Stainless Steel Coil Tube (Coiltube) — Technical Product Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube), manufactured by Wenzhou Jixing Metal Materials Co., Ltd., is a precision-engineered continuous tube product formed into a helical coil configuration. This product is specifically designed for integration into Fan Coil Unit (FCU) systems, HVAC (Heating, Ventilation, and Air Conditioning) applications, and industrial heat exchanger assemblies. The coil tube delivers superior thermal conductivity, exceptional corrosion resistance, and mechanical durability under cyclic thermal loading conditions, making it an optimal choice for high-performance fluid transport and heat exchange systems.
The helical coil geometry enhances turbulent flow characteristics within the tube, thereby improving heat transfer coefficients compared to straight-tube configurations. This design principle is particularly advantageous in fan coil unit systems where compact spatial requirements must be reconciled with maximum thermal exchange efficiency.
2. Material & Properties
2.1 Base Materials
Coiltube products are manufactured from high-grade austenitic stainless steel grades, including but not limited to:
- Grade 304 (UNS S30408) — General-purpose corrosion resistance with excellent formability
- Grade 316 (UNS S31608) — Enhanced resistance to pitting and crevice corrosion due to molybdenum (Mo) addition
- Grade 316L (UNS S31603) — Low-carbon variant for superior weldability and resistance to intergranular corrosion
- Grade 321 (UNS S32103) — Stabilized with titanium (Ti) for high-temperature applications
2.2 Key Mechanical Properties
- Tensile Strength (UTS): 515–720 MPa (grade-dependent)
- Yield Strength (0.2% Offset): 205–310 MPa
- Elongation at Break: ≥40% (minimum)
- Hardness: 100–200 HV (annealed condition)
- Thermal Conductivity: 14.6–16.3 W/(m·K) at 20°C
- Thermal Expansion Coefficient: 16–17.5 × 10⁻⁶ /°C (20–100°C)
2.3 Corrosion Resistance
The austenitic microstructure provides outstanding resistance to atmospheric corrosion, chemical media, and high-temperature oxidation. Grade 316/316L variants exhibit critical pitting temperature (CPT) values exceeding 25°C in chloride environments, ensuring long service life in aggressive conditions.
3. Specifications
| Parameter | Specification Range | Unit | Standard Reference |
|---|---|---|---|
| Outer Diameter (OD) | 6.0 – 50.8 | mm | ASTM A269 / EN 10217-7 |
| Wall Thickness | 0.5 – 3.0 | mm | ASTM A269 / EN 10217-7 |
| Coil Diameter | 50 – 500 | mm | Manufacturer Specification |
| Coil Pitch (Turn Spacing) | 3 – 25 | mm | Manufacturer Specification |
| Coil Length (Developed) | 1.0 – 60.0 | m | Customizable |
| Surface Finish | Ra ≤ 0.8 (Polished) / Ra ≤ 1.6 (Pickled) | μm | ASTM A270 |
| Operating Temperature Range | -196 to +870 | °C | Grade-dependent |
| Maximum Operating Pressure | Up to 4.0 | MPa | ASME B31.3 / EN 13480 |
| Heat Transfer Coefficient Improvement | +30% to +60% vs. straight tube | % | Experimental Data |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection: Certified stainless steel seamless or welded tube stock conforming to ASTM A269 / EN 10217-7 specifications.
- Pre-Treatment: Annealing (1050–1150°C) followed by controlled cooling to achieve uniform austenitic grain structure and relieve residual stresses.
- Precision Coiling: Computer-controlled CNC coiling machines form the tube into the specified helical geometry with controlled bending radii to prevent ovality and wall thinning.
- Post-Coil Heat Treatment: Solution annealing at 1050°C with rapid water quenching to restore full austenitic properties and eliminate cold-work hardening from the coiling process.
- Pickling & Passivation: Acid immersion (HNO₃/HF blend) to remove oxide scale, followed by passivation treatment to establish a stable chromium oxide (Cr₂O₃) protective film.
- Quality Inspection: Dimensional verification, hydrostatic pressure testing, and surface integrity examination.
4.2 Critical Process Parameters
- Bending Radius: Minimum 3D (3 × outer diameter) to prevent tube collapse or excessive ovality
- Ovality Tolerance: ≤ 2% of nominal outer diameter
- Wall Thickness Reduction: ≤ 10% at inner bending radius
- Coil Concentricity: ±1.5 mm from centerline
5. Applications
5.1 Fan Coil Unit (FCU) Systems
In fan coil unit design, the coil tube serves as the primary heat exchange element. The helical configuration maximizes surface area within a compact envelope, facilitating efficient sensible and latent heat transfer between the circulating fluid (hot water or chilled water) and the airstream. Key design considerations include:
- Optimal coil pitch selection to balance heat transfer area against pressure drop (ΔP)
- Tube row arrangement (2-row, 4-row, 6-row) to achieve target capacity
- Flow distribution uniformity across parallel coil circuits
- Condensate drainage provisions for cooling mode operation
5.2 Additional Application Domains
- Industrial Heat Exchangers: Shell-and-tube, plate-fin, and air-cooled heat exchangers
- Refrigeration Systems: Evaporators and condensers in commercial refrigeration
- Automotive Radiators: Coolant circuit components requiring high thermal efficiency
- Food & Pharmaceutical Processing: Sanitary-grade heat exchange where hygienic surface requirements (Ra ≤ 0.4 μm) are mandated
- Power Generation: Condenser tubes and superheater coils in thermal power plants
6. Quality Certifications & Standards Compliance
6.1 Applicable Standards
| Standard | Title | Scope |
|---|---|---|
| ASTM A269/A269M | Welded Austenitic Stainless Steel Tube | Material & manufacturing |
| ASTM A270/A270M | Welded Austenitic Stainless Steel Sanitary Tube | Surface finish requirements |
| EN 10217-7 | Non-Alloy and Alloy Steel Tubes for Heat Exchangers | Heat exchanger tube specification |
| GB/T 12771 | Stainless Steel Seamless Tubes for General Purposes | Chinese national standard |
| ASME B31.3 | Process Piping | Design & pressure rating |
| ISO 9001:2015 | Quality Management Systems | Manufacturing quality assurance |
6.2 Inspection & Testing Protocols
- Hydrostatic Pressure Test: 1.5 × maximum working pressure, held for minimum 10 seconds with zero leakage
- Dimensional Inspection: CMM (Coordinate Measuring Machine) verification of OD, wall thickness, coil diameter, and pitch
- Chemical Composition Analysis: Spectrographic verification of Ni, Cr, Mo, C content per grade specification
- Hardness Testing: Vickers hardness (HV) verification at multiple locations along coil length
- Surface Defect Detection: Eddy current testing (ECT) for internal and external discontinuities
- Intergranular Corrosion Test: ASTM A262 Practice E (for stabilized grades)
7. Unique Selling Points
Wenzhou Jixing Metal Materials Co., Ltd. distinguishes its Coiltube product line through the following value propositions:
- Superior Heat Transfer Performance: The helical coil geometry inherently promotes secondary flow (Dean vortices), achieving 30–60% improvement in overall heat transfer coefficient compared to equivalent straight-tube configurations.
- Precision CNC Coiling: Computer-numeric-controlled coiling ensures geometric accuracy (±0.5 mm tolerance on coil diameter) and consistent turn-to-turn spacing, critical for uniform flow distribution in FCU applications.
- Full Traceability: Each coil tube batch carries heat number traceability from mill certificate through final inspection, enabling complete quality lineage documentation.
- Customization Capability: Flexible manufacturing parameters accommodate project-specific requirements for coil diameter, pitch, developed length, and surface finish grade.
- Extended Service Life: The combination of austenitic stainless steel metallurgy and proper post-forming heat treatment ensures resistance to stress corrosion cracking (SCC) and maintains mechanical integrity over extended thermal cycling.
- Design Optimization Support: Technical engineering team provides coil tube selection guidance aligned with Fan Coil Unit system design principles, including pressure drop analysis and capacity matching.
8. Technical Notes for Fan Coil Unit System Integration
Based on established engineering practice in FCU system design, the following considerations are critical when specifying and integrating stainless steel coil tubes:
- Flow Velocity Management: Water-side velocity should be maintained between 0.5–2.0 m/s to balance heat transfer efficiency against erosion-corrosion risk and pump power consumption.
- Anti-Vibration Mounting: Coil tube assemblies must incorporate flexible connectors or vibration isolators to prevent fatigue cracking at tube-sheet joints under fan-induced vibration.
- Water Quality Control: Circulating water conductivity should be maintained below 50 μS/cm with appropriate inhibitors to prevent under-deposit corrosion on coil tube surfaces.
- Freeze Protection: Coil tube systems must incorporate low-temperature cutoff controls or antifreeze provisions to prevent hydraulic fracture at temperatures below 0°C.
- Condensate Management: Proper coil pitch and row arrangement must accommodate condensate drainage in cooling mode to prevent waterlogging and subsequent efficiency degradation.
Document Classification: Technical Product Specification | Product Code: No. 847 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Category: Coil Tube (Coiltube) Products