Stainless Steel Coil Tube for Thermal Energy Storage Applications
Product Overview
The Stainless Steel Coil Tube (Coil Tube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed specifically for thermal energy storage systems, including ice storage (ice thermal storage) and heat exchange applications. The coil tube is formed through continuous coiling processes that produce uniform helical geometries, enabling superior heat transfer performance in compact configurations. This product has been extensively studied in academic literature, notably in the research paper titled "Simulation Research on Ice Storage Performance of Different Pipe Coils", which validated the thermal efficiency and structural integrity of stainless steel coil tubes under cryogenic and thermal cycling conditions.
The coil tube represents a critical component in latent heat thermal energy storage (LHTES) systems, where it serves as the primary heat transfer medium between the refrigerant/coolant and the phase-change material (PCM), typically water-ice systems. The helical coil geometry maximizes the surface-area-to-volume ratio, thereby enhancing heat transfer rates and improving the overall efficiency of ice storage tanks.
Material Composition & Properties
Base Material
- Primary Alloy: Austenitic Stainless Steel (奥氏体不锈钢)
- Standard Grades: SUS304, SUS316, SUS316L (ASTM A269 / ASTM B462)
- Alternative Grades: SUS321, SUS304L (for specialized cryogenic applications)
Mechanical Properties (Typical for SUS304 Coil Tube)
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 520 MPa (75,400 psi) | ASTM A269 |
| Yield Strength (屈服强度) | ≥ 205 MPa (29,730 psi) | ASTM A269 |
| Elongation (延伸率) | ≥ 40% | ASTM A269 |
| Hardness (硬度) | ≤ 237 HB | ASTM A262 |
| Operating Temperature Range (工作温度范围) | −196°C to +870°C | — |
| Cryogenic Performance (低温性能) | Retains full ductility at LN₂ temperatures (−196°C) | ASTM E10 |
Chemical Composition (SUS304 — Typical)
| Element | C (Carbon) | Si | Mn | P | S | Cr | Ni | N |
|---|---|---|---|---|---|---|---|---|
| Max/Range (%) | 0.08 | 1.00 | 2.00 | 0.045 | 0.030 | 18.0–20.0 | 8.0–10.5 | 0.10 |
Corrosion Resistance
- Excellent resistance to atmospheric corrosion (大气腐蚀) and general aqueous environments
- High resistance to pitting (点蚀) and crevice corrosion (缝隙腐蚀) in chloride-containing solutions
- Outstanding resistance to intergranular corrosion (晶间腐蚀) after stabilization treatment
- Non-magnetic in annealed condition (无磁性)
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (外径, OD) | 6 mm – 25 mm (customizable up to 50 mm) | ASTM A269 |
| Wall Thickness (壁厚, WT) | 0.5 mm – 3.0 mm | ASTM A269 |
| Coil Diameter (盘管直径, CD) | 50 mm – 500 mm | Custom specification |
| Coil Length (盘管长度, CL) | 10 m – 100 m (per coil) | Custom specification |
| Coil Pitch (盘管间距, CP) | 3 mm – 25 mm (adjustable) | Custom specification |
| Surface Finish (表面处理) | Bright annealed (BA) / 2B / Polished (Ra ≤ 0.4 μm) | ASTM A473 |
| Tolerance on OD (外径公差) | ±0.1 mm (±4% for OD > 10 mm) | ASTM A269 |
| Tolerance on Wall Thickness (壁厚公差) | ±10% of nominal | ASTM A269 |
| End Form (端部形式) | Plain / Beveled / Threaded / Flanged | Custom specification |
| Delivery Condition (交货状态) | Cold-worked, annealed (冷轧退火) | — |
| Maximum Working Pressure (最大工作压力) | Up to 4.0 MPa (580 psi) | ASME B31.3 |
| Hydrostatic Test Pressure (水压试验压力) | 1.5 × Maximum Working Pressure | ASME B31.3 |
| Heat Transfer Coefficient (传热系数) | 15,000 – 35,000 W/(m²·K) (internal, depending on flow velocity) | — |
Manufacturing Process
Step 1: Raw Material Procurement & Inspection
High-purity stainless steel wire rod (线材) is procured from certified mills (e.g., Outokumpu, POSCO, Taigang). Each batch undergoes spectroscopic analysis (光谱分析) to verify chemical composition and mechanical testing to confirm tensile properties meet ASTM A269 requirements.
Step 2: Tube Drawing & Forming
The wire rod is cold-drawn through precision dies (冷拔成形) to achieve the target outer diameter and wall thickness. This process is performed on multi-stage drawing machines with controlled reduction ratios to ensure uniform wall thickness and dimensional accuracy.
Step 3: Intermediate Annealing (中间退火)
After drawing, the tubing undergoes solution annealing (固溶退火) at 1050°C – 1100°C in a protective atmosphere (argon or vacuum) to relieve cold-work hardening, restore ductility, and dissolve carbides for optimal corrosion resistance. This is followed by controlled cooling to prevent sensitization (敏化).
Step 4: Surface Treatment
The annealed tubes receive surface finishing according to specification:
- Bright Annealed (BA): For general corrosion resistance with smooth surface
- Pickling & Passivation (酸洗钝化): Removes scale and oxide layers, forming a protective chromium oxide film
- Electropolishing (电解抛光): For food-grade or pharmaceutical applications (Ra ≤ 0.25 μm)
Step 5: Coil Forming (盘管成型)
The straight tubing is coiled into helical shapes using precision coiling machines (卷管机). Key process parameters include:
- Coil diameter control: ±1% tolerance maintained through hydraulic forming
- Pitch uniformity: ±0.5 mm tolerance on coil pitch
- Post-forming annealing: Optional low-temperature stress relief (350°C – 450°C) to prevent spring-back (回弹) and residual stress
- Seam integrity: For welded coil tubes, TIG (Tungsten Inert Gas) welding is used with argon gas shielding to maintain interior cleanliness
Step 6: Quality Inspection & Testing
- Dimensional inspection: Optical measurement of OD, wall thickness, coil diameter, and pitch
- Hydrostatic testing: 100% testing at 1.5× working pressure with 30-second hold
- Visual inspection: Surface defect detection (cracks, dents, discoloration)
- Chemical spot check: Spectroscopic verification of alloy composition
- Corrosion testing: Salt spray test (ASTM B117, 1000 hours minimum) and intergranular corrosion test (ASTM A262 Practice E)
- Thermal cycling test: 500+ cycles between −20°C and +60°C to validate cryogenic performance
Applications
Primary Application: Ice Thermal Energy Storage (蓄冰储能系统)
Based on the research findings from "Simulation Research on Ice Storage Performance of Different Pipe Coils," stainless steel coil tubes are the preferred heat exchanger geometry for ice storage tanks. The helical coil design provides:
- High heat transfer efficiency: Enhanced turbulent flow within coils increases Nusselt number (努塞尔数) by 20–40% compared to straight tubes
- Compact configuration: High surface-area-to-volume ratio enables smaller tank footprints
- Uniform ice formation: Spiral geometry promotes even ice nucleation and growth patterns
- Reduced thermal stress: Coil flexibility accommodates volumetric expansion of water during freezing (9% expansion)
Additional Applications
| Application Sector | Specific Use | Key Advantage |
|---|---|---|
| Building HVAC (暖通空调) | Ice storage air conditioning systems (蓄冰空调) | Peak shaving, energy cost reduction (20–35%) |
| Food & Beverage (食品饮料) | Cold chain refrigeration coils (冷链制冷盘管) | Corrosion resistance, food-grade surface finish |
| Pharmaceutical (制药) | Cryogenic storage and cooling systems (低温储存) | Non-reactive, cleanable, hygienic design |
| Process Industry (化工) | Heat exchange coils in reactors (反应换热盘管) | High-temperature resistance, chemical inertness |
| Marine (海洋工程) | Heat recovery and refrigeration coils (余热回收) | Seawater corrosion resistance (SUS316L) |
| Power Generation (电力) | Waste heat recovery systems (废热回收系统) | Durability under thermal cycling |
Quality Certifications & Standards
| Certification/Standard | Description | Applicable Scope |
|---|---|---|
| ISO 9001:2015 | Quality Management System (质量管理体系) | Manufacturing process |
| ISO 14001:2015 | Environmental Management System (环境管理体系) | Production operations |
| ASME B31.3 | Process Piping Code (工艺管道规范) | Pressure vessel/pipe design |
| ASTM A269 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing | Material specification |
| EN 10217-7 | Non-ferrous metal tubes for pressure purposes — Stainless steel tubes | European standard compliance |
| GB/T 12771 | Chinese National Standard for Stainless Steel Tubes for General Industry | Domestic market compliance |
| PED 2014/68/EU | Pressure Equipment Directive (压力设备指令) | Pressure-containing applications |
| NSF/ANSI 61 | Drinking Water System Components (饮用水系统组件) | Food/water applications |
| 3-A Sanitary Standards | Hygienic Design for Dairy, Food, and Pharmaceutical Equipment | Pharmaceutical/food grade |
Unique Selling Points
1. Cryogenic Performance Validated by Simulation Research: The coil tube design has been rigorously validated through computational fluid dynamics (CFD) and thermal simulation studies published in peer-reviewed academic literature, demonstrating superior ice storage performance compared to alternative geometries (plate coils, shell-and-tube configurations).
2. Precision Coil Geometry: Advanced coiling technology ensures ±1% dimensional accuracy on coil diameter and ±0.5 mm pitch tolerance, guaranteeing uniform heat transfer distribution throughout the storage tank.
3. Full Material Traceability: Each coil tube batch includes mill certificates (MTC), heat number traceability, and full chemical/mechanical test reports in accordance with ISO 9001:2015 requirements.
4. Custom Engineering Support: Wenzhou Jixing Metal Materials Co., Ltd. offers custom coil configurations tailored to specific thermal storage system requirements, including variable pitch, multi-circuit designs, and specialized end fittings.
5. Extended Service Life: With proper design, stainless steel coil tubes deliver a service life exceeding 25 years in ice storage applications, significantly outperforming carbon steel alternatives (5–10 years) due to superior corrosion resistance and fatigue strength.
Performance Data — Ice Storage Simulation Results
| Performance Metric | Stainless Steel Coil Tube | Carbon Steel Coil Tube | Improvement |
|---|---|---|---|
| Icing Time (结冰时间) | 45 min (standard 10 m³ tank) | 48 min |