Stainless Steel Coil Tube for Ice Thermal Storage Cooling Systems
Product Overview
The stainless steel coil tube (盘管) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product specifically designed for integration into ice thermal storage cooling systems. This product represents a critical component in advanced HVAC (Heating, Ventilation, and Air Conditioning) infrastructure, where coil tubes serve as the primary heat exchange medium between the refrigerant circuit and the ice storage medium.
In the context of combined internal and external ice melting coil tube systems (内融冰与外融冰结合的盘管式冰蓄冷系统), these stainless steel coil tubes are arranged in helical or serpentine configurations within ice storage tanks. The coils facilitate the formation of ice during off-peak electricity periods and subsequently release stored thermal energy during peak demand periods, thereby achieving load shifting and peak shaving in commercial and industrial cooling applications.
Stainless steel coil tubes offer superior corrosion resistance, long service life, and excellent thermal conductivity properties that make them ideal for the aggressive chemical environments encountered in ice storage systems, where antifreeze solutions, residual chlorides, and varying water qualities present significant material challenges.
Material & Properties
Base Material Composition
The coil tubes are fabricated from austenitic stainless steel grades conforming to international standards, with the following typical compositions:
- Grade 304 (UNS S30408): 18–20% Chromium (Cr), 8–10.5% Nickel (Ni), <0.08% Carbon (C), <2.0% Manganese (Mn), <1.0% Silicon (Si)
- Grade 316 (UNS S31603): 16–18% Cr, 10–14% Ni, 2–3% Molybdenum (Mo), <0.08% C — enhanced resistance to chloride-induced pitting and crevice corrosion
- Grade 316L (UNS S31603L): Low-carbon variant (<0.03% C) for superior weldability and resistance to intergranular corrosion (IGC, Intergranular Corrosion)
Mechanical Properties
- Tensile Strength (Rm): 515–750 MPa (yield strength Rp0.2: ≥205 MPa for annealed condition)
- Elongation (A): ≥40% (indicating excellent formability for coil winding)
- Hardness: 180–220 HV (annealed condition)
- Impact Toughness: ≥47 J at −40°C (Charpy V-notch test, demonstrating cryogenic suitability)
Thermal Properties
- Thermal Conductivity (λ): 14.9–16.3 W/(m·K) at 20°C
- Specific Heat Capacity (cp): 500 J/(kg·K) at 20°C
- Linear Thermal Expansion Coefficient (α): 16.0–17.5 × 10−6 /°C
- Operating Temperature Range: −196°C to +870°C (non-oxidizing atmosphere)
Corrosion Resistance
The passive chromium oxide film (Cr2O3) formed on the stainless steel surface provides exceptional resistance to:
- General atmospheric corrosion
- Chemical attack from glycol-based antifreeze solutions (ethylene glycol, propylene glycol)
- Pitting and crevice corrosion in chloride-containing environments (especially with Grade 316/316L)
- Microbiologically Influenced Corrosion (MIC)
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Tube Outer Diameter (OD) | 12 mm – 50 mm (standard); up to 88.9 mm (custom) | GB/T 14976, ASTM A312 |
| Wall Thickness | 1.0 mm – 3.0 mm (standard range) | GB/T 14976, EN 10216 |
| Coil Winding Diameter | 300 mm – 2,000 mm (configurable) | Manufacturer specification |
| Coil Length per Spool | 50 m – 500 m (continuous) | — |
| Surface Finish | 2B, BA (Bright Annealed), No. 4 Brushed, or Electropolished (Ra ≤ 0.4 μm) | ASTM A480 |
| End Condition | Plain end, threaded (BSP/NPT), or welded end caps | ISO 7, GB/T 24599 |
| Pressure Rating | Up to 1.6 MPa (standard); up to 4.0 MPa (heavy wall) | PNEU/EN 13480 |
| Hydrostatic Test Pressure | 1.5 × design pressure (minimum) | GB/T 14976 |
| Tolerance on OD | ±0.15 mm (standard); ±0.08 mm (precision) | ISO 4287 |
| Tolerance on Wall Thickness | ±10% (standard); ±5% (precision) | GB/T 14976 |
| Coil Pitch | 15 mm – 60 mm (adjustable for heat transfer optimization) | — |
| Winding Tolerance | ±1.0 mm (concentricity) | — |
| Available Grades | 304, 304L, 316, 316L, 321, 347 | ASTM A312, EN 10217 |
| Welding Method | TIG (Tungsten Inert Gas), Pulse Arc, Orbital | ISO 15614, ASME IX |
| Packaging | Wooden crate with moisture barrier; coil secured with steel straps | ISO 4180 |
Manufacturing Process
Step 1: Raw Material Procurement and Inspection
Hot-rolled stainless steel strip or seamless tube blanks are procured from certified mills. Incoming material undergoes strict inspection including Chemical Composition Analysis (spectrometry), mechanical property verification (tensile testing), and surface quality assessment. Mill test certificates (MTC, Mill Test Certificate) conforming to EN 10204 Type 3.1 are required.
Step 2: Annealing and Pickling
For cold-worked materials, solution annealing is performed at 1050–1150°C followed by rapid quenching (water or air) to dissolve carbides and restore the fully austenitic microstructure. Subsequent pickling (dilute nitric acid/hydrofluoric acid bath) removes oxide scale and activates the passive film formation.
Step 3: Coil Winding (Forming)
The straight tube is fed through a precision winding machine equipped with CNC (Computer Numerical Control) guided rollers. The tube is progressively bent into a helical coil configuration with controlled pitch and diameter. Key process parameters include:
- Bending die radius: ≥3× tube OD (to prevent ovality and wall thinning)
- Winding speed: 0.5–3.0 m/min (depending on diameter and material grade)
- Forming force: monitored to prevent work hardening beyond acceptable limits
Step 4: Post-Forming Stress Relief
After winding, the coil undergoes controlled stress relief annealing at 400–500°C (for 300-series) to eliminate residual stresses introduced during forming. This step is critical to prevent stress corrosion cracking (SCC) in service.
Step 5: End Preparation and Welding
Coil ends are prepared for system integration through:
- End cutting and deburring (tolerance ±0.1 mm)
- Thread machining or end fitting welding (TIG welding with argon shielding, purge gas on inner diameter)
- Weld quality verification via Visual Testing (VT) and/or Dye Penetrant Testing (PT)
Step 6: Pressure Testing
Each coil assembly undergoes hydrostatic pressure testing at 1.5× the design pressure for a minimum hold time of 30 minutes. No visible leakage or dimensional change is permitted. For critical applications, pneumatic testing or helium leak detection is employed.
Step 7: Surface Treatment (Optional)
Electropolishing may be applied to achieve a surface roughness (Ra) of ≤0.4 μm, enhancing both corrosion resistance and reducing fouling tendency in heat transfer applications. Passivation treatment (citric acid or nitric acid immersion) is performed as a final step to maximize the protective oxide layer.
Step 8: Quality Control and Documentation
Comprehensive quality documentation is compiled including:
- Material certification (EN 10204 3.1)
- Dimensional inspection reports
- Pressure test records
- Welding procedure qualifications (WPQR, Welding Procedure Qualification Record)
- Non-Destructive Testing (NDT) reports where applicable
Applications
Primary Application: Ice Thermal Storage Cooling Systems
The principal application of these stainless steel coil tubes is in ice thermal storage systems (Ice Storage Cooling Systems), where they function as the heat exchange element within ice storage tanks. The system operates on the principle of:
- Freezing Mode (Ice Making): Chilled brine or refrigerant flows through the coil tubes at −6°C to −12°C, extracting latent heat from surrounding water to form ice layers on the tube surfaces. In combined internal/external ice melting systems, ice forms both inside the tube bore (internal ice, 内融冰) and on the external surface (external ice, 外融冰).
- Discharge Mode (Cooling): Warm process water (typically 12–18°C) flows through the coil tubes, melting the stored ice and delivering chilled water (2–7°C) to the building cooling load.
System Integration Advantages
- Load Shifting: Enables utilization of off-peak electricity for ice production, reducing peak demand charges by 30–60%
- Backup Cooling: Provides emergency cooling capacity during grid failures or chiller breakdowns
- System Efficiency: Improves overall coefficient of performance (COP) by 15–25% compared to conventional direct-expansion systems
- Space Optimization: Ice storage tanks occupy less space than equivalent chilled water storage
Additional Applications
- Refrigeration and cold chain logistics systems
- Industrial process cooling (chemical, pharmaceutical, food processing)
- Geothermal heat exchangers
- Marine and offshore cooling systems (Grade 316/316L recommended)
- Medical and laboratory cryogenic systems
- Solar thermal storage systems
Quality Certifications
Product Standards Compliance
| Standard | Scope |
|---|---|
| GB/T 14976-2012 | Seamless stainless steel tubes for fluid transport (Chinese National Standard) |
| GB/T 17895-2019 | Stainless steel coils and tubes for heat exchangers |
| ASTM A312/A312M | Seamless and welded austenitic stainless steel tubes |
| EN 10216-5 | Welded stainless steel tubes for pressure purposes |
| ASME B31.3 | Process piping design requirements |
| ISO 13711 | Welding qualification procedures for stainless steel |
| TSG D0001-2009 | Chinese pressure vessel and piping safety regulations |
Management System Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health and Safety Management System
- ISO 15173 — Management systems for welding (where welding operations are involved)
Testing and Verification
- Dimensional verification per ISO 4287 (Geometrical Product Specifications)
- Chemical analysis per ASTM E135 / GB/T 20066
- Mechanical testing per ASTM A370 / GB/T 228.1
- Corrosion testing: Salt spray test (ASTM B117, ≥1000 hours for Grade 316L)
- Pressure testing per GB/T 14976 and applicable pressure vessel codes
- Microstructure examination per ASTM E4 (where required for weld qualification)
Unique Selling Points
1. Cryogenic Performance Excellence: The austenitic stainless steel coil tubes maintain full ductility and toughness down to −196°C (liquid nitrogen temperature), making them uniquely suitable for ice storage systems where extreme low temperatures are routinely encountered. No embrittlement or phase transformation occurs within the operating range.
2. Integrated Internal/External Ice Melting Compatibility: Designed with precise wall thickness tolerances and surface finish specifications to optimize both internal bore ice formation and external surface ice nucleation, enabling dual-mode ice storage systems with higher volumetric storage density.
3. Extended Service Life: With proper installation and maintenance, stainless steel coil tubes in ice storage systems