Stainless Steel Coil Tube (Coiltube) — Model 538
Wenzhou Jixing Metal Materials Co., Ltd. presents the Model 538 Stainless Steel Coil Tube, a precision-engineered continuous coil product designed for high-performance thermal energy storage, heat exchanger, and industrial piping applications. This product line integrates advanced metallurgical formulations with state-of-the-art coil forming technology to deliver superior thermal conductivity, mechanical integrity, and long-term corrosion resistance in demanding service environments.
Product Overview
The Model 538 Stainless Steel Coil Tube is manufactured as a continuous, non-segmented coil (spool) configuration, eliminating the need for field welding at inter-pipe joints. This design principle is particularly advantageous in coil-type ice storage tanks (蓄冰槽), thermal energy storage systems, and complex heat exchange assemblies where uninterrupted fluid flow paths and uniform heat transfer characteristics are critical.
Based on extensive research into the heat transfer performance of coil-type ice storage tanks (盘管式蓄冰槽传热性能), the Model 538 coil tube has been optimized to maximize the overall heat transfer coefficient (OHTC) while minimizing pressure drop across the coil assembly. The continuous coil geometry promotes turbulent flow even at moderate Reynolds numbers, significantly enhancing convective heat exchange between the working fluid and the phase-change material (PCM) surrounding the coil.
Key advantages of the continuous coil configuration include:
- Seamless Fluid Path: No weld joints within the coil length, reducing leak risk and eliminating potential points of corrosion initiation.
- Uniform Heat Transfer: Consistent tube geometry along the entire coil length ensures predictable and homogeneous thermal performance.
- Compact Footprint: The coiled arrangement maximizes heat exchange surface area within a confined spatial volume, ideal for underground or contained ice storage tanks.
- Reduced Installation Labor: Factory-coiled delivery minimizes on-site assembly time and reduces the risk of installation defects.
- Enhanced Durability: Continuous material integrity provides superior fatigue resistance under cyclic thermal loading conditions.
Material & Properties
Base Material Composition
The Model 538 Coil Tube is fabricated from 304 (UNS S30408) or 316 (UNS S31608) austenitic stainless steel, with 316L (UNS S31603) available upon specification for chloride-rich or aggressive chemical environments. The austenitic microstructure provides excellent ductility, weldability, and resistance to stress corrosion cracking (SCC).
| Property | 304 Grade | 316 Grade | 316L Grade |
|---|---|---|---|
| Carbon (C) max | 0.08% | 0.08% | 0.03% |
| Chromium (Cr) | 18.0–20.0% | 16.0–18.0% | 16.0–18.0% |
| Nickel (Ni) | 8.0–10.5% | 10.0–14.0% | 10.0–14.0% |
| Molybdenum (Mo) | — | 2.0–3.0% | 2.0–3.0% |
| Thermal Conductivity (W/m·K) at 20°C | 16.3 | 14.6 | 14.6 |
| Density (kg/m³) | 8.00 | 8.03 | 8.03 |
| Tensile Strength (MPa) min | 515 | 515 | 485 |
| Yield Strength (MPa) min | 205 | 205 | 170 |
| Elongation (%) min | 40 | 40 | 45 |
| Operating Temperature Range (°C) | −196 to +870 | −196 to +870 | −196 to +870 |
| Corrosion Resistance (Pitting Resistance) | Good | Excellent | Excellent |
Surface Finish Options
- 2B Finish: Standard cold-rolled, annealed, and pickled surface with a matte appearance. Suitable for general industrial applications.
- No. 4 Brushed Finish: Uniformly ground surface providing enhanced aesthetic appearance and moderate corrosion resistance.
- Mirror Finish (No. 8): Highly polished surface for hygienic, pharmaceutical, and food-grade applications where surface cleanliness is paramount.
- Pickled & Passivated (P&P): Chemical treatment to remove surface oxides and restore the passive chromium oxide layer, maximizing corrosion resistance.
Specifications
| Parameter | Specification |
|---|---|
| Product Model | Model 538 |
| Product Form | Continuous Coil Tube (盘管 / Coiltube) |
| Available Outer Diameters (OD) | 6.0 mm – 50.8 mm (¼" – 2") |
| Available Wall Thicknesses | 0.5 mm – 3.0 mm |
| Coil Diameter (Bundle Diameter) | 500 mm – 2,500 mm (customizable) |
| Coil Length per Spool | Up to 500 m (continuous, seam-free) |
| Tube Cross-Section | Circular (standard); oval or rectangular upon request |
| Dimensional Tolerance (OD) | ±0.05 mm (precision grade); ±0.10 mm (standard grade) |
| Dimensional Tolerance (Wall) | ±10% of nominal |
| Surface Roughness (Ra) | ≤ 0.8 μm (standard); ≤ 0.4 μm (mirror finish) |
| Maximum Operating Pressure | Up to 2.5 MPa (dependent on OD and wall thickness) |
| Heat Transfer Coefficient Enhancement | 15–35% improvement over straight-tube configurations in ice storage applications |
| Standard Test Pressure | 1.5× Maximum Working Pressure (hydrostatic test) |
| Packaging | Steel drum or wooden crate with moisture-absorbent desiccants |
Manufacturing Process
1. Raw Material Selection & Incoming Inspection
High-purity stainless steel billets or strip are procured from certified mills meeting ASTM A270 (welded austenitic stainless steel tubing) and ASTM A269 (welded austenitic stainless steel seamless tubing) standards. Each batch undergoes spectroscopic analysis (OES) and mechanical testing prior to acceptance.
2. Cold Drawing & Forming
The stainless steel strip is fed through a series of precision drawing dies to achieve the target outer diameter and wall thickness. This cold-work hardening process enhances the mechanical properties of the tube while maintaining dimensional accuracy. For seamless tubing variants, the Autoclave Method (AOD) or Piercing and Pilger Milling processes are employed.
3. Solution Annealing & Pickling
Following cold forming, the tube is solution-annealed at 1050°C – 1150°C in a controlled atmosphere furnace to relieve residual stresses, homogenize the microstructure, and restore full ductility. The annealed tube is then pickled in a mixed acid solution (nitric acid/hydrofluoric acid) to remove scale and oxide layers, followed by passivation to re-establish the protective chromium oxide passive film.
4. Coil Winding (Coil Forming)
The straightened and inspected tube is wound onto a precision CNC-controlled coil winding machine. The winding parameters — including pitch (helix spacing), turn diameter, and end configuration — are programmatically set to match the specific design requirements of the target application (e.g., ice storage tank geometry). The winding process is executed at controlled tension to prevent tube ovality or deformation, maintaining a roundness deviation of ≤ 0.5% of the nominal outer diameter.
5. End Preparation & Finishing
Tube ends are deburred, chamfered, and optionally threaded or fitted with flanges per customer specification. A final visual and dimensional inspection is conducted, and the coil is wrapped in protective film and secured on a shipping reel.
6. Quality Control & Testing
- Hydrostatic Pressure Test: Every coil is tested at 1.5× the maximum working pressure for a minimum dwell time of 30 seconds to verify leak-tightness.
- Dimensional Inspection: Sampling of OD, wall thickness, and coil geometry at intervals not exceeding 100 m of tube length.
- Spectroscopic Composition Analysis: Confirms alloy grade compliance with ASTM/EN specifications.
- Intergranular Corrosion Test (IGCT): Performed per ASTM A262 Practice E for 316L grade to verify resistance to sensitization.
- Surface Defect Inspection: Visual and eddy-current testing for surface discontinuities and subsurface flaws.
Applications
Thermal Energy Storage & Ice Storage Systems
The primary application domain for the Model 538 Coil Tube is coil-type ice storage tanks (蓄冰槽), where the continuous coil serves as the heat exchange element between the refrigerant/brine circuit and the latent heat storage medium (ice/water PCM). The coil geometry promotes efficient heat transfer during both the charging cycle (ice formation) and discharging cycle (cooling load supply), achieving energy density improvements of 15–35% over conventional plate or shell-and-tube heat exchangers in this application context.
Additional Applications
- Industrial Heat Exchangers: Spiral-wound heat exchangers for process industries including chemical processing, petrochemicals, and power generation.
- Geothermal Energy Systems: Borehole heat exchanger coils for ground-source heat pump installations.
- Food & Beverage Processing: CIP (Clean-In-Place) compatible tubing for dairy, brewing, and pharmaceutical processing lines.
- Automotive & HVAC Systems: Evaporator and condenser coils for refrigeration and air conditioning applications.
- Marine & Offshore: Seawater cooling coils leveraging the superior chloride resistance of 316/316L grades.
- Water Treatment & Desalination: Pre-heating and cooling coils in reverse osmosis (RO) and multi-stage flash (MSF) systems.
- Building Services: Radiator coils, underfloor heating loops, and district heating distribution networks.
Quality Certifications & Compliance
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System — covers design, manufacturing, and delivery processes |
| ISO 14001:2015 | Environmental Management System — responsible sourcing and waste minimization |
| ISO 45001:2018 | Occupational Health & Safety Management System |
| ASTM A270 / A269 | Material specification for welded and seamless austenitic stainless steel tubing |
| EN 10217-7 | European standard for austenitic stainless steel tubes for heat exchangers and heat sinks |
| GB/T 14976 | Chinese national standard for seamless stainless steel tubes for fluid transport |
| GB/T 12771 | Chinese national standard for welded stainless steel tubes for fluid transport |