributions.
- Cutting and Forming: Tubes are cut to precise lengths using plasma or laser cutting, followed by cold coiling on precision mandrels to achieve the designed coil geometry without introducing residual stresses or work hardening.
- Welding: Inlet and outlet headers are connected via orbital TIG welding (GTAW) or laser welding, ensuring full penetration, minimal heat-affected zone (HAZ), and preservation of the base metal's metallurgical properties.
- Post-Weld Heat Treatment (PWHT): Solution annealing at 1050°C–1150°C followed by water quenching to restore full austenitic structure and eliminate residual stresses.
- Surface Finishing: Mechanical polishing and/or electropolishing to achieve mirror-like surface finish (Ra ≤ 0.4 μm), reducing hydraulic resistance and preventing scale deposition.
- Passivation and Cleaning: Acid pickling and passivation per ASTM A967 to restore and enhance the chromium oxide protective layer.
- Pressure Testing and Non-Destructive Testing (NDT): Hydrostatic pressure testing at 1.5× working pressure; radiographic testing (RT) or ultrasonic testing (UT) of all weld joints per ASME Section V.
Applications
The stainless steel coil tubes are integral components in a wide range of thermal energy storage and heat exchange systems:
- Ice-Storage Chilled Water Systems (蓄冰冷水系统): Primary heat exchangers in off-peak ice storage systems for commercial buildings, hospitals, and data centers, enabling load shifting and peak demand reduction.
- Cryogenic Energy Storage: Utilization in liquid nitrogen or liquid oxygen storage vessels for industrial cryogenic applications.
- Solar Thermal Energy Storage: Hot water storage in solar heating systems for residential and commercial use.
- Industrial Process Cooling: Thermal buffering in manufacturing processes requiring stable temperature control.
- Food and Beverage Industry: Rapid cooling systems and refrigeration in food processing plants.
- Pharmaceutical and Biomedical: Cryopreservation and temperature-controlled storage facilities.
- Marine and Offshore: Seawater cooling systems with high corrosion resistance requirements.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring traceability, compliance, and performance verification:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System
- ASME B36.19M — Compliance for stainless steel pipe dimensions and tolerances
- ASME BPV Section VIII Div. 1 — Pressure vessel fabrication standards
- ASME Section IX — Welding qualification procedures
- EN 10217-7 / EN 10216-5 — European standards for stainless steel tubes
- PED 2014/68/EU — Pressure Equipment Directive compliance
- ASTM A269 / A270 — Material specifications for austenitic stainless steel tubes
- 3.1 / 3.2 Material Certificates — Third-party verified chemical and mechanical property documentation per EN 10204
- Hydrostatic Test Reports — 100% batch testing with documented results
- NDT Reports — Radiographic and ultrasonic testing certificates for critical welds
Unique Selling Points
- Simulation-Driven Design: Each coil tube assembly is validated through rigorous numerical simulation of the ice-storage process, ensuring optimal thermal performance and energy efficiency before fabrication.
- Full Cryogenic Capability: Materials and fabrication methods guarantee reliable operation across the full cryogenic temperature spectrum without brittle fracture risk.
- Customizable Geometry: Coil pitch, diameter, and turn count are tailored to specific thermal load requirements, enabling seamless integration into diverse system architectures.
- Extended Service Life: Superior corrosion resistance and fatigue endurance ensure 25+ years of reliable operation with minimal maintenance.
- End-to-End Traceability: From raw material mill certificates to final NDT reports, complete quality documentation supports regulatory compliance and lifecycle management.