Stainless Steel Spiral Coil Tube (Coiltube) — PCM Heat Storage Application
Product Overview
The Stainless Steel Spiral Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered helical tubing product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. (Serial No. 692). This product is specifically designed for use in Phase Change Material (PCM) heat storage systems, where it serves as the primary heat transfer conduit within composite PCM heat accumulators. The helical coil geometry maximizes the surface-area-to-volume ratio, enabling efficient thermal exchange between the working fluid and the surrounding phase change medium.
Based on rigorous numerical research into the structural and performance characteristics of helical coil heat storage tanks utilizing composite phase change materials, this Coiltube product has been optimized for superior thermal performance, mechanical integrity, and long-term operational reliability under repeated thermal cycling conditions.
Material and Properties
The Coiltube is fabricated from high-grade austenitic stainless steel, selected for its exceptional combination of corrosion resistance, thermal conductivity, and mechanical strength across a wide temperature range. The primary material grades utilized include:
- 304 (UNS S30408) — General-purpose austenitic stainless steel with excellent corrosion resistance and formability
- 316L (UNS S31603) — Low-carbon variant with superior resistance to chlorides and aggressive chemical environments
- 321 (UNS S32100) — Titanium-stabilized grade offering enhanced resistance to intergranular corrosion at elevated temperatures
Key material properties:
- Thermal Conductivity (at 20°C): 14.9–16.3 W/(m·K)
- Specific Heat Capacity: 498–503 J/(kg·K)
- Thermal Expansion Coefficient (20–100°C): 16–18 × 10⁻⁶ /K
- Yield Strength (minimum): 205 MPa (304 grade)
- Tensile Strength (minimum): 515 MPa (304 grade)
- Operating Temperature Range: −196°C to +870°C (depending on grade)
- Corrosion Resistance: Excellent against atmospheric, aqueous, and many chemical environments
Specifications
| Parameter | Specification | Unit |
|---|---|---|
| Product Name | Stainless Steel Spiral Coil Tube (Coiltube) | — |
| Serial Number | 692 | — |
| Material Grade | 304 / 316L / 321 (customizable) | — |
| Outer Diameter (OD) | 6.0 – 50.0 (customizable) | mm |
| Wall Thickness | 0.5 – 3.0 | mm |
| Coil Pitch (Helix Spacing) | 10.0 – 100.0 (customizable) | mm |
| Coil Diameter (Mean) | 50.0 – 500.0 (customizable) | mm |
| Coil Length (Developed) | 1.0 – 50.0 | m |
| Surface Finish | No. 4 Brushed / 2B / Mirror Polish (Ra ≤ 0.4 μm) | — |
| Pressure Rating | Up to 2.5 MPa (tested) | MPa |
| Manufacturing Standard | ASTM A269 / ASTM A270 / EN 10216-5 | — |
| Testing Standard | ASTM A314 / ASME BPV Section VIII | — |
| Heat Treatment | Solution Annealed (1010–1150°C, water quench) | — |
| Available Configurations | Single Helix / Double Helix / Multi-Pass / Fin-Enhanced | — |
Manufacturing Process
The production of the Stainless Steel Spiral Coil Tube follows a multi-stage precision manufacturing workflow, adhering to international quality standards:
- Raw Material Inspection — Incoming stainless steel seamless or welded tubes are verified for chemical composition (via Spectrometer), mechanical properties, and dimensional accuracy per ASTM A213/A269 specifications.
- Cold Forming / Helical Coiling — Straight tube stock is fed through a CNC-controlled coiling machine, forming the helical geometry with precise pitch control (tolerance ±0.5 mm). The process utilizes progressive die tooling to maintain dimensional integrity throughout the coil.
- Heat Treatment (Solution Annealing) — Coiled assemblies undergo solution annealing at 1010–1150°C followed by rapid water quenching to relieve residual stresses, restore full austenitic microstructure, and maximize corrosion resistance.
- Precision Welding — Tube ends are joined using Tungsten Inert Gas (TIG) / Gas Tungsten Arc Welding (GTAW) under argon shielding to ensure penetration welds with minimal heat-affected zone (HAZ) distortion. Weld joints achieve full fusion with smooth, uniform bead profiles.
- Surface Finishing — Electropolishing or mechanical polishing is applied to achieve the required surface roughness, critical for minimizing flow resistance and fouling in heat transfer applications.
- Quality Inspection — Each unit undergoes hydrostatic pressure testing (1.5× working pressure), dimensional verification (CMM or laser scanning), and visual inspection for surface defects.
- Packaging and Delivery — Coils are secured in protective packaging to prevent mechanical deformation and surface damage during transit.
Applications
The Stainless Steel Spiral Coil Tube is engineered for demanding thermal management applications, particularly within the domain of latent heat energy storage:
- Phase Change Material (PCM) Heat Storage Systems — Primary application as heat transfer coils embedded within composite PCM accumulators for solar thermal energy storage, district heating, and industrial waste heat recovery.
- Solar Thermal Energy Storage — Integration into concentrated solar power (CSP) systems where the coil transfers heat from the heat transfer fluid (HTF) to the PCM during charging, and extracts stored heat during discharge cycles.
- Industrial Process Heat Recovery — Recovery and storage of waste heat from manufacturing processes, enabling thermal energy on-demand utilization and improved energy efficiency.
- Building Thermal Management — Integration into building envelope systems for peak load shifting and thermal buffering in commercial and residential HVAC applications.
- Automotive Thermal Management — Compact coil configurations for battery thermal regulation and waste heat recovery in hybrid and electric vehicle platforms.
- Cryogenic Applications — 304/316L grade coils operating at cryogenic temperatures for liquefied natural gas (LNG) processing and scientific instrumentation.
- Food and Pharmaceutical Processing — Sanitary-grade coil assemblies for heat exchange in hygienic processing environments requiring high corrosion resistance and cleanability.
- Geothermal Energy Systems — Heat extraction coils for closed-loop geothermal heat pump systems.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality assurance systems and holds the following certifications and compliances:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001 — Environmental Management System Certification
- ASME BPV Code — Compliance with Boiler and Pressure Vessel Code (where applicable)
- CE Marking — European Conformity for machinery and pressure equipment directives
- Material Traceability — Full mill certification (MTC) provided per EN 10204 Type 3.1 for every production batch
- NDT Testing — Non-Destructive Testing including radiographic testing (RT) and dye penetrant testing (PT) available upon request
- Hydrostatic Testing — 100% hydrostatic pressure testing per ASTM A314
Unique Selling Points
The Coiltube product from Wenzhou Jixing Metal Materials Co., Ltd. distinguishes itself through the following technical advantages:
- Optimized Helical Geometry for PCM Integration — Numerically validated coil configurations that maximize heat transfer coefficients within composite PCM matrices, achieving superior charging/discharging rates compared to conventional straight-tube designs.
- Thermal Cycling Durability — Engineered to withstand thousands of thermal cycling events (up to 10,000+ cycles) without degradation of mechanical properties or structural integrity, validated through accelerated fatigue testing.
- Customizable Configurations — Flexible manufacturing capability accommodating single-helix, double-helix, multi-pass, and fin-enhanced geometries tailored to specific thermal performance requirements and spatial constraints.
- High-Precision Coiling — CNC-controlled manufacturing ensuring dimensional tolerances of ±0.5 mm on coil pitch and ±0.1 mm on tube diameter, guaranteeing seamless integration into compact heat storage assemblies.
- Superior Surface Finish — Electropolished surfaces with Ra ≤ 0.4 μm minimize thermal boundary layer resistance and reduce fouling accumulation, maintaining long-term thermal efficiency.
- Full Material Traceability — End-to-end traceability from raw material mill certificates through finished product testing, ensuring compliance with the most stringent regulatory requirements.
- Research-Backed Design — Product specifications informed by numerical simulation research on composite PCM heat storage systems, providing performance predictability and reliability assurance.
Technical Note: The helical coil configuration employed in this product leverages the enhanced secondary flow (Dean vortices) generated in curved tube geometries, which significantly improves the convective heat transfer coefficient compared to straight tubes of equivalent diameter. This effect, combined with the high surface-area-to-volume ratio of the spiral geometry, results in substantially improved thermal performance within PCM heat storage systems, as validated by computational fluid dynamics (CFD) and finite element analysis (FEA) studies.
Compliance with International Standards
- ASTM A269 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Similar Severe Service
- ASTM A270 — Standard Specification for Austenitic Stainless Steel Tubing for Chemical and Similar Severe Service
- EN 10216-5 — Non-ferrous metal seamless tubes for pressure purposes — Part 5: Technical delivery conditions for austenitic stainless steel tubes
- GB/T 12771 — Chinese National Standard for Stainless Steel Tubes for General Purposes
- JIS G3459 — Japanese Industrial Standard for Stainless Steel Tubes for General Purposes