Stainless Steel Coil Tube — Wenzhou Jixing Metal Materials Co., Ltd.
1. Product Overview
The Stainless Steel Coil Tube (盘管, Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a continuous-length tubular product supplied in coiled form, designed to maximize material utilization and facilitate downstream forming, bending, and cutting operations. Unlike conventional straight-length seamless or welded pipes, coil tubes are wound into large-diameter coils, enabling uninterrupted supply to high-volume fabrication lines. This product category falls under the industrial classification of literature-based technical learning resources (文献学习), with specific emphasis on correct installation, handling, and operational best practices — particularly within HVAC (Heating, Ventilation, and Air Conditioning) fan coil unit (风机盘管) systems.
Coil tubes serve as critical structural and functional components across a broad spectrum of industries, including refrigeration, heat exchangers, fluid transport systems, and HVAC equipment. Their coiled configuration offers significant logistical advantages, reducing the number of butt welds required during assembly and minimizing material waste associated with straight-length pipe cutting.
2. Material & Properties
Stainless steel coil tubes are predominantly fabricated from austenitic stainless steel grades, selected for their outstanding corrosion resistance, mechanical strength, and formability. The primary material specifications are as follows:
2.1 Common Grades
- SAE 304 / UNS S30400: The most widely used austenitic grade, offering excellent general corrosion resistance, good formability, and non-magnetic properties. Suitable for food-grade, chemical, and HVAC applications.
- SAE 316 / UNS S31600: Enhanced resistance to pitting and crevice corrosion due to the addition of 2–3% Molybdenum (Mo). Preferred in marine, chemical processing, and pharmaceutical environments.
- SAE 321 / UNS S32100: Stabilized with Titanium (Ti) to prevent sensitization at elevated temperatures. Ideal for high-temperature service above 425°C (800°F).
- SAE 304L / UNS S30403: Low-carbon variant of 304 (C ≤ 0.03%), designed to minimize intergranular corrosion during welding.
- SAE 316L / UNS S31603: Low-carbon variant of 316, offering superior weldability and resistance to sensitization.
2.2 Mechanical Properties (Typical Values for 304 Grade)
- Tensile Strength (抗拉强度): ≥ 515 MPa (75,000 psi)
- Yield Strength (屈服强度, 0.2% offset): ≥ 205 MPa (30,000 psi)
- Elongation (伸长率): ≥ 40% in 50 mm (2 inches)
- Hardness (硬度): ≤ 92 HRB (Rockwell B Scale)
- Density (密度): 8.0 g/cm³
2.3 Physical Properties
- Thermal Conductivity (热导率): 16.3 W/(m·K) at 20°C
- Thermal Expansion Coefficient (热膨胀系数): 17.3 × 10⁻⁶ /°C (20–100°C)
- Electrical Resistivity (电阻率): 72 μΩ·cm at 20°C
- Maximum Service Temperature (最高使用温度): 870°C (1598°F) in oxidizing atmospheres
2.4 Surface Finish Options
- 2B Finish: Cold-rolled and annealed in a protective atmosphere; smooth, slightly reflective surface. Most common for general industrial use.
- No. 4 Brushed Finish: Uniformly directional grain pattern; decorative and functional, commonly used in architectural and food service applications.
- Mirror Finish (8K): Highly polished, reflective surface; used in high-end architectural and sanitary applications.
- Pickled & Passivated: Chemical treatment to remove mill scale and restore full corrosion resistance; essential for welded assemblies.
3. Specifications
The following table summarizes the dimensional and performance specifications for Wenzhou Jixing Metal Materials Co., Ltd. stainless steel coil tubes, conforming to international standards including ASTM A511, ASTM A269, EN 10216-5, and GB/T 14976.
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD, 外径) | 6.0 mm – 108.0 mm (¼" – 4") | ASTM A511 / EN 10216-5 |
| Wall Thickness (壁厚) | 0.5 mm – 3.0 mm | ASTM A511 / GB/T 14976 |
| Coil Weight (盘重) | 500 kg – 3,000 kg (per coil) | Manufacturer Specification |
| Coil Inner Diameter (盘内径) | 300 mm – 600 mm | Manufacturer Specification |
| Material Grades (材质牌号) | 304, 304L, 316, 316L, 321, 310S | ASTM A269 / EN 10216-5 |
| Surface Treatment (表面处理) | 2B, No.4, Mirror (8K), Pickled & Passivated | ASTM A478 |
| Manufacturing Method (制造工艺) | ERW (Electrical Resistance Welded), CW (Continuous Welding) | ASTM A511 |
| Heat Treatment (热处理) | Solution Annealed (固溶退火), 1050–1150°C, followed by water quench | ASTM A269 |
| Tolerance — OD (外径公差) | ±0.05 mm (±0.002") | ASTM A511 |
| Tolerance — Wall Thickness (壁厚公差) | ±10% of nominal | ASTM A511 |
| End Condition (端部状态) | Plain, Beveled (坡口), or Custom per drawing | ASME B36.19M |
| Roundness (圆度) | ≤ 0.5% of OD | ASTM A511 |
| Maximum Length per Coil (单盘最大长度) | Up to 3,000 m (continuous) | Manufacturer Specification |
| Test Pressure (试验压力) | Hydrostatic test at 2× working pressure | ASTM A511 |
| Delivery Condition (交货状态) | Coiled, Annealed, Pickled & Passivated | ASTM A511 |
4. Manufacturing Process
The production of stainless steel coil tubes follows a rigorous, multi-stage manufacturing process designed to ensure dimensional accuracy, metallurgical integrity, and surface quality. The process flow is outlined below:
- Raw Material Preparation (原材料准备): Cold-rolled stainless steel strip (带钢) is sourced from certified mills and inspected for chemical composition (via Optical Emission Spectroscopy, OES) and mechanical properties. The strip is verified for flatness, surface quality, and edge integrity prior to coil tube forming.
- Coil Forming & Welding (成型与焊接): The flat strip is fed through a series of roll-forming stations (辊成型机组) that progressively bend it into a circular cross-section. The formed tube is then welded using Electrical Resistance Welding (ERW, 电阻焊) or Continuous Welding (CW, 连续焊). In ERW, high-frequency current is applied to the seam edges, generating localized resistance heating that fuses the edges together. The welding parameters — current, voltage, speed, and electrode pressure — are precisely controlled to produce a uniform, defect-free weld seam.
- Weld Seam Finishing (焊缝处理): The weld seam is ground or trimmed (焊缝修磨) to achieve flush continuity with the tube surface. For high-quality applications, the weld is further polished or buffed to minimize residual stress and surface imperfections.
- Solution Annealing (固溶退火): The formed and welded tube is heated to 1050–1150°C (1922–2092°F) in a protective atmosphere (hydrogen or dissociated ammonia) to dissolve carbides and restore full austenitic microstructure. This is followed by rapid water quenching to lock in the solution-treated condition, ensuring optimal corrosion resistance and ductility.
- Pickling & Passivation (酸洗钝化): The annealed tube is immersed in a mixed acid solution (typically nitric acid + hydrofluoric acid, 硝酸+氢氟酸) to remove oxide scale, discoloration, and weld residue. Subsequent passivation with a nitric acid or citric acid solution forms a thin, protective chromium oxide (Cr₂O₃) layer on the surface, enhancing long-term corrosion resistance.
- Hydrostatic Testing (水压试验): Each coil is subjected to a hydrostatic pressure test at twice the maximum working pressure (per ASTM A511). The tube is pressurized and held for a specified dwell time to verify weld seam integrity and detect any leaks or defects.
- Dimensional Inspection (尺寸检验): Automated gauging systems measure outer diameter (OD), wall thickness, roundness, and straightness at regular intervals. Non-Conformance (不合格) sections are marked and removed.
- Coiling & Packaging (卷取与包装): The finished tube is wound onto a coil (盘管) using a controlled tension system to prevent deformation or kinking. Coils are wrapped with protective film (保护膜), strapped with steel bands, and labeled with material certificates, heat numbers, and dimensional data. Export coils are additionally wrapped in VCI (Vapor Corrosion Inhibitor, 气相防锈) paper and wooden pallets.
5. Applications
Stainless steel coil tubes find extensive use across multiple industrial sectors. The following highlights the primary application domains, with specific reference to the fan coil unit (风机盘管) context noted in the product literature:
5.1 HVAC & Fan Coil Units (暖通空调与风机盘管)
In fan coil unit (FCU) systems, stainless steel coil tubes serve as the core heat exchange elements. The correct selection, installation, and maintenance of these coils are critical to system performance. Key considerations include:
- Proper coil tube spacing and row configuration to optimize airflow and heat transfer efficiency
- Adequate support and hanger spacing to prevent vibration-induced fatigue failure
- Correct refrigerant or hot water flow direction to ensure uniform heat exchange
- Regular inspection for corrosion, blockage, or fin damage to maintain thermal performance
- Use of compatible materials to prevent galvanic corrosion at joints and connections
5.2 Additional Application Areas
- Food & Beverage Industry (食品饮料工业): Sanitary-grade 316L coil tubes for dairy processing, brewing, and pharmaceutical fluid transfer systems. The smooth, non-porous surface prevents bacterial adhesion and facilitates CIP (Clean-in-Place) cleaning.
- Chemical Processing (化工处理): Resistance to aggressive acids, alkalis, and solvents makes 316 and 316L grades suitable for chemical reactors, distillation columns, and pipeline systems.
- Automotive Industry (汽车工业): Coil tubes used in exhaust systems, fuel lines, and emission control components. High-temperature grades (310S, 321) withstand extreme thermal cycling.
- Architectural & Decoration (建筑装饰): Mirror-finish and brushed coil tubes for handrails, balustrades, structural facades, and interior design elements.
- Medical Equipment (医疗设备): Biocompatible 316L tubes for surgical instruments, implant manufacturing, and hospital fluid distribution systems.
- Energy & Power Generation (能源与发电): Heat exchanger tubes, boiler tubes, and condensate lines in power plants and nuclear facilities.
- Refrigeration & Air Conditioning (制冷与空调): Condenser and evaporator coils requiring high thermal conductivity and corrosion resistance.
6. Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system to ensure product conformity with international and national standards. The following certifications and compliance frameworks are in place:
- ISO 9001:2015: Quality Management System (质量管理体系) certification, demonstrating commitment to consistent product quality and customer satisfaction.
- ISO 14001:2015: Environmental Management System (环境管理体系) certification, ensuring environmentally responsible manufacturing practices.
- ISO/IEC 17025: Testing and calibration laboratory accreditation, validating the accuracy and reliability of internal quality control testing.
- CE Marking (European Conformity): Compliance with European Union directives for safety, health, and environmental protection.
- EN 10204 3.1 / 3.2: Material test certificates (材质证明书) issued per European standard, providing traceable chemical and mechanical test data.
- ASME / PED: Products conform to ASME Boiler and Pressure Vessel Code (BPV Code) and European Pressure Equipment Directive (PED 2014/68/EU) where applicable.
- GB/T Standards (Chinese National Standards): Full compliance with GB/T 14976 (Seamless and Welded Steel Tubes for General Fluid Delivery), GB/T 12771 (Stainless Steel Tubes for Fluid Transport), and related standards.
- Mill Test Reports (MTR, 熔炼报告): Each heat lot is accompanied by a comprehensive Mill Test Report documenting chemical composition, mechanical properties, and heat treatment history.
Note on Fan Coil Unit (FCU) Best Practices: The product literature associated with this coil tube product emphasizes the importance of correct installation and operation of fan coil units. Key learning points include: (1) ensuring proper drainage slope to prevent water accumulation and microbial growth; (2) maintaining adequate air filtration to protect coil surfaces from fouling; (3) performing seasonal maintenance checks on refrigerant charge, airflow balance, and electrical connections; and (4) using compatible stainless steel materials throughout the system to prevent galvan