Stainless Steel Coil Tube — Ice Storage Air Conditioning System Application
Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd, specifically designed for integration into Ice Storage Air Conditioning Systems (Ice Storage HVAC Systems). These coil tubes serve as the primary heat exchange elements within secondary loop piping networks, where they facilitate the transfer of thermal energy between the refrigerant circuit and the ice-storage medium (typically water or ethylene glycol brine). The coil tube geometry — characterized by a continuous helical or serpentine winding configuration — maximizes the surface-area-to-volume ratio, thereby enhancing heat transfer efficiency under the low-temperature operating conditions typical of ice accumulation cycles.
From a metallurgical standpoint, the coil tube represents a critical component in which material integrity, dimensional precision, and corrosion resistance must be maintained under cyclic thermal loading, chemical exposure to brine solutions, and sustained mechanical stress from fluid pressure. The product is engineered to meet the demanding requirements of Ice Storage Air Conditioning System Evaluation standards, ensuring long-term reliability in energy-efficient building climate control applications.
Material & Properties
The coil tube is fabricated from high-grade stainless steel (Stainless Steel), predominantly from the austenitic family, selected for their exceptional combination of corrosion resistance, mechanical strength, and thermal stability across the operating temperature range of ice storage systems (typically -5 °C to +15 °C for the ice accumulation phase and up to +45 °C for the discharge phase).
Base Material Grades
- AISI 304 (UNS S30408) — Chromium-Nickel austenitic stainless steel (18% Cr, 8% Ni). The primary grade used for general ice storage coil applications due to its excellent resistance to chloride-induced pitting corrosion and superior weldability.
- AISI 316 (UNS S31608) — Molybdenum-bearing austenitic stainless steel (16-18% Cr, 10-14% Ni, 2-3% Mo). Specified for applications involving ethylene glycol brine solutions or elevated chloride concentrations, providing enhanced resistance to pitting and crevice corrosion.
- AISI 316L (UNS S31603) — Low-carbon variant of 316, offering improved weldability and reduced susceptibility to sensitization during welding operations, critical for maintaining corrosion resistance at weld joints in coil assemblies.
Mechanical and Physical Properties
- Tensile Strength (UTS): ≥ 520 MPa (AISI 304); ≥ 550 MPa (AISI 316L)
- Yield Strength (0.2% Proof Stress): ≥ 205 MPa
- Elongation (at Break): ≥ 40% (ensuring ductility for cold-forming and coil winding operations)
- Thermal Conductivity: 14.9 W/(m·K) at 20 °C (AISI 304), providing adequate heat transfer performance
- Linear Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (critical for thermal stress analysis in cyclic temperature environments)
- Corrosion Resistance: Passivation layer (Cr₂O₃) self-healing capability in oxidizing environments; pitting resistance equivalent number (PREN) ≥ 19 for AISI 316L
Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm – 25.4 mm (¼" – 1") | ASTM A213 / GB/T 12771 |
| Wall Thickness | 0.5 mm – 1.5 mm | ASTM A269 / GB/T 12771 |
| Coil Winding Diameter | 150 mm – 600 mm (configurable) | Custom / Project-Specific |
| Coil Length (Uncoiled) | Up to 100 m per coil (continuous) | Manufacturer Specification |
| Surface Finish | No. 4 Brushed / 2B Annealed / Electropolished (Ra ≤ 0.4 μm) | ASTM A403 |
| Operating Pressure | ≤ 1.6 MPa (design); ≤ 2.4 MPa (burst) | GB/T 12459 / EN 10217 |
| Operating Temperature Range | −50 °C to +450 °C | Material Data Sheet |
| Minimum Bend Radius | ≥ 3D (D = outer diameter) | GB/T 12771 |
| Heat Exchange Efficiency | Overall heat transfer coefficient U ≥ 200 W/(m²·K) | ASHRAE Handbook — HVAC Systems |
| Welding Method | TIG (GTAW) / Orbital / Resistance Butt Welding | ASTM A213 / ASME B31.9 |
| Hydrostatic Test Pressure | 1.5 × Design Pressure | EN 10204 / GB/T 12459 |
| Applicable Media | Water, Ethylene Glycol Brine (≤ 50%), Refrigerant Secondary Loop Fluids | Project Specification |
Manufacturing Process
The production of stainless steel coil tubes for ice storage air conditioning systems follows a rigorous multi-stage manufacturing workflow, integrating modern metallurgical processing with precision forming technologies:
- Raw Material Selection & Incoming Inspection — Ingots or mill-finished seamless tubes are sourced from certified stainless steel producers. Incoming material undergoes spectroscopic analysis (Optical Emission Spectrometry, OES) to verify chemical composition compliance with the specified grade (e.g., AISI 304 or 316L), along with mechanical property testing and surface quality assessment.
- Hot Rolling & Annealing — Billet stock is hot-rolled into seamless tube blanks. Subsequent solution annealing (typically at 1050–1150 °C for austenitic grades) in a controlled atmosphere furnace ensures a fully recrystallized, strain-free microstructure with uniform grain size, eliminating residual stresses from prior forming operations.
- Precision Cold Drawing & Sizing — The annealed tube blanks undergo multi-pass cold drawing through tungsten carbide (WC-Co) dies to achieve the precise final outer diameter and wall thickness tolerances (typically ±0.05 mm). This process enhances surface finish and improves mechanical properties through strain hardening.
- Intermediate Annealing — Periodic solution annealing is performed between cold drawing passes to restore ductility and prevent excessive work hardening, ensuring the material maintains sufficient formability for subsequent coil winding operations.
- Coil Winding & Forming — The precision-drawn tube is fed through a computer-controlled coil winding machine, where it is helically or serpentine-wound around mandrels of the specified diameter. The winding process is executed under constant tension control to maintain uniform coil spacing and prevent tube ovalization or kinking. Minimum bend radius requirements (≥ 3D) are enforced to prevent wall thinning and microstructural damage at bend regions.
- Welding & Joint Assembly — Coil ends are joined using TIG (Gas Tungsten Arc Welding, GTAW) or orbital welding techniques with matching filler wire (e.g., ER308L for AISI 304; ER316L for AISI 316L). Weld joints are subsequently ground flush and, where required, passivated to restore the chromium oxide passive film.
- Surface Treatment & Passivation — The formed coil tube undergoes pickling and passivation treatment (nitric acid / citric acid solution immersion) to remove oxide scale, mill contaminants, and free iron particles. The resulting chromium oxide passive layer (Cr₂O₃) is thermodynamically stable and provides long-term corrosion protection.
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Quality Control & Testing — Comprehensive final inspection includes:
- Dimensional verification (OD, wall thickness, coil diameter, pitch) via laser micrometry and coordinate measurement
- Hydrostatic pressure testing at 1.5× design pressure for a minimum hold time of 10 minutes
- Visual and penetrant inspection (PT) of weld joints per ASTM E165
- Chemical composition re-verification via X-ray fluorescence (XRF) spectroscopy
- Hardness testing (Vickers HV) to confirm annealed condition
- Packaging & Dispatch — Completed coil tubes are wound on protective cores, wrapped in moisture-proof packaging with desiccant packs, and labeled with full traceability documentation (heat number, batch code, material certificate) for shipment to end users or system integrators.
Applications
The stainless steel coil tube from Wenzhou Jixing Metal Materials Co., Ltd is engineered for a diverse portfolio of applications, with a primary focus on Ice Storage Air Conditioning Systems:
Primary Application: Ice Storage Air Conditioning Systems
- Secondary Loop Heat Exchangers — The coil tube serves as the heat transfer surface in the secondary refrigerant loop, where it absorbs or rejects thermal energy from the ice-storage tank. During the ice accumulation phase (typically operated at −5 °C to −10 °C), the coil tube transfers heat from the water/brine medium to the refrigerant, facilitating ice formation on the tube surface. During the discharge phase, the coil tube extracts stored thermal energy from the melting ice for building cooling.
- Ice-on-Tube (IOT) Systems — In IOT configurations, the coil tube is directly embedded within the ice storage tank, with ice forming on its outer surface. The high surface-area-to-volume ratio of the helical coil geometry maximizes heat transfer efficiency, enabling rapid ice accumulation and discharge cycles.
- Ice-in-Tube (IIT) Systems — In IIT configurations, the coil tube is sealed and filled with ice or ice slurry, with heat exchange occurring across the tube wall with the surrounding water. The austenitic stainless steel provides excellent thermal conductivity and corrosion resistance under these cyclic conditions.
Secondary Applications
- Commercial Building HVAC Systems — Large-scale commercial, institutional, and industrial facilities requiring peak-load shifting and demand-side energy management
- District Cooling Systems — Centralized cooling plants utilizing thermal energy storage for load balancing
- Process Cooling — Industrial processes requiring precise temperature control with thermal buffering capability
- Food & Beverage Industry — Cold storage facilities, beverage processing lines, and dairy cooling systems
- Pharmaceutical Manufacturing — Temperature-controlled storage and processing environments requiring hygienic-grade stainless steel components
- Marine & Offshore Applications — Shipboard HVAC systems and offshore platform climate control where corrosion resistance is paramount
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework, ensuring that all stainless steel coil tube products comply with international and national standards:
- ISO 9001:2015 — Quality Management Systems (QMS) certification, demonstrating organizational commitment to consistent product quality and continuous improvement
- ISO 14001:2015 — Environmental Management Systems certification, ensuring environmentally responsible manufacturing practices
- ASTM A213 — Standard specification for austenitic stainless steel seamless tubes for high-temperature service
- ASTM A269 — Standard specification for austenitic stainless steel seamless, welded, and heavily cold-worked austenitic stainless steel welded tubing
- GB/T 12771 — Chinese National Standard for stainless steel seamless tubes for general application
- GB/T 14976 — Chinese National Standard for seamless stainless steel tubes for fluid transport
- EN 10217-7 — European Standard for non-alloy and alloy steel tubes for mechanical and technological uses (stainless steel)
- EN 10204-3.1 / 3.2 — European Standard for inspection documents, ensuring material traceability and conformity
- ASME B31.9 — Code for Pressure Piping (Refrigeration Piping), applicable to the design and construction of ice storage system piping
- ASHRAE 90.1 — Standard for energy-efficient building design, relevant to the energy performance evaluation of ice storage HVAC systems
- Mill Test Certificates (MTC) — Full chemical composition and mechanical property documentation provided for every production batch, traceable to the heat number
Note: All material certificates and quality documentation are issued in accordance with EN 10204 standards. Customers requiring additional third-party inspection (e.g., SGS, BV, TÜV) can request pre-shipment verification at the point of order. Wenzhou Jixing Metal Materials Co., Ltd maintains full batch traceability from raw material through to finished product dispatch.
Unique Selling Points
- Superior Corrosion Resistance in Brine Environments — The austenitic stainless steel grade selection (AISI 304/316L) provides exceptional resistance to chloride-induced pitting and crevice corrosion, critical for long-term operation in ethylene glycol brine solutions used in ice storage systems.
- Optimized Coil Geometry for Maximum Heat Transfer — The helical winding configuration provides a high surface-area-to-volume ratio, enabling rapid ice formation and melting