Stainless Steel Coil Tube for FFU Clean Air Conditioning Systems
Product Catalog No.: 1165 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
1. Product Overview
The Stainless Steel Coil Tube (盘管) is a precision-engineered tubular component designed specifically for the coil assemblies within FFU (Fan Filter Unit) Clean Air Conditioning Systems used in high-purity electronic manufacturing environments. These coil tubes serve as the primary heat exchange elements in evaporator and condenser coils, enabling precise temperature and humidity control within Class 1–Class 100 cleanrooms as defined by FED-STD-209E and ISO 14644-1 standards.
Unlike conventional coil tubes used in general HVAC applications, the stainless steel coil tubes produced by Wenzhou Jixing Metal Materials Co., Ltd. are engineered to meet the stringent contamination-control, corrosion-resistance, and thermal-performance requirements of semiconductor fabrication, photolithography, flat-panel display manufacturing, and other ultra-clean industrial processes. The coiled configuration maximizes surface area-to-volume ratio, ensuring efficient heat transfer while minimizing refrigerant volume and system footprint.
2. Material & Properties
2.1 Base Material
The coil tubes are manufactured from austenitic stainless steel, predominantly conforming to the following grades:
- SAE 304 (UNS S30408) — General-purpose austenitic stainless steel offering excellent corrosion resistance and formability. Composition: 18–20% Cr, 8–10% Ni, ≤0.08% C.
- SAE 316 (UNS S31608) — Enhanced molybdenum-bearing austenitic grade providing superior resistance to pitting and crevice corrosion in aggressive chemical environments. Composition: 16–18% Cr, 10–14% Ni, 2–3% Mo, ≤0.08% C.
- SAE 316L (UNS S31603) — Low-carbon variant of 316 (≤0.03% C) designed to prevent intergranular corrosion during welding operations.
2.2 Mechanical Properties
| Property | SAE 304 | SAE 316 / 316L |
|---|---|---|
| Tensile Strength (ASTM A270) | ≥ 515 MPa (75 ksi) | ≥ 515 MPa (75 ksi) |
| Yield Strength (0.2% Offset) | ≥ 205 MPa (30 ksi) | ≥ 205 MPa (30 ksi) |
| Elongation (50 mm gauge length) | ≥ 40% | ≥ 40% |
| Density | 7.93 g/cm³ | 8.00 g/cm³ |
| Thermal Conductivity (20 °C) | 16.3 W/(m·K) | 14.6 W/(m·K) |
| Thermal Expansion Coefficient (20–100 °C) | 17.3 × 10⁻⁶ /K | 16.0 × 10⁻⁶ /K |
| Specific Heat Capacity | 500 J/(kg·K) | 500 J/(kg·K) |
| Electrical Resistivity (20 °C) | 7.2 × 10⁻⁷ Ω·m | 6.3 × 10⁻⁷ Ω·m |
2.3 Surface Finish & Cleanliness
The internal and external surfaces of the coil tubes undergo rigorous cleaning and polishing to achieve a surface roughness of Ra ≤ 0.5 μm (electropolished) or Ra ≤ 1.6 μm (mechanically polished), ensuring minimal particle generation and facilitating efficient airflow across the coil bundle. Internal surfaces are passivated using citric acid or nitric acid solutions per ASTM A967 to restore and enhance the passive chromium oxide film.
3. Specifications
| Parameter | Specification |
|---|---|
| Tube Outer Diameter (OD) | 6.35 mm (1/4"), 9.52 mm (3/8"), 12.7 mm (1/2"), 15.88 mm (5/8") |
| Tube Wall Thickness | 0.5 mm – 1.5 mm (customizable) |
| Coil Bend Diameter | Min. 2.0 × OD (cold-bent); Min. 1.5 × OD (hot-bent) |
| Coil Pitch (Turn Spacing) | 12 mm – 25 mm (adjustable per heat exchanger design) |
| Coil Length (Total Tube Length) | 1 m – 50 m per coil (custom lengths available) |
| Coil Winding Direction | Left-hand or Right-hand helical (per customer specification) |
| Operating Pressure | Up to 2.5 MPa (365 psi) for refrigerant circuits |
| Operating Temperature Range | −40 °C to +250 °C |
| Refrigerant Compatibility | R-134a, R-410A, R-404A, R-407C, R-32, Ammonia (NH₃) |
| Surface Treatment | Electropolished / Mechanically polished / Passivated |
| End Finishing | Deburred, chamfered, capped (plastic or metal plugs) |
| Packaging | Anti-static polyethylene wrapping; wooden crates for export |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Inspection: Incoming stainless steel seamless tubes or welded tubes undergo spectroscopic analysis (OES) for chemical composition verification and dimensional gauging per ASTM A213 or ASTM A269 standards.
- Cutting & Straightening: Tubes are cut to required lengths using precision band saws and straightened via rotary or pneumatic straightening machines to achieve straightness tolerance of ≤ 0.5 mm/m.
- Internal Cleaning & Passivation: Tubes are cleaned using ultrasonic baths with alkaline degreasers, followed by acid pickling and passivation to remove mill scale, oils, and contaminants.
- Coil Forming (Bending): Tubes are formed into helical coils using CNC-controlled rotary draw bending machines. The bending process is performed at controlled temperatures (cold for SAE 304; warm at 100–200 °C for SAE 316) to prevent work-hardening cracking and maintain dimensional accuracy.
- Dimensional Inspection: Each coil is inspected for OD uniformity, wall thickness, bend radius consistency, pitch accuracy, and overall length using laser scanning and coordinate measuring machines (CMM).
- Pressure Testing: Coils are hydrostatically pressure-tested at 1.5× the maximum operating pressure for a minimum dwell time of 10 minutes to verify integrity and absence of leaks.
- Surface Finishing: Final polishing and electropolishing operations achieve the specified surface roughness. Tubes are then passivated and dried in clean-room conditions.
- Packaging & Traceability: Each coil is labeled with a unique batch identifier, material certificate reference, and manufacturing date for full traceability throughout the supply chain.
4.2 Key Process Controls
- Work Hardening Management: Austenitic stainless steels exhibit significant strain hardening during cold forming. Intermediate annealing at 1050–1100 °C in protective atmosphere is performed when cumulative deformation exceeds 30% to restore ductility.
- Contamination Prevention: All handling surfaces are free of ferrous contamination. Non-magnetic stainless steel tooling and gloves are used throughout to prevent iron particle adhesion, which could cause localized corrosion.
- Helical Geometry Accuracy: CNC bending systems maintain bend radius tolerance of ±0.5% and pitch uniformity of ±0.3 mm across the entire coil length.
5. Applications
5.1 Primary Application: FFU Clean Air Conditioning Systems
In the electronic industry, FFU (Fan Filter Unit) Clean Air Conditioning Systems are the backbone of cleanroom environmental control. The stainless steel coil tubes serve as the heat exchange core within the air-handling units (AHUs) and chilled water coils that regulate supply air temperature, humidity, and cleanliness before it passes through HEPA (High Efficiency Particulate Air) or ULPA (Ultra-Low Penetration Air) filters.
Key application scenarios include:
- Semiconductor Fabrication: Temperature control of process gases and ambient cleanroom air in photolithography, etching, and chemical mechanical polishing (CMP) areas requiring ISO Class 1–Class 5 cleanliness.
- Flat-Panel Display (FPD) Manufacturing: Environmental conditioning for TFT-LCD and OLED production lines where particulate contamination must be minimized.
- Photovoltaic (PV) Cell Production: Cleanroom HVAC coils for wafer cleaning and thin-film deposition areas.
- Biotechnology & Pharmaceutical: GMP (Good Manufacturing Practice) cleanroom systems requiring hygienic, corrosion-resistant coil assemblies.
- Lithium-Ion Battery Manufacturing: Environmental control for electrode coating, drying, and cell assembly areas.
5.2 Secondary Applications
- Chilled water coil assemblies in precision air conditioners (PACs)
- Condenser and evaporator coils in industrial refrigeration systems
- Heat exchangers in chemical processing and food-grade equipment
- Custom coil assemblies for laboratory and analytical instrumentation
6. Quality Certifications & Standards Compliance
| Standard / Certification | Description |
|---|---|
| ASTM A213 / A269 | Standard specification for austenitic stainless steel seamless and welded tubing for high-temperature service |
| ASTM A967 | Standard practice for chemical cleaning and passivation of stainless steel parts |
| ISO 14644-1 | Cleanroom classification compliance for the coil's application environment |
| ISO 9001:2015 | Quality Management System certification covering manufacturing processes |
| ISO 14001:2015 | Environmental Management System certification |
| RoHS 2.0 (EU 2011/65/EU) | Restriction of Hazardous Substances compliance |
| REACH (EC 1907/2006) | Registration, Evaluation, Authorization and Restriction of Chemicals compliance |
| EN 10217-7 | European standard for austenitic stainless steel cold-drawn seamless tubes |
| 3.1 Material Certification (EN 10204) | Full material traceability documentation including chemical analysis and mechanical test reports |
7. Unique Selling Points
Wenzhou Jixing Metal Materials Co., Ltd. differentiates its stainless steel coil tube product line through the following value propositions:
- Industry-Specific Design Optimization: Coil geometry parameters (pitch, bend radius, tube diameter, and winding pattern) are co-engineered with FFU system integrators to maximize heat transfer efficiency while minimizing pressure drop and airflow resistance within the cleanroom AHU.
- Ultra-Low Particle Generation: Electropolished internal surfaces with Ra ≤ 0.5 μm significantly reduce particle shedding compared to standard mechanically polished tubes, preserving cleanroom integrity over extended service life.
- Full Material Traceability: Every coil is accompanied by a 3.1-type material certificate (EN 10204) with complete chemical composition analysis, mechanical test data, heat treatment records, and heat number traceability back to the steel mill.
- Customization Capability: Flexible manufacturing capacity enables production of non-standard coil dimensions, special alloys (including duplex 2205 and super-austenitic grades), and custom surface treatments tailored to specific refrigerant and operating conditions.
- Pressure-Tested Integrity: 100% hydrostatic testing at 1.5× operating pressure ensures zero-defect delivery and eliminates field failures that could compromise cleanroom containment.
- Supply Chain Reliability: Strategic inventory management and multi-shift production schedules ensure consistent lead times (typically 15–25 business days for standard configurations) even during peak semiconductor capital expenditure cycles.
8. Technical Learning Summary
From a metallurgical and thermal engineering perspective, the application of stainless steel coil tubes in FFU clean air conditioning systems represents a convergence of multiple disciplines:
- Metal Forming Science: Understanding the deformation behavior of austenitic stainless steels during cold bending, including strain hardening (σ = σ₀ + Kεⁿ per Hollomon equation), anisotropic mechanical response, and residual stress distribution around bend centers.
- Heat Transfer Engineering: Optimization of coil geometry to maximize the overall heat transfer coefficient (U-value) while balancing refrigerant-side and air-side thermal resistances, including consideration of the Nusselt number correlations for turbulent flow within helical passages.
- Corrosion Science: Selection of appropriate alloy grades based on the specific chemical exposure environment, including resistance to chloride-induced pitting (Critical Pitting Temperature, CPT) and intergranular sensitization.
- Cleanroom Engineering: Integration of coil performance with the broader cleanroom HVAC architecture, including laminar airflow maintenance, pressure differential management, and contamination source control.
This multidisciplinary approach ensures that the stainless steel coil tube product