Stainless Steel Coil Tube (Coiltube) — Ice Storage Tank Application Grade
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd (Product No. 481) is a precision-engineered tubular product designed for integration into coil-type ice storage tanks (Ice Storage Tanks, IST) and thermal energy storage systems. The coil tube serves as the primary heat exchange medium within the tank, facilitating efficient heat transfer between the refrigerant/brine circuit and the phase-change material (typically water/ice). This product is engineered to meet the stringent requirements of large-scale district cooling, peak-load shifting, and thermal energy management applications.
Based on numerical simulation research concerning the uniformity of water distribution in coil-type ice storage tanks with different outlet configurations (Water Distributor Uniformity Analysis), the coil tube design incorporates optimized geometry to ensure homogeneous flow distribution, minimize thermal stratification, and maximize ice formation efficiency within the storage vessel.
2. Material & Properties
2.1 Base Material Composition
- Material Grade: Austenitic Stainless Steel (奥氏体不锈钢), conforming to ASTM A213 / GB/T 12771 standards
- Typical Grades: SUS304 (UNS S30400), SUS316L (UNS S31603), SUS321 (UNS S32100)
- Chemical Composition (SUS304, wt%): C ≤ 0.08%, Si ≤ 1.00%, Mn ≤ 2.00%, P ≤ 0.045%, S ≤ 0.030%, Cr 18.0–20.0%, Ni 8.0–10.5%, Fe balance
2.2 Mechanical Properties
- Tensile Strength (Rm): ≥ 520 MPa
- Yield Strength (Rp0.2): ≥ 205 MPa
- Elongation (A50mm): ≥ 40%
- Hardness: ≤ 217 HB (as delivered, annealed condition)
2.3 Physical & Thermal Properties
- Density (ρ): 7.93 g/cm³
- Thermal Conductivity (λ) at 20°C: 16.3 W/(m·K)
- Specific Heat Capacity (cp) at 20°C: 502 J/(kg·K)
- Thermal Expansion Coefficient (α) 100–500°C: 16.5 × 10⁻⁶ K⁻¹
- Operating Temperature Range: −196°C to +870°C
2.4 Corrosion Resistance
- Excellent resistance to atmospheric corrosion, dilute acids, and alkaline solutions
- SUS316L grade provides superior resistance to chloride-induced pitting and crevice corrosion (耐点蚀, PREN ≥ 24)
- Resistance to intergranular corrosion (IGC, 晶间腐蚀) after stabilization treatment or low-carbon formulation
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | φ12 mm – φ50 mm (customizable) | ASTM A213, GB/T 12771 |
| Wall Thickness (WT) | 0.5 mm – 2.0 mm | ±10% tolerance |
| Coil Length | 5 m – 500 m per coil (continuous) | — |
| Coil Inner Diameter (CID) | 200 mm – 1200 mm | — |
| Surface Finish | Mirror polish (Ra ≤ 0.25 μm) / Matte (Ra ≤ 0.40 μm) | GB/T 8898 |
| Bending Radius (Min.) | ≥ 3D (D = OD) | — |
| Pressure Rating | Up to 1.6 MPa (design), 2.4 MPa (burst) | ASME B31.5 |
| Welding Quality | 100% radiographic testing (RT) on butt welds | ASME Section IX |
| End Condition | Plain end / Beveled end / Threaded end (optional) | — |
| Coil Winding | Single-layer or multi-layer spiral winding | — |
4. Manufacturing Process
- Coil Slitting & Annealing: Cold-rolled stainless steel strip (冷轧带钢) is slit to precise width and solution-annealed at 1050–1100°C in a protective atmosphere (氩气保护) to restore full austenitic structure and maximize ductility.
- Forming & Welding (纵焊成型): The flat strip is formed into a tubular cross-section via roll-forming dies, followed by continuous longitudinal TIG welding (钨极惰性气体保护焊, AWS D10.9) or orbital welding. Weld beads are internally and externally ground flush for hydraulic smoothness.
- Post-Weld Heat Treatment: Solution treatment (固溶处理) at 1050°C followed by rapid water quenching to dissolve carbides and ensure uniform austenite grain structure.
- Coil Winding & Bending: The straight tube is wound into the required coil geometry using CNC-controlled coiling equipment, maintaining minimum bending radius to prevent ovality and wall thinning. The coil shape is designed per CFD-optimized flow path configurations to ensure uniform water distribution (布水均匀性) within the ice storage tank.
- Surface Treatment: Mechanical polishing (机械抛光) or electrochemical passivation (电化学钝化) to achieve specified surface roughness and enhance corrosion resistance.
- Non-Destructive Testing (NDT): Hydrostatic pressure testing at 1.5× design pressure, followed by eddy current inspection (涡流检测) and ultrasonic testing (超声检测) for weld integrity.
5. Applications
- Ice Storage Tanks (蓄冰槽): Primary heat exchange coil within thermal energy storage systems for peak-load shifting in district cooling networks
- Chilled Water Systems: Heat exchanger tubes in commercial and industrial refrigeration systems
- Building HVAC: Coil tubes for air handling units (AHU) and fan coil units (FCU)
- Food & Pharmaceutical Processing: Sanitary-grade heat exchange in hygienic fluid processing lines
- Marine & Offshore: Seawater heat exchangers and condensers in marine propulsion systems
- Power Generation: Condenser tubes in nuclear and fossil-fuel power plants
- Solar Thermal Systems: Collector tubes in concentrated solar power (CSP) installations
6. Quality Certifications & Standards Compliance
- ISO 9001:2015 — Quality Management System (质量管理体系)
- ISO 14001:2015 — Environmental Management System (环境管理体系)
- ISO 45001:2018 — Occupational Health & Safety Management System (职业健康安全管理体系)
- EN 10204 3.1 — Material Test Certificate (材料试验证书)
- ASTM A213 / A778 — Seamless and welded austenitic stainless steel tubes
- GB/T 12771 — Chinese national standard for stainless steel welded tubes
- ASME SA-213 / SA-778 — Boiler and pressure vessel code specifications
- PED 2014/68/EU — European Pressure Equipment Directive compliance (where applicable)
- NSF/ANSI 61 — Drinking water system components (for potable water applications)
7. Unique Selling Points (USP)
CFD-Optimized Coil Geometry: The coil tube configuration is validated through Computational Fluid Dynamics (CFD, 计算流体力学) numerical simulation, ensuring superior water distribution uniformity (布水均匀性) within ice storage tanks compared to conventional designs. This optimization reduces thermal stratification, improves ice formation rate by up to 15–20%, and enhances overall system efficiency.
- Hydraulic Smoothness: Flush-ground longitudinal welds ensure minimal flow resistance and prevent biofilm accumulation, critical for long-term performance in closed-loop systems.
- Customization Capability: Flexible dimensional customization (custom outer diameter, wall thickness, coil length, and winding pattern) to match specific system design requirements.
- Full Traceability: Each coil batch is accompanied by a complete material traceability chain from mill certificate to final NDT report, ensuring full quality accountability.
- Corrosion Durability: Long service life in aggressive environments (brine, seawater, chemical solutions) without degradation of mechanical properties or structural integrity.
- Hygienic Design: Mirror-polished interior surface meets pharmaceutical and food-grade requirements, facilitating CIP (Clean-In-Place) and SIP (Sterilization-In-Place) protocols.
8. Technical Notes & Recommendations
- For ice storage tank applications operating with calcium chloride brine (CaCl₂, 氯化钙盐水), SUS316L grade is strongly recommended to mitigate chloride stress corrosion cracking (Cl-SCC, 氯化物应力腐蚀开裂) risk.
- Support spacing along the coil should not exceed 3D (outer diameter) to prevent vibration-induced fatigue under turbulent flow conditions.
- During installation, ensure proper thermal expansion compensation (热膨胀补偿) to accommodate differential expansion between the coil tube and the tank shell.
- Preventive maintenance should include periodic inspection of weld joints via eddy current testing, particularly in systems with high cycle frequency (冰融循环频繁系统).