Stainless Steel Coil Tube (Coiltube) — Product No. 910

1. Product Overview

The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is designed in the form of a continuous helical coil, offering superior flexibility, compact installation footprint, and excellent heat transfer performance. Unlike conventional straight seamless or welded pipes, coil tubes are formed through cold coiling or hot coiling processes, resulting in a uniform cross-sectional geometry with minimal residual stress distribution along the tube body.

The coil tube is particularly valued in thermal management systems where high surface-area-to-volume ratios are critical. Its helical configuration promotes turbulent flow characteristics, significantly enhancing convective heat transfer coefficients compared to straight-tube alternatives. This product is integral to composite cooling tower systems, heat exchangers, and process cooling applications across industrial sectors.

2. Material & Properties

2.1 Base Material Composition

The coil tube is manufactured from austenitic stainless steel grades conforming to international standards. The primary alloying elements include chromium (Cr), nickel (Ni), and molybdenum (Mo), which collectively provide outstanding corrosion resistance, high-temperature strength, and non-magnetic properties.

2.2 Key Mechanical Properties

• Tensile Strength (R_m): Typically ≥ 520 MPa (depending on grade and cold work level)
• Yield Strength (R_p0.2): Typically ≥ 205 MPa
• Elongation (A₅₀): ≥ 35%
• Hardness (HV10): ≤ 250 HV
• Impact Energy (KV2, 20°C): ≥ 30 J

2.3 Corrosion Resistance

• Excellent resistance to atmospheric corrosion and industrial atmospheres
• High resistance to pitting and crevice corrosion in chloride-containing environments (especially 316L grade with Mo)
• Resistance to intergranular corrosion (IGC) suitable for welded structures
• Outstanding performance in food-grade, pharmaceutical, and chemical processing environments

2.4 Thermal Properties

• Thermal Conductivity: 14–16 W/(m·K) at 20°C
• Specific Heat Capacity: 500 J/(kg·K)
• Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (20–100°C)
• Maximum Service Temperature: Up to 870°C (depending on grade)

3. Technical Specifications

Parameter	Specification
Product Name	Stainless Steel Coil Tube (Coiltube)
Product No.	910
Manufacturer	Wenzhou Jixing Metal Materials Co., Ltd.
Outer Diameter (OD)	6.0 mm – 50.8 mm (customizable)
Wall Thickness	0.5 mm – 3.0 mm
Coil Pitch	8 mm – 50 mm (adjustable per application)
Coil Length	Up to 30,000 mm (continuous coil)
Material Grade	SUS304 / SUS316L / SUS321 / SUS310S (ASTM A269 / A270)
Surface Finish	Mirror polished (Ra ≤ 0.2 μm) / Satin / BA (Bright Annealed)
Tolerance on OD	±0.1 mm (standard); ±0.05 mm (precision grade)
Tolerance on Wall Thickness	±10% of nominal
Helix Angle Deviation	±1.0°
Applicable Standards	ASTM A269, ASTM A270, ASME SA-269, EN 10217-7, GB/T 12771
End Condition	Plain end / Beveled / Threaded (upon request)
Packaging	Wooden crate / Sealed coil package with moisture-absorbent desiccant

4. Manufacturing Process

4.1 Process Flowchart

1. Raw Material Selection: Cold-rolled stainless steel strip (CRSS) of certified grade is sourced with full traceability documentation.
2. Surface Preparation: The strip undergoes degreasing, pickling, and passivation to remove oxides and organic contaminants.
3. Forming (Cold Rolling into Tube): The flat strip is fed through a multi-roller forming station where it is progressively shaped into a tubular profile. The seam is either welded (TIG/Orbital) or left open depending on the application.
4. Welding (if applicable): Orbital TIG (Tungsten Inert Gas) welding is employed for seamless-quality joints, with internal and external purge gas (argon) to prevent oxidation.
5. Coiling: The formed tube is wound onto a precision-driven mandrel system at controlled tension to produce the helical coil geometry. CNC-controlled systems ensure uniform pitch and helix angle.
6. Heat Treatment (Annealing): Solution annealing at 1050–1150°C followed by controlled cooling to relieve residual stresses and restore full austenitic microstructure.
7. Pickling & Passivation: Post-welding and post-forming chemical treatment to restore the protective chromium oxide layer.
8. Final Inspection & Testing: Dimensional verification, hydrostatic pressure testing, and surface inspection.
9. Packaging & Dispatch: Coils are secured, protected against mechanical damage, and packaged for shipment.

4.2 Critical Process Controls

• Closed-loop tension control during coiling to prevent ovality and dimensional drift
• Orbital welding parameters monitored in real-time (current, voltage, gas flow, travel speed)
• In-line laser measurement for OD and wall thickness verification
• Spectroscopic analysis (PMI — Positive Material Identification) for alloy verification

5. Applications

5.1 Cross-Flow Cooling Tower Systems

As highlighted in the structural design and performance analysis literature for composite cooling towers, the coil tube serves as a primary heat transfer element in the "Coil Tube + Packing" composite configuration. In cross-flow cooling tower designs, the stainless steel coil tube is arranged in serpentine or helical formations within the fill section. This configuration achieves:

• Enhanced heat transfer area density compared to conventional straight-tube arrangements
• Improved water distribution uniformity across the tower cross-section
• Reduced pressure drop due to streamlined helical flow paths
• Lower overall tower height and footprint for equivalent cooling capacity

5.2 Other Industrial Applications

• Heat Exchangers: Condensers, evaporators, and reboilers in chemical and petrochemical plants
• Food & Beverage Processing: CIP (Clean-in-Place) compatible heat transfer coils in brewing, dairy, and pharmaceutical equipment
• HVAC Systems: Chilled water coil assemblies and condenser units
• Power Generation: Feedwater heaters and steam coil applications
• Automotive Industry: Intercoolers and oil coolers requiring compact, corrosion-resistant geometries
• Marine Applications: Seawater coolers and ballast water system components
• Energy Storage: Thermal management coils in battery cooling systems

6. Quality Certifications & Standards Compliance

6.1 Manufacturing Certifications

• ISO 9001:2015 — Quality Management System
• ISO 14001 — Environmental Management System
• EN 10204 3.1 — Inspection Certificate (Material and Product Testing)

6.2 Product Standards

• ASTM A269: Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing
• ASTM A270: Standard Specification for Welded Austenitic Stainless Steel Tubing
• ASME SA-269 / SA-270: Boilers and Pressure Vessel Code
• EN 10217-7: Stainless Steel Tubes for Fluid Service
• GB/T 12771: Chinese National Standard for Stainless Steel Tubes

6.3 Testing & Inspection Protocol

1. Chemical analysis (OES / wet chemistry) for alloy verification
2. Dimensional inspection using CMM (Coordinate Measuring Machine) or laser gauges
3. Hydrostatic pressure test at 1.5× working pressure for minimum 30 seconds
4. Visual and dye penetrant inspection (DPI) of weld seams
5. Radiographic testing (RT) for critical applications (upon request)
6. Surface roughness measurement (profilometer)
7. Corrosion resistance testing: Salt spray test (ASTM B117), ASTM A923 intergranular corrosion test

7. Unique Selling Points

Integrated Performance-Geometry Optimization: The coil tube design inherently maximizes heat transfer efficiency per unit volume by combining the high surface-area characteristics of a helical geometry with the proven corrosion resistance of austenitic stainless steel. This dual advantage is particularly significant in cross-flow cooling tower applications where both thermal performance and long-term durability in humid, chemically aggressive environments are paramount.

• Compact Installation: The pre-coiled configuration reduces on-site fabrication time by up to 40% compared to field-forming straight tubes into coils.
• Superior Thermal Performance: Helical geometry induces secondary flow (Dean vortices), increasing the Nusselt number by 20–35% over straight-tube equivalents.
• Low Pressure Drop: Despite enhanced heat transfer, the streamlined helical path maintains lower frictional losses than zig-zag or finned alternatives.
• Full Traceability: Each coil lot is accompanied by mill test certificates, heat number traceability, and complete process documentation.
• Customization Capability: OD, wall thickness, pitch, and coil length can be tailored to specific project requirements within standard production tolerances.
• Long Service Life: With proper design, service life exceeds 25 years in most industrial environments without degradation of mechanical or thermal properties.

8. References

1. "Structural Design and Performance Analysis of Cross-Flow Cooling Tower with Coil Tube and Packing Composite Type" — Academic study on composite cooling tower configurations utilizing stainless steel coil tubes.
2. ASTM A269/A269M — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and General Applications.
3. EN 10217-7 — Stainless Steel Tubes for Fluid Service.