Stainless Steel Spiral Coil Tube — Coiltube (Model No. 427)
Product Overview
The Stainless Steel Spiral Coil Tube (Model No. 427), manufactured by Wenzhou Jixing Metal Materials Co., Ltd, is a precision-engineered coiled piping product designed for high-efficiency heat transfer and mass transfer applications. The coil tube is formed from continuous lengths of stainless steel seamless or welded tubing, wound into a consistent helical geometry to maximize surface-area-to-volume ratio and thermal exchange efficiency within confined equipment footprints.
This product is particularly distinguished by its application in closed-loop cooling tower systems, where it serves as the primary heat exchange element. Extensive research on the heat transfer and mass transfer performance of spiral coil tubes in closed cooling towers has validated the superior convective characteristics of helically wound stainless steel tubing compared to straight-tube alternatives. The helical geometry induces secondary flow patterns (Dean vortices) that disrupt boundary layer development, thereby enhancing turbulent mixing and significantly increasing the overall heat transfer coefficient.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel grades, selected for their outstanding corrosion resistance, mechanical strength, and thermal stability across a wide range of operating conditions.
- Grade 304 (UNS S30408 / 1.4301): General-purpose austenitic stainless steel containing approximately 18% Chromium (Cr) and 8% Nickel (Ni). Offers excellent resistance to atmospheric, freshwater, and mildly aggressive chemical environments.
- Grade 316 (UNS S31608 / 1.4401): Molybdenum-enhanced austenitic stainless steel (~16.5% Cr, ~10% Ni, ~2% Mo). Provides superior resistance to pitting and crevice corrosion in chloride-containing environments, making it ideal for coastal and industrial cooling applications.
- Grade 321 (UNS S32108 / 1.4541): Titanium-stabilized austenitic stainless steel. Exhibits enhanced resistance to intergranular corrosion at elevated temperatures, suitable for high-temperature cooling and process heat exchange.
Key Mechanical Properties (Grade 304, Annealed Condition):
- Tensile Strength (UTS): ≥ 515 MPa
- Yield Strength (0.2% offset): ≥ 205 MPa
- Elongation at Break: ≥ 40%
- Hardness (Brinell): ≤ 217 HB
- Density: 8.0 g/cm³
Key Thermal Properties:
- Thermal Conductivity (at 100°C): ~16.3 W/(m·K)
- Specific Heat Capacity (at 100°C): ~0.50 kJ/(kg·K)
- Thermal Expansion Coefficient (20–100°C): ~17.3 × 10⁻⁶ /°C
- Maximum Operating Temperature: ~870°C (continuous)
Technical Specifications
| Parameter | Specification | Unit |
|---|---|---|
| Product Designation | Stainless Steel Spiral Coil Tube (Coiltube) | — |
| Model / Item No. | 427 | — |
| Outer Diameter (OD) | 12 – 159 (customizable) | mm |
| Wall Thickness | 0.5 – 6.0 (customizable) | mm |
| Coil Diameter (Center-to-Center) | 100 – 2000 (customizable) | mm |
| Coil Pitch (Center-to-Center) | 1.2 – 3.0 × OD | — |
| Coil Length (Total Tube Length) | 5 – 500 (customizable) | m |
| Number of Turns | 10 – 2000 (customizable) | — |
| Material Grades | 304, 316, 316L, 321, 321H, 347H | — |
| Tube Manufacturing Standard | ASTM A213 / A269 / GB/T 12771 | — |
| Coil Forming Tolerance (OD) | ± 0.5 mm | mm |
| Surface Finish (Roughness Ra) | 0.4 – 1.6 (electropolished option available) | μm |
| Maximum Operating Pressure | Up to 4.0 (dependent on OD and wall thickness) | MPa |
| Maximum Operating Temperature | Up to 400 | °C |
| End Treatment | Plain, beveled, threaded, or with welding collar | — |
| Packaging | Wooden crate with protective wrapping; foam-padded | — |
Manufacturing Process
The production of the stainless steel spiral coil tube follows a rigorous multi-stage manufacturing sequence to ensure dimensional accuracy, mechanical integrity, and surface quality:
- Raw Material Selection: Cold-rolled stainless steel strip or seamless/welded stainless steel tubing conforming to ASTM or GB standards is sourced from certified mill producers. Incoming material undergoes spectroscopic verification (PMI — Positive Material Identification) to confirm chemical composition.
- Pre-Forming Annealing (if applicable): For cold-drawn tubing, a stress-relief annealing cycle is performed at 870–900°C followed by controlled air cooling to eliminate residual stresses and restore ductility prior to coil winding.
- Spiral Coil Winding: The straight tube is fed into a CNC-controlled coil winding machine equipped with precision guide mandrels. The tube is wound helically around a forming mandrel at a controlled feed rate to maintain uniform coil pitch and diameter. The winding process is monitored in real time using laser displacement sensors to ensure dimensional consistency within tolerance.
- Post-Winding Stress Relief: The formed coil is subjected to a low-temperature stress-relief heat treatment (450–550°C for 1–2 hours) to minimize springback and residual bending stresses introduced during the winding process.
- End Preparation: Coil ends are trimmed to specified lengths and prepared according to the required end treatment (beveling, threading, or welding collar attachment). End faces are cleaned and deburred.
- Surface Treatment (Optional): Electropolishing or passivation treatment may be applied to achieve a low-roughness, corrosion-resistant surface finish suitable for hygienic or high-purity applications.
- Quality Inspection: Each coil undergoes comprehensive dimensional inspection (OD, wall thickness, coil diameter, pitch), hydrostatic pressure testing (per ASTM A269), and visual surface inspection. Chemical composition is verified via XRF (X-ray Fluorescence) analysis.
- Packaging and Shipping: Coils are individually wrapped in protective plastic film, padded with foam inserts, and secured in export-grade wooden crates with desiccant bags to prevent moisture ingress during transit.
Applications
The stainless steel spiral coil tube (Model No. 427) is engineered for demanding thermal management and fluid transport applications across multiple industries:
- Closed Cooling Tower Systems: The primary application domain. The spiral coil tube serves as the heat exchange surface in closed-loop evaporative cooling towers. Research has demonstrated that the helical geometry enhances both heat transfer (via induced turbulence and Dean flow) and mass transfer (via increased vapor-liquid interfacial area), resulting in 20–40% improvement in overall heat transfer coefficient compared to equivalent straight-tube configurations.
- Industrial Process Heat Exchangers: Shell-and-coil heat exchangers, plate-and-coil assemblies, and custom process cooling/heating systems in chemical, pharmaceutical, and food processing industries.
- Oil and Gas Processing: Subsea coil tubing for oil well injection, flow control, and well stimulation services. The corrosion resistance of 316-grade stainless steel makes it suitable for sour service environments.
- Power Generation: Auxiliary cooling systems, condensate recovery coils, and steam trap assemblies in thermal power plants and combined heat and power (CHP) systems.
- Food and Beverage Industry: CIP (Clean-in-Place) compatible coil assemblies for pasteurization, sterilization, and product cooling circuits. Electropolished 304/316 coils meet sanitary design standards.
- Pharmaceutical and Biotechnology: Heat exchange coils in bioreactors, fermentation tanks, and cleanroom HVAC systems requiring high-purity, corrosion-resistant fluid handling.
- HVAC (Heating, Ventilation, and Air Conditioning): Coil assemblies for air handling units, chillers, and condenser units where compact thermal exchange is required.
- Automotive and Aerospace: Compact coil heat exchangers for engine cooling, fuel systems, and thermal management in aircraft and spacecraft.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management system and ensures full compliance with international and national standards:
- ISO 9001:2015 — Quality Management System certification, demonstrating systematic commitment to consistent product quality and continuous improvement.
- ISO 14001:2015 — Environmental Management System certification, reflecting responsible environmental practices throughout the manufacturing lifecycle.
- CE Marking (EU) — Conformity with European health, safety, and environmental protection standards for market access in the European Economic Area.
- ASTM Compliance: Product specifications conform to ASTM A213 (seamless tubing), ASTM A269 (welded tubing), and ASTM A751 (general requirements for stainless steel products).
- GB/T Standards (China National Standards): GB/T 12771 (welded stainless steel tubing for fluid transport), GB/T 13296 (seamless stainless steel tubing), and GB/T 24511 (welded stainless steel tubing for general purposes).
- EN/DIN Standards: EN 10216-5 (welded stainless steel tubes), DIN EN 10217 (seamless stainless steel tubes for pressure purposes).
- ASME / PED: Available for pressure-containing applications per ASME BPV Code Section VIII and EU Pressure Equipment Directive 2014/68/EU.
Unique Selling Points
1. Enhanced Heat Transfer Performance: The spiral coil geometry inherently generates Dean vortices within the flowing fluid, promoting turbulent mixing and disrupting the thermal boundary layer. This results in significantly higher heat transfer coefficients — validated by research on closed cooling tower spiral coil performance — compared to straight-tube configurations of equivalent cross-sectional area.
2. Superior Corrosion Resistance: Fabricated from premium austenitic stainless steel grades (304, 316, 321), the coil tube exhibits exceptional resistance to atmospheric, chemical, and chloride-induced corrosion. This extends service life and reduces maintenance frequency in aggressive industrial environments.
3. Precision Manufacturing: CNC-controlled coil winding with real-time laser monitoring ensures dimensional accuracy within ±0.5 mm tolerance, guaranteeing seamless integration into engineered heat exchange systems and eliminating assembly-related thermal bypasses.
4. Customization Flexibility: Full customization of outer diameter, wall thickness, coil diameter, pitch, and total tube length allows the product to be tailored to specific system design requirements, from compact laboratory-scale heat exchangers to large industrial cooling tower installations.
5. Comprehensive Quality Assurance: End-to-end quality control — from PMI material verification through hydrostatic testing and dimensional inspection — ensures every coil meets or exceeds specified performance parameters. Full traceability documentation is provided for each production batch.
6. Multi-Industry Applicability: A single product platform serving cooling, chemical processing, food, pharmaceutical, oil and gas, and power generation industries, reducing supply chain complexity for multi-sector customers.
Technical Reference: Heat Transfer Performance in Closed Cooling Towers
As documented in the referenced study on heat transfer and mass transfer performance of spiral coil tubes in closed cooling towers, the following key findings inform the engineering design of this product:
- The spiral coil configuration achieves a Nusselt number (Nu) enhancement of 15–35% over straight-tube baselines at equivalent Reynolds numbers, attributable to secondary Dean flow effects.
- The mass transfer coefficient (kLa) is improved by up to 25% due to the increased vapor-liquid contact area and prolonged residence time within the helical path.
- The pressure drop penalty associated with the spiral geometry is moderate (10–20% increase), representing a favorable trade-off between enhanced thermal performance and pumping power consumption.
- Optimal coil pitch-to-diameter ratios (P/D = 1.5–2.5) were identified as the balance point between maximum heat transfer enhancement and minimum hydraulic resistance.
These research-validated performance characteristics position the Model No. 427 Stainless Steel Spiral Coil Tube as a technically superior solution for closed-loop cooling and thermal exchange applications demanding high efficiency, reliability, and long-term corrosion resistance.