Stainless Steel Coil Tube (Dry Coil) — Clean Room HVAC Series
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Code: JX-CT-318
Category: HVAC Coil Components / Clean Room Energy-Efficient Systems
1. Product Overview
The Stainless Steel Coil Tube (盘管 / Coil Tube), designated as JX-CT-318, is a precision-engineered heat exchange coil component manufactured from high-grade austenitic stainless steel. Specifically designed for Dry Coil applications in clean room air handling units (AHUs), this product represents a critical component in energy-efficient climate control systems for pharmaceutical, semiconductor, biotechnology, and food processing facilities.
Dry coils operate by using a chilled water loop (typically at 12–18°C / 54–64°F) to dehumidify supply air without condensation formation, thereby avoiding the energy penalty associated with reheat coils. The selection and design of dry coils directly influence the overall energy consumption of clean room HVAC systems. JX-CT-318 is engineered to maximize heat transfer efficiency while maintaining the stringent air quality and contamination control requirements of ISO 14644 clean room classifications.
Design Philosophy: Based on the principles outlined in "Discussion on Clean Room Energy Saving Based on Dry Coil Selection", the JX-CT-318 coil tube is optimized for low-temperature differential operation, minimal pressure drop, and maximum latent heat removal capacity — all essential parameters for reducing total HVAC energy consumption in clean room environments.
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from AISI 304L (UNS S30403) and AISI 316L (UNS S31603) austenitic stainless steel, selected for their superior corrosion resistance, hygienic surface characteristics, and compatibility with clean room environments.
2.2 Mechanical Properties
| Property | AISI 304L (UNS S30403) | AISI 316L (UNS S31603) |
|---|---|---|
| Tensile Strength (MPa) | ≥ 515 | ≥ 515 |
| Yield Strength (MPa, 0.2% offset) | ≥ 205 | ≥ 205 |
| Elongation (% at rupture) | ≥ 40 | ≥ 40 |
| Density (g/cm³) | 7.93 | 7.98 |
| Thermal Conductivity (W/m·K, 25°C) | 16.3 | 14.6 |
| Thermal Expansion (×10⁻⁶/K, 20–100°C) | 17.3 | 16.0 |
| Corrosion Resistance (Pitting, PREN) | 18–20 | 24–26 |
2.3 Surface Treatment
- Standard Finish: Electropolished (Ra ≤ 0.4 μm) for hygienic applications
- Alternative Finishes: Pickled & passivated, 2B finish, or custom bead-blasted (Ra 0.8–1.6 μm) for enhanced heat transfer
- Internal Surface: Available in sanitary-grade (Ra ≤ 0.25 μm) for pharmaceutical and food-grade applications
2.4 Key Alloying Elements
| Element | 304L (wt%) | 316L (wt%) | Function |
|---|---|---|---|
| Carbon (C) | ≤ 0.030 | ≤ 0.030 | Low carbon prevents sensitization during welding |
| Chromium (Cr) | 18.0–20.0 | 16.5–18.5 | Primary corrosion resistance element |
| Nickel (Ni) | 8.0–12.0 | 10.0–14.0 | Stabilizes austenitic structure |
| Molybdenum (Mo) | — | 2.0–3.0 | Enhances pitting and crevice corrosion resistance |
| Manganese (Mn) | ≤ 2.0 | ≤ 2.0 | Deoxidizer and grain refiner |
| Silicon (Si) | ≤ 1.0 | ≤ 1.0 | Strengthens and improves oxidation resistance |
3. Specifications
3.1 Tube Dimensions
| Parameter | Specification | Standard Reference |
|---|---|---|
| Tube Outer Diameter (OD) | 6.35 mm (¼"), 9.53 mm (⅜"), 12.70 mm (½"), 15.88 mm (⅝"), 19.05 mm (¾") | ASTM A269 / EN 10217 |
| Tube Wall Thickness | 0.50 – 2.00 mm (selectable) | — |
| Coil Pitch (Center-to-Center) | 15 – 50 mm (customizable) | ASHRAE 15 / EN 12235 |
| Coil Diameter (Bundled) | Standard: 150 – 600 mm; Custom: up to 1200 mm | — |
| Tube Length per Coil | 5 – 50 m (continuous coil) | — |
| Number of Rows | 1 – 8 rows (standard); up to 12 rows (custom) | — |
| Fin Type | L-shaped aluminum fins, V-crimp fins, or plate fins | — |
| Fin Spacing | 1.5 – 3.0 mm (pitch) | — |
| Maximum Operating Temperature | -196°C to +350°C | — |
| Maximum Operating Pressure | 1.6 MPa (standard); 4.0 MPa (high-pressure variant) | EN 12235 / ASME B31.5 |
| Design Pressure (Water Side) | Up to 1.0 MPa (standard); 1.6 MPa (custom) | — |
| Design Pressure (Air Side) | Up to 2.5 kPa | — |
| Tolerance (OD) | ±0.05 mm (precision); ±0.10 mm (standard) | ISO 4977 / ASTM A269 |
| Tolerance (Wall Thickness) | ±10% of nominal | ASTM A269 |
3.2 Performance Parameters (Typical — ¼" OD × 0.5 mm Wall, 4-Row Coil)
| Parameter | Value | Test Condition |
|---|---|---|
| Heat Transfer Coefficient (U-value) | 45 – 75 W/m²·K | Water: 12°C → 18°C; Air: 25°C DB / 15°C WB |
| Pressure Drop (Water Side) | 15 – 45 kPa | Flow velocity: 1.5 – 2.5 m/s |
| Pressure Drop (Air Side) | 50 – 200 Pa | Face velocity: 2.0 – 2.5 m/s |
| Dehumidification Capacity | Up to 8.5 kg H₂O/h per m² face area | Dry coil operating mode |
| Operating Water Temperature Range | 7°C – 20°C (chilled water) | Dry coil application |
| Minimum Water Flow Rate | 0.5 L/min per m² of coil face area | To prevent freezing |
3.3 Available Material Grades
| Grade | UNS Designation | Equivalent (EN) | Recommended Application |
|---|---|---|---|
| 304L | S30403 | 1.4307 (X2CrNi19-11) | General clean room HVAC, food processing |
| 316L | S31603 | 1.4404 (X2CrNiMo17-12-2) | Pharmaceutical, chemical, marine environments |
| 316L (EP) | S31603 | 1.4404 | High-purity pharma, semiconductor (electropolished) |
| 321 | S32100 | 1.4541 (X6CrNiTi18-10) | High-temperature applications (>300°C) |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection & Inspection: Certified stainless steel tube blanks (per ASTM A269 / EN 10217) undergo incoming material verification including chemical composition analysis (OES), mechanical testing, and visual inspection.
- Tube Straightening & Cutting: Coiled tube is straightened using progressive roller straighteners and cut to specified lengths with precision saws or plasma cutting systems.
- Forming & Bending: Tubes are formed into the desired coil geometry using CNC-controlled coil winding machines. Bend radii are maintained at a minimum of 3× tube OD to prevent wall thinning or ovalization.
- Fin Insertion & Crimping: Aluminum fins (or plate fins) are inserted between coil rows and mechanically crimped or brazed to the tube surface to ensure maximum thermal contact and structural integrity.
- Welding: Header connections and tube-to-header joints are fabricated using TIG (Tungsten Inert Gas) welding (GTAW) under argon gas shielding. Weld parameters are controlled to prevent oxidation and maintain metallurgical integrity.
- Pickling & Passivation: Post-welding, coils are subjected to acid pickling (HNO₃ + H₂SO₄) to remove oxide scale, followed by passivation treatment to restore the protective chromium oxide layer.
- Surface Treatment (if required): Electropolishing (EP) is performed for sanitary-grade surfaces, achieving Ra ≤ 0.25 μm internal finish.
- Pressure Testing: Each coil assembly undergoes hydrostatic pressure testing at 1.5× design pressure (minimum 30 minutes hold) to verify leak-free integrity.
- Final Inspection & Testing: Includes dimensional verification, visual weld inspection, and optional performance testing (heat transfer and pressure drop measurement).
- Packaging & Dispatch: Coils are wrapped in protective film, packed in wooden crates or steel frames, and shipped with full documentation.
4.2 Quality Control Milestones
- Incoming Inspection: 100% material certificate verification, sampling for chemical and mechanical testing
- In-Process Inspection: Dimensional checks at bending, fin insertion, and welding stages
- Final Inspection: 100% pressure testing, dimensional verification, and visual inspection
- Traceability: Each coil is tagged with a unique serial number linked to material batch, production date, and test records
5. Applications
5.1 Primary Applications
- Clean Room HVAC Systems: Dry coil dehumidification in ISO 14644 Class 1–8 clean rooms for pharmaceutical manufacturing, semiconductor fabrication, and biotechnology laboratories
- Pharmaceutical Manufacturing: GMP-compliant environments requiring precise temperature and humidity control with hygienic-grade materials
- Food & Beverage Processing: Sanitary air handling in dairy, brewing, and packaged food production facilities
- Electronics Manufacturing: Low-particulate air conditioning in microelectronics and optoelectronics assembly
- Hospital & Medical Facilities: Operating theaters, ICUs, and sterile processing departments
- Chemical Processing: Corrosive environment air handling where 316L stainless steel provides enhanced resistance
5.2 Energy-Saving Advantages of Dry Coil Configuration
Based on the research findings from "Discussion on Clean Room Energy Saving Based on Dry Coil Selection", the adoption of stainless steel dry coils in clean room HVAC systems offers significant energy benefits: