Stainless Steel Spiral Coil Tube — Composite Interlayer Rising-Tube Heat Exchanger Series (Product No. 584)
1. Product Overview
The Stainless Steel Spiral Coil Tube (Coil Tube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a high-performance tubular component engineered specifically for composite interlayer spiral coil structure rising-tube heat exchangers. This product integrates the geometric advantages of spiral coiling with the corrosion resistance and thermal efficiency of austenitic stainless steel, enabling superior heat transfer performance in demanding industrial applications.
The design philosophy draws upon advanced research into the heat transfer characteristics of composite interlayer spiral coil structures. By leveraging the turbulent flow enhancement inherent in curved geometries, the coil tube achieves a significant increase in the overall heat transfer coefficient (U-value) compared to conventional straight-tube heat exchangers. The rising-tube configuration facilitates natural circulation and buoyancy-driven flow, reducing pumping energy requirements while maintaining efficient thermal exchange.
2. Material & Properties
2.1 Base Material
- Grade: Austenitic stainless steel — AISI 304 (UNS S30408), AISI 316L (UNS S31603), or AISI 321 (UNS S32100) per ASTM A213 / ASME SA-213 standards
- Carbon Equivalent (CE): ≤ 0.04% (for 316L grade), ensuring excellent weldability and resistance to intergranular corrosion
- Chromium (Cr) Content: 18–20 wt%
- Nickel (Ni) Content: 8–12 wt%
- Molybdenum (Mo) Content: 2–3 wt% (for 316L grade)
2.2 Mechanical Properties
| Property | Specification (AISI 304) | Specification (AISI 316L) |
|---|---|---|
| Tensile Strength (UTS) | ≥ 515 MPa (75 ksi) | ≥ 485 MPa (70 ksi) |
| Yield Strength (0.2% offset) | ≥ 205 MPa (30 ksi) | ≥ 170 MPa (25 ksi) |
| Elongation at Break | ≥ 40% | ≥ 40% |
| Hardness (HB) | ≤ 201 | ≤ 187 |
| Density | 7.93 g/cm³ | 8.00 g/cm³ |
2.3 Thermal Properties
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (AISI 304); 14.6 W/(m·K) at 20°C (AISI 316L)
- Specific Heat Capacity: 500 J/(kg·K) at 20°C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (AISI 304); 15.8 × 10⁻⁶ /°C (AISI 316L)
- Maximum Service Temperature: 870°C (AISI 304); 870°C (AISI 316L)
- Minimum Service Temperature: −196°C (cryogenic capable)
2.4 Corrosion Resistance
- Excellent resistance to atmospheric corrosion, dilute mineral acids, and organic acids
- High resistance to pitting and crevice corrosion (particularly 316L grade in chloride-containing environments)
- Resistance to stress corrosion cracking (SCC) enhanced by low carbon and controlled interstitial content
- PASSINATE™ / Passivation treatment per ASTM A967 for optimal surface protection
3. Specifications
| Parameter | Specification / Range |
|---|---|
| Outer Diameter (OD) | 6.35 mm – 50.8 mm (¼" – 2") |
| Wall Thickness | 0.5 mm – 3.0 mm (customizable) |
| Coil Diameter (Mandrel OD) | 100 mm – 2000 mm (configurable per application) |
| Coil Length | Up to 500 m continuous (seamless tube drawing) |
| Spiral Pitch | 15 mm – 80 mm (adjustable for flow rate optimization) |
| Surface Finish | 2B (Cold Rolled & Annealed), BA (Bright Annealed), or Electropolished (Ra ≤ 0.4 μm) |
| Internal Surface Roughness | ≤ 0.8 μm Ra (standard); ≤ 0.2 μm Ra (electropolished) |
| Helix Angle Deviation | ± 0.5° from nominal |
| Dimensional Tolerance (OD) | ± 0.1 mm (precision coil); ± 0.25 mm (standard) |
| Dimensional Tolerance (Wall) | ± 10% of nominal |
| End Condition | Plain end, beveled end, or threaded end (per client specification) |
| Standard References | ASTM A213, ASME SA-213, EN 10216-5, JIS G3459 |
| Pressure Rating | Up to 6.3 MPa (PN63) at 200°C (grade-dependent) |
| Packaging | Wooden crate with moisture-proof wrapping, or custom bulk packaging |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection: Certified stainless steel seamless tube (cold-drawn per ASTM A213) or precision cold-rolled coil strip, verified by mill test certificates (MTC) and spectroscopic analysis.
- Material Inspection & Pre-Treatment: Incoming inspection including chemical composition analysis (OES), mechanical testing, and surface defect examination. Surface degreasing and pickling preparation.
- Coil Forming (Cold Bending): The straight tube is fed through a precision rotary draw bending machine equipped with a custom mandrel and die system. The bending process is executed at controlled speed (≤ 5 m/min) to prevent wall thinning, ovalization, or internal wrinkling. The helical geometry is formed by synchronized rotation and linear advancement of the tube.
- In-Process Quality Control: Continuous monitoring of bend radius, wall thickness reduction (≤ 15% at inner fiber), and ovality (≤ 3% of OD) via laser scanning and ultrasonic thickness gauging.
- Stress Relief Annealing: Post-coiling annealing at 1050°C – 1150°C followed by controlled cooling (air or water quench depending on grade) to relieve residual stresses introduced during cold forming and restore full mechanical properties.
- Pickling & Passivation: Immersion in mixed acid solution (HNO₃/HF) per ASTM A967 to remove oxide scale and form a uniform passive chromium oxide film (Cr₂O₃) on the surface.
- Final Dimensional Inspection: Coordinate Measuring Machine (CMM) verification of coil diameter, pitch uniformity, and overall length. Non-destructive testing (NDT) including dye penetrant inspection (DPI) and hydrostatic pressure testing.
- Packaging & Dispatch: Coils are wound on protective spools, wrapped in moisture-barrier film, and secured in export-grade wooden crates with desiccant packs.
4.2 Key Process Advantages
- Cold coiling eliminates the need for post-forming heat treatment in many applications, reducing energy consumption
- Precision mandrel design ensures uniform wall thickness throughout the helical geometry
- Automated CNC-controlled bending achieves repeatable dimensional accuracy (± 0.1 mm)
- Full traceability from raw material heat number to finished coil serial number
5. Applications
5.1 Primary Application Domains
- Composite Interlayer Spiral Coil Heat Exchangers: As rising-tube components in multi-pass heat exchanger bundles where enhanced turbulence and natural circulation improve thermal efficiency by 25–40% over straight-tube designs.
- Petroleum & Chemical Industry: Heat recovery systems, condensers, and reboilers processing corrosive hydrocarbons, acids, and solvents.
- Pharmaceutical & Food Processing: Sanitary-grade heat exchangers requiring electropolished surfaces for CIP (Clean-in-Place) compatibility and regulatory compliance (FDA 21 CFR, EU 1935/2004).
- Power Generation: Economizers, superheaters, and condensers in thermal power plants operating under high-temperature and high-pressure conditions.
- Marine & Offshore: Sea water coolers, distillation plants, and heat exchangers exposed to chloride-rich environments.
- Cryogenic Systems: LNG (Liquefied Natural Gas) heat exchange systems requiring reliable performance at temperatures as low as −196°C.
5.2 Heat Transfer Performance Enhancement
Research on composite interlayer spiral coil structure rising-tube heat exchangers has demonstrated that the helical geometry generates centrifugal forces that induce secondary Dean vortices within the tube. These vortices disrupt the thermal boundary layer, increasing the Nusselt number (Nu) by 30–60% compared to equivalent straight tubes at the same Reynolds number. The composite interlayer design further enhances heat transfer by creating additional flow channels and reducing thermal resistance at the tube-wall interface.
6. Quality Certifications & Compliance
6.1 Management System Certifications
- ISO 9001:2015 — Quality Management System
- ISO 14001:2015 — Environmental Management System
- ISO 45001:2018 — Occupational Health & Safety Management System
- ISO 3834-2:2005 — Welding Quality Requirements (where welding is involved)
6.2 Product & Industry Certifications
- ASME "S" Stamp — Sectional Heating Boilers and Pressure Vessels
- ASME "U" Stamp — Pressure Vessels
- EN 10204 3.1 Certificate — Mill Test Certificate with third-party inspection
- CE Marking — Compliance with European Pressure Equipment Directive (PED 2014/68/EU)
- NACE MR0175 / ISO 15156 — Resistance to Sulfide Stress Cracking (for oil & gas applications)
- NSF/ANSI 61 — Drinking Water System Components (for food/pharma grade)
6.3 Inspection & Testing Protocols
| Test Method | Standard | Purpose |
|---|---|---|
| Hydrostatic Pressure Test | ASTM A213 / ASME B31.3 | Verify structural integrity and leak tightness |
| Dye Penetrant Inspection (DPI) | ASTM E709 | Detect surface-breaking defects at bends |
| Eddy Current Testing (ECT) | ASTM E309 | Continuous internal and external defect detection |
| Ultrasonic Thickness Measurement | ASTM E797 | Verify wall thickness uniformity |
| Pitting Corrosion Test | ASTM G48 (Ferric Chloride) | Assess pitting resistance equivalent number (PREN) |
| Intergranular Corrosion Test | ASTM A262 Practice E (65°C) | Confirm resistance to intergranular attack |
| Hardness Testing | ASTM E10 (Brinell) | Verify annealing effectiveness |
7. Unique Selling Points
- Research-Validated Thermal Performance: The spiral coil geometry is optimized based on peer-reviewed research into composite interlayer rising-tube heat exchanger configurations, delivering quantifiable improvements in heat transfer coefficients.
- Full Material Traceability: Each coil is traceable to the original steel mill heat number, enabling complete quality documentation for critical applications.
- Custom Geometric Configuration: Coil diameter, pitch, tube OD, and wall thickness are all customizable to match specific heat exchanger bundle designs and process requirements.
- Multi-Grade Availability: Options across 304, 316L, 321, and duplex stainless steel grades to address diverse corrosion environments.
- Cryogenic to High-Temperature Capability: