Stainless Steel Spiral Coil Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Spiral Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is formed by cold-drawing or hot-forming stainless steel seamless tubes into a continuous helical (spiral) geometry, resulting in a coiled configuration that maximizes surface area within a compact footprint. The unique helical structure imparts superior convective heat transfer characteristics, as demonstrated by extensive research on forced convection heat transfer in spiral coil tubes (强制对流换热), making this product an ideal solution for high-efficiency thermal management systems.
The spiral geometry induces secondary Dean vortices within the flow channel, which enhance turbulent mixing, reduce thermal boundary layer thickness, and significantly increase the Nusselt number (Nu) compared to straight tubes of equivalent diameter. This fundamental thermohydraulic advantage positions the Coiltube as a premier choice for heat exchangers, evaporators, condensers, and process engineering applications demanding maximum thermal performance per unit volume.
2. Material & Properties
2.1 Material Grades
- AISI 304 / ASTM A213 TP304 — General-purpose austenitic stainless steel with excellent corrosion resistance and formability
- AISI 316 / ASTM A213 TP316 — Molybdenum-enhanced grade for superior resistance to pitting and crevice corrosion in chloride environments
- AISI 316L / ASTM A213 TP316L — Low-carbon variant suitable for welded applications and harsh chemical environments
- AISI 321 / ASTM A213 TP321 — Titanium-stabilized grade for elevated temperature service up to 870°C
- AISI 347 / ASTM A213 TP347 — Niobium-stabilized alternative to 321 for high-temperature structural integrity
- AISI 310S / ASTM A213 TP310S — High-temperature grade for extreme thermal cycling and oxidizing atmospheres
2.2 Key Physical and Mechanical Properties
| Property | 304 Grade | 316 Grade | 316L Grade | Unit |
|---|---|---|---|---|
| Density (密度) | 8.00 | 8.03 | 8.03 | g/cm³ |
| Thermal Conductivity (热导率) at 20°C | 16.3 | 14.6 | 14.6 | W/(m·K) |
| Thermal Conductivity at 100°C | 21.5 | 17.3 | 17.3 | W/(m·K) |
| Specific Heat (比热容) at 20°C | 0.50 | 0.50 | 0.50 | J/(g·K) |
| Thermal Expansion (热膨胀系数) 20–100°C | 17.3 | 16.8 | 16.8 | ×10⁻⁶/K |
| Tensile Strength (抗拉强度) min. | 515 | 515 | 485 | MPa |
| Yield Strength (屈服强度) min. (0.2% offset) | 205 | 205 | 170 | MPa |
| Elongation (延伸率) min. | 40 | 40 | 35 | % |
| Maximum Service Temperature | 870 | 870 | 870 | °C |
2.3 Surface Finish Options
- Pickled & Passivated (酸洗钝化) — Standard finish with Cr₂O₃ passive film for general corrosion protection
- Mechanically Polished (机械抛光) — Ra ≤ 0.5 μm for hygienic and optical applications
- Electro-Polished (电解抛光) — Ra ≤ 0.25 μm for pharmaceutical and food-grade service
- Brushed Finish (拉丝处理) — Aesthetic finish for architectural and decorative applications
3. Specifications
3.1 Geometric Dimensions
| Parameter | Range / Options | Standard Reference |
|---|---|---|
| Outer Diameter (外径, OD) | Φ3.0 mm – Φ63.5 mm (1/8" – 2-1/2") | ASTM A213 / ASME SA-213 |
| Wall Thickness (壁厚, WT) | 0.3 mm – 6.0 mm | ASTM A213 / ASME SA-213 |
| Coil Diameter (盘管外径, CD) | Φ50 mm – Φ2000 mm (customizable) | Customer specification |
| Coil Length (盘管长度, L) | 1 m – 500 m per coil | Customer specification |
| Number of Turns (圈数, N) | Calculated per design requirement | Derived parameter |
| Helix Pitch (螺旋节距, P) | 1.5 × OD to 5 × OD (typical) | Design dependent |
| End Condition (端部状态) | Flat-cut / Beveled / Threaded / Weld prep | Customer specification |
| Tolerance on OD | ±0.05 mm – ±0.2 mm (per grade) | ASTM A213 |
| Tolerance on WT | ±10% of nominal | ASTM A213 |
| Maximum Eccentricity (最大偏心率) | ≤ 10% of nominal WT | ASTM A213 |
3.2 Thermohydraulic Performance Parameters
| Performance Metric | Typical Enhancement Factor (vs. Straight Tube) | Relevant Condition |
|---|---|---|
| Nusselt Number Ratio (Nu_spiral / Nu_straight) | 1.5 – 2.5× | Re > 2300 (turbulent flow) |
| Heat Transfer Coefficient Enhancement | 20% – 150% | Forced convection, single-phase |
| Pressure Drop Penalty | 1.2 – 2.0× | Acceptable trade-off for enhanced heat transfer |
| Compactness Ratio (Surface Area per Volume) | 3 – 10× | Compared to equivalent shell-and-tube design |
| Minimum Effective Reynolds Number | Re > 1000 | Below which laminar flow dominates |
| Dean Number Range (De = Re × √(d/D_c)) | 10 – 5000 | Primary dimensionless parameter for spiral flow |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Inspection (原材料检验): Incoming stainless steel seamless tubes are verified against ASTM A213 chemical composition and mechanical property requirements. Certificate of Conformance (CoC) and Mill Test Reports (MTR) are reviewed.
- Pre-Forming Treatment (预成形处理): Tubes are cleaned, deburred, and pre-stretched to ensure uniform wall thickness and consistent mechanical properties throughout the length.
- Spiral Coiling (螺旋盘绕): Precision CNC-controlled coiling machines form the straight tube into the specified helical geometry. The forming process is carefully controlled to minimize cross-sectional deformation (ovality) and maintain dimensional tolerances.
- Spring-Back Compensation (回弹补偿): The coiling system incorporates mathematical spring-back models to achieve the target coil diameter and pitch after elastic recovery.
- Pickling & Passivation (酸洗钝化): Post-forming pickling removes surface oxides and scale; subsequent passivation establishes a chromium oxide protective film (minimum 10% chromium content in passive layer).
- Non-Destructive Testing (无损检测): Eddy current testing (ECT) and/or ultrasonic testing (UT) verify wall integrity. Visual inspection confirms surface quality and geometric conformity.
- Dimensional Verification (尺寸验证): Final product dimensions (OD, WT, coil diameter, length) are measured and documented against the purchase order specification.
- Protective Packaging (保护包装): Coils are wrapped in moisture-barrier film, placed on wooden pallets or steel drums, and labeled with full traceability documentation.
4.2 Forming Considerations
During the coiling process, the tube experiences complex multiaxial stress states including bending moments, torsional shear, and potential cross-sectional distortion. The manufacturing process is optimized to maintain ovality below 3% and to prevent work-hardening that could compromise subsequent weldability. For tight-radius applications, warm forming (at 300–500°C) may be employed to reduce forming stresses while preserving material properties.
5. Applications
5.1 Primary Application Domains
- Heat Exchangers (热交换器): Spiral coil tubes serve as the primary heat transfer surface in plate-fin heat exchangers, air-cooled condensers, and evaporators. The enhanced turbulence from Dean vortices reduces the required surface area by 30–50% compared to straight tube designs.
- Refrigeration & HVAC Systems (制冷与暖通空调系统): Coiltubes are integral components of evaporator and condenser units, where compactness and high thermal efficiency are critical design constraints.
- Automotive Industry (汽车行业): Used in intercoolers, oil coolers, and HVAC components where space-constrained environments demand maximum heat transfer density.
- Chemical Processing (化工处理): Reactor cooling coils, heat recovery systems, and process heating/cooling circuits benefit from the corrosion resistance of austenitic stainless steels combined with superior thermal performance.
- Power Generation (发电): Condenser tubes in power plants, economizers, and superheaters in boiler systems utilize spiral geometries to enhance heat absorption rates.
- Food & Beverage Processing (食品饮料加工): Hygienic-grade coiltubes (electro-polished, 316L) are employed in pasteurization systems, CIP (Clean-In-Place) circuits, and heat recovery units.
- Pharmaceutical Industry (制药行业): Sanitary process coils meet FDA and EU GMP requirements for cleanability and material compatibility.
- Oil & Gas (石油天然气): Subsea heat exchangers, wellhead cooling systems, and process skid-mounted heat transfer units.
- Electronics Cooling (电子冷却): Compact heat sinks and liquid cooling loops for high-power electronics and data center thermal management.
5.2 Design Advantage in Forced Convection
Research on forced convection heat transfer in spiral coil tubes (螺旋盘管中强制对流换热的研究) has established that the centrifugal force acting on the fluid within the curved channel generates a pair of counter-rotating Dean vortices. These secondary flow structures continuously refresh the near-wall fluid, thinning the thermal boundary layer and significantly augmenting convective heat transfer. The correlation between the Nusselt number and the Dean number (De) demonstrates that heat transfer enhancement follows a power-law relationship (Nu ∝ Deⁿ, where n ≈ 0.5–0.7 for turbulent flow), providing predictable and quantifiable thermal performance improvement.
6. Quality Certifications & Standards Compliance
6.1 Applicable Standards
| Standard | Description | Applicability |
|---|---|---|
| ASTM A213 / ASME SA-213 | Standard Specification for Seamless Austenitic Stainless Steel Tubes for High-temperature Service | Material & mechanical properties |
| ASTM A778 / ASME SA-778 | Standard Specification for Seamless Ferritic/Austenitic Stainless Steel Tubes for High-temperature Service | Duplex grade options |
| GB/T 14976 | Chinese National Standard — Stainless Steel Tubes for Fluid Transport | Domestic compliance (China) |
| GB/T 4237 | Chinese National Standard — Stainless Steel Plates, Sheets, and Strips | Flat product reference |
| EN 10216-5 | European Standard — Heat Exchanger Tubes, European Technical Delivery Conditions | European market compliance |
| ISO 4287 | Surface Texture — Profile Method — Surface Texture Parameters | Surface finish verification |
| ASME BPVC Section VIII | Pressure Vessel Code — Rules for Construction of Pressure Vessels | Pressure-containing applications |
| 3-A Sanitary Standards | International Association for Properties of Water — Sanitary Engineering | Food & pharmaceutical applications |
6.2 Quality Management Certifications
- ISO 9001:2015 — Quality Management System certification ensuring consistent product quality and continuous improvement
- ISO 14001 — Environmental Management System for sustainable manufacturing practices
- ISO 45001