Stainless Steel Coil Tube (盘管 Coiltube) — Technical Product Specification
1. Product Overview
The Stainless Steel Coil Tube (盘管 Coiltube) is a precision-engineered continuous tubular product supplied in coiled form, designed for applications demanding high corrosion resistance, thermal efficiency, and mechanical integrity. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product series is specifically optimized for use in heat exchange systems, including fan coil unit (FCU) air conditioning assemblies where multi-speed, low-noise single-phase capacitor motor-driven systems require reliable thermal transfer media.
Unlike discrete pipe segments, coil tubes are produced in continuous lengths wound into coils, offering significant advantages in installation efficiency, reduced joint count, and minimized leakage risk in heat transfer and fluid distribution applications. The coiled configuration also facilitates easier integration into compact HVAC (Heating, Ventilation, and Air Conditioning) enclosures and industrial heat exchanger assemblies.
2. Material & Properties
2.1 Base Material Grades
The coil tube is available in multiple austenitic and duplex stainless steel grades, selected to meet specific environmental and performance requirements:
- AISI 304 (UNS S30408 / 06Cr19Ni10): General-purpose austenitic grade with excellent corrosion resistance, formability, and weldability. Contains 18–20% Chromium (Cr) and 8–10% Nickel (Ni).
- AISI 316 (UNS S31603 / 022Cr19Ni12Mo2): Enhanced austenitic grade with 2–3% Molybdenum (Mo) addition for superior resistance to pitting and crevice corrosion in chloride-containing environments.
- AISI 316L (UNS S31603 / 022Cr17Ni12Mo2): Low-carbon variant of 316, suitable for welding applications where sensitization resistance is critical.
- AISI 321 (UNS S32101 / 06Cr18Ni11Ti): Titanium-stabilized austenitic grade with excellent resistance to intergranular corrosion at elevated temperatures (up to 870°C).
2.2 Mechanical Properties
| Property | Unit | Typical Value (AISI 304) | Typical Value (AISI 316L) |
|---|---|---|---|
| Tensile Strength (抗拉强度) | MPa | ≥ 520 | ≥ 515 |
| Yield Strength (屈服强度) | MPa | ≥ 205 | ≥ 170 |
| Elongation (延伸率) | % | ≥ 40 | ≥ 40 |
| Hardness (硬度) | HV | ≤ 200 | ≤ 190 |
| Thermal Conductivity (导热系数, 100°C) | W/(m·K) | 16.3 | 14.6 |
| Specific Heat (比热容) | J/(kg·K) | 500 | 500 |
| Thermal Expansion Coefficient (热膨胀系数, 20–100°C) | ×10⁻⁶ /K | 17.2 | 16.5 |
2.3 Surface Finish Options
- 2B Finish: Cold-rolled, annealed, and pickled surface; matte appearance; suitable for general industrial applications.
- No. 4 Brushed Finish: Uniformly brushed surface with grain lines; aesthetic and functional for visible installations.
- Mirror Finish (8K): High-polish reflective surface; used in food processing and pharmaceutical applications.
- Electro-Polished (EP): Smooth, passive surface with enhanced corrosion resistance; critical for hygienic and semiconductor applications.
3. Specifications
| Parameter (参数) | Specification Range | Standard Reference |
|---|---|---|
| Outer Diameter (外径, OD) | Φ6.0 mm – Φ50.8 mm | ASTM A213 / GB/T 14976 |
| Wall Thickness (壁厚, WT) | 0.3 mm – 3.0 mm | ASTM A269 / GB/T 14975 |
| Coil Length (盘管长度) | 5 m – 50 m per coil (customizable) | — | Coil Inner Diameter (盘圈内径) | Φ200 mm – Φ1000 mm | — |
| Tolerance on OD (外径公差) | ±0.05 mm (precision); ±0.10 mm (standard) | ASTM A213 |
| Tolerance on Wall Thickness (壁厚公差) | ±10% of nominal | ASTM A269 |
| Straightness (直线度) | ≤ 0.5 mm/m | GB/T 14976 |
| Surface Roughness (表面粗糙度, Ra) | ≤ 1.6 μm (2B); ≤ 0.4 μm (EP) | ISO 1302 |
| Maximum Operating Temperature (最高使用温度) | 870°C (304); 870°C (316L); 900°C (321) | ASM Section VIII |
| Design Pressure Rating (设计压力等级) | Up to 4.0 MPa (grade-dependent) | ASME BPV Code |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection (原材料选择): Hot-rolled stainless steel strip (热轧不锈钢带) sourced from certified mills, verified for chemical composition via Optical Emission Spectrometry (OES, 光学发射光谱分析) and X-Ray Fluorescence (XRF, X射线荧光分析).
- Coil Winding (盘绕成型): Continuous strip is precisely wound around mandrels using CNC-controlled coiling machines to achieve specified coil diameters and pitch uniformity.
- Forming & Sizing (成型与定径): Multi-roller forming stations progressively shape the strip into tubular geometry; precision sizing rolls ensure dimensional accuracy within tolerance.
- Welding (焊接): For welded coil tube, High-Frequency Induction Welding (HF-W, 高频感应焊接) is employed, achieving full-penetration welds with minimal heat-affected zone (HAZ, 热影响区). Argon (Ar) gas shielding prevents oxidation.
- Pickling & Passivation (酸洗钝化): The coil tube undergoes pickling in mixed acid baths (HNO₃ + H₂SO₄) followed by passivation treatment to restore and enhance the chromium oxide passive layer (Cr₂O₃).
- Surface Treatment (表面处理): Depending on specification, additional brushing, polishing, or electro-polishing operations are performed.
- Quality Inspection (质量检验): Comprehensive testing including hydrostatic pressure testing (水压试验), ultrasonic testing (UT, 超声波检测), and dimensional verification.
- Coiling & Packaging (成盘包装): Finished product is wound into coils, wrapped in protective film, and packaged for shipment.
4.2 Key Process Controls
- Temperature Control: Annealing (退火) performed at 1050–1150°C in protective atmosphere (N₂ + H₂) to ensure uniform microstructure and stress relief.
- Weld Seam Inspection: 100% visual and dye penetrant testing (PT, 渗透检测); spiral eddy current testing (ECT, 涡流检测) for weld seam integrity.
- Grain Structure Control: Annealing parameters optimized to produce uniform austenitic grain structure (ASTM grain size 5–8) for optimal mechanical properties.
5. Applications
5.1 HVAC & Fan Coil Units (风机盘管)
In fan coil unit air conditioning systems driven by multi-speed, low-noise single-phase capacitor motors, stainless steel coil tubes serve as the primary heat exchange medium. The coil tube configuration enables:
- Compact heat exchanger design with high surface-area-to-volume ratio
- Efficient thermal transfer between refrigerant/water and ambient air
- Resistance to condensation-induced corrosion in humid environments
- Long service life under cyclic thermal loading conditions
5.2 Additional Application Domains
- Food & Beverage Industry (食品饮料工业): Hygienic fluid transfer, brewing systems, pasteurization equipment (316L, EP finish).
- Pharmaceutical Manufacturing (制药工业): Clean-in-place (CIP) compatible fluid handling, reactor coils, heat exchangers.
- Chemical Processing (化工处理): Corrosive fluid transfer, heat exchanger tubes, condensate collection systems.
- Automotive Industry (汽车工业): Exhaust system components, fuel lines, turbocharger cooling circuits.
- Oil & Gas (石油天然气): Downhole instrumentation tubing, wellhead connections, marine platform piping.
- Water Treatment (水处理): Desalination systems, reverse osmosis (RO) membrane housings, chlorine-resistant piping.
6. Quality Certifications & Standards Compliance
6.1 Applicable Standards (适用标准)
| Standard (标准) | Description |
|---|---|
| ASTM A213 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for High-temperature and High-pressure Boilers and Heat Exchangers |
| ASTM A269 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Heat-Transfer Applications |
| GB/T 14975 | Stainless Steel Seamless Tubing for Fluid Transport (中国国家标准) |
| GB/T 14976 | Stainless Steel Seamless Tubing for Heat Exchangers and Heat Sinks |
| EN 10216-5 | Welded Circular Hollow Sections of Stainless Steels — Technical Delivery Conditions |
| JIS G3459 | Stainless Steel Tubes (Japanese Industrial Standard) |
| ASME BPV Code Section VIII | Boiler and Pressure Vessel Code — Rules for Construction of Pressure Vessels |
6.2 Quality Management System
- ISO 9001:2015 — Quality Management Systems certification for consistent production quality
- ISO 14001:2015 — Environmental Management Systems certification
- ISO 45001:2018 — Occupational Health and Safety Management Systems
- CE Marking (欧盟CE认证) — Conformity with European health, safety, and environmental protection standards
- PED (Pressure Equipment Directive 2014/68/EU) — For pressure-rated applications
6.3 Inspection & Testing Protocol
- Chemical Analysis (化学成分分析): Spectrometric verification of Cr, Ni, Mo, C, Ti, S, P content per grade specification; third-party lab certification available.
- Mechanical Testing (力学性能测试): Tensile testing per ASTM A370; yield strength, ultimate tensile strength, and elongation verified.
- Hydrostatic Testing (水压试验): 100% pressure testing at 1.5× working pressure, held for minimum 5 seconds with zero leakage tolerance.
- Non-Destructive Testing (无损检测): Eddy Current Testing (ECT) for weld seam integrity; Ultrasonic Testing (UT) for wall thickness verification; Dye Penetrant Testing (PT) for surface defect detection.
- Corrosion Testing (腐蚀测试): Salt Spray Test (盐雾试验) per ASTM B117 — minimum 500 hours without red rust; Pitting Resistance (点蚀抗性) verified via ASTM G48.
- Intergranular Corrosion Testing (晶间腐蚀测试): ASTM A262 Practice E (Acid Solution Test) for sensitized condition verification.
7. Unique Selling Points
- Continuous Coil Configuration: Eliminates field welding and joint failures; reduces installation time by up to 60% compared to discrete pipe segments.
- Multi-Grade Availability: Comprehensive material portfolio (304, 316, 316L, 321) enables optimal material selection for specific environmental conditions.
- Precision Dimensional Control: CNC-controlled forming achieves ±0.05 mm OD tolerance, critical for press-fit and brazing applications.
- Enhanced Corrosion Performance: Post-manufacturing pickling and passivation treatment ensures maximum passive layer integrity.
- HVAC System Integration: Specifically engineered for compatibility with multi-speed low-noise fan coil unit systems, providing reliable thermal transfer under variable-speed operating conditions.
- Customization Capability: Flexible coil length, diameter, and wall thickness options tailored to specific project requirements.
- Full Traceability: Each coil is accompanied by a Mill Test Certificate (MTC,