Spiral Coil Tube (Stainless Steel Coiltube) — Technical Specification
Product Catalogue No.: 1563
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Classification: Literature Learning / Technical Reference Series
1. Product Overview
The Spiral Coil Tube (SCT) is a specialized form of stainless steel tube fabricated into a helical or spiral geometry, engineered to maximize heat transfer efficiency within confined spatial envelopes. Unlike conventional straight tubes, the spiral configuration inherently induces secondary flow patterns—specifically Dean vortices—within the fluid channel. These vortices continuously disrupt the thermal boundary layer, resulting in significantly enhanced convective heat transfer coefficients compared to straight-tube baselines.
Based on extensive research literature, including the seminal study "Research on Heat Transfer of Spiral Coil Tubes", the Spiral Coil Tube demonstrates superior thermal performance characterized by:
- Enhanced Nusselt number (Nu) due to secondary flow effects governed by the Dean number (De)
- Compact heat exchanger design with high surface-area-to-volume ratio
- Reduced flow maldistribution in multi-tube heat exchanger bundles
- Improved pressure drop characteristics under turbulent flow regimes
The product is manufactured from high-grade austenitic stainless steel grades, ensuring exceptional corrosion resistance, mechanical integrity under thermal cycling, and long-term operational reliability in aggressive chemical environments.
2. Material & Properties
2.1 Base Material Grades
The Spiral Coil Tube is available in the following standard stainless steel grades, selected according to application-specific corrosion and mechanical requirements:
- SUS304 / AISI 304 (UNS S30400): General-purpose grade with excellent formability and weldability. Suitable for food processing, pharmaceutical, and chemical applications.
- SUS316L / AISI 316L (UNS S31603): Low-carbon variant with added molybdenum (Mo 2.0–2.5%) for superior resistance to pitting and crevice corrosion in chloride-containing environments.
- SUS321 / AISI 321 (UNS S32100): Titanium-stabilized grade offering enhanced resistance to intergranular corrosion at elevated temperatures (up to 870°C).
- SUS310S / AISI 310S (UNS S31008): High-temperature grade with elevated chromium (25%) and nickel (19%) content for sustained service above 1000°C.
2.2 Mechanical Properties (Annealed Condition)
| Property | Grade 304 | Grade 316L | Grade 321 | Grade 310S |
|---|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 485 | ≥ 515 | ≥ 515 |
| Yield Strength (MPa, 0.2% offset) | ≥ 205 | ≥ 170 | ≥ 205 | ≥ 205 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 40 | ≥ 35 |
| Hardness (HB) | ≤ 217 | ≤ 217 | ≤ 217 | ≤ 217 |
2.3 Thermal Properties
- Thermal Conductivity (λ): 14–16 W/(m·K) at 20°C (Grade 304)
- Specific Heat Capacity (cp): 478–502 J/(kg·K) at 20°C
- Linear Thermal Expansion Coefficient (α): 16–18 × 10⁻⁶ /K (20–800°C)
- Maximum Service Temperature: 870°C (304/316L), 870°C (321), 1093°C (310S)
2.4 Corrosion Resistance
- Pitting Resistance: PREN (Pitting Resistance Equivalent Number) of 18–20 (304), 24–26 (316L)
- Resistance to Intergranular Corrosion: Verified per ASTM A240 and ASTM A479 standards
- Chloride Tolerance: Up to 2000 ppm Cl⁻ at ambient temperature (316L)
3. Specifications
| Parameter | Specification |
|---|---|
| Tube Outer Diameter (OD) | φ6 mm – φ32 mm (custom sizes available) |
| Wall Thickness (WT) | 0.3 mm – 2.0 mm |
| Spiral Coil Diameter (CD) | φ50 mm – φ500 mm |
| Coil Pitch (P) | 10 mm – 60 mm |
| Coil Length (L) | Up to 6000 mm (custom lengths upon request) |
| Number of Turns (N) | 5 – 500 turns |
| Diameter-to-Tube OD Ratio (D/d) | ≥ 5 (optimal range: 8–20 for enhanced heat transfer) |
| Surface Finish | Ra ≤ 0.8 μm (polished); Ra ≤ 1.6 μm (pickled); Ra ≤ 0.4 μm (electropolished) |
| Tolerance on OD | ±0.05 mm (precision drawn); ±0.1 mm (standard) |
| Tolerance on Wall Thickness | ±0.02 mm (precision); ±0.05 mm (standard) |
| Dimensional Standard | ASTM A269 / ASTM A554 / GB/T 14976 / DIN 11850 |
| End Condition | Plain cut, beveled, threaded, or with fittings (brazed/welded) |
3.1 Helix Geometry Parameters
The geometric configuration of the spiral coil tube is defined by the following parameters, which directly influence fluid dynamics and heat transfer performance:
- D/d Ratio: The ratio of coil diameter to tube outer diameter. Higher D/d ratios reduce centrifugal forces and pressure drop but may diminish secondary flow enhancement.
- Pitch-to-Diameter Ratio (P/D): Governs the tightness of the coil winding. Lower ratios indicate tighter coils with enhanced turbulence.
- Curvature Number (κ = d/D): A dimensionless parameter central to the Dean number calculation (De = Re · √(κ/2)), which characterizes the intensity of secondary flow.
4. Manufacturing Process
4.1 Process Flowchart
- Raw Material Selection: Seamless stainless steel tubes (per ASTM A269) or precision drawn tubes (per ASTM A554) are sourced from certified mills with full chemical composition and mechanical property traceability.
- Incoming Quality Inspection: Verification of chemical composition (OES analysis), dimensional accuracy, and surface quality. Each batch is accompanied by a Mill Test Certificate (MTC) conforming to EN 10204 3.1.
- Surface Preparation: Tubes undergo mechanical cleaning, degreasing, and optional pickling/acid passivation to remove scale, oxides, and contaminants. Electropolishing is available for critical applications requiring ultra-smooth internal surfaces.
- Coil Forming: The straight tube is fed into a precision coiling machine equipped with CNC-controlled forming dies. The tube is bent into the desired helical geometry through controlled rolling and winding operations. The forming process is executed under carefully controlled strain rates to avoid excessive work hardening and maintain mechanical properties.
- Solution Annealing: Post-forming annealing at 1050–1150°C followed by rapid water quenching restores the fully solution-treated condition, eliminating residual stresses introduced during forming. This ensures optimal corrosion resistance and mechanical ductility.
- Final Dimensional Inspection: All coils are verified for dimensional accuracy using coordinate measuring machines (CMM), laser diameter gauges, and ultrasonic wall thickness scanners. Geometric parameters (coil diameter, pitch, number of turns) are confirmed within specified tolerances.
- End Processing: Tubes are cut to specified lengths and end-conditioned (beveling, threading, or fitting attachment) as required by the customer specification.
- Final Quality Assurance: Non-destructive testing (NDT) including eddy current testing (ECT) for wall thickness verification and surface defect detection. Hydrostatic pressure testing at 1.5× working pressure for leak integrity confirmation.
- Packaging and Dispatch: Coils are protected with corrosion-inhibiting packaging, cushioning materials, and moisture-absorbing desiccants to ensure product integrity during transit.
4.2 Forming Technology
The coiling process employs a combination of rotary bending and helical winding techniques. The tube is guided through a series of precision rollers that progressively impart curvature while maintaining cross-sectional shape integrity. For small diameter tubes (OD ≤ φ12 mm), a single-pass forming approach is utilized. For larger diameters or thicker walls, multi-pass incremental forming is employed to prevent ovalization and maintain dimensional accuracy within ±0.05 mm.
The forming equipment is equipped with real-time feedback systems that monitor bending force, tube position, and dimensional accuracy throughout the forming cycle, ensuring consistent quality across production batches.
5. Applications
5.1 Heat Exchanger Systems
- Shell-and-tube heat exchangers: Spiral coil tubes serve as the tube bundle in compact heat exchangers, providing enhanced heat transfer with reduced footprint.
- Plate-fin heat exchangers: Used in cryogenic and low-temperature applications where high surface density is critical.
- Air-cooled heat exchangers: Spiral configurations provide uniform flow distribution and reduced fouling tendencies.
5.2 Process Industries
- Chemical processing: Reactor cooling coils, evaporator coils, and condensers for corrosive process fluids.
- Petrochemical: Crude oil fractionation, distillation column condensers, and heat recovery systems.
- Pharmaceutical: Sterile heat exchange systems for CIP (Clean-in-Place) and SIP (Sterilization-in-Place) compatible applications.
- Food and beverage: Milk pasteurization, juice concentration, and beverage cooling systems (Grade 316L for hygienic compliance).
5.3 Energy and Power
- Solar thermal collectors: Absorber tubes in evacuated tube solar collectors and flat plate collectors.
- Geothermal systems: Heat extraction coils for geothermal energy utilization.
- Refrigeration and HVAC: Evaporator and condenser coils in industrial refrigeration systems.
5.4 Specialized Applications
- Automotive: Turbocharger intercoolers and exhaust gas recirculation (EGR) coolers.
- Oil and gas: Subsea heat exchangers and gas cooling systems.
- Marine: Boiler economizers, condensers, and ballast water heat exchangers.
- Research and development: Laboratory-scale heat transfer studies and thermal performance validation.
6. Quality Certifications
6.1 Product Certifications
- ISO 9001:2015: Quality Management System certification ensuring consistent product quality and process control.
- ISO 14001:2015: Environmental Management System certification demonstrating environmental responsibility.
- CE Marking: Compliance with European Union directives for pressure equipment and machinery safety.
- ASME Section IX: Welding qualification for pressure vessel and piping applications.
6.2 Testing and Inspection Standards
| Test Type | Standard Reference | Purpose |
|---|---|---|
| Chemical Composition Analysis | ASTM E1251 / GB/T 20066 | Verification of alloy composition |
| Mechanical Testing (Tensile) | ASTM E8 / GB/T 228.1 | Confirmation of strength and ductility |
| Hydrostatic Pressure Test | ASTM A213 / GB/T |