Stainless Steel Coil Tube — Induced-Flow Heat Transfer Coil (Coiltube Series)
1. Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered heat exchange element manufactured by Wenzhou Jixing Metal Materials Co., Ltd. Specifically designed for integration into agitated vessel systems, this coil tube functions as an immersed heat transfer surface within stirred tanks, reactors, and process vessels. The product is engineered to facilitate efficient heat exchange between a working fluid circulating through the coil and the bulk process medium surrounding it, particularly under non-steady-state (transient) convective conditions induced by mechanical agitation.
Unlike conventional straight-tube heat exchangers, the Coiltube series leverages the inherent secondary flow enhancement generated by the helical or spiral geometry. When deployed within a vessel equipped with a four-blade inclined paddle agitator, the interaction between the agitator-induced bulk flow and the coil's curved geometry produces complex vortex structures that significantly augment the local heat transfer coefficient. This synergistic effect has been extensively validated through both computational fluid dynamics (CFD) simulation and experimental verification, demonstrating superior thermal performance compared to straight-tube alternatives under equivalent operating conditions.
2. Material & Properties
2.1 Base Material
The Coiltube is fabricated from high-purity austenitic stainless steel, with the following grades available upon request:
- AISI 304 (UNS S30408) — General-purpose corrosion resistance; suitable for food, pharmaceutical, and mild chemical environments
- AISI 316L (UNS S31603) — Enhanced chloride pitting resistance; ideal for marine, chemical processing, and pharmaceutical applications
- AISI 321 (UNS S32100) — Stabilized grade with titanium addition; resistant to intergranular corrosion at elevated temperatures (up to 870 °C)
- AISI 316Ti (UNS S31635) — Titanium-stabilized variant of 316L for high-temperature service with superior weldability
2.2 Key Physical and Thermal Properties
| Property | Unit | 304 | 316L | 321 |
|---|---|---|---|---|
| Density (ρ) | kg/m³ | 8000 | 8030 | 8000 |
| Thermal Conductivity (λ) @25 °C | W/(m·K) | 16.3 | 14.6 | 16.3 |
| Thermal Conductivity (λ) @100 °C | W/(m·K) | 18.0 | 16.3 | 18.0 |
| Thermal Expansion Coefficient (α) @20–100 °C | ×10⁻⁶/K | 17.3 | 16.0 | 17.3 |
| Specific Heat (cₚ) @25 °C | J/(kg·K) | 500 | 500 | 500 |
| Maximum Service Temperature | °C | 870 | 870 | 1093 |
| Minimum Service Temperature | °C | −196 | −196 | −196 |
| Yield Strength (0.2% offset) | MPa | 205 | 170 | 205 |
| Tensile Strength | MPa | 515 | 485 | 515 |
2.3 Corrosion Resistance
The austenitic microstructure provides excellent resistance to oxidation, atmospheric corrosion, and a wide range of dilute acids and alkaline solutions. The low-carbon variant (316L) offers superior resistance to intergranular corrosion following welding operations, making it the preferred selection for pharmaceutical and food-grade coil assemblies where surface integrity post-fabrication is critical.
3. Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) |
| Material Grade | 304 / 316L / 321 / 316Ti (custom upon request) |
| Outer Diameter (OD) | φ12 mm – φ114.3 mm (customizable) |
| Wall Thickness (WT) | 0.5 mm – 6.0 mm (standard: 1.0–3.0 mm) |
| Coil Inner Diameter (ID) | φ100 mm – φ2000 mm (customizable) |
| Coil Height | 50 mm – 3000 mm (customizable) |
| Helix Pitch | 15 mm – 150 mm (adjustable per application) |
| Surface Finish | BA (Bright Annealed), No. 4 Brushed, Mirror (Ra ≤ 0.2 μm), EP (Electro-polished) |
| End Connection | Welded, Threaded (BSP/NPT), Flanged (ASME/EN), Tri-Clamp |
| Pressure Rating | Up to 4.0 MPa (600 PSI) at 20 °C (design pressure dependent on geometry) |
| Operating Temperature Range | −196 °C to +870 °C |
| Manufacturing Standard | GB/T 14976, ASTM A213, EN 10216-5, ISO 3506 |
| Traceability | Full material traceability with mill certificates (EN 10204 3.1) |
| Minimum Order Quantity | 100 meters (negotiable for standard configurations) |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection & Inspection: Stainless steel seamless tube or welded tube is sourced from certified mills. Incoming material undergoes 100% chemical composition analysis (via Optical Emission Spectroscopy, OES) and mechanical property verification (tensile testing, hardness testing per ASTM E92).
- Dimensional Cutting & End Preparation: Tubes are cut to required lengths using precision plasma or laser cutting systems. End faces are prepared for subsequent welding or forming operations.
- Coil Forming (Rolling): The tube is mandrel-coiled or free-coiled to the specified helical geometry using CNC-controlled coil forming equipment. The forming process is carefully controlled to avoid excessive cold work, which could compromise the metallurgical properties and induce residual stresses. For tight-tolerance applications, a mandrel is inserted during forming to prevent ovality and collapse.
- Welding (if multi-pass or multi-coil assembly required): Spiral-wound coils are assembled using orbital TIG (Tungsten Inert Gas) welding in accordance with AWS D10.9 or ISO 13919 standards. Weld parameters are optimized to minimize heat-affected zone (HAZ) sensitization.
- Stress Relief Annealing: For applications requiring reduced residual stress, coils undergo solution annealing at 1050–1150 °C followed by controlled water or air quenching to restore full austenitic properties and eliminate work-hardening effects.
- Surface Finishing: Final surface treatment is applied per customer specification — bright annealing, mechanical brushing, mechanical polishing, or electro-polishing. Electro-polishing removes up to 25–50 μm of surface material, producing a smooth, passivated finish with Ra values as low as 0.1 μm.
- End Connection Fabrication: Fittings, flanges, or threaded connections are welded or mechanically joined to coil terminals. Orbital welding ensures consistent weld quality and visual appearance.
- Pressure Testing & Non-Destructive Testing (NDT): Each coil assembly undergoes hydrostatic pressure testing at 1.5× the design pressure. Additional NDT methods include dye penetrant inspection (DPI) for surface defects and radiographic testing (RT) for internal weld integrity where required.
- Final Inspection & Packaging: Coils are cleaned, passivated (citric acid or nitric acid passivation per ASTM A967), inspected for dimensional accuracy, and packaged with protective end caps and moisture-absorbing desiccants.
4.2 Quality Control Milestones
- Incoming material certification verification (Mill Test Certificate, MTC)
- In-process dimensional checks at each forming stage
- Post-weld visual and NDT inspection
- Post-annealing mechanical property re-verification
- Final hydrostatic pressure test with documented results
- Surface finish verification via roughness profilometry
5. Applications
5.1 Primary Application Domains
- Pharmaceutical Processing: Heating and cooling of batch reactors, mixing tanks, and crystallization vessels. The coil tube provides high surface-area-to-volume ratio for rapid thermal response under non-steady-state conditions.
- Food & Beverage Industry: Pasteurization tanks, fermentation vessels, and CIP (Clean-in-Place) compatible heating/cooling coils for dairy, brewing, and juice processing.
- Chemical Processing: Exothermic reaction temperature control in agitated reactors, solvent recovery condensers, and intermediate storage tank temperature maintenance.
- Biotechnology & Bioprocessing: Temperature control in bioreactors where precise thermal management is essential for cell culture viability and product quality.
- Oil & Gas / Petrochemical: Subsea and surface equipment heat tracing, separator vessel heating, and process fluid conditioning.
- Power Generation: Auxiliary heating coils in condensate tanks and feedwater preheating systems.
5.2 Performance Under Agitated Conditions
Research and experimental validation have demonstrated that when the Coiltube is deployed within a vessel equipped with a four-blade inclined paddle (45° blade angle) agitator, the following performance characteristics are observed:
- The non-steady-state (transient) heat transfer coefficient on the coil outer surface increases by 30–80% compared to static (unagitated) conditions, depending on Reynolds number (Re) and Prandtl number (Pr) of the process fluid.
- The helical geometry of the coil generates Dean vortices within the tube lumen, enhancing internal heat transfer and reducing thermal boundary layer thickness.
- The interaction between the agitator's pumping action and the coil's radial orientation creates a periodic variation in local flow velocity, which, while introducing thermal transients, results in a higher time-averaged heat transfer rate.
- Optimal coil placement (typically in the mid-to-lower third of the vessel) maximizes the synergy between the agitator flow field and the coil heat exchange surface.
6. Quality Certifications & Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification covering design, manufacturing, and testing |
| ISO 3834-2 | Quality requirements for welding of metallic materials |
| EN 10204 Type 3.1 | Material inspection certificate with test results issued by authorized personnel |
| ASTM A213 / A269 | Standard specification for seamless and welded austenitic stainless steel tubing |
| GB/T 14976 | Chinese national standard for cold-rolled stainless steel seamless tubes for fluid conveyance |
| EN 10216-5 | European standard for heat exchanger tubes and condenser tubes — austenitic stainless steel |
| CE Marking (PED 2014/68/EU) | Compliance with European Pressure Equipment Directive for pressure-containing components |
| 3-A Sanitary Standards | Food Equipment and Machinery Association standards for hygienic design (available upon request) |
| EHEDG | European Hygienic Engineering and Design Group guidelines for process equipment design |
| NACE MR0175 / ISO 15156 | Resistance to sulfide stress cracking (for oil and gas applications with 316L/316Ti grades) |
7. Unique Selling Points
- Geometry-Enhanced Heat Transfer: The helical coil geometry inherently generates secondary Dean-type flows that increase turbulence and heat transfer coefficients without requiring additional internal turbulators or fins.
- Agitator Synergy: Specifically optimized for use in mechanically agitated vessels, where the combined effect of bulk fluid motion and coil geometry yields superior transient thermal performance — validated through both CFD simulation and experimental study.
- Customizable Geometry: Full customization of coil diameter, pitch, tube OD, wall thickness, and overall dimensions to match specific vessel internals and process requirements.
- Hygienic Design Capability: Available in electro-polished finish with Ra ≤ 0.2 μm, fully compliant with pharmaceutical and food-grade sanitary standards.
- Wide Temperature and Pressure Envelope: Operational range from cryogenic (−196 °C) to high-temperature (870 °C) service with pressure ratings up to 4.0 MPa, accommodating virtually all industrial process conditions.
- Full Traceability: Every coil is accompanied by complete documentation including material certificates, welding records, NDT reports, and pressure test certificates.
- Corrosion Resilience: Austenitic stainless steel construction ensures long service life even in aggressive chemical environments, minimizing maintenance frequency and total cost of ownership (TCO).