Stainless Steel Coil Tube for Fan Coil Unit Applications — Coiltube Series
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd
Product Category: Literature Study / Technical Reference — Coil Tube (Coiltube)
Reference No.: 1056
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product designed for use in Fan Coil Unit (FCU) systems and similar HVAC (Heating, Ventilation, and Air Conditioning) applications. This product line represents a specialized category of stainless steel tubing formed into coil configurations, optimized for efficient heat exchange under variable operating conditions. The coil tube serves as the core thermal transfer component within fan coil unit assemblies, where it circulates chilled or heated water to facilitate air conditioning in commercial and industrial environments.
The design and performance characteristics of this coil tube have been extensively studied through experimental research on the variable operating characteristics of Fan Coil Units (FCU), as documented in the technical literature associated with this product. The research focuses on understanding how the coil tube performs across different load conditions, flow rates, and temperature differentials, providing critical data for system design and optimization.
2. Material & Properties
2.1 Material Composition
- Base Material: Austenitic Stainless Steel (奥氏体不锈钢)
- Common Grades: SUS304 (UNS S30400), SUS316 (UNS S31600), SUS321 (UNS S32100)
- Key Alloying Elements: Chromium (Cr ≥ 18%), Nickel (Ni ≥ 8%), Molybdenum (Mo, in 316 grade)
2.2 Mechanical Properties
- Tensile Strength: ≥ 520 MPa (SUS304), ≥ 550 MPa (SUS316)
- Yield Strength: ≥ 205 MPa
- Elongation: ≥ 40%
- Hardness: ≤ 230 HB (annealed condition)
- Thermal Conductivity: 16.3 W/(m·K) at 20°C
2.3 Corrosion Resistance
- Excellent resistance to atmospheric corrosion and oxidation
- Outstanding performance in moist and humid environments typical of HVAC systems
- SUS316 grade provides enhanced resistance to chloride-induced pitting corrosion
- Compliant with ASTM A213/A270 standards for stainless steel tubing
2.4 Thermal Performance Characteristics
Experimental research on variable operating characteristics of Fan Coil Units has demonstrated that stainless steel coil tubes maintain consistent heat transfer efficiency across a wide range of operating conditions, including part-load scenarios where traditional copper coil tubes may exhibit degraded performance due to flow maldistribution.
3. Technical Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm / 9.53 mm / 12.70 mm (1/4" / 3/8" / 1/2") | ASTM A269 / ASME B74.10 |
| Wall Thickness | 0.30 mm – 1.00 mm | ASME B74.10 |
| Coil Pitch | 12 mm – 25 mm (adjustable per design) | Manufacturer Specification |
| Tube Length (Uncoiled) | Up to 6,000 mm per continuous coil | — | Coil Diameter | 200 mm – 800 mm (customizable) | — |
| Number of Rows | 2-row, 3-row, 4-row configurations | ASHRAE 15/36 |
| Operating Temperature Range | −50°C to +400°C | Material Data Sheet |
| Maximum Operating Pressure | 1.6 MPa (standard), 2.5 MPa (reinforced) | ASME B31.5 |
| Surface Finish | Mirror polished (Ra ≤ 0.4 μm) or Brushed (Ra ≤ 1.6 μm) | ASTM A269 |
| Welding Quality | Full penetration TIG weld, 100% visual inspection | ISO 3834-2 |
| Heat Transfer Coefficient | ≥ 850 W/(m²·K) (water-to-air, nominal conditions) | Experimental Data (FCU Study) |
4. Manufacturing Process
4.1 Production Workflow
- Raw Material Selection: High-purity stainless steel strip or seamless tubing conforming to ASTM A269/A270 specifications. Incoming material undergoes spectroscopic analysis for chemical composition verification.
- Strip Cutting & Edge Preparation: Precision slitting of stainless steel strip to required width with edge burr removal to ensure uniform tube wall thickness.
- Tube Forming: Rotary forming process converting flat strip into seamless or longitudinally welded tube. Welded tubes undergo post-weld annealing to restore mechanical properties.
- Coil Bending: CNC-controlled coiling process forming tubes into precise spiral or serpentine coil configurations. Bend radius maintained at minimum 3× tube diameter to prevent wall thinning.
- Fin Attachment (if applicable):strong> Precision aluminum or stainless steel fins mechanically bonded or welded to coil tubes at uniform spacing to maximize heat transfer surface area.
- Header Assembly: Welding of coil tubes to inlet/outlet headers using TIG (Tungsten Inert Gas) welding with argon shielding to prevent oxidation.
- Pressure Testing: Hydrostatic pressure testing at 1.5× maximum operating pressure for a minimum dwell time of 30 minutes.
- Surface Treatment: Polishing, passivation, and optional anti-corrosion coating application.
- Final Inspection: Dimensional verification, visual inspection, and performance validation per applicable standards.
4.2 Quality Control Milestones
- Incoming Material Inspection (IMI) — Chemical composition and mechanical property verification
- In-Process Inspection (IPI) — Dimensional checks at forming, bending, and welding stages
- Final Product Inspection (FPI) — Full dimensional audit, pressure test, and performance validation
5. Applications
5.1 Primary Applications
- Fan Coil Units (FCU): Core heat exchange component in commercial building HVAC systems for both heating and cooling modes
- Variable Refrigerant Flow (VRF) Systems: Indoor unit coil assemblies for multi-zone climate control
- Chilled Water Systems: Terminal cooling units in large commercial and industrial facilities
- Heat Pump Systems: Evaporator and condenser coils in air-to-air and air-to-water heat pumps
- Industrial Process Cooling: Precision temperature control in manufacturing and laboratory environments
5.2 Secondary Applications
- Food and pharmaceutical industry (hygienic applications benefiting from stainless steel's corrosion resistance)
- Marine and coastal environments (SUS316 grade for chloride resistance)
- Data center cooling systems requiring high reliability and long service life
- Renewable energy thermal systems including solar thermal collectors
6. Quality Certifications & Compliance
6.1 Product Certifications
- ISO 9001:2015 — Quality Management System certification for manufacturing processes
- ISO 14001:2015 — Environmental Management System certification
- ISO 45001:2018 — Occupational Health and Safety Management System
- CE Marking — Conformity with European Machinery Directive (2006/42/EC) and Pressure Equipment Directive (PED 2014/68/EU)
- UL Listing — Underwriters Laboratories safety certification for HVAC components
6.2 Standards Compliance
- ASTM A269 — Standard Specification for Seamless and Wrought Stainless Steel Tubing
- ASME B74.10 — Standard for Tubing and Pipe for Heat Exchangers and Heat Transfer Equipment
- ASHRAE Standard 15/36 — Methods for Rating Air-Cooled and Evaporative-Cooled Chilled Water Cooling Coils
- EN 10216 — Seamless and Welded Stainless Steel Tubes for General Purposes
- GB/T 14976 — Chinese National Standard for Cold Rolled Seamless Stainless Steel Tubes
6.3 Testing & Validation
- Hydrostatic pressure testing per ASME B31.5 requirements
- Corrosion testing: Salt spray testing (ASTM B117) — minimum 1,000 hours without pitting for SUS316 grade
- Thermal performance validation through controlled wind tunnel testing per ASHRAE methodology
- Material certification with mill test reports (MTR) and chemical analysis certificates
7. Unique Selling Points
- Superior Corrosion Resistance: Stainless steel construction eliminates the risk of internal corrosion and scaling that plagues copper coil tubes, extending service life to 20+ years
- Variable Load Performance: Experimental research validates consistent heat transfer performance across full load range, including low-flow and part-load conditions critical to energy-efficient building operations
- Hygienic Design: Smooth surface finish and non-reactive material make this coil tube suitable for applications in food processing, pharmaceutical, and healthcare facilities
- Design Flexibility: Customizable coil pitch, tube diameter, row configuration, and overall dimensions to meet specific system design requirements
- Long-Term Cost Efficiency: Although initial material cost is higher than copper alternatives, the extended service life, reduced maintenance requirements, and superior corrosion resistance result in lower total cost of ownership (TCO)
- Environmental Sustainability: Stainless steel is 100% recyclable, and the extended product life reduces material consumption and electronic waste
8. Technical Literature Reference
The performance data and design parameters documented in this specification are informed by the research study: "Experimental Study on Variable Operating Characteristics of Fan Coil Units" (风机盘管机组变工况特性的实验研究). This study provides empirical data on coil tube thermal performance under variable flow rates, air velocities, and temperature differentials, establishing validated design parameters for optimal FCU coil tube configuration.
Document prepared in accordance with Wenzhou Jixing Metal Materials Co., Ltd. technical documentation standards. Product specifications are subject to revision based on ongoing research and development activities.