Stainless Steel Coil Tube — Direct Evaporative Ice Storage Application
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Product No. 1689). This coiltube is specifically designed and optimized for Direct Evaporative Ice Storage (DEIS) systems, where it serves as the primary heat exchange medium for latent heat storage applications. The coiltube integrates the advantages of stainless steel's corrosion resistance, mechanical strength, and thermal conductivity with a continuous spiral geometry that maximizes surface-area-to-volume ratio, enabling efficient heat transfer between the refrigerant and the phase-change medium (typically water-ice).
This product represents a specialized engineering solution for thermal energy storage systems, particularly in commercial HVAC (Heating, Ventilation, and Air Conditioning) applications, district cooling networks, and industrial process cooling where load shifting and peak demand management are critical.
2. Material & Properties
2.1 Base Material
- Primary Alloy: Austenitic Stainless Steel, conforming to AISI 304 / AISI 316L standards
- Equivalent Grades: EN 1.4301 (304), EN 1.4401 (316L), GB/T 20878-2007
- Composition (AISI 316L): C ≤ 0.03%, Mn ≤ 2.0%, Si ≤ 1.0%, Cr 16.0–18.0%, Ni 10.0–14.0%, Mo 2.0–3.0%, P ≤ 0.035%, S ≤ 0.030%
2.2 Mechanical Properties
- Tensile Strength (Rm): ≥ 520 MPa (AISI 304), ≥ 485 MPa (AISI 316L)
- Yield Strength (Rp0.2): ≥ 205 MPa
- Elongation (A50mm): ≥ 40%
- Hardness: ≤ 217 HB (annealed condition)
2.3 Thermal Properties
- Thermal Conductivity (λ): 16.3 W/(m·K) at 20°C
- Specific Heat Capacity (cp): 500 J/(kg·K)
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (20–100°C)
- Operating Temperature Range: −196°C to +870°C
2.4 Corrosion Resistance
- Excellent resistance to atmospheric, chemical, and food-grade environments
- Superior pitting and crevice corrosion resistance (especially AISI 316L grade with molybdenum addition)
- Resistance to chloride-induced stress corrosion cracking (SCC)
- Long-term durability in brine-based and glycol-based heat transfer media
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) | — |
| Product Code | 1689 | Internal Catalog |
| Outer Diameter (OD) | φ6.35 mm / φ9.52 mm / φ12.7 mm (standard); custom available | ASTM B534 / ASME B75.1 |
| Wall Thickness (WT) | 0.50 mm / 0.70 mm / 1.00 mm / 1.50 mm | ASTM B534 |
| Coil Diameter (CD) | φ200 mm – φ1,200 mm (configurable) | Custom per project requirements |
| Coil Length | Up to 500 m continuous coil | — |
| Pitch (Coil Spacing) | 1.2× OD to 3.0× OD (adjustable) | Per heat exchanger design |
| Surface Finish | 2B (cold rolled & annealed) or BA (Bright Annealed) | ASTM A666 |
| Tolerance (OD) | ±0.05 mm (precision grade) | ASTM B534 |
| Tolerance (WT) | ±10% of nominal | ASTM B534 |
| Maximum Working Pressure | 1.6 MPa (standard); up to 4.0 MPa (thick-wall) | ASME B31.3 |
| Refrigerant Compatibility | R-134a, R-404A, R-410A, R-407C, NH₃, CO₂ | ASHRAE 34 |
| Hydrostatic Test Pressure | 1.5× working pressure | EN 10216 / ASTM A269 |
| Packaging | Wooden reel with moisture-proof wrapping | ISO 4180 |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Inspection: Incoming stainless steel strip or seamless pipe undergoes chemical composition analysis (OES — Optical Emission Spectroscopy) and mechanical property verification per ASTM A276 / ASTM A270.
- Coil Forming (Cold Coiling): Continuous stainless steel tubing is cold-formed into a helical coil shape using precision CNC coil-forming machinery. The forming process maintains controlled bend radii to prevent wall thinning and ovality distortion.
- Pitch Adjustment: The coil pitch is precisely controlled to meet heat exchanger design requirements, ensuring uniform spacing for optimal refrigerant flow distribution and ice formation uniformity.
- Heat Treatment (if applicable): Solution annealing at 1050–1100°C followed by water quenching for stress relief and restoration of full annealed mechanical properties.
- Surface Treatment: Optional electropolishing or passivation treatment to enhance corrosion resistance and reduce surface roughness (Ra ≤ 0.4 μm), improving heat transfer efficiency.
- Quality Inspection: Dimensional verification (OD, WT, pitch, coil diameter), hydrostatic pressure testing, visual inspection, and non-destructive testing (EDDY CURRENT TESTING — ECT) per ASTM E309.
- Packaging & Dispatch: Coils are wound onto wooden reels, wrapped in moisture-proof polyethylene film, and labeled with material certificates and traceability data.
4.2 Process Controls
- Online dimensional monitoring with feedback-controlled forming parameters
- 100% hydrostatic testing at production line
- Batch-level chemical and mechanical property verification
- Full traceability from raw material mill certificate to finished product
5. Applications
5.1 Direct Evaporative Ice Storage (DEIS) Systems
The primary application of this coiltube product is in Direct Evaporative Ice Storage systems, where the refrigerant evaporates directly on the external surface of the stainless steel coil, causing ice to form on the coil's exterior. This mechanism offers:
- High latent heat utilization: Ice formation releases 334 kJ/kg of latent heat, providing 8–12× the energy density of sensible heat storage
- Uniform ice layer formation: The continuous coil geometry promotes even ice nucleation and growth
- Low refrigerant charge: Direct contact eliminates intermediate heat transfer fluid, reducing system volume
- Peak demand shifting: Enables "make-shift" operation, shifting cooling load from peak to off-peak electrical periods
5.2 Additional Applications
- Commercial HVAC (Heating, Ventilation, and Air Conditioning) systems
- District cooling and chilled water distribution networks
- Industrial process cooling (pharmaceutical, food & beverage)
- Cryogenic heat exchangers
- Marine and offshore refrigeration systems
- Supermarket refrigeration and cold storage facilities
- Building energy management systems (BEMS) for load management
6. Quality Certifications & Compliance
6.1 Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ASME B75.1 — Specification for Seamless Stainless Steel Hydraulic and Pneumatic Tubing
- ASTM B534 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Pipe, Tubing, and Bar for Chemical and Fossil Fuel Process Applications
- EN 10216-5 — Non-alloy, fine grain and alloy steel tubes for technical purposes
- GB/T 14976 — Chinese National Standard for Cold-rolled Seamless Steel Tubes for Fluid Transport
6.2 Testing & Verification
- Chemical composition analysis (OES / ICP — Inductively Coupled Plasma)
- Mechanical testing (tensile, hardness, impact per ASTM A370)
- Hydrostatic pressure testing (100% coverage)
- Eddy current testing (ECT) for wall thickness and defect detection
- Corrosion testing (salt spray per ASTM B117, intergranular corrosion per ASTM A262 Practice E)
- Dimensional inspection with CMM (Coordinate Measuring Machine)
6.3 Traceability
Each coil tube batch is accompanied by a Mill Test Certificate (MTC) conforming to EN 10204 Type 3.1, providing full traceability of raw material origin, heat number, chemical composition, mechanical properties, and all test results. Product-specific certificates include coil dimension data, hydrostatic test records, and dimensional inspection reports.
7. Unique Selling Points
- Optimized for Ice Storage: Coil geometry specifically engineered for uniform ice nucleation and growth in direct evaporative systems, maximizing latent heat storage efficiency
- Precision Manufacturing: CNC-controlled coil forming ensures consistent pitch, bend radius, and dimensional accuracy critical for heat exchanger performance
- Superior Corrosion Resistance: AISI 316L grade with molybdenum provides exceptional resistance to chloride-containing brine solutions used in ice storage systems
- Full Traceability: End-to-end material traceability from mill to finished product with EN 10204 Type 3.1 certification
- Custom Configurability: Flexible specifications including OD, wall thickness, coil diameter, and pitch to meet project-specific thermal design requirements
- Extended Service Life: Austenitic stainless steel construction ensures 25+ year operational lifespan in aggressive thermal cycling environments
8. Technical Notes
Design Consideration: In direct evaporative ice storage systems, the coil tube operates under repeated freeze-thaw cycles. The selected stainless steel grade must maintain ductility and fatigue resistance over thousands of thermal cycles. AISI 316L's low carbon content (≤ 0.03%) minimizes sensitization risk, ensuring long-term mechanical integrity.
Heat Transfer Optimization: The coil pitch should be selected to balance ice layer thickness against refrigerant flow resistance. Typical design parameters include pitch ratios of 1.5× OD to 2.5× OD, with outer coil diameter optimized for tank geometry and accessibility for periodic defrosting.
9. Manufacturer Information
Wenzhou Jixing Metal Materials Co., Ltd. is a specialized manufacturer of stainless steel pipes, tubes, and coiltube products with expertise in thermal management applications. The company maintains advanced manufacturing facilities, comprehensive quality control systems, and technical engineering capabilities to support custom product development for energy storage and heat exchange applications.