Stainless Steel Coil Tube — HVAC Fan Coil Unit Grade
1. Product Overview
The Stainless Steel Coil Tube (盘管/Coil Tube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed for integration into HVAC (Heating, Ventilation, and Air Conditioning) systems, particularly partition-type fan coil unit (FCU) workstation air conditioning systems. These coil tubes serve as the core heat exchange elements, facilitating efficient thermal transfer between refrigerant or hydronic media and ambient air. The product is engineered to meet rigorous performance standards in commercial, industrial, and residential climate control applications, with a focus on optimized airflow organization, pressure drop minimization, and long-term corrosion resistance.
2. Material & Properties
The coil tubes are fabricated from high-grade austenitic stainless steel, primarily conforming to the following material specifications:
- Primary Grades: SUS304 (UNS S30400), SUS316L (UNS S31603), and SUS321 (UNS S32100)
- Alloy Composition (SUS304): Carbon ≤ 0.08%, Chromium 18.0–20.0%, Nickel 8.0–10.5%, Manganese ≤ 2.0%, Silicon ≤ 1.0%
- Alloy Composition (SUS316L): Carbon ≤ 0.03%, Chromium 16.0–18.0%, Nickel 10.0–14.0%, Molybdenum 2.0–3.0%
- Mechanical Properties: Tensile strength ≥ 520 MPa (SUS304), Yield strength ≥ 205 MPa, Elongation ≥ 40%
- Corrosion Resistance: Excellent resistance to atmospheric, chemical, and intergranular corrosion; pitting resistance equivalent number (PREN) ≥ 24 for SUS316L
- Thermal Conductivity: Approximately 16.3 W/(m·K) at 20°C
- Operating Temperature Range: −196°C to +870°C (SUS304), −273°C to +427°C (SUS316L)
- Surface Finish: 2B finish, BA (Bright Annealed) finish, or custom polishing to Ra ≤ 0.4 μm
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm (1/4"), 9.52 mm (3/8"), 12.7 mm (1/2"), 15.88 mm (5/8"), 19.05 mm (3/4"), 25.4 mm (1") | ASTM A269 / ASTM A213 |
| Wall Thickness | 0.5 mm – 2.0 mm (customizable) | EN 10217-7 / GB/T 12771 |
| Coil Pitch | 10 mm – 50 mm (adjustable based on thermal load requirements) | Manufacturer Specification |
| Coil Diameter | 150 mm – 600 mm (custom coil configuration available) | ISO 11612 |
| Tube Length (Coiled) | 5 m – 50 m per coil (continuous lengths available upon request) | — |
| Bend Radius (Minimum) | ≥ 3D (3 × outer diameter) for cold bending | ASTM A269, Section 6 |
| Heat Exchanger Efficiency | U-value: 450 – 850 W/(m²·K) (depending on configuration) | ASHRAE Standard 15 |
| Pressure Rating | Up to 1.6 MPa (design pressure); 2.4 MPa (hydrostatic test) | EN 12163 / GB/T 15386 |
| Flow Velocity (Maximum) | 3.0 m/s (hydronic); 15 m/s (refrigerant) | ASHRAE Handbook — HVAC Systems and Equipment |
| Finish Options | 2B, BA, No.4 Polished, Mirror Polished (Ra ≤ 0.1 μm) | ASTM A480 / GB/T 4237 |
| Welding Method | Full-penetration TIG (Tungsten Inert Gas) welding; orbital welding for high-integrity joints | ASME Section IX / EN 12544 |
| Coating (Optional) | PVD (Physical Vapor Deposition) passivation layer; electropolished surface | — |
4. Manufacturing Process
The production of these stainless steel coil tubes follows a rigorous multi-stage manufacturing workflow to ensure dimensional accuracy, metallurgical integrity, and thermal performance:
- Raw Material Procurement & Inspection: Cold-rolled stainless steel strip is sourced from certified mills and subjected to incoming inspection including spectrographic analysis (OES), chemical composition verification, and mechanical property testing.
- Precision Forming & Welding: The strip is fed through high-precision roll-forming dies to achieve the target tube geometry. Seam welding is performed using high-frequency induction welding (HF) or laser welding, followed by internal and external weld bead grinding to achieve uniform wall thickness.
- Heat Treatment & Stress Relief: Tubes undergo solution annealing at 1050–1150°C in a controlled atmosphere (argon or vacuum) to eliminate residual stresses, restore full austenitic microstructure, and ensure intergranular corrosion resistance. This step is critical for achieving the mechanical and corrosion properties specified above.
- Precision Coiling: The straight tube sections are coiled using CNC-controlled coiling machines to achieve exact coil pitch, coil diameter, and number of turns. The coiling process is monitored via laser displacement sensors to ensure geometric consistency within ±0.5 mm tolerance.
- Bending & Header Integration: U-bends are formed at the coil ends using precision bending equipment with controlled bend radius and springback compensation. Header tubes (inlet/outlet manifolds) are welded to the coil ends using TIG welding with helium backing gas to prevent oxidation of the inner weld surface.
- Surface Treatment & Passivation: The finished coil tube assembly undergoes acid pickling and passivation treatment to remove mill scale, welding discoloration, and chromium-depleted zones, forming a protective chromium oxide passive film (Cr₂O₃) on the surface.
- Final Testing & Quality Assurance: Each unit undergoes hydrostatic pressure testing (1.5× design pressure, held for 30 minutes), dimensional inspection, visual inspection of weld seams, and (optionally) dye penetrant testing (PT) or eddy current testing (ET) for defect detection.
5. Applications
These stainless steel coil tubes are engineered for demanding thermal management applications, with particular emphasis on the following sectors:
- Commercial HVAC Systems: Partition-type fan coil units (FCU) for office workstations, open-plan offices, and commercial spaces. The coil tubes serve as the primary evaporator or condenser heat exchange elements, enabling efficient temperature and humidity control with optimized airflow organization across workstations.
- Industrial Process Cooling: Heat exchange in chemical processing, pharmaceutical manufacturing, and food-grade applications where corrosion resistance and hygiene standards are critical.
- Refrigeration Systems: Evaporator and condenser coils in commercial refrigeration units, cold storage facilities, and industrial chillers.
- Automotive & Transportation: Compact heat exchanger coils for vehicle air conditioning systems and thermal management in rail transit.
- Medical & Laboratory Equipment: Precision temperature control in medical devices, laboratory incubators, and cleanroom HVAC systems where biocompatibility and corrosion resistance are paramount.
- Renewable Energy Systems: Heat recovery coils in building energy management systems and thermal storage applications.
Key Application Context — Partition-Type Fan Coil Unit Systems: Numerical simulations and computational fluid dynamics (CFD) analyses of partition-type fan coil unit workstation systems have demonstrated that the geometry, pitch, and material properties of the coil tube directly influence airflow organization, temperature uniformity, and energy consumption. The optimized coil tube design from Wenzhou Jixing Metal Materials Co., Ltd. contributes to reduced pressure drops, improved heat transfer coefficients, and enhanced thermal comfort at the workstation level.
6. Quality Certifications & Compliance
All products are manufactured and tested in accordance with the following international and national standards:
- ISO 9001:2015 — Quality Management System certification
- ISO 14001:2015 — Environmental Management System certification
- ASTM A269 / A213 — Standard specification for wrought austenitic stainless steel seamless, welded, and heavily cold-worked tubing for high-temperature service
- EN 10217-7 — Technical delivery conditions for seamless and welded cold-drawn stainless steel tubes for mechanical and thermal applications
- GB/T 12771 — Technical requirements for seamless stainless steel tubes for general purposes (Chinese National Standard)
- ASME BPV Code — Boiler and Pressure Vessel Code compliance (for pressure-containing applications)
- ASME Section IX — Welding, brazing, and soldering qualifications
- EN 12163 / GB/T 15386 — Pressure parts for refrigerating systems and heat pumps
- CE Marking — Conformity with European directives for product safety
- RoHS Compliance — Restriction of Hazardous Substances directive adherence
7. Unique Selling Points
- Superior Corrosion Resistance: The austenitic stainless steel construction provides exceptional resistance to condensation corrosion, chemical attack, and microbial growth — critical for long service life in humid HVAC environments.
- Precision Geometric Control: CNC-controlled coiling and bending processes ensure coil pitch uniformity within ±0.5 mm, directly contributing to consistent airflow distribution and thermal performance in fan coil unit applications.
- Optimized Heat Transfer Performance: Smooth inner bore surfaces (Ra ≤ 0.4 μm) minimize flow resistance and fouling, maximizing the overall heat transfer coefficient (U-value) and reducing energy consumption.
- Hygienic Welding: Full-penetration TIG welding with helium backing ensures oxidation-free internal weld surfaces, eliminating dead zones for microbial contamination in food-grade and pharmaceutical applications.
- Custom Engineering Capability: Flexible customization of coil diameter, pitch, tube dimensions, and header configurations to meet specific thermal load and spatial constraints of end-user applications.
- Comprehensive Testing Protocol: Every production batch undergoes hydrostatic pressure testing, dimensional verification, and material certification traceability, ensuring full quality assurance from raw material to finished product.
8. Technical Notes
Note 1: When integrating these coil tubes into partition-type fan coil unit workstation systems, CFD (Computational Fluid Dynamics) simulation should be employed to optimize the coil tube orientation, fin spacing, and airflow path to achieve uniform temperature distribution and minimize stratification effects at the workstation level.
Note 2: For applications involving aggressive chemical media or marine environments, SUS316L grade with molybdenum content ≥ 2.0% is recommended for enhanced pitting and crevice corrosion resistance.
Note 3: All dimensional specifications are nominal values. Custom configurations are available upon submission of detailed engineering drawings and thermal performance requirements to the manufacturer's technical team.