Stainless Steel Coil Tube — Thermal Energy Storage Application Series
Product Overview
The Stainless Steel Coil Tube is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd., designed primarily for advanced thermal energy storage (TES) systems, refrigeration heat exchangers, and partial-freezing ice storage applications. This coil tube product line is engineered to deliver superior thermal conductivity, mechanical integrity, and long-term corrosion resistance under demanding cryogenic and sub-zero operating conditions. The product designation is catalogued under internal reference number 1318 and falls within the company's technical documentation and literature-based product development framework.
Grounded in rigorous academic research — specifically the study titled "Research on Heat Transfer Performance of Thermal Plastic Ice Storage Coil Tubes under Partial Freezing Conditions" — this product line incorporates validated thermodynamic principles to optimize heat transfer efficiency during phase-change thermal energy storage cycles. The coil tube geometry and material selection have been refined through empirical and computational fluid dynamics (CFD) analysis to maximize surface-area-to-volume ratios, minimize thermal resistance, and ensure uniform heat flux distribution across the tube bundle.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its exceptional combination of thermal, mechanical, and chemical properties under cryogenic and ambient operating environments.
- Base Material: Austenitic Stainless Steel (e.g., Type 304 / Type 316 / Type 321), conforming to ASTM A213, ASTM A269, and EN 10216 standards
- Corrosion Resistance: Excellent resistance to pitting, crevice corrosion, and intergranular corrosion due to high chromium (Cr ≥ 18%) and nickel (Ni ≥ 8%) alloy content; Type 316 variants include molybdenum (Mo 2–3%) for enhanced chloride resistance
- Thermal Conductivity: 14–16 W/(m·K) at 20°C, providing efficient heat transfer during both sensible and latent heat exchange phases
- Cryogenic Performance: Maintains full ductility and fracture toughness at temperatures as low as −196°C (Liquid Nitrogen temperature), with no risk of brittle fracture
- Mechanical Properties: Tensile strength ≥ 515 MPa, yield strength ≥ 205 MPa, elongation ≥ 40% (typical for annealed austenitic grades)
- Surface Finish: Electropolished or passivated inner and outer surfaces (Ra ≤ 0.4 μm) to minimize fouling resistance and reduce pressure drop
- Hygienic Compliance: Suitable for food-grade (FDA 21 CFR) and pharmaceutical (USP Class VI) applications where applicable
Specifications
| Parameter | Specification / Range | Standard / Reference |
|---|---|---|
| Product Designation | Stainless Steel Coil Tube (Ref. No. 1318) | Internal Catalog |
| Tube Outer Diameter (OD) | 6 mm – 50 mm (customizable) | ASTM A213 / ASTM A269 |
| Wall Thickness | 0.5 mm – 3.0 mm | EN 10216-5 |
| Coil Winding Diameter | 100 mm – 2,000 mm (configurable) | Project-Specific Design |
| Coil Length / Total Tube Length | Up to 200 m per coil (continuous) | — |
| Material Grades | 304, 304L, 316, 316L, 321 | ASTM A240 / ASME SA-240 |
| Operating Temperature Range | −196°C to +450°C | ASME BPV Code Section II |
| Maximum Operating Pressure | Up to 4.0 MPa (design-dependent) | ASME BPV Code |
| Heat Transfer Coefficient (h) | 2,500 – 6,000 W/(m²·K) (partial freezing regime) | Research-based validation |
| Surface Roughness (Ra) | ≤ 0.4 μm (electropolished) | ASTM A967 |
| End Treatment | Butt-welded, flanged, or thread-fitted connections | ASME B16.9 / ISO 14288 |
| Quality Testing | Hydrostatic pressure test, dimensional inspection, spectral analysis, radiographic testing (RT) | EN 10204 3.1 |
Manufacturing Process
The production of the Stainless Steel Coil Tube follows a multi-stage precision manufacturing workflow designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Material Selection & Incoming Inspection: Raw stainless steel wire or tube stock is sourced from certified mills with full material traceability (Mill Test Certificate per EN 10204 3.1). Incoming materials undergo positive material identification (PMI) via optical emission spectrometry (OES) to verify alloy composition.
- Hot/Fine Drawing: Wire or tube blanks are drawn through calibrated tungsten carbide dies to achieve precise outer diameter and wall thickness tolerances (±0.02 mm). Multiple drawing passes may be applied for tight tolerance requirements.
- Intermediate Annealing: Periodic solution annealing at 1050–1150°C followed by controlled cooling relieves work hardening, restores full austenitic microstructure, and eliminates residual stresses introduced during cold forming.
- Coil Winding: The drawn tube is wound onto precision mandrels using CNC-controlled coil winding machinery to produce uniform helical or spiral coil geometries. Winding tension is carefully controlled to prevent ovalization or permanent deformation of the tube cross-section.
- Final Annealing & Pickling: The wound coil undergoes final annealing to stabilize dimensions, followed by acid pickling (HNO₃/HF blend) to remove oxide scale and restore the natural passive chromium oxide layer.
- Surface Finishing: Electropolishing is applied to achieve Ra ≤ 0.4 μm surface roughness, critical for minimizing fouling resistance and enhancing convective heat transfer coefficients in thermal storage applications.
- Quality Assurance & Testing: Each coil batch undergoes comprehensive non-destructive testing (NDT), including hydrostatic pressure testing (at 1.5× design pressure), dimensional verification via coordinate measuring machine (CMM), and optional radiographic testing (RT) or ultrasonic testing (UT) for weld integrity.
Applications
The Stainless Steel Coil Tube is engineered for a broad spectrum of industrial and commercial applications, with particular strength in thermal energy storage and heat exchange systems:
- Thermal Energy Storage (TES) Systems: Core heat transfer element in ice storage (latent heat storage) systems, where the coil tube facilitates efficient heat transfer between the refrigerant and the phase-change material (PCM) during both charging (freezing) and discharging (melting) cycles. Research has validated that partial freezing conditions optimize heat transfer performance by maintaining a stable solid-liquid interface along the tube surface.
- Cryogenic Refrigeration: Evaporator and condenser coils for industrial refrigeration systems, ammonia-based refrigeration, and liquid nitrogen handling equipment, leveraging the material's exceptional cryogenic toughness.
- Food & Beverage Processing: Heat exchanger coils for pasteurization, sterilization, and rapid cooling processes in dairy, beverage, and pharmaceutical manufacturing, compliant with food-grade hygiene standards.
- Chemical & Petrochemical Industry: Reactor cooling coils, heat recovery units, and process heat exchangers where resistance to corrosive media and high-pressure operation is required.
- Building HVAC Systems: Coil assemblies for chiller plants, district cooling networks, and peak-load management systems utilizing ice storage for energy efficiency optimization.
- Power Generation: Feedwater heaters, economizer coils, and steam generator tube bundles in fossil fuel and nuclear power plants.
- Automotive & Aerospace: Precision coil tubes for fuel systems, hydraulic lines, and thermal management components requiring high purity and leak-free performance.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring that every Stainless Steel Coil Tube product meets or exceeds international standards:
- ISO 9001:2015 — Quality Management Systems certification covering all manufacturing, inspection, and delivery processes
- ISO 14001:2015 — Environmental Management Systems certification demonstrating commitment to sustainable manufacturing practices
- EN 10204 Type 3.1 — Third-party inspection certificates issued by independent survey organizations (e.g., BV, SGS, Lloyd's Register) for material and workmanship verification
- ASME BPV Code — Compliance with American Society of Mechanical Engineers Boiler and Pressure Vessel Code for pressure-containing applications
- CE Marking — Conformity with European directives for pressure equipment (PED 2014/68/EU) and machinery safety
- Mill Test Certificates (MTC) — Full chemical composition analysis and mechanical property reports provided with each shipment, traceable to the original steel mill heat number
- NACE MR0175 / ISO 15156 — Compliance for sour service applications (H₂S-containing environments), where applicable
- 3-A Sanitary Standards — Certification for dairy and food industry applications, ensuring hygienic design and cleanability
Unique Selling Points
Research-Validated Thermal Performance: Unlike conventional coil tubes, this product line is engineered based on peer-reviewed academic research into heat transfer performance under partial freezing conditions. This research-driven approach ensures that the coil tube geometry, surface finish, and material properties are specifically optimized for latent heat storage efficiency, delivering measurable improvements in system COP (Coefficient of Performance) and cycle time.
- Superior Cryogenic Integrity: Full austenitic microstructure provides unmatched ductility and toughness at extreme low temperatures, eliminating the risk of catastrophic brittle failure common in ferritic or martensitic steel alternatives.
- Electropolished Surface for Maximum Heat Transfer: The Ra ≤ 0.4 μm surface finish minimizes thermal boundary layer resistance, directly increasing the convective heat transfer coefficient by up to 20% compared to standard pickled surfaces.
- Full Material Traceability: Every coil tube is traceable from the original steel mill heat number through all manufacturing stages, providing complete supply chain transparency and quality accountability.
- Customizable Geometry: Flexible manufacturing capabilities allow for custom coil winding diameters, tube lengths, and end treatments tailored to specific system integration requirements.
- Multi-Grade Availability: A range of stainless steel grades (304, 316, 321) accommodates diverse chemical environments, from clean water systems to aggressive chloride-containing solutions.
Technical Reference
This product specification is informed by the academic study: "Research on Heat Transfer Performance of Thermal Plastic Ice Storage Coil Tubes under Partial Freezing Conditions" (Internal Reference No. 1318). The research demonstrates that under partial freezing conditions — where the phase-change material (water/ice) exists in a mixed solid-liquid state along the coil tube surface — the heat transfer coefficient can be significantly enhanced compared to fully frozen or fully liquid states. This phenomenon is attributed to the maintenance of a thin liquid film between the tube wall and the growing ice layer, which reduces conductive thermal resistance and promotes natural convection currents within the storage medium. The product design incorporates these findings to optimize coil spacing, tube diameter, and surface characteristics for maximum thermal performance in practical ice storage system deployments.