Stainless Steel Coil Tube (Coiltube) — Ice Storage & Industrial Heat Exchange Application
1. Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered continuous coil-shaped tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Designed primarily for ice storage thermal energy systems and industrial heat exchange applications, this product leverages the superior corrosion resistance, thermal conductivity, and mechanical integrity of austenitic stainless steel to deliver reliable performance in demanding cryogenic and thermal cycling environments.
The Coiltube is specifically optimized for ice storage cooling systems (Ice Storage Thermal Energy Storage Systems), where ultrasonic nucleation technology is employed to enhance the supercooling release behavior and improve ice formation efficiency. Research and development efforts—documented in the technical study "Analysis of the Effect of Ultrasonic Waves on the Nucleation Temperature of Ice Storage Coil Tubes"—have demonstrated that the geometric configuration, surface finish, and material composition of the Coiltube play a critical role in determining the nucleation temperature (Tnucleation) of ice formation within the system.
2. Material & Properties
2.1 Base Alloy Composition
The Coiltube is fabricated from high-purity austenitic stainless steel grades, with the following primary options:
- SAE 304 / AISI 304 (UNS S30408): The standard grade offering excellent general corrosion resistance, weldability, and formability. Chromium (Cr) content of 18–20% and Nickel (Ni) content of 8–10.5% provide robust passive film formation.
- SAE 316 / AISI 316 (UNS S31603): Enhanced grade incorporating 2–3% Molybdenum (Mo) for superior resistance to pitting and crevice corrosion, particularly suitable for marine or chemically aggressive environments.
- SAE 321 / AISI 321 (UNS S32103): Titanium-stabilized grade (Ti ≥ 5×C) designed to prevent intergranular corrosion during heat treatment or welding at elevated temperatures.
2.2 Key Physical and Mechanical Properties
- Thermal Conductivity (k): 14–16 W/(m·K) at 20°C, ensuring efficient heat transfer between the coolant and the ice formation medium.
- Coefficient of Thermal Expansion (CTE): 16–17 × 10⁻⁶ /°C, providing dimensional stability during repeated thermal cycling between ambient and sub-zero temperatures.
- Yield Strength (σy): ≥ 205 MPa (annealed condition), ≥ 310 MPa (cold-worked condition).
- Tensile Strength (σu): ≥ 515 MPa (annealed), ≥ 690 MPa (cold-worked).
- Elongation (A50): ≥ 40% (annealed), ≥ 20% (cold-worked).
- Operating Temperature Range: −196°C to +870°C (depending on grade).
- Magnetic Permeability: Non-magnetic (μr ≤ 1.05), advantageous for ultrasonic transducer coupling in ice storage nucleation systems.
2.3 Surface Characteristics
The internal and external surface finish of the Coiltube is critical to ice nucleation performance. A controlled surface roughness (Ra) of 0.2–0.8 μm provides an optimal balance between frictional heat loss and nucleation site density. Surface treatments such as electropolishing or passivation may be applied to remove surface contaminants and enhance the passive chromium oxide film (Cr₂O₃), thereby improving long-term corrosion resistance and reducing biofilm formation.
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) | — |
| Product Catalog No. | 454 | Wenzhou Jixing Internal Catalog |
| Material Grade | SAE 304, 316, 321 (selectable) | AISI / ASTM / EN |
| Outer Diameter (OD) | Φ3.0 mm – Φ25.0 mm (customizable) | ASTM A269 / A213 |
| Wall Thickness (WT) | 0.3 mm – 3.0 mm | ASTM A269 / A213 |
| Coil Outer Diameter (COD) | Φ100 mm – Φ1500 mm | Customer Specification |
| Coil Length (per roll) | 5 m – 500 m (continuous) | — |
| Surface Finish | Pickled & Passivated (P&P), Electropolished (EP), or Brushed | ASTM A478 |
| Surface Roughness (Ra) | 0.2 – 1.6 μm | ISO 4287 |
| Tolerance on OD | ±0.05 mm (precision) / ±0.10 mm (standard) | ASTM A269 |
| Tolerance on WT | ±10% of nominal | ASTM A269 |
| Delivery Condition | Annealed (Solution Heat Treated), Cold-Drawn, or Semi-Cold-Drawn | ASTM A269 |
| Maximum Operating Pressure | Up to 40 MPa (PN40), depending on OD/WT | EN 10217-7 |
| Applicable Standards | ASTM A269, ASTM A213, EN 10217-7, GB/T 12771, JIS G3459 | Multi-standard compliance |
| Packaging | Wooden reel / steel drum with desiccant and protective wrapping | ISO 4180 (Packaging for Transport) |
4. Manufacturing Process
4.1 Process Flow Overview
- Raw Material Inspection: Incoming stainless steel strip or rod undergoes chemical composition verification (via Optical Emission Spectroscopy, OES), mechanical property testing, and visual surface inspection to ensure conformance with the specified grade.
- Coil Forming / Cold Drawing: The material is formed into the desired OD and WT dimensions through precision cold-drawing over tungsten carbide (WC) or ceramic dies. Continuous coiling is achieved using a programmable coil forming machine with real-time diameter and tension control.
- Solution Annealing (Heat Treatment): The formed coil is subjected to solution heat treatment at 1010–1150°C followed by rapid quenching (water or air) to dissolve carbides, restore full austenitic microstructure, and achieve maximum ductility and corrosion resistance.
- Pickling and Passivation: The annealed coil is immersed in a mixed acid bath (HNO₃ + HF) to remove heat scale, followed by passivation in a nitric acid solution to regenerate the chromium oxide passive film.
- Surface Finishing (Optional): Electropolishing or mechanical polishing may be applied to achieve the required surface roughness (Ra ≤ 0.4 μm) for enhanced nucleation performance in ice storage applications.
- Dimensional Inspection: Each coil is inspected for OD, WT, straightness, and coil diameter tolerance using laser micrometers, ultrasonic thickness gauges, and optical measurement systems.
- Non-Destructive Testing (NDT): Eddy current testing (ECT) and magnetic particle inspection (MT) are performed to detect surface and near-surface defects (cracks, inclusions, laps) in accordance with ASTM E309.
- Coil Winding and Packaging: The inspected coil is wound onto a precision reel with controlled tension to prevent springback deformation, then packaged with protective wrapping and desiccant for moisture protection during storage and transportation.
4.2 Ultrasonic Nucleation Optimization
In ice storage applications, the Coiltube surface serves as the primary nucleation substrate for ice crystal formation. Based on the research documented in "Analysis of the Effect of Ultrasonic Waves on the Nucleation Temperature of Ice Storage Coil Tubes", the following design considerations are integrated:
- Surface micro-texturing: Controlled micro-pitting or laser-induced surface patterns may be applied to increase nucleation site density, thereby raising the effective nucleation temperature (Tn) from the typical −20°C to −5°C range, significantly reducing supercooling depth.
- Acoustic impedance matching: The non-magnetic austenitic structure of the stainless steel ensures minimal acoustic attenuation when ultrasonic transducers (typically 40–80 kHz) are coupled to the coil surface, promoting uniform ice nucleation across the heat exchange area.
- Coil geometry optimization: The coil pitch and diameter are engineered to maximize the contact area between the coolant and the ice formation medium while maintaining laminar flow conditions that facilitate uniform nucleation.
5. Applications
5.1 Ice Storage Thermal Energy Systems
The primary application domain for this Coiltube product is in ice storage thermal energy storage (TES) systems used in commercial and industrial HVAC (Heating, Ventilation, and Air Conditioning) installations. These systems store cooling capacity in the form of ice during off-peak electrical periods and release it during peak demand, thereby reducing peak electrical load and lowering energy costs. The Coiltube functions as the heat exchange element through which the refrigerant or brine transfers heat to/from the ice matrix.
5.2 Additional Application Domains
- Food and Beverage Processing: Heat exchangers for pasteurization, pasteurization, and refrigeration systems where hygiene and corrosion resistance are paramount.
- Pharmaceutical Manufacturing: Sterilizable heat exchange coils for cleanroom processes requiring autoclave-compatible materials.
- Chemical and Petrochemical Industry: Reactor cooling coils, condenser tubes, and heat exchangers operating in corrosive media.
- Marine and Offshore Engineering: Seawater-cooled heat exchangers where resistance to chloride-induced pitting corrosion is essential (SAE 316 grade).
- Automotive and Aerospace: Precision coil tubing for fuel lines, hydraulic systems, and thermal management circuits.
- Water Treatment and Desalination: Heat recovery coils in multi-stage flash (MSF) and reverse osmosis (RO) systems.
- Ultrasonic Cleaning and Processing: Immersion coils for ultrasonic-assisted chemical processes requiring precise temperature control.
6. Quality Certifications and Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a rigorous quality management system and holds the following certifications and complies with the following standards:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System — ensures consistent product quality and customer satisfaction through documented processes and continuous improvement. |
| ISO 14001:2015 | Environmental Management System — demonstrates commitment to minimizing environmental impact during manufacturing. |
| ISO 45001:2018 | Occupational Health and Safety Management System — ensures safe working conditions and risk mitigation. |
| CE Marking (EU) | Conformity with European Union directives including PED 2014/68/EU (Pressure Equipment Directive) where applicable. |
| EN 10204 3.1 | Inspection Certificate — provides detailed material test reports including chemical composition, mechanical properties, and dimensional verification. |
| ASTM A269 / A213 | Product specification compliance for welded and seamless stainless steel tubing. |
| GB/T 12771 | Chinese national standard for welded stainless steel tubes, ensuring compliance with domestic regulatory requirements. |
| Material Test Reports (MTR) | Every batch is accompanied by a full MTR including chemical analysis (OES), mechanical test results, and dimensional inspection data. |
7. Unique Selling Points
- Ultrasonic-Nucleation-Optimized Design: The Coiltube is specifically engineered with surface and geometric parameters validated through research on ultrasonic-assisted ice nucleation, offering superior nucleation temperature control compared to conventional heat exchange coils.
- Precision Dimensional Control: Tight tolerances on OD (±0.05 mm) and WT (±10%) ensure consistent hydraulic performance and reliable fit in heat exchanger assemblies.
- Multi-Grade Material Options: Availability in SAE 304, 316, and 321 grades provides flexibility to match the specific corrosion and mechanical requirements of each application.
- Full Traceability: Each coil is individually traceable from raw material heat number through final inspection, supported by EN 10204 3.1 inspection certificates.
- Customizable Coil Configuration: Flexible range of OD, WT, coil diameter, and coil length allows tailored solutions for diverse system designs.
- Multi-Standard Compliance: