Stainless Steel Coil Tube (Coiltube) — TIG-Welded Cooling Coil Assembly
Product Overview
The Stainless Steel Coil Tube (Product No. 1533) is a precision-engineered coiled tubing product manufactured by Wenzhou Jixing Metal Materials Co., Ltd, designed primarily for heat exchanger applications, refrigeration systems, and industrial cooling circuits. This product category encompasses both the raw coiled tubing material and the fabricated cooling coil assemblies produced through Tungsten Inert Gas (TIG) welding using flux-coated welding wire. The coil tube is formed into continuous spiral or helical configurations, enabling efficient heat transfer surface area within compact spatial footprints.
The technical development of this product line is informed by advanced welding research, particularly the application of flux-coated welding wire in TIG welding processes for copper and stainless steel cooling coil assemblies. This approach addresses critical challenges in joint integrity, thermal distortion control, and long-term corrosion resistance in demanding service environments.
Material & Properties
Base Material Composition
- Stainless Steel Grades: Primarily 304 (UNS S30400), 316 (UNS S31600), and 321 (UNS S32100) austenitic stainless steels, selected for their excellent corrosion resistance, formability, and high-temperature strength.
- Alternative Material: Copper (紫铜, electrolytic tough pitch copper, Cu-ETP, ≥99.9% Cu) is used in specific cooling coil variants where superior thermal conductivity is required.
- Welding Consumable: Flux-coated welding wire (涂药皮焊丝) compatible with TIG welding processes, providing slag protection and enhanced weld pool fluidity without requiring external shielding gas in certain configurations.
Mechanical Properties (Typical — Grade 304)
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 515 MPa (74,700 psi) | ASTM A270 / ASTM A580 |
| Yield Strength (屈服强度) | ≥ 205 MPa (29,700 psi) | ASTM A270 |
| Elongation (伸长率) | ≥ 40% | ASTM A270 |
| Hardness (硬度) | ≤ 92 HRB | ASTM A270 |
| Thermal Conductivity (热导率) | 16.3 W/(m·K) @ 300K | — |
| Density (密度) | 8.00 g/cm³ | — |
| Maximum Service Temperature (最高使用温度) | 870 °C (1,598 °F) | — |
Chemical Composition (Grade 316 — Typical)
| Element | C | Mn | P | S | Si | Cr | Ni | Mo | N |
|---|---|---|---|---|---|---|---|---|---|
| Max / Range | 0.08 | 2.00 | 0.045 | 0.030 | 1.00 | 16.0–18.0 | 10.0–14.0 | 2.0–3.0 | 0.10 |
Specifications
| Parameter (参数) | Specification / Range | Unit |
|---|---|---|
| Outer Diameter (外径) | 6.0 – 127.0 | mm |
| Wall Thickness (壁厚) | 0.5 – 8.0 | mm |
| Coil Inner Diameter (盘管内径) | 50 – 500 | mm |
| Coil Length (盘管展开长度) | 1 – 500 (custom) | m |
| Coil Pitch (盘管节距) | 1.5 × OD – 3.0 × OD | mm | Winding Angle (缠绕角度) | 85° – 90° (adjustable) | ° |
| Surface Finish (表面光洁度) | 2B / No.4 / BA / Mirror (Ra ≤ 0.4 μm) | — |
| Welding Method (焊接方法) | TIG (GTAW) with flux-coated wire | — |
| Weld Joint Efficiency (焊缝接头效率) | ≥ 95% | % |
| Pressure Test (耐压试验) | 1.5 × Working Pressure | — |
| Applicable Standards (适用标准) | ASTM A213, ASTM A269, GB/T 12771, EN 10216-5 | — |
Manufacturing Process
Step 1: Raw Material Preparation
Hot-rolled stainless steel strip or seamless tubing is procured and subjected to incoming quality inspection (IQC), including spectrographic analysis (直读光谱分析) to verify chemical composition and mechanical property testing. The material is annealed (退火) and pickled (酸洗) to achieve the required crystallographic structure and surface cleanliness.
Step 2: Cold Drawing & Forming
The tubing undergoes cold drawing (冷拔) to achieve precise dimensional tolerances (±0.1 mm on OD). The drawn tube is then passed through a coil-winding machine (盘管成型机) where it is helically wound at controlled tension and pitch to form the desired coil geometry. Springback compensation (回弹补偿) is calculated and applied to ensure dimensional accuracy post-release.
Step 3: TIG Welding with Flux-Coated Wire
The critical joining process employs Tungsten Inert Gas welding (TIG/GTAW) utilizing flux-coated welding wire (涂药皮焊丝). This specialized technique provides the following advantages:
- Slag Protection: The flux coating decomposes during welding, forming a protective slag layer (保护渣) over the molten weld pool, preventing atmospheric oxidation and nitrogen pickup.
- Enhanced Wetting: Improved molten pool fluidity results in superior joint penetration and reduced porosity.
- Reduced Distortion: Lower heat input compared to MIG welding minimizes thermal distortion of the coil geometry.
- Joint Strength: Welded joints achieve ≥95% of parent material tensile strength, critical for pressure-containing applications.
Step 4: Post-Weld Treatment
Welded coil assemblies undergo slag removal (清渣), followed by acid pickling and passivation (酸洗钝化) to restore the passive chromium oxide film on the weld zone. Solution annealing (固溶处理) at 1050–1150 °C with rapid water quenching may be performed for stress relief and microstructural homogenization.
Step 5: Quality Inspection & Testing
- Visual Inspection (目视检测): 100% examination of all weld joints for defects.
- Dimensional Inspection (尺寸检测): CMM or laser measurement of coil geometry.
- Non-Destructive Testing (无损检测): Penetrant testing (PT) per ASTM E165; radiographic testing (RT) per ASTM E94 for critical joints.
- Hydrostatic Pressure Test (水压试验): Performed at 1.5× working pressure with 10-minute hold time, zero leakage acceptance criterion.
- Corrosion Testing (腐蚀试验): Salt spray testing (盐雾试验) per ASTM B117, minimum 500 hours without red rust.
Applications
- Refrigeration & HVAC: Evaporator and condenser coils in commercial and industrial refrigeration systems.
- Heat Exchangers: Shell-and-coil heat exchangers, plate-fin coils, and air-to-liquid heat transfer units.
- Chemical Processing: Reactor cooling coils, condensation systems, and heat recovery units in petrochemical and pharmaceutical plants.
- Power Generation: Turbine cooling systems, condensers, and auxiliary heat exchange circuits.
- Food & Beverage Industry: Pasteurization coils, pasteurizers, and sanitary-grade heat transfer systems (316L grade).
- Marine & Offshore: Seawater cooling coils, desalination systems, and marine HVAC applications.
- Automotive: Intercoolers, oil coolers, and transmission cooler coils.
Quality Certifications & Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System Certification |
| ISO 14001:2015 | Environmental Management System Certification |
| ASME Stamp | American Society of Mechanical Engineers — Pressure Vessel & Piping |
| EN 10204 3.1 | European Material Test Certificate — Inspection Report |
| ASTM A213 | Standard Specification for Seamless Austenitic Chromium-Nickel Alloy Steel Tubing for High Temperature Service |
| GB/T 12771 | Chinese National Standard — Stainless Steel Seamless Tubes for General Purposes |
| NACE MR0175 | Sour Service Material Requirements (if applicable for oil & gas) |
| CE Marking | European Conformity — Pressure Equipment Directive (PED 2014/68/EU) |
Unique Selling Points
1. Advanced TIG Welding Technology with Flux-Coated Wire: Wenzhou Jixing Metal Materials Co., Ltd leverages specialized research in flux-coated wire TIG welding to produce coil tube assemblies with exceptional joint integrity. This proprietary process eliminates the need for external shielding gas in certain configurations, reducing production costs while maintaining or exceeding weld quality benchmarks.
2. Precision Coil Geometry: Computer-controlled winding ensures consistent pitch, tension, and alignment throughout the coil length, with dimensional tolerances as tight as ±0.15 mm — critical for drop-in replacement and OEM integration.
3. Multi-Grade Material Flexibility: The product line covers austenitic (304, 316, 321), duplex (2205), and copper alloy coil tubes, allowing engineers to optimize material selection for specific thermal, chemical, and mechanical requirements.
4. Full Traceability: Each coil tube batch carries a unique heat number and traceability code, enabling complete material and process history documentation from raw mill certificate to final pressure test report.
5. Custom Engineering Support: The company provides application-specific engineering consultation, including thermal simulation (热仿真), flow analysis, and custom coil design to meet unique OEM specifications.
Technical Notes
The integration of flux-coated welding wire in TIG welding processes for coil tube fabrication represents a significant advancement in manufacturing efficiency and joint quality. Research published in metallurgical journals (《涂药皮焊丝对紫铜冷却盘管的TIG焊》) demonstrates that this approach produces weld beads with reduced dilution ratios, lower porosity rates, and superior mechanical properties compared to conventional pure-gas TIG methods. The slag layer formed by the flux coating acts as a thermal barrier, reducing heat-affected zone (HAZ) width by approximately 15–20%, which minimizes sensitization risk in austenitic stainless steels and preserves the corrosion resistance of the parent material.
For copper coil variants, the flux-coated wire TIG process addresses the well-known challenges of copper's high thermal conductivity and low melting point, achieving consistent penetration depths and uniform bead profiles across varying wall thicknesses.