Stainless Steel Coil Tube (Dry Coil) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coil Tube" or "Dry Coil") manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed primarily for air-conditioning and refrigeration systems, with particular emphasis on energy-efficient cleanroom environments. The product is formed by cold-drawing seamless stainless steel tubes into continuous helical or serpentine configurations, enabling optimal heat exchange performance in a compact footprint.
Unlike conventional finned-tube heat exchangers, the dry coil design operates without a secondary water circuit, thereby eliminating risks of microbial contamination, condensate leakage, and associated maintenance costs — making it an ideal solution for pharmaceutical, semiconductor, and biotechnology cleanrooms where particulate and moisture control are critical.
This product specification draws upon industry best practices and academic literature, including the study "Discussion on Energy-Saving in Cleanrooms Based on Dry Coil Selection", which validates the superior thermodynamic efficiency and operational reliability of properly selected dry coil configurations in high-efficiency HVAC systems.
2. Material & Properties
2.1 Base Material Grades
- Austenitic Stainless Steel: Grade 304 (UNS S30400), Grade 304L (UNS S30403), Grade 316 (UNS S31600), Grade 316L (UNS S31603)
- Super-Austenitic Stainless Steel: Grade 317L (UNS S31703), Grade 904L (UNS N08904)
- Optionally available: Duplex Stainless Steel Grade 2205 (UNS S31803), Nickel Alloy Inconel 625 (UNS N06625)
2.2 Key Mechanical & Physical Properties
| Property | Grade 304 | Grade 316L | Grade 904L |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 485 | ≥ 550 |
| Yield Strength (MPa, 0.2% offset) | ≥ 205 | ≥ 170 | ≥ 275 |
| Elongation (% A) | ≥ 40 | ≥ 40 | ≥ 35 |
| Thermal Conductivity (W/m·K, 25°C) | 16.3 | 14.6 | 11.4 |
| Linear Thermal Expansion (μm/m·K, 25–100°C) | 17.3 | 16.0 | 13.2 |
| Density (kg/m³) | 8,000 | 8,000 | 8,100 |
| Maximum Service Temperature (°C) | 870 | 870 | 1040 |
| Corrosion Resistance (Pitting Resistance Equivalent Number, PREN) | 19 | 24 | 45 |
2.3 Surface Finish Options
- Mill Finish: Standard as-rolled surface with matte appearance
- Electrolytic Polishing: Surface roughness Ra ≤ 0.4 μm, suitable for pharmaceutical and food-grade applications
- Mechanical Polishing: Surface roughness Ra ≤ 0.2 μm, mirror-like finish for ultra-clean environments
- Pickled & Passivated: Removal of scale and formation of a passive chromium oxide layer for enhanced corrosion resistance
3. Specifications
3.1 Dimensional Parameters
| Parameter | Specification | Tolerance | Standard Reference |
|---|---|---|---|
| Outer Diameter (OD) | φ6.0 – φ50.8 mm (¼" – 2") | ±0.05 mm | ASTM A269 / EN 10217-7 |
| Wall Thickness (WT) | 0.5 – 3.0 mm | ±0.03 mm | ASTM A269 / EN 10217-7 |
| Coil Length (per spool) | 5 – 100 m (customizable) | ±0.5% | Manufacturer Standard |
| Coil Inner Diameter (ID) | φ150 – φ600 mm | ±5 mm | Manufacturer Standard |
| Coil Outer Diameter (OD) | φ300 – φ1200 mm | ±5 mm | Manufacturer Standard |
| Bend Radius (Minimum) | ≥ 3× OD | — | ASTM A269 |
| End Condition | Plain, Beveled, Threaded, or Flanged | Per drawing | ASME B1.20.1 |
| Helix Pitch | 10 – 50 mm (adjustable) | ±0.5 mm | Custom Specification |
| Maximum Working Pressure | Up to 4.0 MPa (600 PSI) | — | ASME BPV Code Section I |
| Hydrostatic Test Pressure | 1.5× Working Pressure | — | ASME BPV Code |
3.2 Coil Configuration Options
| Configuration Type | Description | Typical Application |
|---|---|---|
| Single Helix Coil | Continuous spiral winding with uniform pitch | Standard HVAC coils, heat exchangers |
| Serpentine Coil | Zigzag pattern with 180° bends | Compact heat exchangers, refrigeration |
| Double-Helix Coil | Two intertwined helical tubes for enhanced heat transfer | High-efficiency dry coolers, cleanroom systems |
| U-Tube Coil Array | Multiple U-shaped tube circuits connected in parallel | Large-capacity air handlers, industrial cooling |
| Finned Coil Tube | Coil tube with attached aluminum or stainless steel fins | Enhanced air-side heat transfer applications |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Inspection: Incoming stainless steel seamless tubes are verified for chemical composition (via Optical Emission Spectroscopy, OES), mechanical properties, and surface quality against ASTM/EN standards.
- Tube Straightening & Cutting: Seamless tubes are straightened using a multi-roller straightener and cut to required coil lengths with precision saws, achieving end-face perpendicularity within ±0.1 mm.
- Tube Cleaning & Pickling: Tubes undergo ultrasonic cleaning followed by acid pickling (HNO₃/HF solution) and passivation to remove surface contaminants and establish a stable passive oxide film.
- Coil Forming: Straight tubes are fed into a CNC-controlled coil forming machine that bends the tube into the specified helical or serpentine geometry. The forming process utilizes a combination of roller bending and mandrel-assisted bending to maintain dimensional accuracy and prevent tube ovalization (ovality ≤ 2% of OD).
- Welding & Joining (if applicable): Butt welds or socket welds are performed using Argon Arc Welding (TIG/GTAW) with inert gas shielding (Ar ≥ 99.99% purity) to ensure weld integrity and prevent oxidation. Weld quality is verified by radiographic testing (RT) or ultrasonic testing (UT) per ASME Section IX.
- Heat Treatment (if required): Solution annealing at 1050–1150°C followed by rapid water quenching to restore full solution-hardened condition and eliminate cold-work effects, ensuring maximum corrosion resistance and ductility.
- Final Surface Treatment: Electrolytic polishing or mechanical polishing to achieve specified surface roughness. Final passivation treatment with citric acid or nitric acid solution.
- Quality Inspection: Dimensional verification (OD, WT, coil geometry), pressure testing (hydrostatic at 1.5× working pressure for 30 minutes), visual inspection, and non-destructive testing (NDT) as required.
- Packaging & Shipping: Coils are wrapped in protective plastic film, secured with steel strapping, and packed in wooden crates or on custom pallets for safe transportation.
4.2 Key Process Parameters
| Process Step | Control Parameter | Specification |
|---|---|---|
| Coil Forming | Forming speed | 0.5 – 2.0 m/min |
| Coil Forming | Maximum bending force | ≤ 80 kN (depending on OD and WT) |
| Coil Forming | Post-forming ovality | ≤ 2% of nominal OD |
| TIG Welding | Shielding gas flow rate | 10 – 15 L/min |
| TIG Welding | Welding current | 80 – 200 A (depending on tube size) |
| Solution Annealing | Temperature | 1050 – 1150°C |
| Solution Annealing | Soaking time | 30 – 60 min |
| Hydrostatic Testing | Test pressure | 1.5 × working pressure |
| Hydrostatic Testing | Hold time | ≥ 30 min |
5. Applications
5.1 Primary Application Domains
- Cleanroom HVAC Systems: Dry coil air handlers for pharmaceutical manufacturing (GMP Grade A–D), semiconductor fabrication (Class 1–1000), biotechnology, and hospital operating theaters. The dry coil design eliminates the need for a secondary chilled water circuit, thereby removing the primary vector for microbial contamination and condensate-related particulate generation.
- Food & Beverage Processing: Heat exchangers for pasteurization, sterilization, and temperature control systems in dairy, brewing, and food processing industries where hygienic design and corrosion resistance are paramount.
- Chemical & Petrochemical Industry: Corrosion-resistant heat exchange coils for handling aggressive chemical media including acids, alkalis, and halide-containing solutions.
- Marine & Offshore Applications: Seawater-cooled heat exchangers and condensers leveraging the exceptional chloride pitting resistance of Grade 316L and 904L stainless steels.
- Commercial Refrigeration: Evaporator and condenser coils for cold storage facilities, supermarket display cases, and industrial refrigeration systems.
- Energy-Saving Retrofits: Replacement of legacy finned-tube coils with high-efficiency dry coil configurations to achieve measurable energy savings in existing HVAC systems, as demonstrated in academic studies on cleanroom energy optimization.
5.2 Energy-Saving Performance in Cleanrooms
Based on the academic study "Discussion on Energy-Saving in Cleanrooms Based on Dry Coil Selection", properly selected dry coil configurations can achieve:
- Energy savings of 15–30% compared to conventional indirect evaporative cooling systems
- Elimination of secondary pump energy consumption (typically 2–5 kW per 100,000 m³/h air flow)
- Reduced maintenance labor costs by 40–60% due to the absence of a secondary water loop
- Improved indoor air quality (IAQ) by eliminating condensate formation and associated microbial growth risks