Stainless Steel Coil Tube (盘管 Coiltube) — Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (盘管 Coiltube), manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered tubular product formed into continuous helical or spiral configurations. This product is specifically designed for high-performance thermal energy storage systems, including ice storage (Ice Storage) devices, where the coil tube serves as the primary heat exchange element. The coiled geometry maximizes surface area within a compact envelope, enabling efficient heat transfer between the working fluid and the surrounding medium.
As a specialist in stainless steel pipe and tube manufacturing, Wenzhou Jixing Metal Materials Co., Ltd. leverages decades of metallurgical expertise to deliver coil tubes with exceptional dimensional accuracy, mechanical integrity, and corrosion resistance. The product is engineered to withstand cyclic thermal loading, pressure differentials, and prolonged exposure to aggressive chemical environments inherent in thermal storage applications.
2. Material Composition & Properties
2.1 Base Alloy Selection
The coil tube is primarily fabricated from austenitic stainless steel (Austenitic Stainless Steel) grades conforming to international standards. The most commonly specified grades include:
- 304 Stainless Steel (UNS S30400) — Chromium-Nickel austenitic grade with balanced corrosion resistance and formability. Composition: 18.0–20.0% Cr, 8.0–10.5% Ni, ≤0.08% C, ≤2.0% Mn, ≤0.50% Si, ≤0.03% P, ≤0.03% S.
- 316 Stainless Steel (UNS S31600) — Molybdenum-bearing austenitic grade offering superior resistance to pitting and crevice corrosion. Composition: 16.0–18.0% Cr, 10.0–14.0% Ni, 2.0–3.0% Mo, ≤0.08% C, ≤2.0% Mn, ≤0.50% Si, ≤0.03% P, ≤0.03% S.
- 316L Stainless Steel (UNS S31603) — Low-carbon variant of 316 with enhanced weldability and resistance to sensitization. Carbon content ≤0.03%.
2.2 Mechanical Properties
- Tensile Strength (Ultimate Tensile Strength, UTS): ≥515 MPa (75 ksi) for Grade 304; ≥515 MPa for Grade 316L (as per ASTM A269/A270).
- Yield Strength (0.2% Proof Stress): ≥205 MPa (30 ksi).
- Elongation: ≥40% (minimum) in the as-supplied condition.
- Hardness: ≤220 HV (Brinell) / ≤95 HRB (Rockwell B) in annealed condition.
- Impact Toughness: Excellent at both ambient and cryogenic temperatures (−196°C / −320°F) due to the austenitic crystal structure (Face-Centered Cubic, FCC).
2.3 Physical & Thermal Properties
- Density: ~8.0 g/cm³ (79,200 kg/m³).
- Thermal Conductivity: 16.3 W/(m·K) at 100°C (Grade 304).
- Specific Heat Capacity: ~500 J/(kg·K) at 20°C.
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (20–100°C).
- Maximum Service Temperature: 870°C (continuous); 1100°C (intermittent).
2.4 Corrosion Resistance
The passive chromium oxide film (Cr₂O₃) formed on the surface provides inherent resistance to atmospheric corrosion, acidic environments, and chlorinated solutions. Grade 316L, with its molybdenum addition, exhibits exceptional resistance to pitting corrosion (Pitting Corrosion), crevice corrosion (Crevice Corrosion), and stress corrosion cracking (Stress Corrosion Cracking, SCC) in chloride-containing environments — making it particularly suitable for ice storage systems where brine or antifreeze solutions may be employed.
3. Technical Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Product Type | Stainless Steel Coil Tube (盘管 Coiltube) | — |
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (¼" – 2") | ASTM A269 / A270 |
| Wall Thickness (WT) | 0.5 mm – 3.0 mm | ASTM A269 / A270 |
| Coil Diameter (Helix Diameter) | 100 mm – 1,500 mm (customizable) | ISO 1198 |
| Coil Pitch | 5 mm – 50 mm (adjustable per application) | — |
| Tube Length (Uncoiled) | Up to 12,000 mm (continuous) | — |
| Surface Finish | Mill Finish / Electro-polished / Passivated (Ra ≤ 0.4 μm) | ASTM A967 |
| End Condition | Plain, Beveled, or Threaded | ASME B1.20.1 |
| Forming Method | Warm Rolling / Cold Bending / Springback Compensated | — |
| Pressure Rating | Up to 4.0 MPa (at 20°C, design dependent) | ASME B31.3 |
| Temperature Range | −196°C to +870°C (continuous) | — |
| Material Grade | 304 / 304L / 316 / 316L / 321 / 904L | ASTM A269 / A270 / EN 10216-5 |
| Tolerance — OD | ±0.05 mm (precision grade); ±0.1 mm (standard grade) | ASTM A269 |
| Tolerance — Wall Thickness | ±10% of nominal | ASTM A269 |
| Coil Roundness | ≤ 0.5% of coil diameter | ISO 1198 |
| Maximum Springback | ≤ 2° per 100 mm bend radius | — |
| Packaging | Wooden crate / Palletized with VCI (Vapor Corrosion Inhibitor) film | ISO 4180 |
4. Manufacturing Process
4.1 Raw Material Selection & Incoming Inspection
High-purity stainless steel wire rod (Wire Rod) or seamless tube blanks (Seamless Tube Blanks) are procured from certified mills. Each batch undergoes rigorous incoming quality control (Incoming Quality Control), including spectrographic analysis (Spectrographic Analysis) via Optical Emission Spectroscopy (OES) to verify chemical composition, and ultrasonic testing (Ultrasonic Testing, UT) to detect internal defects such as laminations, inclusions, or voids.
4.2 Annealing & Pickling
Before forming, the tube blanks are subjected to solution annealing (Solution Annealing) at 1050–1150°C followed by rapid air cooling to achieve a fully austenitic microstructure with optimal ductility. Subsequently, the tubes undergo acid pickling (Acid Pickling) and passivation (Passivation) per ASTM A967 to remove mill scale (Mill Scale) and restore the protective chromium oxide passive layer.
4.3 Coil Forming Process
- Feed Preparation: Straight stainless steel tube is loaded into the coiling machine (Coiling Machine) with precise feed rate control.
- Warm Forming: The tube is heated to 300–500°C (Warm Forming temperature range) to reduce forming forces and minimize residual stresses while preserving the austenitic structure. This approach avoids the ductile-to-brittle transition concerns associated with cold forming of stainless steel.
- Helical Bending: Using CNC-controlled (Computer Numerical Control) mandrel-based coiling equipment, the heated tube is wrapped around a precision mandrel (Precision Mandrel) to form the desired helical geometry. The mandrel diameter and feed rate are controlled to achieve exact coil diameter, pitch, and cross-sectional integrity.
- Springback Compensation: Advanced numerical models account for elastic springback (Elastic Springback) inherent in stainless steel to ensure dimensional accuracy post-forming.
- Welding of Coil Ends (if required): For continuous coil configurations, the tube ends are joined using orbital welding (Orbital TIG Welding) per ASME B31.3, ensuring full penetration welds with radiographic inspection (Radiographic Testing, RT) verification.
4.4 Post-Forming Heat Treatment
Following coil formation, the product may undergo stress-relief annealing (Stress-Relief Annealing) at 425–550°C for 1–2 hours to eliminate residual stresses introduced during forming. This treatment ensures dimensional stability during subsequent thermal cycling in service.
4.5 Final Inspection & Testing
- Dimensional Inspection: Laser scanning (Laser Scanning) and coordinate measurement machine (Coordinate Measurement Machine, CMM) verification of coil diameter, pitch uniformity, and cross-sectional roundness.
- Pressure Testing: Hydrostatic testing (Hydrostatic Testing) per ASTM A269 at 1.5× design pressure for 10 minutes, with zero leakage tolerance.
- Visual & Surface Inspection: Examination for kinks, wrinkles, ovality, or surface defects. Electro-polished surfaces are verified for Ra ≤ 0.4 μm using surface profilometry (Surface Profilometry).
- Magnetic Particle Inspection (MPI): Applied to weld joints to detect surface and near-surface discontinuities.
- Intergranular Corrosion Testing: ASTM A262 Practice 1E (oxalic acid test) to verify resistance to sensitization.
5. Applications
5.1 Ice Storage Thermal Energy Systems (冰蓄冷装置)
The primary application domain for this coil tube product is thermal energy storage (Thermal Energy Storage, TES) systems, specifically ice storage (Ice Storage) configurations. In such systems, the stainless steel coil tube is immersed in a phase-change material (Phase-Change Material, PCM) — typically water — within a storage tank. During off-peak electrical periods, refrigeration systems circulate a cold brine or antifreeze solution through the coil tubes, causing ice to form on the external surfaces of the tubes. The latent heat of fusion (Latent Heat of Fusion, ~334 kJ/kg for water) is stored as ice. During peak demand periods, the ice melts, releasing stored thermal energy to provide cooling. The coil tube geometry maximizes the heat transfer area (Heat Transfer Area) per unit volume, enhancing both charging and discharging rates.
5.2 Additional Applications
- Heat Exchangers (Heat Exchangers): Spiral-wound heat exchangers (Spiral-Wound Heat Exchangers) for chemical processing, power generation, and HVAC systems.
- Industrial Process Cooling: Coil tubes in condensers, evaporators, and refrigeration systems requiring high corrosion resistance.
- Food & Pharmaceutical Processing: Sanitary-grade coil assemblies for pasteurization, sterilization, and hygienic fluid handling (meeting 3-A Sanitary Standards).
- Automotive & Aerospace: Compact heat exchange coils for thermal management systems requiring lightweight, corrosion-resistant construction.
- Geothermal & Solar Thermal: Coil collectors for ground-source heat pumps (Ground-Source Heat Pumps, GSHP) and solar thermal energy collection.
- Cryogenic Applications: Storage and transfer of cryogenic fluids (LNG, Liquid Nitrogen) where austenitic stainless steel's superior low-temperature toughness is essential.
6. Quality Certifications & Standards Compliance
6.1 International Standards
- ASTM A269: Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubes for Chemical and Fossil Fuel Process Plants.
- ASTM A270: Standard Specification for Austenitic Stainless Steel Tubing, Seamless and Welded.
- ASTM A312: Standard Specification for Seamless, Welded, and Heavy-Walled Austenitic Stainless Steel Tubes for High-Pressure Boilers and Heaters.
- ASTM A967: Standard Practice for Chemical Cleaning and Passivation of Stainless Steel Parts.
- EN 10216-5: Non-alloy and Alloy Steel Tubes for Mechanical and Technical Purposes — Heat Resistant Stainless Steel Tubes.
- ISO 1198: Steel Tubes — Welded Steel Tubes — Dimensions.
- ISO 3506: Stainless Steel Fasteners — General Specifications.
6.2 Quality Management System Certifications
- ISO 9001:2015: Quality Management Systems — Requirements.
- ISO 14001:2015: Environmental Management Systems — Requirements.
- ISO 45001:2018: Occupational Health and Safety Management Systems.
- ISO 13485:2016: Quality Management Systems for Medical Devices (for pharmaceutical-grade applications).
6.3 Product-Specific Certifications
- NACE MR0175 / ISO 15156: Materials for Use in H₂S-Containing Environments in Oil and Gas Production (for oil and gas sector applications).
- PED (Pressure Equipment Directive) 2014/68/EU: Conformity assessment for pressure equipment (Category II and above).
- ASME "U" Stamp: Certification for pressure vessel and piping components.
- TÜV Certification: Third-party verification of manufacturing processes and product conformity.
7. Unique Selling Points
Precision Coil