Stainless Steel Coil Tube (Coiltube) — Technical Specification
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered continuous length tubing product designed for demanding thermal management, heat exchange, and energy storage applications. Supplied in coiled form, this product offers exceptional flexibility in installation configurations while maintaining structural integrity and corrosion resistance throughout its service life.
This coil tube product is specifically engineered for applications involving natural convection heat transfer in vertical ice storage and cooling-release cycle systems. The design accommodates the unique thermodynamic conditions encountered during phase-change thermal energy storage (TES), where the tube serves as the working fluid conduit facilitating efficient heat exchange between the refrigerant and the phase-change material (PCM), typically ice or ice slurry.
The product is categorized under the Industrial Heat Exchange & Thermal Storage segment and is suitable for integration into district cooling systems, commercial refrigeration plants, and building energy efficiency solutions.
Material & Properties
Base Material Composition
The coil tube is fabricated from high-grade stainless steel conforming to international metallurgical standards. The primary alloy grades utilized include:
- Austenitic Stainless Steel (Grade 304 / 0Cr18Ni9) — Excellent general corrosion resistance, weldability, and formability
- Austenitic Stainless Steel (Grade 316 / 0Cr17Ni12Mo2) — Superior resistance to chlorides and pitting corrosion for aggressive environments
- Duplex Stainless Steel (Grade 2205 / S32205) — Enhanced mechanical strength and resistance to stress corrosion cracking for high-pressure applications
Mechanical Properties
| Property | Grade 304 | Grade 316 | Grade 2205 | Test Standard |
|---|---|---|---|---|
| Tensile Strength (MPa) | ≥ 515 | ≥ 485 | ≥ 450 | ASTM A270 / ASTM A269 |
| Yield Strength (MPa, 0.2% offset) | ≥ 205 | ≥ 170 | ≥ 220 | ASTM A270 / ASTM A269 |
| Elongation (%) | ≥ 40 | ≥ 35 | ≥ 35 | ASTM A270 / ASTM A269 |
| Density (kg/m³) | 8000 | 8000 | 8000 | — |
| Thermal Conductivity (W/m·K, at 20°C) | 16.3 | 14.6 | 13.0 | ASTM A270 |
| Thermal Expansion Coefficient (×10⁻⁶/°C, 20–100°C) | 17.3 | 17.2 | 15.0 | ASTM A270 |
Chemical Composition (Typical, wt%)
| Element | Grade 304 | Grade 316 | Grade 2205 |
|---|---|---|---|
| Carbon (C) | ≤ 0.08 | ≤ 0.08 | ≤ 0.03 |
| Chromium (Cr) | 18.0 – 20.0 | 16.0 – 18.0 | 22.0 – 23.0 |
| Nickel (Ni) | 8.0 – 10.5 | 10.0 – 14.0 | 4.5 – 6.5 |
| Molybdenum (Mo) | — | 2.0 – 3.0 | 3.0 – 3.5 |
| Nitrogen (N) | — | — | 0.14 – 0.20 |
| Silicon (Si) | ≤ 1.0 | ≤ 1.0 | ≤ 1.0 |
| Manganese (Mn) | ≤ 2.0 | ≤ 2.0 | ≤ 2.0 |
Specifications
Dimensional Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 3.0 mm – 25.4 mm (1/8" – 1") | ASTM A270 / GB/T 12771 |
| Wall Thickness (WT) | 0.25 mm – 2.0 mm | ASTM A270 / GB/T 12771 |
| Coil Diameter (CD) | 300 mm – 1200 mm | Manufacturer Specification |
| Coil Length (per coil) | 50 m – 300 m (customizable) | Manufacturer Specification |
| OD Tolerance | ± 0.1 mm (precision grade) | ASTM A270 |
| Wall Thickness Tolerance | ± 10% of nominal | ASTM A270 |
| Roundness (Ovality) | ≤ 5% of OD | ASTM A270 |
| Straightness (for cut lengths) | ≤ 1.5 mm per meter | ASTM A270 |
Surface Finish Options
| Finish Type | Roughness (Ra, μm) | Application |
|---|---|---|
| Industrial Pickled | ≤ 1.6 | General industrial use |
| Mechanically Polished | ≤ 0.8 | Food-grade, sanitary applications |
| Electropolished | ≤ 0.4 | Pharmaceutical, ultra-pure fluid systems |
| Brushed (No. 4 Finish) | ≤ 1.2 | Aesthetic and decorative applications |
Performance Parameters for Thermal Applications
| Parameter | Value / Range | Notes |
|---|---|---|
| Maximum Operating Temperature | -196°C to +870°C (Grade 304) | Grade-dependent |
| Maximum Operating Pressure | Up to 6.0 MPa (design dependent) | Hydrostatic tested at 1.5× working pressure |
| Heat Transfer Coefficient (Natural Convection) | 100 – 1500 W/m²·K | Depends on fluid, geometry, and flow regime |
| Corrosion Resistance (Pitting) | PREN ≥ 19 (Grade 316); PREN ≥ 34 (Grade 2205) | Pitting Resistance Equivalent Number |
| Service Life (design) | ≥ 25 years | Under normal operating conditions |
Manufacturing Process
Production Workflow
- Raw Material Procurement & Inspection: Cold-rolled stainless steel strip (CRSS) is sourced from certified mills and subjected to incoming quality control including chemical analysis (OES — Optical Emission Spectroscopy), mechanical property verification, and surface inspection.
- Slitting & Edge Preparation: The cold-rolled strip is slit to precise widths using high-precision slitting lines with laser edge detection to ensure dimensional accuracy within ± 0.05 mm.
- Coil Forming (Roll Forming): The slit strip passes through a series of precision-drawn forming rolls that progressively shape the flat strip into the desired circular or elliptical cross-section. This cold-forming process induces beneficial work hardening, improving mechanical strength by 15–30%.
- Seam Welding: The formed tube is seam-welded using Resistance Seam Welding (RSW) or Laser Welding technology. Weld parameters are continuously monitored to ensure weld integrity, with weld penetration depth controlled at 30–50% of wall thickness.
- Post-Weld Heat Treatment (PWHT): Where required, the welded tube undergoes solution annealing at 1050–1150°C followed by rapid quenching to restore full austenitic microstructure and eliminate residual welding stresses.
- Precision Sizing: The tube passes through a series of sizing rolls to achieve the final dimensional tolerances for OD and wall thickness.
- Coiling & Packaging: The finished tube is coiled to specified diameters using automated coiling equipment, ensuring uniform winding tension to prevent deformation. Coils are then wrapped in protective film and secured for transport.
Quality Control Integration Points
- Inline Eddy Current Testing (ECT): Continuous detection of wall thickness variations, internal defects, and weld quality at production speeds up to 60 m/min.
- Hydrostatic Pressure Testing: Each coil is subjected to hydrostatic testing at 1.5× the maximum working pressure with a minimum hold time of 30 seconds.
- X-Ray Fluorescence (XRF) Analysis: Non-destructive verification of chemical composition at multiple points along the coil length.
- Surface Roughness Measurement: Verified using contact profilometry at defined intervals.
Applications
Thermal Energy Storage Systems
The primary application domain for this coil tube product is in vertical ice storage systems for district cooling and commercial refrigeration. In these systems, the coil tube serves as the refrigerant circuit within the ice storage tank. During the charging cycle (ice-making), sub-zero brine or refrigerant flows through the coil tube, extracting latent heat from water to form ice layers on the tube surface. During the discharging cycle (cooling release), warm secondary coolant flows through the coil, absorbing stored thermal energy as the ice melts.
Academic Reference: The design and performance optimization of such systems have been extensively studied in the context of natural convection heat transfer mechanisms. Research published under the title "Natural Convection Regulation Mechanism of Vertical Ice Storage Coil Tube Cooling-Release Cycle Process" demonstrates that the geometric parameters of the coil tube — including tube diameter, pitch, and arrangement — critically influence the natural convection flow patterns within the ice tank, directly affecting charging/discharging efficiency and cycle time.
Additional Application Domains
- Commercial & Industrial Refrigeration: Evaporator and condenser coils for walk-in coolers, freezers, and cold storage facilities.
- Heat Exchangers: Compact coil-type heat exchangers for HVAC (Heating, Ventilation, and Air Conditioning) systems, chiller units, and thermal oil heaters.
- Food & Beverage Industry: Sanitary-grade coil tubing for pasteurization systems, dairy processing, and beverage cooling lines.
- Pharmaceutical Manufacturing: Electropolished coil tubes for cleanroom fluid distribution and CIP (Clean-in-Place) systems.
- Geothermal & Solar Thermal Systems: Heat collection coils for ground-source heat pumps and solar thermal collectors.
- Marine & Offshore: Corrosion-resistant coil tubing for