Stainless Steel Coil Tube — Fan Coil Unit Series (Ref. No. 1535)
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Category: Literature Learning / Technical Reference — Fan Coil Unit (FCU) Standard Compliance Documentation
Document Reference: 《风机盘管机组有关标准讨论》 — Discussion on Standards for Fan Coil Unit Assemblies
1. Product Overview
The Stainless Steel Coil Tube (Ref. No. 1535) is a precision-engineered tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd., specifically designed for integration into Fan Coil Units (FCUs) and related hydronic air conditioning systems. These coil tubes serve as the primary heat exchange elements within FCU assemblies, facilitating efficient thermal transfer between circulating refrigerant (water or glycol solution) and ambient air drawn through the unit.
This product line is developed in strict accordance with the technical discussions documented in the internal study report "Discussion on Standards for Fan Coil Unit Assemblies", which addresses critical compliance requirements spanning dimensional tolerances, thermal performance benchmarks, material specifications, and assembly integration protocols. The coil tubes are engineered to meet or exceed the performance criteria outlined in relevant national and international standards governing FCU design and operation.
Wenzhou Jixing Metal Materials Co., Ltd. positions these stainless steel coil tubes as a premium-grade alternative to conventional copper or aluminum coil tubes, offering superior corrosion resistance, extended service life, and reduced maintenance requirements in demanding HVAC (Heating, Ventilation, and Air Conditioning) environments.
2. Material & Properties
2.1 Base Material
- Primary Alloy: Austenitic stainless steel conforming to ASTM A269 / ASME SA-269 (seamless) or ASTM A554 (welded)
- Equivalent Grades: SUS 304 (JIS), 1.4301 (EN), 08Cr18Ni9 (GB/T 12771)
- Alternative Grade (for high-chloride environments): SUS 316L / 1.4404 (EN) — ASTM A554 Type 316L
- Surface Finish: No. 4 brushed finish or 2B cold-rolled finish; electropolished finish available upon request for enhanced hygiene compliance
2.2 Mechanical Properties (Typical — Grade 304)
- Tensile Strength: ≥ 515 MPa (74,700 psi)
- Yield Strength (0.2% offset): ≥ 205 MPa (29,700 psi)
- Elongation (at break): ≥ 40%
- Hardness (Brinell): ≤ 210 HB
- Density: 8.0 g/cm³ (0.289 lb/in³)
2.3 Thermal & Corrosion Resistance Properties
- Thermal Conductivity (at 20°C): 16.3 W/(m·K)
- Specific Heat Capacity (at 20°C): 0.50 J/(g·K)
- Linear Thermal Expansion Coefficient (20–100°C): 17.3 × 10⁻⁶ /°C
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, mild acids, alkalis, and chloride-containing fluids; superior to copper in ammonia and certain chemical environments
- Operating Temperature Range: −196°C to +870°C (−320°F to +1,598°F)
- Maximum Service Pressure (typical coil configuration): 1.6 MPa (232 psi) at ambient; derated at elevated temperatures
3. Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Product Designation | Stainless Steel Coil Tube — FCU Series | Internal Ref. No. 1535 |
| Material Grade | SUS 304 / 1.4301 (Standard); SUS 316L / 1.4404 (Optional) | ASTM A554 / GB/T 12771 |
| Outer Diameter (OD) | 9.52 mm (3/8"), 12.7 mm (1/2"), 15.88 mm (5/8") | ASTM A269 |
| Wall Thickness | 0.50 mm – 1.00 mm (typical); ±0.05 mm tolerance | ASME B36.19M |
| Coil Pitch (Center-to-Center) | 10 mm – 25 mm (configurable per FCU design) | Manufacturer's design specification |
| Coil Row Depth | 1 row – 6 rows (standard configurations) | ASHRAE 36 / GB/T 19232 |
| Fins Per Inch (FPI) | 10 FPI – 14 FPI (hydrophilic aluminum fins, optional) | ANSI/ASHRAE 22 |
| Fin Material | Aluminum 1100 / 3003 (standard); Copper (optional) | ASTM B209 / B308 |
| Maximum Operating Pressure | 1.6 MPa (232 psi) @ 25°C | GB/T 19232 |
| Hydrostatic Test Pressure | 2.4 MPa (348 psi) — 1.5× working pressure | ISO 4437 / GB/T 19232 |
| Maximum Operating Temperature | 95°C (203°F) for liquid-side; air-side up to 60°C | ASHRAE 36 |
| Connection Type | Threaded (G, NPT), Flanged, or Welded ends | GB/T 577 / ASME B1.20.1 |
| Surface Treatment | Pickling & passivation; optional electropolishing | ASTM A967 |
| Coil Length (Standard) | 600 mm – 1,200 mm (custom lengths available) | Per project specification |
| Weight (Typical, 9.52 mm OD × 0.8 mm WT) | 0.18 kg/m (0.10 lb/ft) | Calculated per ASTM A554 |
4. Manufacturing Process
4.1 Raw Material Selection & Incoming Inspection
All incoming stainless steel strip or seamless tube stock is verified against certified mill test reports (MTRs) confirming chemical composition, mechanical properties, and heat treatment status. Spectroscopic analysis (OES) is performed on each heat lot to ensure compliance with ASTM A554 / GB/T 12771 chemical requirements. Rejected materials are quarantined and returned to the supplier per the company's incoming quality control (IQC) protocol.
4.2 Coil Forming
- Flat Coil (Snake Coil) Configuration: Continuous stainless steel tube is precisely formed into a serpentine pattern using CNC-controlled bending equipment with hydraulic actuation. Bend radii are maintained at a minimum of 2× tube OD to prevent wall thinning or ovality exceeding 5%.
- Spiral Coil Configuration: Tubes are wound into helical spirals using automated coiling machinery, with pitch and diameter controlled to ±0.5 mm tolerance.
- U-Turn & Return Bend Fabrication: Multi-row coil configurations require precision U-bends connecting tube passes. These are formed using mandrel-assisted bending to ensure uniform wall thickness distribution and prevent wrinkling.
4.3 Fin Application (Finned Coil Variant)
For finned coil tube assemblies, aluminum fins are applied via one of the following methods:
- Insert Fin (Slotted Fin): Pre-slotted aluminum fins are pressed onto the coil tube body using hydraulic fin-pressing equipment, ensuring uniform fin contact and minimal thermal contact resistance.
- Stamped Fin (Continuous Fin): A continuous aluminum fin strip is stamped and wrapped around the coil tube using automated fin-winding machinery.
- Hydrophilic Coating: Fins may be coated with a hydrophilic polymer treatment to enhance moisture drainage and improve latent heat transfer performance in dehumidification applications.
4.4 Heat Treatment & Surface Preparation
- Solution Annealing: Tubes are annealed at 1050°C ± 50°C followed by rapid air or water quenching to restore full austenitic structure, relieve cold-work hardening, and maximize ductility.
- Pickling: Surface oxide scale is removed using a controlled acid bath (typically a mix of nitric and hydrofluoric acid) to achieve a clean, uniform surface.
- Passivation: A controlled citric acid or nitric acid passivation treatment is applied to enrich the chromium oxide layer, enhancing corrosion resistance per ASTM A967.
4.5 Quality Assurance & Testing
- Dimensional Inspection: Outer diameter, wall thickness, coil pitch, and bend radii are measured using calibrated micrometers, calipers, and optical comparators. Critical dimensions are verified via Coordinate Measuring Machine (CMM) for batch sampling.
- Hydrostatic Pressure Testing: Each coil tube is pressure-tested at 1.5× the maximum working pressure (typically 2.4 MPa) for a minimum dwell time of 60 seconds to detect leaks or structural defects.
- Helium Leak Testing: For critical applications, helium mass spectrometer leak detection is performed to identify micro-leaks below 1×10⁻⁶ atm·cc/s.
- Visual Inspection: 100% visual examination for surface defects, corrosion, dents, and workmanship quality per ASTM E165.
- Chemical Spot Testing: Random lot sampling for chemical composition verification via optical emission spectrometry (OES) or wet chemistry analysis.
5. Applications
5.1 Primary Application — Fan Coil Units (FCUs)
The primary application domain for this stainless steel coil tube product is within Fan Coil Units (FCUs) used in commercial, institutional, and residential HVAC systems. FCUs are terminal units that condition air by passing it over a coil (heating or cooling) and distributing the conditioned air into the served space. The stainless steel coil tube serves as the core heat exchange element, with hot or chilled water (or glycol) circulating through the coil while a fan draws ambient air across the coil fins.
Key FCU application sub-categories include:
- Concealed Ceiling-Mounted FCUs: Installed within suspended ceilings in offices, hotels, and retail spaces
- Wall-Hung FCUs: Mounted on interior walls in residential and light commercial spaces
- Horizontal Concealed FCUs: Installed within floor plenums or ceiling voids for high-capacity applications
- Vertical FCUs: Floor-standing units for larger commercial and industrial spaces
- Cassette FCUs: Four-way or six-way diffuser units for uniform air distribution in open-plan spaces
5.2 Secondary Applications
- Chilled Water Systems: Integration into central chilled water distribution networks for large commercial buildings
- Heat Pump Systems: Use as evaporator or condenser coils in air-to-water and air-to-air heat pump units
- Industrial Process Cooling: Application in food processing, pharmaceutical manufacturing, and laboratory environments requiring hygienic-grade heat exchange
- Marine HVAC Systems: Deployment in shipboard air conditioning systems where chloride resistance is critical
- Cleanroom HVAC: Use in pharmaceutical, semiconductor, and biotechnology facilities requiring contamination-free air handling
- Refrigeration Systems: Integration into medium-temperature and low-temperature refrigeration circuits
6. Quality Certifications & Standards Compliance
6.1 Product Standards
- GB/T 19232 — Technical conditions for fan coil units (Chinese National Standard)
- GB/T 12771 — Stainless steel seamless tubes for general purpose (Chinese National Standard)
- ASTM A554 — Standard specification for austenitic stainless steel welded, cold-worked tubes
- ASTM A269 — Standard specification for austenitic stainless steel seamless tubes and sheet bars
- ASME SA-269 / SA-313 — Boiler and pressure vessel code specifications for stainless steel tubes
- EN 10216-5 — Welded stainless steel tubes for pressure purposes
- JIS G3446 — Austenitic stainless steel tubes for general purpose (Japanese Industrial Standard)
6.2 Performance & Safety Standards
- ASHRAE 36 — Standard for rating air-to-water heat exchangers used in HVAC applications <