Stainless Steel Spiral Coil Tube — Coiltube Series (Product No. 723)
1. Product Overview
The Stainless Steel Spiral Coil Tube (hereinafter referred to as "Coiltube") manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product formed by cold-drawing or hot-rolling stainless steel wire or strip into a continuous helical geometry. This product is specifically designed for applications in heat exchanger systems, fluid transfer lines, and thermal management assemblies where compact volumetric footprint, high surface-area-to-volume ratio, and superior mechanical integrity are critical performance parameters.
Distinct from conventional straight-pipe assemblies, the Coiltube series leverages the inherent geometric advantages of a spiral configuration to achieve enhanced convective heat transfer coefficients, reduced pressure drop penalties, and improved structural resilience under cyclic thermal loading conditions. The product line encompasses both seamless and welded variants, available in a wide range of coil diameters, pitch intervals, and wall thicknesses to accommodate diverse engineering requirements.
2. Material Composition & Mechanical Properties
The Coiltube series is fabricated from austenitic stainless steel grades conforming to international material specifications. The primary grades utilized include:
- AISI 304 / UNS S30400 — General-purpose austenitic grade with excellent corrosion resistance and formability
- AISI 316 / UNS S31600 — Molybdenum-enhanced grade offering superior resistance to pitting and crevice corrosion in chloride-containing environments
- AISI 316L / UNS S31603 — Low-carbon variant suitable for high-temperature service and post-welding environments
- AISI 321 / UNS S32100 — Titanium-stabilized grade resistant to intergranular corrosion at elevated temperatures
- AISI 310S / UNS S31008 — High-temperature grade with exceptional oxidation resistance up to 1150 °C
2.1 Typical Mechanical Properties (Annealed Condition)
| Property | AISI 304 | AISI 316 | AISI 321 | AISI 310S |
|---|---|---|---|---|
| Tensile Strength (MPa) | ≥ 515 | ≥ 515 | ≥ 515 | ≥ 515 |
| Yield Strength (MPa, 0.2% offset) | ≥ 205 | ≥ 205 | ≥ 205 | ≥ 205 |
| Elongation (% at break) | ≥ 40 | ≥ 40 | ≥ 40 | ≥ 40 |
| Density (g/cm³) | 7.93 | 8.00 | 7.93 | 7.95 |
| Thermal Conductivity (W/m·K, 20 °C) | 16.3 | 16.3 | 16.3 | 14.2 |
| Maximum Continuous Service Temperature (°C) | 870 | 870 | 980 | 1150 |
2.2 Surface Finish Options
- 2B (Cold Rolled & Annealed) — Standard industrial finish, moderate reflectivity
- No. 4 Brushed — Unidirectional grain pattern, aesthetic and functional
- Mirror Polish (Ra ≤ 0.1 μm) — Hygienic-grade finish for pharmaceutical and food processing
- Pickled & Passivated — Enhanced corrosion resistance through removal of surface oxides and formation of passive chromium oxide layer
3. Geometric Specifications
| Parameter | Range / Options | Unit |
|---|---|---|
| Outer Diameter (OD) of Tube | 3.0 – 50.8 | mm |
| Wall Thickness | 0.3 – 4.0 | mm |
| Coil Mean Diameter (CMD) | 20 – 600 | mm |
| Coil Pitch (Helix Spacing) | 5 – 50 | mm |
| Number of Turns | 1 – 500 (customizable) | — |
| Tube Length per Coil | 0.5 – 50.0 | m |
| Surface Roughness (Ra) | 0.4 – 1.6 (standard); ≤ 0.1 (mirror) | μm |
| Tolerance on OD | ±0.05 – ±0.20 | mm |
| Tolerance on Wall Thickness | ±10% (standard); ±5% (precision) | — |
| End Treatment | Flat cut, beveled, threaded, or flanged | — |
3.1 Dimensional Tolerance Classes
- Class A (Precision): OD tolerance ±0.05 mm; Pitch tolerance ±0.5 mm; CMD tolerance ±1.0 mm
- Class B (Standard): OD tolerance ±0.10 mm; Pitch tolerance ±1.0 mm; CMD tolerance ±2.0 mm
- Class C (General): OD tolerance ±0.20 mm; Pitch tolerance ±2.0 mm; CMD tolerance ±3.0 mm
4. Manufacturing Process
The production of the Coiltube series follows a rigorously controlled multi-stage manufacturing workflow to ensure dimensional accuracy, material integrity, and consistent surface quality:
- Raw Material Inspection & Incoming Quality Control: Each lot of stainless steel wire rod or flat strip undergoes spectroscopic analysis (OES) for chemical composition verification, along with mechanical property testing (tensile test, hardness test) and visual surface inspection per ASTM A968 or EN 10216 standards.
- Wire Drawing / Strip Cold-Rolling: The raw material is cold-worked to the precise cross-sectional dimensions required. For seamless tubes, capillary drawing through hardened tungsten carbide dies is employed; for welded tubes, precision cold-rolling of strip to specified width and thickness is performed.
- Intermediate Annealing: Where applicable, intermediate annealing at 1050–1100 °C in a protective atmosphere (argon or vacuum) is conducted to relieve cold-work hardening and restore ductility, ensuring subsequent forming operations do not result in cracking or excessive residual stress.
- Spiral Coiling / Helical Forming: The tube or wire is wound around a precision-machined mandrel using CNC-controlled coiling machines. The forming process is executed at controlled speeds (typically 5–30 m/min) to minimize work hardening and geometric distortion. Computer Numerical Control (CNC) systems ensure precise pitch control and uniform coil diameter throughout the winding length.
- Final Annealing & Stress Relief: Post-coiling annealing at 800–1050 °C (grade-dependent) eliminates residual stresses introduced during the forming process, stabilizes the microstructure, and restores optimal mechanical properties. Annealing is performed in a controlled-atmosphere furnace to prevent surface oxidation.
- Pickling & Passivation: The annealed coils are treated with a hydrofluoric/nitric acid pickling solution to remove any residual oxide scale, followed by passivation to establish a uniform chromium oxide passive layer (minimum 10–20 nm thickness) for enhanced corrosion resistance.
- Precision Machining of End Connections: Tube ends are machined, beveled, threaded, or fitted with flanges, fittings, or brazed joints according to customer specifications for system integration.
- Final Quality Inspection: Comprehensive dimensional verification using Coordinate Measuring Machines (CMM), surface roughness profiling, hydrostatic pressure testing (typically at 1.5× working pressure for 30 minutes minimum), and visual/magnetic particle inspection for surface defects.
5. Performance Characteristics — Heat Transfer & Fluid Dynamics
The helical geometry of the Coiltube confers distinct thermohydraulic advantages over straight-tube configurations, as substantiated by experimental research on spiral coil heat exchangers:
- Enhanced Heat Transfer Coefficient: The secondary Dean flow (centrifugal-induced vortex) generated within the curved tube geometry disrupts the thermal boundary layer, resulting in heat transfer coefficients 20–40% higher than equivalent straight-tube assemblies at the same Reynolds number.
- Compact Heat Transfer Area: The volumetric heat transfer area (m²/m³) is significantly greater than that of straight-tube bundles, enabling compact heat exchanger designs with reduced footprint.
- Pressure Drop Characteristics: While the friction factor in helical coils is 10–30% higher than in straight tubes due to secondary flow effects, the overall pressure drop per unit heat transfer duty is often favorable due to the reduced tube length required for equivalent thermal performance.
- Thermal Stress Resilience: The inherent flexibility of the spiral configuration accommodates thermal expansion differentials, reducing fatigue failure risks in high-temperature differential applications.
Key Performance Note: Experimental studies on polymer spiral coil heat exchangers have demonstrated that the Nusselt number correlation for helical tubes follows the form Nu = 0.0316 × Re⁰·⁸ × Pr⁰·⁴ × (d/D)⁰·¹, where d is the tube diameter and D is the coil mean diameter. This correlation is validated for Reynolds numbers in the range of 3,000–100,000 and applies analogously to stainless steel coil tubes with appropriate property substitutions.
6. Applications
- Process Heat Exchangers: Shell-and-coil heat exchangers in chemical processing, petrochemical refining, and pharmaceutical manufacturing where high heat flux and compact design are required
- Refrigeration & Air Conditioning: Evaporator and condenser coils for commercial refrigeration units, chiller systems, and industrial air conditioning
- Power Generation: Feedwater heaters, economizers, and steam superheaters in thermal power plants
- Automotive & Transportation: Engine cooling circuits, exhaust gas recirculation (EGR) coolers, and thermal management systems in electric vehicles
- Food & Beverage Processing: Pasteurizers, condensers, and heat recovery systems in dairy, brewing, and beverage industries
- Oil & Gas Industry: Subsea umbilical components, heat tracing coils, and process fluid conditioning systems
- Medical Equipment: MRI cooling systems, autoclave heating elements, and medical device sterilization systems
- Renewable Energy: Geothermal heat exchangers, solar thermal collectors, and biomass energy systems
7. Quality Certifications & Standards Compliance
The Coiltube product line manufactured by Wenzhou Jixing Metal Materials Co., Ltd. adheres to the following international standards and holds the following certifications:
- ISO 9001:2015 — Quality Management Systems
- ISO 14001:2015 — Environmental Management Systems
- ISO 45001:2018 — Occupational Health and Safety Management Systems
- EN 10216-1/2 — Technical delivery conditions for welded and seamless stainless steel tubes
- ASTM A213/A269 — Standard specifications for austenitic stainless steel tubing
- ASTM A312 — Standard specifications for austenitic stainless steel seamless, welded, and heavily cold-worked tubing
- GB/T 12771 — Chinese national standard for stainless steel welded tubes for fluid transport
- GB/T 14976 — Chinese national standard for cold-rolled stainless steel seamless tubes
- CE Marking — Conformity with European Pressure Equipment Directive (PED 2014/68/EU)
- PED Compliance — Module H (Full Quality Assurance) for pressure equipment applications
- API 5L/6A — American Petroleum Institute standards for oil and gas service applications (where applicable)
- NSF/ANSI 61 — Drinking water system components certification (for sanitary-grade products)
8. Unique Selling Points
- Customizable Geometry: Full design flexibility in coil diameter, pitch, tube dimensions, and end configurations to meet specific engineering requirements
- Precision CNC Manufacturing: Computer-controlled coiling ensures repeatable dimensional accuracy and consistent product quality across production batches
- Superior Corrosion Resistance: Available in multiple austenitic grades with optional passivation treatment for extended service life in aggressive environments
- Enhanced Thermohydraulic Performance: Helical geometry provides 20–40% improvement in heat transfer efficiency compared to straight-tube equivalents
- Compact Installation Footprint: High volumetric heat transfer density enables space-constrained system designs
- Full Traceability: Complete material traceability from raw steel mill certification through final product inspection, with digital batch tracking
- Multi-Grade Availability: Broad selection of stainless steel grades accommodates diverse temperature, pressure, and chemical compatibility requirements
- Comprehensive Testing: Every production lot undergoes hydrostatic testing, dimensional verification, and surface inspection prior to shipment
9. Packaging & Delivery
Coiltube products are delivered in export-grade packaging consisting of moisture-proof inner wrapping (polyethylene film or VCI paper), protective wooden or steel crating with adequate cushioning, and secure strapping to prevent transit damage. Each shipment is accompanied by a Mill Test Certificate (MTC), dimensional inspection report, and material composition analysis documentation. Standard lead time for standard configurations is 15–30 calendar days; custom-engineered configurations may require 30–60 days depending on complexity and volume.