Stainless Steel Coil Tube (Coil Tube) — Fan Coil Unit Application Grade
1. Product Overview
The Stainless Steel Coil Tube (盘管/Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered continuous-length tubular product specifically designed for use in fan coil unit (Fan Coil Unit, FCU) systems, HVAC (Heating, Ventilation, and Air Conditioning) assemblies, and related fluid transport applications. Unlike traditional straight seamless tubes, coil tubes are supplied in continuous coiled form, offering superior flexibility in fabrication, reduced welding joints, and enhanced mechanical integrity under cyclic loading conditions.
This product has been extensively studied and refined in the context of fan coil unit exhaust valve integrity, addressing critical failure modes such as stress corrosion cracking (Stress Corrosion Cracking, SCC), fatigue fracture, and thermal cycling degradation that have historically affected stainless steel components in humid, corrosive indoor environments.
2. Material & Properties
The coil tube is fabricated from high-purity austenitic stainless steel, with the primary grades including:
- 304 Stainless Steel (UNS S30400) — General-purpose grade with excellent corrosion resistance and formability
- 316 Stainless Steel (UNS S31600) — Enhanced pitting and crevice corrosion resistance due to molybdenum (Mo) addition
- 316L Stainless Steel (UNS S31603) — Low-carbon variant for superior weldability and resistance to sensitization
2.1 Chemical Composition (Typical, wt%)
| Element | 304 (UNS S30400) | 316 (UNS S31600) | 316L (UNS S31603) |
|---|---|---|---|
| Carbon (C) | ≤ 0.08 | ≤ 0.08 | ≤ 0.03 |
| Chromium (Cr) | 18.0 – 20.0 | 16.0 – 18.0 | 16.0 – 18.0 |
| Nickel (Ni) | 8.0 – 10.5 | 10.0 – 14.0 | 10.0 – 14.0 |
| Molybdenum (Mo) | — | 2.0 – 3.0 | 2.0 – 3.0 |
| Manganese (Mn) | ≤ 2.0 | ≤ 2.0 | ≤ 2.0 |
| Silicon (Si) | ≤ 1.0 | ≤ 1.0 | ≤ 1.0 |
| Phosphorus (P) | ≤ 0.045 | ≤ 0.045 | ≤ 0.045 |
| Sulfur (S) | ≤ 0.030 | ≤ 0.030 | ≤ 0.030 |
2.2 Mechanical Properties
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (抗拉强度) | ≥ 520 MPa (75,400 psi) | ASTM A213 / GB/T 12771 |
| Yield Strength (屈服强度) | ≥ 205 MPa (29,700 psi) | ASTM A213 / GB/T 12771 |
| Elongation (延伸率) | ≥ 35% | ASTM A213 |
| Hardness (硬度) | ≤ 250 HV (Brinell) | ASTM A262 |
| Corrosion Resistance (耐腐蚀性) | PASS — 72h Salt Spray (ASTM B117); Pitting Resistance Index (PREN) ≥ 24 (316L) | ASTM B117 / ISO 9227 |
| Thermal Stability (热稳定性) | Stable up to 870°C (1,598°F); Sensitization resistance (316L) to 450–850°C | ASTM A213 |
| Fatigue Endurance Limit (疲劳极限) | ≥ 280 MPa (cyclic loading, 10⁷ cycles) | ASTM E466 |
3. Dimensions & Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD, 外径) | 6.0 mm – 50.8 mm (¼" – 2") | ASTM A213 / GB/T 12771 |
| Wall Thickness (壁厚) | 0.3 mm – 3.0 mm | ASTM A213 |
| Coil Length (盘管长度) | Up to 2,000 m per coil (continuous) | Manufacturer specification |
| Coil Weight (盘重) | Up to 3,000 kg per coil | Manufacturer specification |
| Surface Finish (表面状态) | Pickled & Passivated (酸洗钝化); Mirror polish available on request | ASTM A478 / ASTM A967 |
| Manufacturing Process (制造工艺) | Continuous Hot/Fine Cold Rolling (连续热轧/冷轧) → Cold Drawing (冷轧拔) | ASTM A213 |
| Heat Treatment (热处理) | Solution Annealing (固溶退火) at 1010–1150°C, water quenched | ASTM A213 |
| Dimensional Tolerance (尺寸公差) | OD: ±0.1 mm; Wall: ±0.05 mm (per ASTM A213) | ASTM A213 |
| End Form (端部形式) | Plain cut ends; Beveled ends available upon request | — |
| Operating Temperature Range (工作温度范围) | −196°C to +870°C (−320°F to +1,598°F) | ASTM A213 |
| Maximum Working Pressure (最大工作压力) | Dependent on OD and wall thickness; typically ≤ 16 MPa | GB/T 12771 / EN 10217 |
4. Manufacturing Process
The production of Wenzhou Jixing's stainless steel coil tubes follows a rigorous, multi-stage manufacturing pipeline designed to ensure metallurgical integrity, dimensional accuracy, and surface quality:
- Raw Material Preparation (原材料准备): High-purity stainless steel billets or slabs are selected from certified suppliers, with incoming chemical composition verified via Optical Emission Spectroscopy (OES) and Positive Material Identification (PMI).
- Continuous Rolling (连续轧制): The material undergoes hot rolling (热轧) or fine cold rolling (冷轧) to produce continuous tube blanks with uniform cross-sectional geometry. The coil form is maintained throughout the process to minimize deformation and residual stress.
- Cold Drawing (冷轧拔): Precision cold drawing is employed to achieve exact dimensional tolerances and enhanced surface finish. This step also introduces beneficial strain hardening, improving tensile and yield strength.
- Solution Annealing (固溶退火): Tubes are heated to 1010–1150°C in a controlled atmosphere furnace and rapidly water-quenched to dissolve carbides, restore full austenitic structure, and maximize corrosion resistance.
- Pickling & Passivation (酸洗钝化): Surface scale and oxide layers are removed via controlled acid pickling, followed by passivation treatment to form a protective chromium oxide (Cr₂O₃) passive film, enhancing long-term corrosion resistance.
- Quality Inspection & Testing (质量检测): Every production batch undergoes comprehensive testing including hydrostatic pressure testing (水压试验), ultrasonic flaw detection (超声波探伤), dimensional measurement, surface inspection, and mechanical property verification.
- Coiling & Packaging (盘卷包装): Finished tubes are coiled at controlled tension to prevent kinking or ovality, wrapped in protective film, and packaged for shipment.
5. Applications
The stainless steel coil tube from Wenzhou Jixing Metal Materials Co., Ltd. is engineered for demanding service environments and finds widespread application across multiple industries:
- Fan Coil Units (风机盘管): Primary application — the coil tube serves as the heat exchanger core in commercial and residential FCUs, providing efficient thermal transfer in HVAC systems. The product's design directly addresses the exhaust valve cracking issue identified in field analyses, through improved material selection, optimized wall thickness, and enhanced fatigue resistance.
- HVAC Systems (暖通空调系统): Refrigerant and water circulation piping in air handling units, chillers, and condenser units.
- Exhaust Valve Assemblies (排气阀组件): The coil tube's superior fatigue endurance and corrosion resistance make it ideal for exhaust valve bodies and connections in FCU systems, mitigating the cracking failure modes documented in technical case studies.
- Food & Beverage Industry (食品饮料行业): Sanitary process piping for milk, beverage, and pharmaceutical processing plants where hygienic surface finish and corrosion resistance are critical.
- Chemical & Petrochemical (化工行业): Transfer lines for aggressive chemical fluids requiring molybdenum-enhanced corrosion resistance (316/316L grades).
- Medical Equipment (医疗设备): Piping for sterilization systems, medical gas delivery, and diagnostic equipment.
- Marine & Coastal Applications (海洋工程): Seawater circulation systems and offshore platform piping where chloride-induced pitting corrosion is a concern.
- Automotive & Aerospace (汽车与航空航天): Exhaust systems, fuel lines, and hydraulic circuit components requiring high temperature and fatigue resistance.
6. Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and holds the following certifications and complies with the following international and national standards:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System (质量管理体系认证) |
| ISO 14001:2015 | Environmental Management System (环境管理体系认证) |
| ISO 45001:2018 | Occupational Health & Safety Management System (职业健康安全管理体系认证) |
| CE Marking | European Conformity — compliance with applicable EU directives |
| ASTM A213 | Standard Specification for Seamless Austenitic Stainless Steel Tubing for High Temperature Service |
| ASTM A269 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Heat-Transfer Service |
| GB/T 12771 | Chinese National Standard — Stainless Steel Seamless Tubes for General Purposes |
| EN 10217 | European Standard — Heat-Resistant, Stain-Resistant and Acid-Resistant Steels and Alloys |
| GB/T 4237 | Chinese National Standard — Cold-Rolled Stainless Steel Sheets and Strips |
7. Unique Selling Points & Technical Advantages
"Engineered for Reliability — Designed to Eliminate Failure Modes"
- Crack Resistance Optimized (抗裂优化): Based on extensive field failure analysis of fan coil