Stainless Steel Coil Tube (Coiltube) — Ice Storage Thermal Management Series
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Catalog No.: 1670
Classification: Literature Study / Technical Reference
Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered continuous tubular product formed into a helical or serpentine coil configuration, specifically designed for thermal storage and heat exchange applications. This product represents a critical component in ice-coil thermal storage air conditioning systems (Ice-Coil Thermal Energy Storage Air Conditioning Systems), where the coil tube serves as the primary heat transfer medium between the refrigerant and the phase-change material (PCM, typically ice or brine solution).
Wenzhou Jixing Metal Materials Co., Ltd. produces coil tubes that meet stringent metallurgical and dimensional standards, ensuring long-term reliability under cyclic thermal loading conditions. The coil geometry maximizes the surface-area-to-volume ratio, enabling efficient heat absorption and release during the charging and discharging phases of thermal energy storage (TES, Thermal Energy Storage) systems.
Material Composition & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its superior corrosion resistance, thermal conductivity, and mechanical integrity under repeated freeze-thaw cycles.
- Primary Alloy Grades: AISI 304 (UNS S30400), AISI 316L (UNS S31603), and AISI 321 (UNS S32100)
- Carbon Equivalent (CE): ≤ 0.03% (for 316L), ensuring excellent weldability and resistance to intergranular corrosion
- Chromium (Cr) Content: 18.0–20.0% — provides passive oxide layer formation
- Nickel (Ni) Content: 8.0–12.0% — stabilizes austenitic microstructure
- Molybdenum (Mo) Content: 2.0–3.0% (316L grade) — enhances chloride pitting resistance
- Titanium (Ti) Stabilization: Present in 321 grade — prevents chromium carbide precipitation at elevated temperatures
- Operating Temperature Range: −196 °C to +870 °C (depending on grade)
- Thermal Conductivity: 14–16 W/(m·K) at 20 °C (304 grade)
- Specific Heat Capacity: 500 J/(kg·K)
- Linear Thermal Expansion Coefficient: 16.5 × 10⁻⁶ /K (20–100 °C)
- Yield Strength (0.2% offset): ≥ 205 MPa (annealed condition)
- Tensile Strength: ≥ 515 MPa
- Elongation: ≥ 40% (minimum)
Technical Specifications
| Parameter | Specification | Unit | Standard Reference |
|---|---|---|---|
| Outer Diameter (OD) | 6.35 / 9.53 / 12.70 / 15.88 / 19.05 / 25.40 | mm | ASTM A213 / GB/T 12771 |
| Wall Thickness | 0.50 / 0.80 / 1.00 / 1.20 / 1.50 / 2.00 | mm | ASTM A213 / GB/T 12771 | Coil Pitch (Center-to-Center) | 15 – 50 (adjustable) | mm | Custom / OEM |
| Coil Diameter (Helical) | 100 – 600 | mm | Custom / OEM |
| Coil Length (Total Tube Length) | 5 – 50 | m | Custom / OEM |
| Surface Finish | Ra ≤ 0.8 μm (interior), Ra ≤ 0.4 μm (exterior) | μm | ASTM A270 |
| Roundness Tolerance | ± 2% of OD | — | GB/T 12771 |
| Wall Thickness Tolerance | ± 10% | — | ASTM A213 |
| Coil Pitch Tolerance | ± 0.5 mm | mm | Internal QC Standard |
| End Condition | Plain end / Beveled end / Threaded connection | — | Customer Specification |
| Heat Treatment | Solution Annealed (1050–1100 °C) + Water Quench | — | ASTM A213 |
| Corrosion Resistance | Passive in 3% NaCl solution; no pitting at ≤ 1000 ppm Cl⁻ | — | ASTM G48 |
Manufacturing Process
The production of the Stainless Steel Coil Tube involves a multi-stage metallurgical and forming process designed to achieve precise dimensional control and optimal microstructural properties:
- Raw Material Procurement: Cold-rolled stainless steel strip or seamless tube stock is sourced from certified mills, conforming to ASTM A240 (plate/strip) or ASTM A213 (tube) specifications.
- Chemical Composition Verification: Each incoming batch undergoes spectrographic analysis (OES, Optical Emission Spectroscopy) to confirm alloying element compliance within specified ranges.
- Coil Forming (Cold Bending): The straight tube is fed through a precision CNC-controlled coil-forming machine. The bending radius is calculated to prevent wall thinning, ovalization, or cracking. The minimum bend radius is maintained at ≥ 3× OD to ensure structural integrity.
- Surface Treatment: Post-forming, the coil tube undergoes electropolishing or mechanical polishing to achieve the required surface roughness (Ra) values, critical for minimizing flow resistance and fouling in heat exchange applications.
- Solution Annealing: The formed coil is heated to 1050–1100 °C in a protective atmosphere (argon or vacuum) followed by rapid water quenching. This process dissolves precipitated carbides, restores full austenitic structure, and eliminates residual stresses from forming.
- Pickling and Passivation: The annealed coil is immersed in a nitric acid/hydrofluoric acid bath to remove oxide scale, followed by passivation treatment to establish a stable chromium oxide passive film (Cr₂O₃).
- Dimensional Inspection: Each coil is measured for OD, wall thickness, pitch, and helical diameter using laser gauges and coordinate measuring machines (CMM). Out-of-tolerance units are rejected.
- Pressure Testing: Hydrostatic pressure testing at 1.5× working pressure for a minimum hold time of 30 seconds ensures leak-tight integrity.
- Packaging and Traceability: Each coil is individually wrapped, labeled with heat number, grade, dimensions, and test certificate reference, and packed for shipment.
Applications
The Stainless Steel Coil Tube is engineered for demanding thermal management applications, with particular emphasis on the following sectors:
- Ice-Coil Thermal Storage Air Conditioning Systems: The primary application domain, where the coil tube is submerged in ice or brine tanks to absorb or release latent heat during peak/off-peak electricity cycles. The high surface area of the coil geometry facilitates rapid heat transfer between the refrigerant circulating within the tube and the phase-change medium externally.
- Cold Storage and Refrigeration: Evaporator coils for walk-in coolers, freezers, and blast freezing chambers where corrosion resistance and low-temperature ductility are paramount.
- Heat Exchangers (Shell-and-Coil Type): Compact heat exchanger assemblies for industrial process cooling, district heating, and building services.
- Medical and Pharmaceutical Equipment: Temperature-controlled storage units, cryogenic equipment, and laboratory refrigeration systems requiring biocompatible, corrosion-resistant tubing.
- Food and Beverage Processing: Pasteurization coils, fermentation temperature control systems, and beverage cooling loops where sanitary-grade stainless steel is mandatory.
- Geothermal and Solar Thermal Systems: Ground-source heat exchanger coils and solar thermal collector manifolds exploiting the alloy's resistance to mineral scale and chemical degradation.
- Marine and Offshore Applications: Seawater cooling coils, ballast water management systems, and shipboard refrigeration where chloride-induced corrosion is a primary concern.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring product conformity to international and national standards:
- ISO 9001:2015 — Quality Management System certification
- ISO 14001:2015 — Environmental Management System certification
- ISO 45001:2018 — Occupational Health and Safety Management System
- EN 10204 3.1 Certificate — Third-party material inspection and testing documentation for each production lot
- ASTM A213 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for High-Temperature Service
- GB/T 12771 — Chinese National Standard for Stainless Steel Seamless Tubes for General Application
- GB/T 14976 — Chinese National Standard for Fluid Transport Stainless Steel Tubes
- ASME B31.3 / B31.5 — Compliance with pressure piping codes for process and refrigeration systems
- NACE MR0175 / ISO 15156 — Resistance to sulfide stress cracking for sour service applications (316L grade)
- CE Marking — Conformity with European Directive 2014/68/EU (Pressure Equipment Directive) where applicable
Unique Selling Points
- Superior Thermal Cycling Performance: The coil tube withstands over 10,000 freeze-thaw cycles without cracking, delamination, or significant dimensional change, validated through accelerated life testing in accordance with the experimental research on ice-coil thermal storage systems.
- Precision Coil Geometry: CNC-controlled forming ensures uniform pitch and helical diameter, guaranteeing consistent heat transfer coefficients across the entire coil length and eliminating flow maldistribution.
- Multi-Grade Availability: Selection of 304, 316L, and 321 grades allows customers to optimize the cost-performance balance based on the specific corrosive environment and temperature requirements.
- Full Traceability: Every coil tube is traceable to its mill heat number, enabling complete supply chain transparency and simplified quality auditing.
- Custom Engineering Support: OEM/ODM capabilities allow customization of coil dimensions, end connections, and surface treatments to meet project-specific thermal design requirements.
- Low-Fouling Surface Finish: Electropolished interior surfaces (Ra ≤ 0.4 μm) reduce biofilm adhesion and mineral scale deposition, extending maintenance intervals and preserving heat transfer efficiency over the system lifetime.
Technical Note: The experimental research referenced in the product literature — "Experimental Study on Ice-Coil Thermal Storage Air Conditioning" — demonstrates that stainless steel coil tubes with optimized pitch-to-diameter ratios achieve heat transfer coefficients of 800–1,200 W/(m²·K) in ice-melting mode and 600–900 W/(m²·K) in ice-freezing mode, validating the product's suitability for high-efficiency thermal energy storage applications.