Stainless Steel Coil Tube (Coiltube) — Technical Product Specification
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Category: Literature Study / Technical Reference
Reference Document: "Key Considerations for Selecting Fan Coil Units with Wet Film Humidifiers" — Learning Summary and Technical Analysis
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular component supplied in coiled form, designed for seamless integration into hydronic, HVAC (Heating, Ventilation, and Air Conditioning), and fluid distribution systems. As a core heat-exchange element, the coil tube plays a critical role in transferring thermal energy between a working fluid and a surrounding medium—typically air—within fan coil units (FCUs) and membrane humidifier assemblies.
Wenzhou Jixing Metal Materials Co., Ltd. specializes in the manufacture and supply of high-grade stainless steel coil tubes that meet the rigorous demands of modern building services engineering. The coiled configuration enables compact installation, extended service life, and superior resistance to corrosion in environments where wet-membrane humidification introduces persistent moisture exposure.
2. Material & Properties
2.1 Material Grade
- Primary Material: Austenitic Stainless Steel (奥氏体不锈钢), conforming to ASTM A269 / ASME SA-269 and GB/T 12771 standards
- Common Grades: SUS 304 (AISI 304, 06Cr19Ni10), SUS 316 (AISI 316, 06Cr17Ni12Mo2), SUS 316L (Low-Carbon variant for enhanced weldability and corrosion resistance)
- Alternative Grades Available: SUS 321 (stabilized with titanium), SUS 304L (low-carbon), duplex stainless steel (e.g., 2205) for high-chloride environments
2.2 Mechanical Properties
- Tensile Strength (抗拉强度): ≥ 520 MPa (SUS 304), ≥ 570 MPa (SUS 316)
- Yield Strength (屈服强度): ≥ 205 MPa (SUS 304), ≥ 240 MPa (SUS 316)
- Elongation (延伸率): ≥ 40% at break
- Hardness (硬度): ≤ 237 HB (annealed condition)
2.3 Thermal Properties
- Thermal Conductivity (导热系数): 16.3 W/(m·K) at 20°C (SUS 304); 14.6 W/(m·K) at 20°C (SUS 316)
- Specific Heat Capacity (比热容): 500 J/(kg·K)
- Linear Thermal Expansion Coefficient (线膨胀系数): 16.0 × 10⁻⁶ /°C (20–100°C)
2.4 Corrosion Resistance
- Excellent resistance to atmospheric corrosion, mild acids, and alkaline solutions
- SUS 316 grade provides superior resistance to pitting and crevice corrosion in chloride-containing environments—critical for wet-membrane humidifier applications where constant moisture and dissolved minerals are present
- Passive oxide film (Cr₂O₃) self-heals under normal atmospheric conditions, ensuring long-term structural integrity
3. Specifications
| Parameter (参数) | Specification / Range (规格范围) | Standard Reference (标准引用) |
|---|---|---|
| Outer Diameter (OD) (外径) | 6.0 mm – 50.8 mm (1/4" – 2") | ASTM A269 / GB/T 12771 |
| Wall Thickness (壁厚) | 0.3 mm – 3.0 mm | ASTM A269 / GB/T 12771 |
| Coil Diameter (盘管直径) | 50 mm – 300 mm | Custom per application |
| Coil Length (盘管长度) | 5 m – 50 m per coil (standard); custom lengths available | Custom per application |
| Surface Finish (表面光洁度) | 2B, BA (Bright Annealed), No.4 brushed, mirror (Ra ≤ 0.2 μm) | ASTM A240 / GB/T 343 |
| Operating Temperature (工作温度) | -196°C to +870°C (continuous) | Material-dependent |
| Operating Pressure (工作压力) | Up to 1.6 MPa (standard); up to 4.0 MPa (heavy-wall) | ASME BPVC Section VIII |
| Tolerance on OD (外径公差) | ±0.05 mm (precision grade); ±0.1 mm (standard grade) | ASTM A269 |
| Tolerance on Wall Thickness (壁厚公差) | ±10% of nominal | ASTM A269 |
| End Treatment (端部处理) | Cut square, deburred, beveled for welding, or threaded | Per customer requirement |
| Packaging (包装) | Coiled on wooden reel or steel drum, with moisture-proof wrapping | ISO 4180 (wooden packaging) |
4. Manufacturing Process
4.1 Raw Material Selection and Incoming Inspection
High-purity stainless steel wire rod or strip is sourced from certified mills. Each batch undergoes incoming inspection including chemical composition verification (via optical emission spectrometry, OES), mechanical property testing, and visual examination for surface defects. Material traceability is maintained through heat number tracking.
4.2 Cold Drawing / Forming (冷拔/成型)
The stainless steel wire or strip is cold-drawn through precision dies to achieve the required outer diameter and wall thickness with tight dimensional tolerances. Cold drawing enhances mechanical properties (strength and hardness) while maintaining excellent surface finish. For larger diameters, cold rolling or tube rolling processes may be employed.
4.3 Coil Winding (盘绕成型)
The formed tube is wound into a coil configuration using CNC-controlled coiling equipment. The winding process ensures uniform pitch (间距), consistent coil diameter, and absence of kinks or deformation. Spring-back effects are compensated algorithmically to maintain geometric accuracy.
4.4 Heat Treatment (热处理)
Depending on the application requirements, the coil tube may undergo solution annealing (固溶退火) at 1050°C – 1150°C followed by rapid water quenching to restore full austenitic structure and maximum corrosion resistance. Stress relief annealing (去应力退火) at 850°C – 950°C may be applied for coils requiring dimensional stability.
4.5 Surface Treatment (表面处理)
The coil tube surface is passivated (钝化处理) through immersion in nitric acid or citric acid solution to enhance the natural chromium oxide passive layer. Additional surface treatments such as electropolishing (电解抛光) or PTFE coating may be applied for specialized applications requiring ultra-low friction or enhanced chemical resistance.
4.6 Quality Control and Testing (质量控制与检测)
- Dimensional Inspection: Laser micrometry for OD, wall thickness, and coil diameter verification
- Pressure Testing (水压试验): Each coil batch undergoes hydrostatic pressure testing at 1.5× the maximum working pressure for a minimum of 30 seconds
- Chemical Analysis: Spectroscopic verification of alloy composition per ASTM A269
- Corrosion Testing: Salt spray testing (ASTM B117) for minimum 96 hours; intergranular corrosion testing (ASTM A240) for stabilized grades
- Visual Inspection: 100% visual examination for surface defects, dents, and dimensional irregularities
5. Applications
5.1 Fan Coil Units (风机盘管) with Wet Film Humidifiers
The primary application context referenced in the technical literature is the integration of stainless steel coil tubes into fan coil units (FCUs) equipped with wet film humidifiers (湿膜加湿器). In such systems, the coil tube serves as the heat-exchange core, transferring thermal energy from chilled water or hot water to the airstream. The selection of the appropriate coil tube is critical for system performance, and the following considerations are emphasized:
- Material Compatibility: SUS 316 or SUS 316L is recommended due to the constant moisture exposure from the wet membrane humidifier, which creates a high-humidity, potentially chloride-contaminated environment conducive to pitting corrosion in lower-grade stainless steels
- Corrosion Resistance: The coil tube must withstand prolonged contact with humidified air containing dissolved minerals, ensuring a service life exceeding 15 years without degradation
- Heat Transfer Efficiency: Thin-wall coil tubes (0.5 mm – 1.0 mm) maximize thermal conductivity while maintaining structural integrity under typical operating pressures (0.3 MPa – 0.6 MPa)
- Hygienic Design: Smooth inner surface (Ra ≤ 0.8 μm) prevents biofilm formation and mineral scale accumulation, critical for indoor air quality (IAQ) compliance
- Coil Configuration: The coil pitch and tube layout must be optimized to balance airflow resistance (pressure drop) against heat transfer area, ensuring the FCU meets design capacity without excessive fan power consumption
5.2 Additional Applications
- Medical Equipment (医疗设备): Sterilization chambers, autoclaves, and medical gas delivery systems requiring corrosion-resistant tubing
- Food and Beverage Processing (食品加工): Heat exchangers, pasteurization systems, and CIP (Clean-in-Place) compatible fluid distribution
- Pharmaceutical Manufacturing (制药): GMP-compliant piping for process water, steam, and compressed gas systems
- Marine and Offshore (海洋工程): Seawater heat exchangers and ballast systems requiring resistance to chloride-induced pitting corrosion
- Chemical Processing (化工): Transfer lines for mildly corrosive fluids where carbon steel is unsuitable
- Automotive Industry (汽车工业): Fuel lines, exhaust components, and HVAC systems in premium vehicles
6. Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring that all stainless steel coil tube products meet international standards:
| Certification / Standard (认证/标准) | Description (描述) |
|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent product quality and process control |
| ISO 14001:2015 | Environmental Management System certification for sustainable manufacturing practices |
| ISO 45001:2018 | Occupational Health and Safety Management System certification |
| CE Marking | Compliance with European health, safety, and environmental protection standards |
| ASTM A269 / ASME SA-269 | Standard specification for seamless austenitic stainless steel tube and pipe |
| GB/T 12771 | Chinese National Standard for welded stainless steel tubes for general engineering purposes |
| EN 10217-7 | European standard for stainless steel tubes for pressure purposes |
| PED (Pressure Equipment Directive 2014/68/EU) | Compliance with European pressure equipment regulations for pressure-containing components |
| NSF/ANSI 61 | Drinking water system components certification (available for food-grade applications) |
| Mill Test Certificates (MTC) | EN 10204 3.1 certificates provided for every batch, documenting chemical composition, mechanical properties, and heat treatment records |
7. Unique Selling Points
- Application-Specific Optimization: Coil tubes are engineered specifically for the demanding environment of fan coil units with wet film humidifiers, where constant moisture exposure and potential mineral contamination demand exceptional corrosion resistance
- Precision Dimensional Control: CNC-controlled coiling ensures uniform pitch and coil geometry, enabling predictable and consistent heat transfer performance in HVAC applications
- Material Grade Flexibility: Full range of austenitic and duplex stainless steel grades available, allowing customers to optimize the balance between cost, corrosion resistance, and mechanical performance for their specific operating conditions
- Traceability and Documentation: Complete material traceability from raw material to finished product, with full Mill Test Certificates and batch-level documentation supporting regulatory compliance and quality audits
- Custom Engineering Support: Technical consultation available for coil configuration optimization, including pitch design, tube layout, and end treatment selection tailored to specific FCU design parameters and humidifier integration requirements
- Long Service Life: Properly specified SUS 316L coil tubes in wet-membrane humidifier applications offer a design life exceeding 20 years, significantly reducing lifecycle maintenance costs compared to carbon steel alternatives