Stainless Steel Coil Tube for Ice Thermal Energy Storage Systems

Product Overview

The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered heat exchanger component specifically designed for ice thermal energy storage (TES) systems. This product represents a critical element in latent heat thermal storage technology, where ice serves as the phase-change material (PCM) for off-peak energy storage and on-peak cooling demand fulfillment. The coil tube facilitates efficient heat transfer between the refrigerant fluid and the ice slurry, enabling the thermal energy storage device to achieve high energy density and superior thermodynamic performance.

Based on extensive research into the thermal performance characteristics of ice storage coil devices, this product has been optimized for maximum heat transfer coefficient, minimal pressure drop, and long-term structural integrity under repeated freeze-thaw cycling conditions. The design adheres to principles established in peer-reviewed thermal engineering studies, ensuring reliable operation in commercial and industrial chilled water systems.

Material & Properties

Base Material

Austenitic Stainless Steel Grades: SUS304 (ASTM A213 TP304), SUS316L (ASTM A213 TP316L), and SUS321 (ASTM A213 TP321) are the primary alloy options, selected for their exceptional corrosion resistance, cryogenic toughness, and non-magnetic properties.
Chromium Content: Minimum 18% Cr, providing passive oxide layer formation and resistance to oxidative degradation in aqueous environments.
Nickel Content: 8–10% Ni, ensuring austenitic microstructure stability across the full operating temperature range of −25°C to +40°C.
Carbon Content: ≤0.08% (L-grade variants ≤0.03%), minimizing intergranular corrosion susceptibility after thermal cycling.

Key Performance Properties

Thermal Conductivity: 16.3 W/(m·K) at 20°C (SUS304), providing efficient conductive heat transfer through the tube wall.
Specific Heat Capacity: 478 J/(kg·K), contributing to thermal mass buffering during transient operating conditions.
Coefficient of Thermal Expansion: 17.3 × 10⁻⁶ /°C, compatible with controlled differential expansion in composite assembly designs.
Mechanical Strength: Minimum tensile strength of 515 MPa (SUS304) and 170 MPa yield strength, ensuring structural integrity under internal hydraulic pressure.
Cryogenic Performance: Maintains ≥80% of room-temperature ductility at −40°C, preventing brittle fracture during ice formation cycles.
Corrosion Resistance: Passive film stability in chloride concentrations up to 2000 ppm, with pitting resistance equivalent number (PREN) ≥24 for 316L grade.

Specifications

Parameter	Specification	Standard Reference
Tube Outer Diameter (OD)	Φ6.0 mm / Φ8.0 mm / Φ10.0 mm / Φ12.7 mm / Φ15.9 mm / Φ19.1 mm / Φ25.4 mm	ASTM A213 / GB/T 12771
Wall Thickness	0.30 mm – 1.50 mm (standard); 0.20 mm – 0.50 mm (thin-wall for high HTC)	ISO 4497
Coil Inner Diameter (ID)	Φ100 mm – Φ1200 mm (customizable per application geometry)	Manufacturer's design specification
Coil Length (Developed)	10 m – 500 m per assembly	Project-specific
Number of Turns	15 – 2000 turns	Calculated per thermal duty
Tube Pitch (Center-to-Center)	1.5× OD – 3.0× OD (optimized for ice slurry flow)	Heat transfer optimization
Operating Temperature Range	−25°C to +40°C	Thermal storage cycle
Maximum Working Pressure	1.6 MPa (standard); 2.5 MPa (reinforced)	ASME B31.5 / EN 10216
Hydrostatic Test Pressure	1.5× Working Pressure (minimum)	ISO 11119
Surface Finish (Internal)	Ra ≤ 0.8 μm (standard); Ra ≤ 0.4 μm (electropolished)	ASTM A967
Surface Finish (External)	Ra ≤ 1.6 μm (brushed); Ra ≤ 0.4 μm (mirror polished)	ASTM A967
Helix Angle	5° – 15° (variable pitch design available)	Thermal performance optimization
End Connections	Flanged / Threaded / Welded (butt-weld) / Sanitary Tri-Clamp	ASME B1.20.1 / EN 10226
Applicable Fluids	Water, Ethylene Glycol solutions (up to 50%), Propylene Glycol solutions, Brine solutions	Material compatibility
Refrigerant Flow Velocity	0.5 m/s – 3.0 m/s (optimal range for nucleate boiling suppression)	Thermal design criteria
Freeze-Thaw Cycle Endurance	≥50,000 cycles (design life)	Accelerated fatigue testing

Manufacturing Process

Material Preparation

Hot-Rolled Strip Selection: High-purity austenitic stainless steel strip is procured from certified mills, with chemical composition verified via optical emission spectrometry (OES) and spectrographic analysis per ASTM E195.
Annealing Treatment: Strip is solution-annealed at 1050°C – 1150°C followed by controlled air cooling to achieve a fully austenitic grain structure with grain size ≤ ASTM No. 6.
Pickling & Passivation: Acid pickling in a nitric/hydrofluoric acid blend removes mill scale, followed by passivation per ASTM A967 to restore the protective chromium oxide layer.

Tube Forming

Slitting: Precision slitting to target width tolerance of ±0.05 mm using diamond-coated slitter blades.
Welded Tube Formation: High-frequency induction welding (HF welding) at 60 kHz – 400 kHz produces a homogenized weld zone with weld strength ≥95% of base metal. Alternatively, orbital TIG welding is employed for thin-wall configurations requiring superior weld integrity.
Weld Homogenization: Post-weld annealing at 1100°C for 30 seconds normalizes the weld zone microstructure, eliminating stress concentrations and ensuring uniform corrosion resistance.
Sizing & Calibration: Multi-stand cold sizing reduces dimensional tolerance to ±0.02 mm on OD and ±0.01 mm on wall thickness.

Coil Forming

Cold Coiling: Continuous cold coiling on precision mandrels with controlled forming speed (5 m/min – 50 m/min) to prevent work hardening beyond acceptable limits. Coiling is performed in a temperature-controlled environment (20°C ± 5°C) to minimize residual stress.
Spring-Back Compensation: CNC-controlled coiling systems incorporate real-time spring-back compensation algorithms, achieving dimensional accuracy of ±0.5% on coil pitch and ±0.3° on helix angle.
Stress Relief: Post-coiling stress relief annealing at 300°C – 400°C for 1 hour eliminates residual stresses introduced during forming, preventing dimensional instability during service.

Finishing & Inspection

Internal Deburring: Wire brush or rotary tool deburring of tube ends to a chamfer of 0.5 mm × 45°, ensuring unobstructed fluid flow at inlet/outlet connections.
Surface Treatment: Electropolishing (optional) reduces surface roughness to Ra ≤ 0.4 μm, enhancing heat transfer coefficient by 15% – 25% and improving cleanability for food-grade applications.
Non-Destructive Testing (NDT): 100% eddy current testing per ASTM E309 for weld seam integrity; 100% dye penetrant testing per ASTM E709 for surface discontinuities; hydrostatic testing per lot at 1.5× working pressure with a 5-minute hold time.
Dimensional Verification: CMM (Coordinate Measuring Machine) inspection of coil geometry, including pitch uniformity, helix angle consistency, and end alignment within ±0.5 mm.

Applications

Ice Thermal Energy Storage (TES) Systems

Ice-on-Plate (IOP) Configurations: The coil tube serves as the primary heat transfer surface within the ice storage tank, circulating sub-zero brine or refrigerant to nucleate and grow ice crystals on the tube surface.
Ice Slurry Generation: In slurry-type thermal storage, the coil tube facilitates controlled ice nucleation in a stirred slurry, producing uniform ice particles (1 mm – 5 mm) suspended in water for direct distribution to cooling loads.
Ice Harp Systems: The coil tube is integrated into vertical ice harp assemblies, where refrigerant flows through the coil and ice forms radially outward, creating a high-surface-area ice matrix for rapid charge/discharge cycles.

Commercial & Industrial HVAC

Peak Load Shifting: Ice storage systems utilizing these coil tubes enable refrigeration plants to operate at full capacity during off-peak electricity hours (typically 10 PM – 6 AM), storing thermal energy as ice for discharge during peak cooling demand periods.
Chilled Water Production: The coil tube facilitates the production of 2°C – 4°C chilled water from the ice storage tank during peak hours, supplementing or replacing mechanical chillers to reduce peak electrical demand by 30% – 60%.
Building Applications: Office towers, shopping malls, hospitals, data centers, and educational facilities with high cooling loads and favorable utility rate structures for time-of-use electricity pricing.

Industrial Process Cooling

Process Heat Recovery: Capturing waste heat from industrial processes and storing it as ice for later use in process cooling, achieving energy integration and process optimization.
Temperature-Controlled Storage: Pharmaceutical cold chain, food processing, and cryogenic storage facilities requiring precise temperature control with high reliability.
Refrigerated Transport: Specialized coil tube assemblies for reefer containers and cold chain logistics, providing extended cooling duration without continuous mechanical refrigeration.

Specialized Applications

Medical & Laboratory: Cryogenic sample storage, MRI cooling systems, and laboratory ice bath systems requiring high-purity ice and precise temperature control.
Energy Storage Research: Coil tubes serve as test articles in research facilities studying thermal performance characteristics of ice storage devices, including heat transfer coefficient measurement, ice growth kinetics, and long-term cycling degradation.
Renewable Energy Integration: Coupling with solar thermal or wind energy systems for thermal energy buffering, enabling load-following operation of intermittent renewable sources.

Quality Certifications & Compliance

Product Certifications

ISO 9001:2015: Quality Management System certification covering the entire manufacturing process from raw material procurement through final inspection and delivery.
ISO 14001:2015: Environmental Management System certification ensuring environmentally responsible manufacturing practices and waste minimization.
ISO 45001:2018: Occupational Health and Safety Management System certification for workplace safety compliance.
CE Marking (EU): Compliance with European pressure equipment directives (PED 2014/68/EU) for components operating above 0.5 bar gauge pressure.
ASME Certification: Compliance with ASME B31.5 (Process Piping) and ASME B31.9 (Refrigeration Piping) standards for pressure-containing components.

Material & Testing Certifications

Mill Test Certificates (MTC): EN 10204 Type 3.1 certificates for each heat of raw material, including full chemical analysis, mechanical property data, and heat treatment records.
Third-Party Inspection: Available upon request by SGS, Bureau Veritas, or TÜV Rheinland for independent verification of material composition, dimensional accuracy, and pressure testing results.
Material Traceability: Full heat-to-heat traceability system linking each finished coil tube assembly to its raw material heat number, manufacturing batch, and inspection records.

Performance Validation

Thermal Performance Testing: Validated per ASHRAE Standard 90.1 methodology for heat transfer coefficient measurement under representative operating conditions, with results documented in test reports.
Pressure Testing: 100% hydrostatic testing per ISO 11119-1 at 1.5× design pressure with minimum 5-minute hold time, with zero leakage tolerance.
Cyclic Fatigue Testing: Accelerated freeze-thaw cycling tests conducted per ASTM F2093 methodology, demonstrating ≥50,000 cycles without structural degradation, weld cracking, or dimensional drift exceeding ±0.5%.
Corrosion Testing: Salt spray testing per ASTM B117 (≥1000 hours without red rust), intergranular corrosion testing per ASTM A262 Practice E (5a method), and pitting resistance testing per ASTM G48 Practice A.
Hydrodynamic Testing: Pressure drop measurement across the coil assembly under specified flow conditions, with results compared to CFD (Computational Fluid Dynamics) simulation predictions for validation.

Industry Standards Compliance

Material Standards: ASTM A213 (Austenitic Stainless Steel Tubing), GB/T 12771 (Stainless Steel Tubing for General Purposes), EN 10216-5 (