Stainless Steel Coil Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (also referred to as Coiltube or Coil Tubing) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered cold-worked stainless steel tubing supplied in continuous coil form. Designed for high-volume fabrication and integration into complex HVAC (Heating, Ventilation, and Air Conditioning) systems, fluid transport networks, and structural assemblies, this product combines superior corrosion resistance, mechanical integrity, and formability in a single solution.
The coil tube format offers significant logistical and manufacturing advantages over straight-length pipe delivery, including reduced material waste, continuous feeding into automated forming lines, and optimized inventory management for high-throughput production environments. This product is particularly suited for applications in metro transit renovation projects, where reliable, long-service-life components are essential for fan coil units (FCU), chilled water distribution circuits, and condensate drainage systems operating in demanding subterranean environments.
2. Material & Properties
2.1 Material Grades
The coil tube is available in the following standard stainless steel grades, each selected to meet specific performance requirements:
- AISI 304 (UNS S30400) — The most widely used austenitic stainless steel, offering excellent general corrosion resistance, good weldability, and outstanding formability. Ideal for HVAC applications, food-grade systems, and atmospheric environments.
- AISI 316 (UNS S31600) — Contains 2–3% molybdenum (Mo), providing enhanced resistance to pitting and crevice corrosion, particularly in chloride-rich environments such as coastal metro systems or chemical processing plants.
- AISI 304L (UNS S30403) — Low-carbon variant of 304 with carbon content ≤0.03%, designed to minimize intergranular corrosion during welding operations.
- AISI 316L (UNS S31603) — Low-carbon variant of 316, combining superior corrosion resistance with improved weldability for critical service applications.
- AISI 321 (UNS S32100) — Titanium-stabilized austenitic grade suitable for elevated-temperature service (up to 870°C) where thermal cycling is a concern.
2.2 Mechanical Properties
| Property | Specification |
|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa (AISI 304/316) |
| Yield Strength (Rp0.2) | ≥ 205 MPa (AISI 304/316) |
| Elongation (A) | ≥ 40% |
| Hardness | ≤ 220 HB (Annealed Condition) |
| Density | 7.93 g/cm³ |
| Thermal Conductivity (at 25°C) | 16.3 W/(m·K) (AISI 304) |
| Thermal Expansion Coefficient (20–100°C) | 17.3 × 10⁻⁶ /°C |
| Maximum Service Temperature | 870°C (AISI 321); 870°C (AISI 304/316) |
2.3 Surface Finish
- Ba&W (Bright Annealed & Pickled) — Standard industrial finish with a matte, non-reflective surface; suitable for most mechanical and HVAC applications.
- No. 1 (Hot-Rolled Annealed & Pickled) — Rougher surface with visible mill marks; used where surface aesthetics are not critical.
- 2B (Cold-Rolled, Annealed, Pickled & Passivated) — Smooth, slightly reflective finish; preferred for visible installations and sanitary applications.
- Custom Finishes — Polished (4#, 8#, 10#), hairline, or sandblasted finishes available upon request.
3. Specifications
| Parameter | Specification Range |
|---|---|
| Product Code | 1015 — Coiltube |
| Outer Diameter (OD) | 3.0 mm – 108.0 mm |
| Wall Thickness (WT) | 0.3 mm – 6.0 mm |
| OD Tolerance | ±0.1 mm (Diameters ≤ 25 mm); ±0.2 mm (Diameters > 25 mm) |
| Wall Thickness Tolerance | ±10% of nominal (thin-wall); ±0.1 mm (thick-wall) |
| Coil Inner Diameter (ID) | 200 mm – 600 mm |
| Coil Length | Custom (typically 50 m – 500 m per coil) |
| Coil Weight | Up to 2,000 kg per coil |
| Manufacturing Standard | ASTM A269 / ASTM A213 / GB/T 14976 / EN 10216-5 |
| Heat Treatment Condition | Annealed (Solution-Annealed) |
| End Condition | Plain, Beveled, or Threaded (upon request) |
| Packaging | Wooden crate / Steel pallet with moisture-proof wrapping |
4. Manufacturing Process
The production of Wenzhou Jixing's stainless steel coil tube follows a rigorous multi-stage manufacturing process to ensure dimensional accuracy, metallurgical quality, and surface integrity:
- Raw Material Selection & Incoming Inspection — Certified stainless steel strip or hollow billet is sourced from approved mill suppliers. Each batch undergoes spectroscopic analysis to verify chemical composition compliance with ASTM/GB standards.
- Hot Rolling & Annealing — For seamless tube production, continuous hot rolling (HFW — Hot Forming Welding or ERW — Electric Resistance Welding) is performed at temperatures between 1,100°C and 1,250°C, followed by controlled cooling to establish the desired grain structure.
- Pickling & Decarbonization — The hot-rolled tube is immersed in a controlled acid bath (typically a mixture of hydrofluoric acid (HF) and nitric acid (HNO₃)) to remove scale, oxide layers, and surface contaminants, revealing a clean metallic substrate.
- Cold Drawing / Cold Rolling — The tube is passed through precision dies or rollers at ambient temperature to achieve final dimensional tolerances. This process enhances surface finish, improves mechanical properties through strain hardening, and ensures consistent wall thickness.
- Intermediate Annealing — Periodic annealing at 1,050°C – 1,150°C with rapid quenching restores ductility and prevents cold work hardening during the forming process.
- Final Annealing & Passivation — The finished tube undergoes a final solution anneal followed by passivation treatment (citric acid or nitric acid-based) to maximize the protective chromium oxide (Cr₂O₃) layer and enhance corrosion resistance.
- Coiling & Packaging — The continuous tube is wound onto precision-machined coil cores. Each coil is wrapped in moisture-barrier film, secured with steel strapping, and packaged in export-grade wooden crates or steel pallets.
5. Applications
The stainless steel coil tube is engineered for a broad spectrum of industrial and commercial applications. Its primary use cases include:
5.1 HVAC & Fan Coil Systems (Metro Transit)
In metro renovation projects, the coil tube serves as the core component of Fan Coil Units (FCU), where it functions as the heat exchange medium for chilled water or hot water distribution. The continuous coil format enables efficient integration into compact, space-constrained underground installations. Key advantages in this context include:
- Resistance to condensation corrosion in high-humidity subterranean environments
- Long service life exceeding 25 years without replacement
- Low maintenance requirements reducing operational downtime for transit systems
- Compatibility with both closed-loop and open-loop hydronic systems
5.2 Additional Application Areas
- Automotive & Aerospace — Fuel lines, brake lines, exhaust system components, and structural tubing
- Food & Pharmaceutical Processing — Sanitary-grade tubing for fluid transfer, CIP (Clean-in-Place) systems, and hygienic equipment
- Chemical & Petrochemical — Process piping for corrosive media transport, reactor internals, and heat exchangers
- Construction & Architecture — Decorative handrails, structural bracing, and façade elements
- Medical Equipment — Endoscopic instrument shafts, surgical tool housings, and sterilization-compatible tubing
- Energy Sector — Solar thermal collectors, geothermal heat exchangers, and nuclear-grade containment tubing
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework to ensure product reliability and regulatory compliance:
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| ISO 45001:2018 | Occupational Health & Safety Management |
| CE Marking | European Conformity for construction and machinery applications |
| ASTM A269 / A213 | Standard specifications for seamless and welded austenitic stainless steel tubing |
| GB/T 14976 | Chinese national standard for seamless stainless steel tubes |
| EN 10216-5 | European standard for non-alloy and alloy steel tubes for pressure purposes |
| Mill Test Certificates (MTC) | EN 10204 3.1 Type certification provided with every shipment |
| NACE MR0175 / ISO 15156 | Availability for sour service applications (upon request) |
7. Unique Selling Points
- Continuous Coil Supply — Eliminates field splicing and welding joints, reducing leak points and improving system reliability, particularly critical in sealed metro environments where maintenance access is limited.
- Multi-Grade Flexibility — Full range of 300-series austenitic stainless steel grades available from a single source, enabling project-specific material optimization without supply chain fragmentation.
- Precision Dimensional Control — Tight tolerances (±0.1 mm OD) ensure seamless integration with standard fittings, flanges, and heat exchanger headers without custom adaptation.
- Metro-Grade Durability — Proven performance in high-humidity, chloride-exposed underground environments with demonstrated service life exceeding 25 years in transit infrastructure applications.
- Full Traceability — Each coil is serialized with complete heat-number traceability, enabling end-to-end quality documentation from mill origin through final installation.
- Custom Fabrication Support — On-site technical support for coil cutting, bending, and forming operations, reducing customer-side processing costs and delivery lead times.
8. Technical Notes
Note: When specifying coil tube for fan coil unit (FCU) applications in metro renovation projects, ensure the selected grade accounts for local water chemistry (chloride content, pH, dissolved oxygen levels). For systems utilizing glycol-based heat transfer fluids, verify compatibility with the selected alloy grade. All installations should comply with local building codes and transit authority specifications. Consult the manufacturer's technical team for application-specific recommendations regarding insulation, support spacing, and thermal expansion accommodation.