Stainless Steel Coil Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered continuous-length tubing product supplied in coil form, manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is designed to meet the rigorous demands of HVAC (Heating, Ventilation, and Air Conditioning), industrial process piping, and architectural applications. The coil form factor enables seamless integration into automated forming, bending, and welding systems, significantly reducing material waste and production cycle times compared to straight-length pipe deliveries.
The Coiltube product line is engineered for high-performance thermal exchange applications, including bar-type cooling coil systems used in commercial building air conditioning, as exemplified by large-scale projects such as the Bank of Communications Financial Tower ceiling-mounted air supply systems. These applications demand tubing with superior corrosion resistance, thermal conductivity, and dimensional stability under continuous cyclic loading.
2. Material & Properties
2.1 Base Material Composition
The Coiltube is fabricated from austenitic stainless steel grades conforming to international standards, with the following typical material options:
- Grade 304 (UNS S30400): 18% Chromium (Cr), 8% Nickel (Ni) — general-purpose corrosion resistance for HVAC and architectural use.
- Grade 316 (UNS S31600): 16–18% Cr, 10–14% Ni, 2–3% Molybdenum (Mo) — enhanced resistance to chlorides and aggressive chemical environments.
- Grade 316L (UNS S31603): Low-carbon variant of 316 with carbon content ≤ 0.03%, optimized for post-welding applications without sensitization risk.
2.2 Mechanical Properties
| Property | Grade 304 | Grade 316 | Grade 316L |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 515 | ≥ 485 |
| Yield Strength (MPa) | ≥ 205 | ≥ 205 | ≥ 170 |
| Elongation at Break (%) | ≥ 40 | ≥ 40 | ≥ 40 |
| Hardness (HB) | ≤ 217 | ≤ 217 | ≤ 217 |
2.3 Physical Properties
- Thermal Conductivity: 14.9 W/(m·K) at 20°C (Grade 304)
- Specific Heat: 0.50 J/(g·K)
- Density: 7.93 g/cm³
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (20–100°C)
- Maximum Service Temperature: 870°C (Grade 304), 870°C (Grade 316)
2.4 Corrosion Resistance
The austenitic microstructure, stabilized by chromium oxide passive film formation, provides exceptional resistance to atmospheric corrosion, pitting, and stress corrosion cracking (SCC). Grade 316 and 316L variants exhibit superior performance in chloride-containing environments, making them suitable for coastal architectural applications and marine HVAC systems.
3. Specifications
| Parameter | Specification / Range |
|---|---|
| Outer Diameter (OD) | Φ3.0 mm – Φ63.5 mm |
| Wall Thickness (WT) | 0.3 mm – 3.0 mm |
| OD Tolerance | ±0.1 mm (precision grade); ±0.25 mm (standard grade) |
| WT Tolerance | ±10% (standard); ±5% (precision grade) |
| Coil Width | Up to 1,500 mm (flat coil configuration) |
| Coil Length | Continuous coil; typical cut lengths 2 m – 12 m per coil |
| Surface Finish | BA (Bright Annealed), No. 2B, No. 4 Brushed, Mirror (8K) |
| Surface Roughness (Ra) | ≤ 0.4 μm (BA); ≤ 1.6 μm (No. 2B); ≤ 0.2 μm (Mirror) |
| Form | Round, Square, Rectangular, Oval, Custom Profile |
| Applicable Standards | ASTM A213, ASTM A269, GB/T 12771, EN 10217, JIS G3446 |
| Delivery Condition | Annealed and Pickled (AP); Annealed and Bright Pickled (ABP) |
| Packaging | Wooden pallet with moisture-proof wrapping; steel band secured |
4. Manufacturing Process
4.1 Process Flow
- Strip Uncoiling: Cold-rolled stainless steel strip (CRSS) is uncoiled from the master coil and fed into the forming line.
- Coil Forming (Cold Forming): The strip passes through a series of progressive roller dies that gradually deform the flat strip into the target tubular cross-section. This cold-forming process imparts beneficial work-hardening, enhancing mechanical strength while maintaining the austenitic microstructure.
- Welding: The formed tube is welded along the longitudinal seam using one of the following methods:
- TIG (Tungsten Inert Gas) Welding: For seamless-quality welds in thin-wall applications (WT ≤ 1.5 mm).
- Electrostatic Capacitor Discharge (ECD) Welding: High-speed welding for continuous production, suitable for WT ≥ 1.0 mm.
- Friction Welding: For high-integrity applications requiring minimal heat-affected zone (HAZ).
- Internal Weld Inspection: X-ray or ultrasonic testing (UT) is performed on the weld seam to detect porosity, lack of fusion, or undercut defects.
- Heat Treatment (Annealing): Where required, the tube undergoes solution annealing at 1050–1150°C followed by controlled cooling to restore full austenitic structure and relieve residual stresses.
- Pickling and Passivation: The tube surface is pickled (typically using a citric acid or nitric/hydrofluoric acid mixture) to remove scale and oxidation, followed by passivation treatment to enhance the chromium oxide protective layer.
- Surface Finishing: Final surface treatment per specification — BA annealing, mechanical polishing, or electrolytic polishing to achieve the target surface roughness.
- Dimensional Inspection: 100% inline measurement of OD, WT, and straightness using laser scanners and CMM (Coordinate Measuring Machine) sampling.
- Coiling and Packaging: The finished tube is re-coiled onto standard coil cores, wrapped with moisture-barrier film, and secured with steel strapping for transport.
4.2 Quality Control Integration
Each production batch undergoes a multi-stage quality assurance protocol:
- Incoming Material Inspection: Spectroscopic analysis (OES) of raw strip to verify chemical composition compliance.
- In-Process Monitoring: Real-time measurement of forming force, weld parameters, and dimensional accuracy.
- Final Product Testing: Hydrostatic pressure testing (per ASTM A213), dye penetrant testing (PT) of weld seams, and hardness verification.
5. Applications
5.1 HVAC Systems
The primary application domain for Coiltube is in the fabrication of cooling coils and heat exchangers for commercial and industrial air conditioning systems. The coil form factor is particularly advantageous for automated coil-bending machines that produce serpentine and zigzag coil configurations used in:
- Bar-type cooling coil ceiling air supply systems (e.g., Bank of Communications Financial Tower project)
- Chilled water coil assemblies for VAV (Variable Air Volume) systems
- Condenser and evaporator tube bundles
5.2 Architectural and Building Services
- Decorative handrails, balustrades, and structural framing
- Suspension ceiling support systems
- Water supply and drainage piping in high-rise buildings
5.3 Industrial Process Applications
- Chemical processing piping (Grade 316/316L)
- Food and pharmaceutical equipment (hygienic-grade BA finish)
- Automotive exhaust systems and fuel lines
- Medical device manufacturing (instrument tubing)
5.4 Energy and Environmental
- Solar thermal collector tubing
- Geothermal heat exchange systems
- Refrigeration and cryogenic applications
6. Quality Certifications and Standards Compliance
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| ISO 45001:2018 | Occupational Health and Safety Management |
| ASTM A213 / A269 | Product specification compliance (Austenitic stainless steel tube) |
| GB/T 12771-2019 | Chinese national standard for seamless and welded stainless steel tube |
| EN 10217-7 | European standard for heat-resistant and pressure-resistant stainless steel tube |
| JIS G3446 | Japanese Industrial Standard for austenitic stainless steel seamless/welded tube |
| NSF/ANSI 61 | Drinking water system components (where applicable) |
| 3-A Sanitary Standards | Food-grade hygienic applications (BA/Mirror finish variants) |
7. Unique Selling Points
- Coil-Form Delivery Advantage: The continuous coil configuration eliminates joint waste, reduces handling operations, and enables high-throughput automated forming — resulting in 15–25% cost reduction compared to straight-length deliveries for large-volume projects.
- Multi-Grade Flexibility: Availability in Grade 304, 316, and 316L provides engineering flexibility across diverse environmental and performance requirements without changing the supply chain.
- Precision Dimensional Control: Advanced inline laser measurement systems ensure OD tolerance of ±0.1 mm and WT tolerance of ±5% (precision grade), critical for tight-fitting coil assembly applications in HVAC.
- Surface Finish Versatility: From industrial No. 2B to optical Mirror 8K finish, the product range accommodates both functional and aesthetic requirements in a single product family.
- Proven Large-Project Track Record: Successfully deployed in landmark commercial buildings including the Bank of Communications Financial Tower, demonstrating reliability at scale.
- Full Traceability: Each coil batch carries a unique heat number with complete material certification (MTC — Material Test Certificate) traceable to the mill of origin.
- Custom Profile Capability: Non-standard cross-sections (oval, rectangular, multi-lobe) can be manufactured to customer specifications, enabling optimized heat transfer surface area in specialized heat exchanger designs.
8. Technical Notes and Recommendations
Storage: Store coils in a dry, well-ventilated indoor environment. Avoid direct contact with carbon steel surfaces to prevent galvanic corrosion (iron contamination). Recommended storage temperature: -20°C to +50°C with relative humidity below 70%.
Handling: Use appropriate lifting equipment (chain slings or C-clamps) rated for the coil weight. Do not drop or drag coils to prevent surface damage and coil distortion.
Welding Considerations: For TIG welding of Grade 304/316 Coiltube, maintain interpass temperature below 150°C and use argon back-purging to prevent internal oxidation of the weld zone.
Post-Forming Treatment: After bending or forming operations, a stress-relief anneal at 1050°C followed by quenching may be required if subsequent corrosion testing is critical.
9. Supplier Information
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Catalog Reference: Item No. 1395
Product Category: Stainless Steel Coil Tube (Coiltube)
Technical Support: Custom engineering consultation available for project-specific requirements including thermal performance modeling, corrosion environment assessment, and dimensional tolerance optimization.