High-Precision Stainless Steel Internal Helical Coil Tube (Coiltube)
Product Overview
The High-Precision Stainless Steel Internal Helical Coil Tube is a specialized heat exchanger component engineered for advanced air conditioning and refrigeration systems. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coiltube integrates a precision-formed internal helical corrugation (Internal Helical Rib) geometry within a seamless stainless steel tube body, significantly enhancing convective heat transfer efficiency while maintaining structural integrity under high differential pressure conditions.
Unlike conventional smooth-bore stainless steel tubing, this product incorporates a continuous internal spiral fin pattern that increases the effective heat exchange surface area by up to 35–45% relative to its nominal bore diameter, thereby delivering superior thermal performance in compact installations. The product is classified under the literature study category of metallurgical and materials engineering, reflecting its foundation in advanced tube-forming research and process optimization.
Material & Properties
The coiltube is fabricated from austenitic stainless steel grades conforming to international standards, ensuring excellent corrosion resistance, mechanical ductility, and long-term service reliability in aggressive thermal environments.
- Primary Material Grades: SUS304 (ASTM 304), SUS316 (ASTM 316), SUS316L (ASTM 316L), and SUS321 (ASTM 321)
- Alloy Composition (SUS316L): Cr 16.0–18.0%, Ni 10.0–14.0%, Mo 2.0–3.0%, Mn ≤2.0%, Si ≤1.0%, C ≤0.03%, P ≤0.045%, S ≤0.030%
- Corrosion Resistance: Superior resistance to chloride-induced pitting corrosion (Pitting Resistance Equivalent Number, PREN ≥ 24) and intergranular corrosion after sensitization at 450–850°C
- Mechanical Properties: Tensile strength (UTS) ≥ 520 MPa; Yield strength (0.2% offset) ≥ 205 MPa; Elongation ≥ 40%
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (SUS304)
- Operating Temperature Range: −196°C to +870°C
- Surface Finish: Electropolished or passivated interior surface, Ra ≤ 0.4 μm
Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Nominal Outer Diameter (OD) | 6.35 mm (1/4") to 25.4 mm (1") | ASTM A269 / GB/T 14976 |
| Wall Thickness (WT) | 0.5 mm to 2.0 mm | ASTM A269 |
| Internal Helical Pitch | 2.0 mm to 8.0 mm | Proprietary design |
| Internal Helical Height | 0.1 mm to 0.5 mm | Proprietary design |
| Coil Diameter (Bundle) | φ 200 mm to φ 1200 mm | Customer-specific |
| Coil Length (Developed) | 3 m to 50 m | Customer-specific |
| Dimensional Tolerance (OD) | ±0.05 mm | ISO 4413 |
| Dimensional Tolerance (WT) | ±5% of nominal | ASTM A269 |
| Pressure Test Rating | Up to 6.0 MPa (hydrostatic) | ASME B31.5 |
| Heat Transfer Enhancement Factor | 1.35 – 1.45 (vs. smooth tube) | Experimental validation |
| Weight (Typical, φ 9.52 mm × 0.5 mm) | ~0.18 kg/m | Calculated |
Manufacturing Process
The production of high-precision internal helical coil tubes involves a multi-stage manufacturing sequence combining advanced metallurgical processing with precision mechanical forming technology:
- Raw Material Selection & Annealing: Cold-rolled stainless steel strip or seamless tube blank is procured in solution-annealed (Solution Annealed, SA) condition. The material undergoes controlled furnace annealing at 1050–1150°C followed by rapid water quenching to achieve a fully austenitic microstructure with optimal formability.
- Tube Forming / Extrusion: The flat strip is rolled into a helical coil form via a precision rotary forming die system, or alternatively, seamless tube is produced through hot extrusion and cold drawing. The internal helical rib is formed using a specialized roller-die (Roller Die) system where shaped rollers progressively imprint the helical corrugation onto the inner wall of the tube under controlled reduction ratios.
- Internal Helical Rib Formation: A dedicated internal forming head (Internal Forming Head) with precisely profiled helical rollers is drawn through the tube bore. The forming rollers, arranged at a calculated pitch angle, create a continuous spiral corrugation on the interior surface. The reduction per pass is limited to ≤ 15% to prevent material cracking or excessive work hardening.
- Intermediate Annealing: After multi-pass forming, the tube undergoes intermediate annealing (Intermediate Annealing) at 1000–1100°C to relieve accumulated residual stresses and restore ductility for subsequent processing.
- Coiling & Sizing: The formed tube is precisely coiled to the specified bundle diameter using a CNC-controlled coiling machine (CNC Coiling Machine), ensuring uniform curvature without inducing ovality or residual bending stresses. Final dimensional sizing is verified through optical or laser-based measurement systems.
- Surface Treatment & Passivation: The finished coiltube receives a final passivation treatment (Passivation Treatment) using citric acid or nitric acid solution to remove surface contamination and establish a stable chromium oxide passive film (Chromium Oxide Passive Film), enhancing long-term corrosion resistance.
- Quality Inspection & Testing: Every batch undergoes comprehensive non-destructive testing (Non-Destructive Testing, NDT), including eddy current inspection (Eddy Current Inspection) for wall thickness verification, hydrostatic pressure testing, and dimensional metrology using coordinate measuring machines (Coordinate Measuring Machine, CMM).
Applications
The High-Precision Stainless Steel Internal Helical Coil Tube finds extensive application across demanding industrial and commercial sectors where enhanced heat transfer performance, corrosion resistance, and compact design are critical requirements:
- Air Conditioning Systems (HVAC): Evaporator and condenser coil tubes in precision air conditioning units, chiller systems, and heat recovery ventilators (Heat Recovery Ventilator, HRV)
- Refrigeration: Freezer coils, cold storage unit heat exchangers, and industrial refrigeration evaporators
- Automotive Air Conditioning: Compact evaporator and condenser tubes for vehicle climate control systems requiring lightweight, high-efficiency heat exchange
- Heat Exchangers: Plate-and-tube heat exchangers, air-to-water heat exchangers, and liquid-to-liquid heat exchangers in process industries
- Food & Beverage Processing: Sanitary-grade heat exchangers for dairy, brewing, and pharmaceutical applications requiring hygienic surface finishes
- Chemical Processing: Corrosive fluid heat transfer systems where stainless steel's chemical inertness is essential
- Marine & Offshore: Seawater-cooled heat exchangers and desalination plant components requiring resistance to chloride environments
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system ensuring that all products meet or exceed international and domestic standards:
- ISO 9001:2015 — Quality Management Systems certification
- ISO 14001:2015 — Environmental Management Systems certification
- ASTM A269 / A270 — Standard specification for seamless and welded austenitic stainless steel tubes for chemical and heat-exchange equipment
- GB/T 14976 — Chinese national standard for stainless steel seamless tubes for fluid transport
- EN 10217-7 — European standard for stainless steel tubes for heat exchangers
- ASME SA-269 — American Society of Mechanical Engineers standard for welded austenitic stainless steel tubing
- JIS G3447 — Japanese Industrial Standard for stainless steel seamless tubes
- Mill Test Reports (MTR): Full chemical composition analysis and mechanical property certification provided with each shipment
Unique Selling Points
1. Superior Heat Transfer Performance: The precision-formed internal helical rib geometry generates controlled turbulent flow within the tube bore, achieving a heat transfer enhancement factor of 1.35–1.45 compared to conventional smooth tubes, while simultaneously reducing overall heat exchanger footprint by 20–30%.
2. High-Precision Manufacturing Tolerance: Advanced CNC-controlled forming technology ensures internal helical pitch accuracy within ±0.1 mm and wall thickness uniformity of ±5%, guaranteeing consistent thermal performance across every meter of production.
3. Corrosion-Resistant Austenitic Construction: The use of SUS316L-grade stainless steel provides outstanding resistance to pitting, crevice, and intergranular corrosion, ensuring service life exceeding 20 years even in chloride-rich or chemically aggressive environments.
4. Energy Efficiency Contribution: By reducing the required heat exchange surface area, the internal helical design directly contributes to lower refrigerant charge quantities and reduced compressor energy consumption, aligning with global energy efficiency regulations.
5. Research-Validated Design: The product design is grounded in rigorous academic research on internal helical coil tube forming processes, with experimentally validated flow and heat transfer correlations supporting its engineering specifications.