Stainless Steel Coil Tube (Coiltube) — High-Efficiency Energy-Saving Thin-Wall Internal Thread Type
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered, continuous-length tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd. in a coiled configuration for efficient storage, transportation, and downstream processing. This product category encompasses high-efficiency energy-saving thin-wall internal thread stainless steel coil tubes, designed to maximize heat transfer performance while minimizing material consumption and energy expenditure in industrial and commercial applications.
The coil tube format eliminates the need for straightening and cutting operations that are typical of straight-length pipe supply, thereby reducing production waste, improving material utilization rates, and offering significant cost advantages in high-volume manufacturing scenarios. The internal threading geometry enhances the effective heat exchange surface area, making these tubes particularly suitable for thermal management applications where compact footprint and superior thermal conductivity are critical requirements.
2. Material Composition & Properties
The coil tubes are fabricated from high-grade austenitic stainless steel alloys, selected for their exceptional combination of corrosion resistance, mechanical strength, and thermal performance. The primary material grades include:
- 304 (UNS S30400 / 1.4301) — General-purpose austenitic grade with excellent formability and corrosion resistance, suitable for most industrial and food-grade applications.
- 316 (UNS S31600 / 1.4401) — Molybdenum-enhanced austenitic grade offering superior resistance to pitting and crevice corrosion, ideal for marine and chemical environments.
- 316L (UNS S31603 / 1.4404) — Low-carbon variant of 316 with enhanced weldability and resistance to intergranular corrosion.
- 321 (UNS S32100 / 1.4541) — Titanium-stabilized grade providing excellent resistance to sensitization at elevated temperatures.
2.1 Key Mechanical & Physical Properties
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa (304); ≥ 515 MPa (316) | ASTM A213 / EN 10216-5 |
| Yield Strength (Rp0.2) | ≥ 205 MPa | ASTM A213 / EN 10216-5 |
| Elongation (A50) | ≥ 40% | ASTM A213 |
| Density | 7.93 g/cm³ (304); 8.00 g/cm³ (316) | — |
| Thermal Conductivity (at 100°C) | 16.3 W/(m·K) (304); 14.6 W/(m·K) (316) | ASTM E1461 |
| Thermal Expansion Coefficient | 16.0–17.3 × 10⁻⁶ /K (20–100°C) | ASTM E1461 |
| Maximum Service Temperature | 870°C (304); 870°C (316) | ASME BPVC Section II |
| Corrosion Resistance (Pitting, ASTM G48) | PREN ≥ 18 (304); PREN ≥ 24–26 (316) | ASTM G48 |
3. Product Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 108.0 mm | ASTM A213 / EN 10216-5 |
| Wall Thickness | 0.5 mm – 6.0 mm (thin-wall variants: 0.5–1.5 mm) | — |
| Coil Inner Diameter (Coil ID) | 150 mm – 1,200 mm | — |
| Coil Length per Spool | 50 m – 500 m (configurable) | — | Internal Thread Pitch | 1.0 mm – 3.0 mm (helical); 120°–160° helix angle | — |
| Surface Finish (Roughness) | Ra ≤ 0.8 μm (standard); Ra ≤ 0.4 μm (electropolished); Ra ≤ 0.2 μm (mirror) | ASTM A269 |
| Tolerance — OD | ±0.05 mm (precision); ±0.10 mm (standard) | ISO 4287 |
| Tolerance — Wall Thickness | ±5% (standard); ±3% (precision) | EN 10216-5 |
| Surface Treatment Options | Pickled & Passivated (P&P); Electropolished; Mirror Polish; Brushed | ASTM A967 |
| End Condition | Plain cut; Beveled; Threaded; Flanged; Custom fabricated | — |
| Delivery Form | Coiled (spooled); Straight lengths available upon request | — |
| Packaging | Wooden pallet with VCI (Volatile Corrosion Inhibitor) wrap; Export-grade packaging available | ISO 4180 |
4. Manufacturing Process
The production of high-efficiency stainless steel coil tubes follows a rigorous multi-stage manufacturing sequence, ensuring dimensional accuracy, metallurgical integrity, and surface quality:
- Hot-Rolled Coil Processing — Raw stainless steel slab is hot-rolled into coil form, establishing the initial cross-sectional geometry and providing the base material for subsequent cold working operations.
- Pickle Line Treatment — The hot-rolled coil undergoes acid pickling (typically HNO₃/HF or H₂SO₄/HNO₃ mixtures) to remove mill scale and oxide layers, followed by passivation to restore the protective chromium oxide passive film.
- Cold Drawing / Cold Forming — The coil is cold-drawn through a series of precision dies to achieve the target outer diameter and wall thickness specifications. This process induces beneficial work hardening and improves surface finish.
- Internal Threading / Helical Grooving — For energy-saving variants, precision internal helical threads are formed using either rotary swaging or high-speed machining techniques. The thread geometry is optimized to increase turbulent flow characteristics and enhance convective heat transfer coefficients by up to 40–60% compared to smooth-bore tubes.
- Heat Treatment (Annealing) — Solution annealing at 1,010°C – 1,150°C followed by rapid quenching relieves residual stresses from cold working, restores full austenitic ductility, and ensures consistent microstructure.
- Coiling & Spooling — The processed tube is wound onto precision-mandrel spools in a controlled coil configuration, maintaining dimensional tolerances and preventing mechanical damage during storage.
- Final Surface Treatment — Electropolishing, mirror polishing, or additional passivation is applied as required by the end-use application specifications.
- Non-Destructive Testing (NDT) — 100% inline inspection via ultrasonic testing (UT), eddy current testing (ECT), and hydrostatic pressure testing ensures zero-defect delivery.
5. Applications
The stainless steel coil tube product range serves a diverse portfolio of industrial and commercial applications:
- Heat Exchangers & Condensers — The internal threading geometry significantly enhances heat transfer efficiency, making these tubes ideal for compact shell-and-tube heat exchangers, air conditioning coils, and refrigeration condensers where space constraints and energy efficiency are paramount.
- Food & Beverage Processing — Compliance with FDA and 3-A sanitary standards (particularly 304/316L grades with electropolished finishes) qualifies these tubes for dairy, brewing, pharmaceutical, and chemical processing systems.
- Automotive Industry — Used in automotive heat exchangers, radiator cores, intercoolers, and fuel cell cooling systems where corrosion resistance and thermal performance are critical.
- Marine & Offshore Engineering — 316/316L grade coil tubes resist seawater corrosion and are employed in ballast water systems, marine cooling circuits, and offshore platform heat exchange equipment.
- Power Generation — Applied in boiler feedwater systems, turbine cooling circuits, and waste heat recovery units in both conventional and renewable energy installations.
- Chemical & Petrochemical Processing — High corrosion resistance ensures reliable performance in aggressive chemical environments, acid handling systems, and process heat exchangers.
- Medical & Laboratory Equipment — Precision-drawn, electropolished coil tubes used in dialysis machines, autoclaves, and laboratory instrumentation requiring biocompatible, contamination-free fluid pathways.
6. Unique Selling Points
- Enhanced Thermal Performance: Internal helical threading increases the effective heat transfer surface area and promotes turbulent flow, achieving thermal efficiency gains of 40–60% over conventional smooth-bore tubes of equivalent dimensions.
- Material Economy: Thin-wall construction (as low as 0.5 mm) reduces material consumption while maintaining structural integrity, offering a favorable strength-to-weight ratio.
- Continuous-Length Supply: Coil format delivery eliminates cut-off waste and enables seamless integration into automated tube-forming and heat exchanger assembly lines.
- Multi-Grade Availability: Comprehensive material range from 304 to 316L and 321 ensures suitability for virtually any corrosive environment or temperature regime.
- Customization Capability: Wenzhou Jixing Metal Materials Co., Ltd. offers fully customized specifications including non-standard diameters, wall thicknesses, thread geometries, surface finishes, and coil configurations.
7. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework and holds the following certifications and compliance credentials:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System — ensures consistent product quality and process control across all manufacturing stages. |
| ISO 14001:2015 | Environmental Management System — demonstrates commitment to sustainable and environmentally responsible manufacturing practices. |
| ISO 45001:2018 | Occupational Health & Safety Management System. |
| CE Marking (EU) | Conformity with European Union directives for pressure equipment and machinery safety. |
| TÜV / SGS Inspection | Independent third-party quality verification and product testing. |
| EN 10204 3.1 / 3.2 | Material test certificates (MTC) — third-party inspection reports available upon request. |
| ASTM / ASME Compliance | Product specifications conform to ASTM A213, ASTM A269, ASME SA-213, and related international standards. |
| EN 10216-5 / EN 10217-7 | European standard compliance for stainless steel tubes intended for pressure purposes. |
| FDA / 3-A Sanitary (Available) | Food-grade compliance for grades and finishes suitable for food, beverage, and pharmaceutical processing. |
8. Technical Notes & Recommendations
Installation Guidance: When uncoiling and installing stainless steel coil tubes, it is recommended to use a tube straightening machine with a gradual feed rate to prevent work hardening and potential cracking. For applications requiring welding, preheating is not typically necessary for austenitic grades, but post-weld annealing (at 1,050°C – 1,150°C) is recommended for welded assemblies to restore corrosion resistance at heat-affected zones.
Storage Recommendations: Coiled tubes should be stored in a dry, ventilated environment away from direct contact with carbon steel or reactive materials. VCI (Volatile Corrosion Inhibitor) packaging should remain intact until immediately prior to installation to prevent surface contamination and intergranular corrosion initiation.
Thread Geometry Optimization: The internal helical thread parameters (pitch, depth, and helix angle) should be selected based on the specific flow regime and thermal load requirements of the application. Computational Fluid Dynamics (CFD) analysis is recommended for critical applications to optimize thread configuration for maximum thermal-hydraulic performance.