Stainless Steel Coil Tube for Thermal Energy Storage Systems

Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.  |  Product No.: 398  |  Category: Coil Tube (Coiltube)

Product Overview

The Stainless Steel Coil Tube is a precision-engineered coiled tubing product specifically designed for thermal energy storage and release systems. Drawing upon advanced metallurgical principles and thermal-fluid dynamics, these coil tubes serve as the critical heat transfer medium in spiral coil heat storage devices, enabling efficient accumulation, retention, and controlled release of thermal energy. The product is manufactured from high-grade austenitic stainless steel, exhibiting exceptional resistance to oxidation, corrosion, and thermal fatigue under prolonged cyclic operating conditions.

The coil geometry is optimized to maximize the surface-area-to-volume ratio, thereby enhancing convective and conductive heat transfer efficiency. These coil tubes are integral components in industrial-scale thermal energy storage systems, solar thermal collectors, geothermal heat exchangers, and waste heat recovery installations.

Material & Properties

The coil tubes are fabricated from premium austenitic stainless steel grades, with 304 (UNS S30400) and 316 (UNS S31600) being the standard material options, and 321 (UNS S32100) available for high-temperature applications. The material composition and resulting properties are as follows:

• Base Alloy System: Iron (Fe) balance with Chromium (Cr) 18–20%, Nickel (Ni) 8–12%, and controlled Manganese (Mn) ≤ 2.0%
• Corrosion Resistance: Superior resistance to pitting (Pitting), crevice corrosion (Crevice Corrosion), and intergranular corrosion (Intergranular Corrosion) due to the high Chromium and Nickel content
• Thermal Conductivity: 16.3 W/(m·K) at 20°C for Grade 304; suitable for efficient heat transfer applications
• Maximum Operating Temperature: Up to 870°C (Grade 321); up to 800°C (Grade 304/316)
• Yield Strength (0.2% Proof Stress): ≥ 205 MPa (Annealed Condition)
• Tensile Strength (R_m): 515–730 MPa
• Elongation (A₅₀): ≥ 40%, ensuring excellent formability during cold coiling
• Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (20–100°C)
• Surface Finish: 2B (Cold Rolled and Annealed Bright) or BA (Bright Annealed), with surface roughness Ra ≤ 0.8 μm

Specifications

Parameter	Specification
Outer Diameter (OD)	6.0 mm – 50.8 mm (¼" – 2")
Wall Thickness (WT)	0.5 mm – 3.0 mm
Coil Diameter (CD)	50 mm – 500 mm (configurable)
Coil Pitch	10 mm – 100 mm (adjustable per thermal design requirements)
Coil Length (per spool)	5 m – 50 m (custom lengths available)
Material Grades	304, 304L, 316, 316L, 321, 310S (upon request)
Surface Treatment	2B, BA, No. 4 Brushed, Electropolished
End Condition	Plain end, Beveled end, Threaded end, Flanged end
Tolerance (OD)	±0.05 mm – ±0.10 mm (per ASTM A213)
Tolerance (WT)	±10% (minimum wall thickness guaranteed)
Operating Pressure (Design)	Up to 2.5 MPa (subject to system design)
Operating Temperature Range	−196°C to +870°C
Applicable Standards	ASTM A213/A213M, ASME SA-213, EN 10216-5, GB/T 12771
Coating Options	Bare (uncoated), PTFE (Polytetrafluoroethylene) lined (special order)
Packaging	Wooden crate with moisture-proof wrapping, or export-standard seaworthy packing

Manufacturing Process

The production of stainless steel coil tubes involves a multi-stage metallurgical and forming process designed to ensure dimensional accuracy, mechanical integrity, and consistent material properties throughout the coil geometry:

1. Raw Material Selection and Inspection: Ingot or rolled strip material conforming to the specified ASTM/EN/GB grade is received and subjected to spectrographic analysis (Spectrographic Composition Analysis) to verify chemical composition. Incoming material undergoes visual inspection and ultrasonic testing (Ultrasonic Testing, UT) for internal soundness.
2. Slitting and Cutting: The stainless steel strip is slit to the precise width corresponding to the desired coil tube outer diameter and wall thickness. Edges are inspected for burrs and defects.
3. Forming (Roll Forming / Pipe Welding): The strip is fed through a series of precision forming rolls to create the circular tube cross-section. For welded coil tubes, the formed strip is joined via Automatic Submerged Arc Welding (SAW), Gas Metal Arc Welding (GMAW), or TIG Welding (Tungsten Inert Gas Welding) with continuous argon shielding. Seamless coil tubes are produced via Cold Drawing (Cold Drawn) through a die set.
4. Coiling / Spiral Winding: The formed tube is wound onto a precision mandrel using CNC-controlled coiling equipment. The coil pitch, coil diameter, and total length are controlled to ±0.5 mm tolerance to meet the thermal design requirements of the heat storage device.
5. Solution Heat Treatment (Annealing): The coiled product is subjected to solution annealing at 1050–1150°C followed by rapid water quenching. This process dissolves carbide precipitates at grain boundaries, restoring full corrosion resistance and eliminating residual stresses introduced during forming.
6. Pickling and Passivation: The annealed coil tube is pickled in a mixed acid bath (Nitric Acid + Hydrofluoric Acid) to remove oxide scale, followed by passivation treatment to form a stable chromium oxide (Cr₂O₃) passive film on the surface.
7. Quality Control and Testing: Each production batch undergoes comprehensive testing including Hydrostatic Testing (water pressure test at 1.5× working pressure), Dimensional Measurement, Surface Defect Inspection, and Dye Penetrant Testing (Dye Penetrant Testing, PT) for weld integrity.
8. Packaging and Dispatch: The finished coil tubes are wound, secured, and packed in export-grade wooden crates with desiccant bags to prevent moisture exposure during transit.

Applications

The Stainless Steel Coil Tube finds extensive application across multiple industrial sectors, particularly in systems requiring efficient thermal energy management:

• Thermal Energy Storage Systems (TES): Spiral coil heat storage devices utilize these coil tubes as the primary heat transfer element, storing excess thermal energy (from solar, industrial waste heat, or grid electricity) in a phase-change material (Phase Change Material, PCM) or sensible heat storage medium for later release.
• Solar Thermal Collectors: Coil tubes serve as the working fluid channel in evacuated tube solar collectors and flat-plate collectors, absorbing solar radiation and transferring thermal energy to a heat transfer fluid.
• Geothermal Heat Exchangers: Used in closed-loop geothermal systems where coil tubes circulate heat transfer fluid through boreholes to extract or inject thermal energy from the ground.
• Industrial Waste Heat Recovery: Integrated into heat exchanger bundles to recover waste heat from industrial processes (smelting, cement production, chemical reactors) for energy reuse.
• Food and Beverage Processing: Employed in pasteurization systems, brewing equipment, and dairy processing plants where sanitary-grade corrosion resistance is critical.
• Pharmaceutical and Chemical Industries: Used in reaction vessel cooling coils and process heat exchangers requiring high purity and resistance to chemical attack.
• HVAC Systems: Coil tubes are used in chiller evaporators, condensers, and air handling units for efficient heat exchange.
• Oil and Gas Industry: Applied in subsea heat exchangers and wellhead equipment requiring resistance to sour gas (H₂S) environments.

Quality Certifications and Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems to ensure every coil tube product meets or exceeds international standards:

• ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and continuous improvement
• ISO 14001:2015 — Environmental Management System certification for sustainable manufacturing practices
• CE Marking — Conformity with European health, safety, and environmental protection standards
• ASTM A213/A213M — Standard Specification for Austenitic Stainless Steel Tubing for High-Temperature Service
• ASME SA-213 — American Society of Mechanical Engineers specification for austenitic stainless steel tubing
• EN 10216-5 — European standard for welded tubes for heat exchangers and similar applications
• GB/T 12771 — Chinese national standard for seamless stainless steel tubes for fluid transport
• Mill Test Certificates (MTC) — EN 10204 3.1 Certificate provided with every shipment, documenting chemical composition, mechanical properties, and test results
• Third-Party Inspection — Available upon request from SGS, BV (Bureau Veritas), or TÜV for pre-shipment verification

Unique Selling Points

1. Optimized Spiral Geometry for Maximum Heat Transfer: The coil tube geometry is engineered with precise pitch and diameter control to maximize the heat transfer surface area within a compact volume, achieving thermal efficiency improvements of 15–30% compared to straight-tube configurations in heat storage devices.

2. Full Process Traceability: Every coil tube batch is traceable from raw material ingot through to final product, with complete documentation of chemical analysis, heat treatment parameters, and mechanical test results.

3. Custom Engineering Capability: Wenzhou Jixing Metal Materials offers fully customizable coil tube solutions — from non-standard dimensions to specialized end preparations — tailored to the specific thermal design requirements of each application.

4. Superior Thermal Fatigue Resistance: The austenitic microstructure and solution-annealed condition provide exceptional resistance to thermal cycling fatigue, enabling reliable operation through thousands of heat storage and release cycles without degradation.

5. Comprehensive Testing Protocol: Hydrostatic testing, dimensional verification, surface defect inspection, and weld integrity testing are performed on 100% of production batches, not merely sampling-based inspection.

For detailed quotations, custom engineering support, and technical consultation, please contact Wenzhou Jixing Metal Materials Co., Ltd. directly. Technical data sheets and material test certificates are available upon request.