Stainless Steel Coil Tube for Fan Coil Unit (FCU) Systems
Product Overview
The Stainless Steel Coil Tube (盘管 Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular component designed for integration into Fan Coil Unit (FCU) air conditioning systems and related hydronic heat exchange applications. This product serves as the core heat transfer element within air-side cooling and heating systems, facilitating efficient thermal exchange between circulating refrigerant or chilled water and ambient air drawn through the unit.
Coil tubes are fundamental to the operational performance of fan coil units, which are widely deployed in commercial buildings, hospitals, hotels, and industrial facilities for localized climate control. The coil tube's geometry, material composition, and manufacturing tolerances directly determine the air-side cooling capacity (风侧冷量), thermal efficiency, and long-term durability of the complete FCU assembly.
Material & Properties
Base Material
The coil tube is fabricated from high-grade austenitic stainless steel, primarily conforming to the following grades:
- SUS 304 (UNS S30408) — The standard grade offering excellent corrosion resistance, formability, and weldability for general HVAC applications.
- SUS 316 (UNS S31608) — Enhanced grade with molybdenum addition for superior resistance to chlorides and aggressive environments, suitable for coastal or industrial settings.
- SUS 321 (UNS S32100) — Stabilized grade with titanium addition for improved resistance to intergranular corrosion at elevated temperatures.
Mechanical & Physical Properties
- Yield Strength (屈服强度): ≥ 205 MPa (SUS 304), ≥ 275 MPa (SUS 316)
- Tensile Strength (抗拉强度): ≥ 520 MPa (SUS 304), ≥ 580 MPa (SUS 316)
- Elongation (延伸率): ≥ 40%
- Thermal Conductivity (导热系数): 16.3 W/(m·K) at 20°C
- Corrosion Resistance (耐腐蚀性): Excellent resistance to atmospheric, chemical, and food-grade corrosion environments
- Operating Temperature Range (工作温度范围): −196°C to +870°C
- Surface Roughness (表面粗糙度): Ra ≤ 0.8 μm (inner surface), Ra ≤ 1.6 μm (outer surface)
Specifications
| Parameter (参数) | Specification (规格) | Standard / Reference |
|---|---|---|
| Product Name (产品名称) | Stainless Steel Coil Tube (盘管) | — |
| Series No. (序号) | 1237 | — |
| Outer Diameter (外径, OD) | Φ6.0 mm, Φ7.0 mm, Φ8.0 mm, Φ9.53 mm (⅜"), Φ12.7 mm (½") | ASTM A269 / EN 10217-7 |
| Wall Thickness (壁厚) | 0.5 mm, 0.6 mm, 0.8 mm, 1.0 mm | ASTM A269 |
| Coil Pitch (盘管间距) | 12 mm, 15 mm, 19 mm, 25 mm (customizable) | ISO 13935 |
| Coil Length (盘管长度) | Up to 3000 mm (continuous forming) | — |
| Number of Rows (排数) | 1–8 rows (configurable) | — |
| Material Grade (材质牌号) | SUS 304 / SUS 316 / SUS 321 | ASTM A269 / GB/T 12771 |
| Surface Finish (表面处理) | Pickled & Passivated (酸洗钝化), Mirror Polish (optional) | GB/T 8170 |
| End Preparation (端部处理) | Flat cut, Beveled, or Threaded | — |
| Max. Operating Pressure (最大工作压力) | 1.6 MPa (standard), 2.5 MPa (reinforced) | GB/T 12771 |
| Max. Operating Temperature (最高工作温度) | +200°C (standard), +450°C (SUS 321) | — |
| Welding Method (焊接方式) | TIG (GTAW) / Laser Welding / Brazing | ASME Section IX |
| Hydrostatic Test Pressure (水压试验压力) | 2.5× working pressure, hold for ≥ 30 seconds | GB/T 12771 |
| Dimensional Tolerance (尺寸公差) | OD: ±0.05 mm; Wall: ±0.03 mm; Pitch: ±0.5 mm | ISO 286 / ASME B36.19M |
| Packaging (包装) | Wooden crate with desiccant, protective end caps | ISO 4180 |
Manufacturing Process
1. Raw Material Procurement & Inspection
Hot-rolled stainless steel coil strip is sourced from certified mills (e.g., POSCO, Outokumpu, Taigang) with full material test certificates (MTC) conforming to ASTM A269 or GB/T 12771. Incoming material undergoes 100% visual inspection, dimensional verification, and spot chemical composition analysis via Optical Emission Spectroscopy (OES).
2. Coil Strip Forming & Welding
The flat strip is fed through a precision roll-forming die set to create the desired tube cross-section. Seams are welded using continuous TIG (Tungsten Inert Gas) welding or high-frequency induction welding, with argon gas back protection to prevent internal oxidation. Weld quality is verified by X-ray or eddy current testing per ASME Section IX.
3. Cold Drawing & Sizing
Welded tube undergoes cold drawing through calibrated die sets to achieve precise outer diameter, wall thickness, and roundness tolerances. This process enhances mechanical properties and improves surface finish quality.
4. Pickling & Passivation (酸洗钝化)
The drawn tube is subjected to pickling in a mixed acid solution (nitric acid + hydrofluoric acid) to remove surface oxides and contaminants. Subsequent passivation with a citric acid or nitric acid solution forms a stable chromium oxide passive film, enhancing corrosion resistance. Passivation effectiveness is verified by the copper sulfate spot test per ASTM A967.
5. Coiling & Heat Exchanger Assembly
The processed tube is coiled into the specified geometry using a CNC-controlled coil winding machine. Fin tubes (if applicable) are expanded or welded to the tube outer surface using mechanical expansion (胀管) or orbital TIG welding. Header connections are fabricated and welded to complete the coil assembly.
6. Final Quality Assurance
Each coil tube assembly undergoes:
- Hydrostatic Pressure Test (水压试验): 2.5× maximum working pressure for ≥ 30 seconds, zero leakage permitted.
- Dimensional Inspection (尺寸检验): Coordinate Measuring Machine (CMM) verification of coil pitch, row alignment, and overall dimensions.
- Visual & Surface Inspection (外观检验): 100% visual examination under controlled lighting for weld defects, surface imperfections, or passivation anomalies.
- Leak Detection (气密性检测): Helium mass spectrometry or nitrogen bubble testing for micro-leak verification.
Applications
The Stainless Steel Coil Tube is integral to the following application domains:
- Fan Coil Unit (FCU) Systems (风机盘管空调系统): Primary heat exchange element in air-side cooling capacity measurement systems. The coil tube's thermal performance directly determines the measured air-side cooling load (风侧冷量), making precise manufacturing tolerances critical for accurate HVAC system commissioning and energy management.
- Commercial HVAC Systems (商用暖通空调系统): Air handling units (AHU), rooftop units (RTU), and packaged terminal units (PTU) in office buildings, shopping malls, and hotels.
- Medical & Pharmaceutical Facilities (医药洁净工程): Cleanroom HVAC systems requiring hygienic-grade stainless steel components with minimal particulate generation.
- Food & Beverage Processing (食品饮料加工): Cooling coils for process equipment where corrosion resistance and washdown compatibility are mandatory.
- Marine & Offshore Applications (海洋工程): HVAC systems on vessels and offshore platforms where chloride-induced corrosion resistance (SUS 316) is essential.
- Industrial Process Cooling (工业过程冷却): Chilled water coils for process temperature control in manufacturing facilities.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains the following certifications and adheres to international standards:
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- ISO 45001:2018 — Occupational Health & Safety Management System
- CE Marking (EU) — Compliance with European Pressure Equipment Directive (PED 2014/68/EU)
- ASME Stamp (US) — Section VIII, Division 1 (where applicable)
- GB/T 12771 — Chinese National Standard for seamless and welded stainless steel tubes
- ASTM A269 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubes for Chemical and Heat-Transfer Equipment
- EN 10217-7 — European Standard for austenitic stainless steel tubes for pressure purposes
- Third-Party Testing — SGS, BV, or TÜV inspection available upon request
Unique Selling Points
- Precision Coil Geometry: CNC-controlled coiling ensures uniform pitch accuracy (±0.5 mm), optimizing airflow distribution and air-side cooling capacity measurement reliability per the methodology outlined in《风机盘管空调系统风侧冷量计量方法研究》.
- Enhanced Corrosion Longevity: Pickled and passivated stainless steel construction provides service life exceeding 25 years, significantly outperforming copper or aluminum alternatives in corrosive environments.
- Hygienic Interior Surface: Mirror-polish option (Ra ≤ 0.4 μm) available for pharmaceutical and food-grade applications, preventing biofilm accumulation and facilitating CIP (Clean-In-Place) protocols.
- Custom Engineering Capability: Full customization of coil geometry, row count, fin configuration, and header design to match specific thermal load requirements and spatial constraints.
- Traceable Material Provenance: Complete Mill Test Certificate (MTC) documentation with heat-number traceability from raw coil to finished assembly.
- Integrated Testing & Commissioning Support: On-site or laboratory air-side cooling capacity verification testing aligned with GB/T 19232 and ASHRAE Standard 17 standards.
Note: This product specification is derived from technical knowledge points associated with the study of air-side cooling capacity measurement methods for Fan Coil Unit (FCU) air conditioning systems. The coil tube's dimensional precision, thermal properties, and surface condition are critical parameters in ensuring accurate and repeatable air-side cooling load measurement in accordance with established metrological methodologies.