Stainless Steel Coil Tube (Coiltube) — Technical Product Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a continuous-length, cold-drawn or cold-rolled tubular product wound into a compact coil configuration. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product is designed to meet the stringent requirements of modern industrial, HVAC, and energy-efficiency applications. The coil form factor enables seamless processing, automated forming, and minimal material waste during downstream fabrication.
Coil tubes are distinguished from straight seamless or welded tubes by their continuous, non-cut length, which facilitates high-throughput manufacturing environments. The product is particularly valued in applications requiring thermal exchange, fluid conveyance, and structural integrity under cyclic loading conditions.
2. Material & Properties
2.1 Material Grades
- Austenitic Stainless Steels: AISI 304 (UNS S30400), AISI 316 (UNS S31600), AISI 316L (UNS S31603)
- Super-Austenitic Grades: AISI 321 (UNS S32100), AISI 347 (UNS S34700)
- Duplex Stainless Steels: UNS S31803 (2205), UNS S32750 (2507) — available upon request
2.2 Key Mechanical Properties
| Property | AISI 304 (Solution Annealed) | AISI 316 (Solution Annealed) | UNS S31803 (Annealed) |
|---|---|---|---|
| Tensile Strength (UTS) | ≥ 515 MPa (75 ksi) | ≥ 515 MPa (75 ksi) | ≥ 550 MPa (80 ksi) |
| Yield Strength (0.2% offset) | ≥ 205 MPa (30 ksi) | ≥ 205 MPa (30 ksi) | ≥ 450 MPa (65 ksi) |
| Elongation (A50mm) | ≥ 40% | ≥ 40% | ≥ 25% |
| Hardness (HBW) | ≤ 217 | ≤ 217 | ≤ 321 |
| Density | 7.93 g/cm³ | 8.03 g/cm³ | 7.86 g/cm³ |
| Thermal Conductivity (20°C) | 16.3 W/(m·K) | 14.6 W/(m·K) | 11.2 W/(m·K) |
| Thermal Expansion (20–100°C) | 17.3 × 10⁻⁶ /K | 16.0 × 10⁻⁶ /K | 13.7 × 10⁻⁶ /K |
2.3 Corrosion Resistance
The chromium content (≥ 18%) and nickel content (≥ 8%) in austenitic grades provide exceptional resistance to atmospheric corrosion, acid solutions, and chloride environments. The addition of molybdenum (Mo ≥ 2%) in AISI 316 enhances pitting and crevice corrosion resistance, making it suitable for marine and chemical processing applications.
2.4 Surface Finish Options
- 2B Finish: Cold-rolled, annealed, and pickled — standard commercial finish
- No. 4 Brushed: Uniform directional grain — aesthetic applications
- Mirror Polish (8K): Ra ≤ 0.05 μm — high-end decorative use
- Satin Finish: Ra 0.4–0.8 μm — architectural applications
3. Specifications
| Parameter | Specification Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | Φ 3.0 mm – Φ 25.4 mm (0.12" – 1.0") | ASTM A213 / A269 |
| Wall Thickness (WT) | 0.3 mm – 3.0 mm (0.012" – 0.118") | ASTM A213 / A269 |
| Coil Length (per coil) | 50 m – 500 m (164 ft – 1,640 ft) | Manufacturer standard |
| Coil Inner Diameter | Φ 150 mm – Φ 300 mm | Customizable |
| OD Tolerance | ± 0.05 mm (for OD ≤ 10 mm); ± 0.1 mm (for OD > 10 mm) | ASTM A213, Table 10 |
| WT Tolerance | ± 10% of nominal thickness | ASTM A213 |
| Roundness | ≤ 5% of nominal OD | ASTM A213 |
| Straightness (per coil) | ≤ 0.15% of coil length | ISO 11286 |
| Surface Roughness (Ra) | ≤ 0.8 μm (standard); ≤ 0.4 μm (polished) | ASTM A967 |
| Operating Temperature Range | −196°C to +870°C (AISI 304); −196°C to +925°C (AISI 316) | ASME BPVC Section II |
| Maximum Working Pressure | Up to 40 MPa (5,800 psi) — depends on OD/WT | ASME BPVC Section VIII |
| Packaging | Wooden pallet with VCI (Volatile Corrosion Inhibitor) wrap, moisture-proof film | ISO 4126 |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection: High-purity stainless steel billets or slabs sourced from certified primary mills, with strict control over sulfur (S ≤ 0.03%), phosphorus (P ≤ 0.045%), and carbon (C ≤ 0.08%) content.
- Hot Rolling: Billets are reheated to 1,150–1,250°C and hot-rolled into seamless capillary stock (precursor tube) with controlled dimensional tolerances.
- Pickling & Annealing: The hot-rolled capillary undergoes acid pickling (H₂SO₄ + HNO₃ blend) to remove scale, followed by solution annealing at 1,050–1,150°C to restore austenitic microstructure and remove residual stresses.
- Continuous Cold Drawing (CCD): The capillary stock is drawn through precision tungsten carbide (WC-Co) dies at controlled reduction ratios (15–25% per pass) to achieve final OD and WT dimensions. This step imparts cold work hardening, improving mechanical strength and dimensional accuracy.
- Intermediate Annealing: Periodic solution annealing between drawing passes prevents excessive work hardening and maintains ductility for further forming.
- Final Annealing & Pickling: Post-drawing annealing at 1,050°C (air or protective atmosphere) followed by final pickling and passivation (ASTM A967) to ensure optimal corrosion resistance.
- Coiling: The finished tube is wound onto precision-mandrel coils using automated coiling equipment that maintains consistent interpass spacing and prevents surface damage.
- Quality Inspection: 100% dimensional verification, hydrostatic testing (per ASTM A213), and surface inspection; sampling for chemical composition (OES), mechanical testing, and NDE (eddy current or ultrasonic).
4.2 Key Process Parameters
| Process Step | Temperature | Time | Atmosphere |
|---|---|---|---|
| Solution Annealing | 1,050–1,150°C | 20–30 min | Still air / H₂-N₂ |
| Hot Rolling | 1,150–1,250°C (furnace); 900–1,000°C (finish) | Continuous | Protective gas |
| Cold Drawing | Ambient (20–30°C) | Continuous | — |
| Pickling | 80–95°C | 5–15 min | Acid bath |
| Passivation | 60–70°C | 10–20 min | Citric acid / HNO₃ |
5. Applications
5.1 HVAC & Energy-Saving Systems
Stainless steel coil tubes are extensively employed in fan coil units (FCUs) and fresh air systems for commercial and institutional buildings. The inherent corrosion resistance and thermal conductivity make these tubes ideal for:
- Evaporator and condenser coils in air conditioning systems
- Heat exchanger elements in energy recovery ventilation (ERV) systems
- Chilled water distribution piping in central HVAC networks
- Energy-saving renovation projects for existing building infrastructure
5.2 Industrial & Process Engineering
- Chemical processing — acid and alkali transport lines
- Food and beverage processing — sanitary fluid conveyance
- Pharmaceutical manufacturing — CIP (Clean-in-Place) compatible systems
- Automotive exhaust and turbocharger systems
- Boiler and superheater tubes in power generation
5.3 Architectural & Decorative Applications
- Handrails, guardrails, and structural framing
- Decorative trim and furniture components
- Lighting fixtures and architectural detailing
5.4 Marine & Offshore
- Ballast water systems
- Desalination plant heat exchangers
- Offshore platform fluid transfer lines
6. Quality Certifications & Compliance
| Certification / Standard | Scope | Applicability |
|---|---|---|
| ISO 9001:2015 | Quality Management System | Full manufacturing process |
| ISO 14001:2015 | Environmental Management System | Production operations |
| ISO/IEC 17025 | Testing & Calibration Laboratory Competence | In-house testing laboratory |
| ASTM A213 | Standard Specification for Seamless Austenitic Cr-Fe Alloys for High-Temperature Service | Material and testing requirements |
| ASTM A269 | Standard Specification for Austenitic Stainless Steel Seamless, Welded, and Heavy-Walled Pipe, Tubing, and Bar for Chemical and Fossil Fuel Plant Service | Material and testing requirements |
| EN 10216-5 | Non-ferrous metallic materials — Heat exchangers |