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 tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd (Product Catalog No. 373). Designed primarily for integration into building HVAC (Heating, Ventilation, and Air Conditioning) systems — particularly fan coil unit (FCU) assemblies — the Coiltube provides high-performance thermal exchange surfaces characterized by superior corrosion resistance, mechanical durability, and thermal efficiency.
This product line is specifically engineered to meet the demanding requirements of modern intelligent building systems, where advanced control methodologies — including deep reinforcement learning-based optimization of fan coil unit operations — necessitate reliable, long-life heat transfer components with predictable thermal and hydraulic performance characteristics.
2. Material & Properties
2.1 Base Material Composition
The Coiltube is fabricated from austenitic stainless steel grades conforming to international metallurgical standards. The primary alloy composition is as follows:
- Grade 304 (UNS S30400): Cr 18–20%, Ni 8–10.5%, Mn ≤ 2.0%, C ≤ 0.08% — standard grade offering excellent general corrosion resistance and formability.
- Grade 316 (UNS S31600): Cr 16–18%, Ni 10–14%, Mo 2–3%, C ≤ 0.08% — enhanced chloride pitting resistance for aggressive environments.
- Grade 321 (UNS S32100): Cr 17–19%, Ni 9–12%, Ti ≥ 5×C — stabilized grade for elevated temperature service.
2.2 Mechanical Properties (Typical Values)
| Property | Grade 304 | Grade 316 | Grade 321 |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 515 | ≥ 515 |
| Yield Strength (MPa) | ≥ 205 | ≥ 205 | ≥ 205 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 40 |
| Hardness (HBW) | ≤ 217 | ≤ 217 | ≤ 217 |
| Density (g/cm³) | 8.00 | 8.03 | 8.00 |
2.3 Thermal Properties
- Thermal conductivity (W/m·K): 14.5 (304), 14.5 (316), 16.3 (321) at 20°C
- Linear thermal expansion coefficient (×10⁻⁶/K): 17.3 (304/316), 17.2 (321) — 20–100°C range
- Maximum service temperature: 870°C (304/316), 925°C (321)
2.4 Corrosion Resistance
The austenitic microstructure provides outstanding resistance to atmospheric corrosion, weak acids, and organic compounds. Grade 316 variants exhibit superior performance in chloride-containing environments (e.g., coastal HVAC installations, chemical processing facilities) due to molybdenum addition enhancing pitting resistance equivalent number (PREN ≥ 24).
3. Specifications
| Parameter | Specification | Tolerance |
|---|---|---|
| Outer Diameter (OD) | Φ6.0 – Φ25.4 mm | ±0.10 mm |
| Wall Thickness | 0.50 – 1.50 mm | ±0.05 mm |
| Coil Pitch (Center-to-Center) | 15.0 – 50.0 mm | ±0.50 mm |
| Coil Diameter (Bundle OD) | Φ100 – Φ500 mm | ±2.0 mm |
| Coil Length (Active) | 200 – 2000 mm | ±3.0 mm |
| Number of Rows | 1 – 8 rows | — |
| Surface Finish | BA (Bright Annealed) / Pickled & Passivated | Ra ≤ 0.8 μm |
| End Treatment | Flat-cut / Beveled / Threaded / Brazed fittings | Per drawing |
| Maximum Operating Pressure | 1.6 – 4.0 MPa | Per design |
| Operating Temperature Range | -40°C to +250°C | — |
3.1 Standard Compliance
- ASTM A213 / A269 — Seamless austenitic stainless steel tubing
- ASTM A554 — Cold-drawn austenitic stainless steel tubing
- EN 10217-7 — Heat exchanger tubing for stainless steels
- GB/T 12771 — Chinese national standard for welded stainless steel tubes
- GB/T 21832 — Seamless stainless steel tubing for heat exchangers
4. Manufacturing Process
- Material Selection & Incoming Inspection: Cold-rolled stainless steel strip or seamless pipe stock is verified for chemical composition (via OES/Spark analysis) and mechanical properties prior to processing.
- Coil Forming: High-precision CNC coil winding machines form the base tube into the required helical geometry, maintaining consistent pitch and concentricity through computerized path control.
- Hydroforming / Cold Drawing (as applicable): Tubes undergo dimensional refinement to achieve tight tolerances on OD and wall thickness. Hydroforming enables complex cross-sectional geometries without additional tooling per size.
- Welding (if applicable): TIG (Tungsten Inert Gas) welding is employed for end connections and header integration, utilizing argon shielding gas (Ar ≥ 99.99%) to prevent oxidation of the weld zone.
- Heat Treatment: Solution annealing at 1050–1150°C followed by rapid water quenching ensures a fully austenitic, stress-free microstructure with maximum corrosion resistance.
- Pickling & Passivation: Acid pickling removes scale and discoloration; subsequent passivation treatment establishes a protective chromium oxide film (Cr₂O₃) on the surface.
- Quality Control: Final inspection includes dimensional verification (CMM measurement), hydrostatic pressure testing (1.5× working pressure for 30 seconds), visual inspection of surface quality, and spectrographic composition verification.
5. Applications
The Coiltube product line serves a broad spectrum of industrial and commercial applications, with particular emphasis on the following domains:
- HVAC Systems (Primary Application): Integration into fan coil units (FCUs), air handling units (AHUs), and chiller coils for commercial buildings, hospitals, and data centers. The product is specifically designed for compatibility with intelligent control systems employing deep reinforcement learning (DRL) algorithms for energy-optimized operation of building internal fan coil unit systems.
- Process Heat Exchangers: Shell-and-tube heat exchangers in food processing, pharmaceutical manufacturing, and chemical plants where sanitary-grade surfaces and corrosion resistance are critical.
- Refrigeration & Cryogenics: Evaporator and condenser coils in commercial refrigeration systems, utilizing the excellent low-temperature ductility of austenitic stainless steels.
- Building Services: Radiator coil assemblies, hydronic heating loops, and district energy distribution systems.
- Specialized Applications: Marine HVAC systems, offshore platform heating, and semiconductor cleanroom environmental control.
6. Quality Certifications
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| CE Marking (EU) | Conformity with European health, safety, and environmental protection standards |
| PED 2014/68/EU | Pressure Equipment Directive compliance for pressure-containing assemblies |
| NB Heat Exchanger | Notified Body certification for pressure-retaining heat exchangers |
| EN 10204 3.1 | Material test certificates with full traceability documentation |
| ASME STAMP (optional) | U-Stamp certification for pressure vessel components (upon request) |
7. Unique Selling Points
- Intelligent System Compatibility: Engineered for seamless integration with AI-driven building management systems utilizing deep reinforcement learning for real-time optimization of fan coil unit performance, ensuring the mechanical component does not become a limiting factor in energy efficiency.
- Precision Manufacturing: CNC-controlled coil winding with ±0.10 mm dimensional accuracy ensures uniform flow distribution and maximized heat transfer coefficient (U-value).
- Extended Service Life: Austenitic stainless steel construction eliminates internal corrosion risks, providing 25–50 year design life without replacement — significantly reducing lifecycle costs (LCC).
- Sanitary-Grade Surface: Bright annealed finish with Ra ≤ 0.8 μm prevents biofilm accumulation, critical for pharmaceutical and food-grade applications.
- Full Traceability: Each coil batch carries unique heat number identification, enabling complete material provenance documentation from mill certificate through final installation.
- Custom Engineering Capability: Flexible manufacturing parameters allow bespoke coil geometries tailored to specific equipment OEM requirements or retrofit applications.
8. Technical Notes & Recommendations
Installation: All joints must be sealed with compatible gaskets (PTFE or EPDM recommended). Avoid direct contact with dissimilar metals (galvanized steel, carbon steel) to prevent galvanic corrosion. Ensure adequate flow velocity (0.5–2.5 m/s) to minimize sedimentation and maintain heat transfer efficiency.
Maintenance: Periodic inspection of coil surfaces for fouling accumulation is recommended. Chemical cleaning with citric acid solution (5% concentration) is suitable for non-destructive descaling. Avoid abrasive cleaning methods that may compromise the passive oxide layer.
Storage: Store in dry, ventilated conditions away from chlorinated contaminants. Coil bundles should be supported to prevent deformation. Original protective packaging should be maintained until installation.