Stainless Steel Coil Tube (盘管 / Coil Tube) — Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (盘管, Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed for thermal exchange applications in heating, ventilation, and air conditioning (HVAC) systems. This product is specifically engineered to meet the demanding requirements of dry coil systems (干盘管系统), where latent heat removal and sensible cooling capacity correction are critical performance parameters. The coil tube is formed from high-grade stainless steel wire or strip, wound into a continuous helical or serpentine configuration, and supplied in coil (盘管) form for downstream fabrication into fan coil units (FCU), air handling units (AHU), and other heat exchange assemblies.
In dry coil system design, the cooling capacity of the fan coil unit must be corrected to account for the separation of sensible and latent heat loads. The stainless steel coil tube serves as the primary heat transfer surface, and its geometric and material properties directly influence the coefficient of heat transfer, pressure drop, and overall thermal efficiency of the system.
2. Material & Properties
2.1 Base Material
- Grade: SUS304 / 1Cr18Ni9Ti (AISI 304) — standard; SUS316L / 00Cr17Ni14Mo2 (AISI 316L) — available upon request
- Composition (SUS304): Carbon (C) ≤ 0.08%, Chromium (Cr) 18.0–20.0%, Nickel (Ni) 8.0–10.5%, Manganese (Mn) ≤ 2.0%, Silicon (Si) ≤ 1.0%, Sulfur (S) ≤ 0.03%
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, waterborne chlorine, and mild chemical environments; suitable for hygienic and food-grade applications
- Thermal Conductivity: 14–16 W/(m·K) at 20°C (ambient temperature)
- Specific Heat Capacity (Cp): 500–520 J/(kg·K)
- Density: 7,930 kg/m³
- Maximum Operating Temperature: 870°C (continuous); 1100°C (intermittent)
- Minimum Operating Temperature: -196°C (cryogenic capability)
2.2 Surface Treatment
- Standard Finish: No. 1 industrial finish (pickled and annealed), Ra ≤ 1.6 μm
- Optional Finish: 2B cold-rolled finish, Ra ≤ 0.8 μm; BA (Bright Annealed) finish, Ra ≤ 0.4 μm
- Internal Surface: Electropolished (EP) available upon request, Ra ≤ 0.2 μm, suitable for pharmaceutical and semiconductor applications
3. Specifications
| Parameter | Specification / Range | Unit |
|---|---|---|
| Outer Diameter (OD) | Φ 3.0 – Φ 12.7 | mm |
| Wall Thickness | 0.3 – 1.5 | mm |
| Inner Diameter (ID) | Φ 2.0 – Φ 11.5 | mm |
| Coil Pitch (Winding Spacing) | 6.0 – 25.4 | mm |
| Coil Diameter (Bundle Diameter) | Φ 100 – Φ 800 | mm |
| Coil Length (Unwound) | 3 – 50 | m |
| Number of Rows | 1 – 4 | — |
| Tube Layout | Serpentine / Helical / Double-Tube | — |
| Fin Type (if finned) | Aluminum or Stainless Steel louvered/flat fins | — |
| Fin Density | 10 – 14 | fins/inch (FPI) |
| Pressure Rating | Up to 1.6 MPa (16 bar) at 20°C | MPa |
| Test Pressure | 2.5 × Working Pressure (hydrostatic) | MPa |
| Flow Rate (Nominal) | 0.5 – 5.0 | L/min |
| Refrigerant Compatibility | R410A, R32, R134a, R404A, R407C, Ammonia (NH₃) | — |
| Water Side Operating Temp. | 5 – 95 | °C |
| Air Side Operating Temp. | -30 – +60 | °C |
| Standard Length (per coil) | Customized; standard 5 m, 10 m, 20 m | m |
| Tolerance on OD | ±0.05 mm (precision grade); ±0.1 mm (standard grade) | mm |
| End Form | Plain end, flared, brazed, threaded (M14×1.5, 1/4" BSP, etc.) | — |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Inspection: Incoming stainless steel wire or strip undergoes spectroscopic analysis (OES) and mechanical property verification per ASTM A270 / GB/T 12771 standards.
- Wire Drawing / Strip Cold Rolling: The raw material is drawn to the precise outer diameter and wall thickness specification through multi-stage cold drawing with intermediate annealing (at 1050–1100°C in a controlled atmosphere furnace) to relieve residual stresses.
- Pickling & Annealing: Post-drawing tubes are subjected to acid pickling (HNO₃/HF mixed acid bath) followed by annealing to restore the full austenitic microstructure and achieve the required surface finish.
- Coil Winding (盘管成型): The straight tube is wound onto a precision mandrel using a CNC-controlled coil winding machine. The winding parameters (pitch, diameter, number of turns) are programmable to meet specific heat exchange design requirements.
- Fin Application (if finned): Aluminum or stainless steel fins are expanded onto the coil tube using a hydraulic fin-expansion machine, ensuring uniform fin-to-tube contact without mechanical deformation of the tube wall.
- Hydrostatic Pressure Testing: Each coil assembly is pressure-tested at 2.5× the maximum working pressure for a minimum dwell time of 60 seconds to verify leak integrity.
- Heat Exchanger Performance Testing: Representative samples undergo air-side and water-side performance testing in accordance with ASHRAE Standard 34 (Rating Methods for Air-Curtain Units) and ARI Standard 430 (Unitary Air-Conditioning and Air-Heating Equipment) to verify cooling capacity, total pressure drop, and COP (Coefficient of Performance).
- Final Inspection & Packaging: Each coil is visually inspected, dimensionally verified, and packaged with moisture-absorbing desiccants in protective cartons or wooden crates for export.
4.2 Key Manufacturing Technologies
- CNC Precision Winding: Ensures consistent coil pitch and diameter, critical for uniform airflow distribution in dry coil systems.
- Double-Tube Configuration (双管结构): Available for enhanced heat transfer area in compact fan coil units, featuring an inner tube and outer tube with a common fin pack.
- Hydrophilic Coating: Optional fluorocarbon-based hydrophilic coating on the coil surface to promote condensate drainage in high-humidity applications, reducing the risk of microbial growth.
5. Applications
5.1 Primary Applications
- Dry Coil Systems (干盘管系统): The coil tube is the core heat exchange element in dry coil systems used in hospitals, laboratories, cleanrooms, and data centers where precise control of both sensible and latent heat loads is essential. In these systems, the dry coil operates at a high water temperature (typically 15–20°C), removing only sensible heat, while latent heat is handled by a separate dehumidification unit.
- Fan Coil Units (FCU / 风机盘管): Used in commercial buildings, hotels, residential complexes, and office spaces for individual zone temperature control.
- Chilled Water Air Handlers (CHW-AHU): Integrated into air handling units for central air conditioning systems.
- Heat Pump Systems: Employed in both the evaporator and condenser sections of air-to-air and air-to-water heat pumps.
- Industrial Cooling: Applied in electronics cooling, semiconductor manufacturing, and precision instrumentation where stainless steel corrosion resistance is required.
- Refrigeration Systems: Used as evaporator coils in commercial refrigeration cabinets, walk-in coolers, and cold storage facilities.
5.2 Dry Coil System Design Considerations
In dry coil system design, the cooling capacity of the fan coil unit must be corrected to account for the following factors:
- Water Supply Temperature Correction: The nominal cooling capacity is rated at a standard water supply temperature (typically 7°C). When operating at higher supply temperatures (e.g., 15–20°C in dry coil mode), the cooling capacity must be derated using manufacturer-provided correction factors.
- Airflow Rate Correction: Variations in actual airflow from the design airflow affect both sensible and latent heat transfer. The correction factor is typically derived from the relationship between the air-side heat transfer coefficient and the Reynolds number (Re).
- Fin Blockage Factor: Over time, dust and particulate accumulation reduces effective heat transfer area. A fouling factor of 0.0002–0.0004 m²·K/W is recommended for long-term capacity calculations.
- Latent Heat Separation: In dry coil systems, the latent load is handled separately, and the coil tube design must ensure that the surface temperature remains above the dew point of the air stream to prevent condensation.
6. Quality Certifications & Standards Compliance
6.1 Product Certifications
- ISO 9001:2015 — Quality Management System (QMS) certification for manufacturing processes
- ISO 14001:2015 — Environmental Management System (EMS) certification
- CE Marking — Conformity with European Union directives for mechanical and pressure equipment
- UL / CSA — Underwriters Laboratories / Canadian Standards Association listing for North American market compliance
- RoHS 2.0 (EU Directive 2011/65/EU) — Restriction of Hazardous Substances compliance
- REACH (EC No 1907/2006) — Registration, Evaluation, Authorisation and Restriction of Chemicals compliance
6.2 Applicable Standards
- ASTM A270 / A270M — Standard Specification for Seamless and Wrought Stainless Steel, Austenitic Steel, Hydraulic and Mechanical Tubing
- ASTM A751 — Standard Guide for Chemical Analysis and Nominal Dimensions of Stainless Steel
- GB/T 12771 — Non-alloy and Alloy Steel Tubes — Welded Tubes for Fluid Transport (Chinese National Standard)
- GB/T 24511 — General Technical Conditions for Stainless Steel Tubes
- JIS G3446 — Cold Rolled Stainless Steel Seamless Tubes (Japanese Industrial Standard)
- EN 10217-7 — Technical Delivery Conditions for Stainless Steel Tubes for Pressure Purposes
- ASHRAE Standard 34-2013 — Rating Methods for Air-Curtain Units
- ARI Standard 430 — Unitary Air-Conditioning and Air-Heating Equipment
6.3 Testing & Inspection Protocols
- Spectroscopic Analysis (OES): 100% batch verification of chemical composition
- Dimensional Inspection: Coordinate Measuring Machine (CMM) and laser micrometer for OD, ID, and wall thickness verification
- Hydrostatic Pressure Test: 100% per-piece testing at 2.5× working pressure
- Visual Inspection: 100% inspection for surface defects, weld seams (if applicable), and dimensional conformity
- Performance Testing: Sample-based thermal performance testing per ASHRAE/ARI protocols
- Corrosion Testing: Salt spray testing (ASTM B117) — minimum 480 hours without red rust for SUS304 grade
7. Unique Selling Points
- Precision Engineering for Dry Coil Applications: Wenzhou Jixing's coil tubes are specifically designed and optimized for dry coil system requirements, with precise control over coil pitch, tube diameter, and fin density to ensure optimal sensible heat transfer performance while maintaining surface temperatures above the dew point.
- Full Material Traceability: Each batch of raw stainless steel material is traceable to its mill of origin, with full chemical composition and mechanical property documentation provided to the end user.
- Customizable Geometric Parameters: The coil tube can be customized in terms of outer diameter, wall thickness, coil pitch, coil diameter, number of rows, and end configuration to meet specific OEM design requirements for fan coil units and air handlers.
- Corrosion Resistance & Long Service Life: The use of high-grade SUS304 or SUS316L stainless steel ensures resistance to corrosion in humid environments, extending the service life of the heat exchanger to 15–20 years or more under normal operating conditions.
- Hygienic Design Options: Electropolished internal surfaces and crevice-free construction are available for pharmaceutical, food processing, and semiconductor manufacturing applications where contamination control is critical.
- Integrated Quality Assurance: