Stainless Steel Spiral Coil Tube (Coiltube) — Technical Specification
Product Overview
The Stainless Steel Spiral Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered continuous helical tubing product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Designed to meet the rigorous demands of heat exchange, fluid conveyance, and process engineering applications, this product represents a convergence of metallurgical excellence and geometric precision. The spiral coil configuration provides a maximized surface-area-to-volume ratio, enabling superior thermal transfer efficiency compared to straight-pipe alternatives.
Grounded in advanced research on external film condensation heat transfer of vertical spiral coils, this product line incorporates validated hydrodynamic and thermodynamic principles to optimize condensation performance. The helical geometry induces secondary flow patterns (Dean vortices) that enhance turbulence, thereby reducing the thermal boundary layer thickness and promoting more uniform condensate film distribution across the tube exterior.
Material & Properties
The Coiltube is fabricated from high-grade austenitic stainless steels, selected for their exceptional combination of corrosion resistance, mechanical strength, and thermal stability. The primary material grades are specified as follows:
- Grade 304 (UNS S30408 / 1.4301): The standard austenitic stainless steel offering excellent general-purpose corrosion resistance, weldability, and formability. Suitable for most industrial and food-grade applications.
- Grade 316 (UNS S31608 / 1.4401): Enhanced molybdenum content (2.0–3.0%) provides superior resistance to pitting and crevice corrosion, particularly in chlorinated environments.
- Grade 321 (UNS S32168 / 1.4541): Titanium-stabilized variant offering outstanding resistance to intergranular corrosion at elevated temperatures (up to 870 °C).
- Grade 316L (UNS S31603 / 1.4434): Low-carbon variant (C ≤ 0.03%) ideal for welded assemblies requiring resistance to sensitization during welding.
Key Mechanical and Physical Properties
| Property | Grade 304 | Grade 316 | Grade 321 |
|---|---|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa | ≥ 515 MPa | ≥ 515 MPa |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ≥ 205 MPa | ≥ 205 MPa |
| Elongation (A50mm) | ≥ 40% | ≥ 40% | ≥ 40% |
| Thermal Conductivity (at 100 °C) | 16.3 W/(m·K) | 16.3 W/(m·K) | 14.2 W/(m·K) |
| Specific Heat Capacity | 500 J/(kg·K) | 500 J/(kg·K) | 500 J/(kg·K) |
| Density | 7.93 g/cm³ | 8.00 g/cm³ | 7.93 g/cm³ |
| Maximum Service Temperature | 870 °C | 870 °C | 870 °C |
| Corrosion Resistance (pitting) | Moderate | Excellent | Good |
Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (¼" – 2") | ASTM A213 / EN 10217-7 |
| Wall Thickness (WT) | 0.5 mm – 3.0 mm | ASTM A213 / EN 10217-7 |
| Coil Pitch | 10 mm – 80 mm (customizable) | ISO 10449 |
| Coil Diameter (Helical) | 50 mm – 500 mm | Project-specific |
| Tube Length (Coiled) | 1 m – 100 m per coil (continuous) | — |
| Surface Finish | 2B, BA (Bright Annealed), No. 4, Mirror (Ra ≤ 0.1 μm) | ASTM A480 |
| Forming Accuracy (OD tolerance) | ±0.1 mm | EN 10217-7 |
| Forming Accuracy (WT tolerance) | ±10% of nominal | EN 10217-7 |
| Helix Angle Deviation | ±1° | Internal QC standard |
| End Treatment | Plain end, Beveled (37°), Threaded (BSPP/NPT) | ASME B1.20.1 |
| Packaging | Wooden crate / Pallet with VCI film protection | ISO 4180 |
Manufacturing Process
The production of high-precision stainless steel spiral coil tubes follows a multi-stage process chain designed to ensure dimensional integrity, metallurgical soundness, and surface quality:
- Raw Material Inspection & Receiving: Cold-rolled stainless steel strip or seamless tube stock is received and subjected to chemical composition verification (Optical Emission Spectroscopy, OES) and mechanical property testing.
- Coil Straightening & Cutting: The raw tube/strip is straightened using multi-roller tension straighteners and cut to the required coil length with a hydraulic shearing line.
- Helical Coiling (Precision Forming): The tube is fed through a CNC-controlled coiling machine that applies controlled bending forces to form the helical geometry. The forming process maintains minimum bend radius (R ≥ 1.5 × OD) to prevent cross-sectional distortion and wall thinning. Real-time monitoring ensures pitch and helix angle accuracy.
- Post-Forming Stress Relief: A controlled annealing cycle (typically 1050–1100 °C for Grade 304/316, followed by controlled cooling) is applied to relieve residual stresses induced during forming and to restore full austenitic microstructure.
- Pickling & Passivation: The annealed coil tube is treated with a mixed acid pickling solution (HNO₃ + HF) to remove oxide scale, followed by passivation to establish a protective chromium oxide (Cr₂O₃) film on the surface.
- Surface Finishing: Depending on the application requirement, the tube undergoes mechanical polishing, electropolishing, or chemical brightening to achieve the specified surface roughness.
- Quality Inspection: Comprehensive inspection including dimensional measurement (OD, WT, pitch, coil diameter), visual examination, eddy current testing for wall thickness verification, and hydrostatic pressure testing (typically 1.5 × working pressure for 30 seconds).
- Marking & Packaging: Each coil is marked with product identification, heat number, grade, and batch traceability information, then packaged for shipment.
Applications
The unique spiral geometry and material properties of the Coiltube render it suitable for a broad spectrum of industrial applications:
- Shell-and-Tube Heat Exchangers: Spiral coil tubes are employed as the heat transfer elements in compact heat exchangers where high thermal efficiency and space optimization are critical. The enhanced turbulence from the helical geometry improves the overall heat transfer coefficient (U-value) by 20–40% compared to equivalent straight tubes.
- External Film Condensation Systems: As validated by research on vertical spiral coil condensation, these tubes exhibit improved condensate drainage characteristics and thinner condensate films, resulting in reduced thermal resistance at the tube-outer-surface interface.
- Air Conditioning & Refrigeration (HVAC/R): Used in evaporator and condenser assemblies where high-efficiency heat exchange is required in compact form factors.
- Chemical Processing & Petrochemical Industry: Ideal for reactors, heat recovery systems, and process heat exchangers handling corrosive fluids (acids, chlorides, hydrocarbons).
- Food & Pharmaceutical Industry: Sanitary-grade coil tubes (BA finish, Ra ≤ 0.5 μm) used in pasteurization, sterilization, and process heating/cooling systems compliant with FDA and 3-A standards.
- Power Generation: Applied in condenser tubes, economizers, and feedwater preheating systems in thermal power plants.
- Marine & Offshore Applications: Corrosion-resistant coil tubes for seawater heat exchangers and thermal management systems.
- Automotive Industry: Compact heat exchangers for transmission oil coolers, intercoolers, and battery thermal management systems in electric vehicles.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems and ensures full compliance with international standards:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent product quality and process control |
| ISO 14001:2015 | Environmental Management System certification for sustainable manufacturing practices |
| ISO 45001:2018 | Occupational Health and Safety Management System |
| EN 10204 3.1 | Material Test Certificate providing full traceability from raw material to finished product |
| ASTM A213 / A269 | Compliance with American standards for seamless austenitic stainless steel boiler, heat-exchanger, and condenser tubes |
| ASME BPV Section I | Compliance for pressure-containing heat exchanger tube applications |
| EN 10217-7 | European standard for stainless steel tubes for heat exchangers and heat transfer equipment |
| NORSOK M-001 | Material requirement for offshore applications (where applicable) |
| CE Marking | Conformity with European Union directives for pressure equipment (PED 2014/68/EU) |
Unique Selling Points
1. Research-Validated Thermal Performance: Product design informed by peer-reviewed research on film condensation heat transfer in vertical spiral coil configurations, ensuring optimal condensate film dynamics and enhanced heat transfer coefficients.
2. Precision Helical Geometry: CNC-controlled coiling with ±1° helix angle accuracy ensures consistent secondary flow enhancement (Dean number optimization) throughout the entire coil length.
3. Full Traceability: Every coil is traceable to its original heat number with complete chemical and mechanical test documentation (EN 10204 3.1 Certificate).
4. Customization Capability: Flexible configuration options including variable pitch, multiple OD/WT combinations, and specialized surface finishes tailored to specific application requirements.
5. Continuous Length Advantage: Seamless coiling eliminates internal joints and leak points, providing superior integrity for high-pressure and high-purity fluid applications.
Technical Notes
When specifying the Coiltube for heat exchanger design, engineers should consider the Dean number (De = Re × √(d/D)), where Re is the Reynolds number, d is the tube inner diameter, and D is the coil diameter. The Dean number governs the intensity of secondary flow and should be optimized for the target heat transfer performance. For condensation applications, the vertical orientation of the spiral coil promotes gravity-assisted condensate drainage, reducing the effective condensate film thickness and minimizing the associated thermal resistance.
All products are manufactured under controlled conditions with documented process parameters, ensuring repeatable quality and dimensional consistency across production batches.