Stainless Steel Coil Tube — Fan Coil Unit (FCU) Grade
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product Code: JX-ST-CT-1034
Classification: Precision Formed Tubing — Coil Configuration for HVAC Systems
1. Product Overview
The Stainless Steel Coil Tube (Product No. 1034) is a precision-formed tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd. for use in Fan Coil Units (FCU) and other HVAC (Heating, Ventilation, and Air Conditioning) applications. Engineered from high-grade austenitic stainless steel, this coil tube is designed to meet the rigorous thermal, mechanical, and corrosion resistance demands of modern fan coil unit selection and design standards.
In the context of fan coil unit system design, the coil tube serves as the critical heat exchange medium. The selection of appropriate coil tube material, geometry, and configuration directly impacts the overall thermal performance, pressure drop characteristics, and long-term service life of the FCU. This product is specifically engineered to address the key design considerations discussed in industry literature regarding FCU selection — including optimal tube diameter, coil pitch, number of rows, and material compatibility with various refrigerants and water-based heat transfer media.
2. Material & Properties
2.1 Base Material Specification
- Primary Grade: AISI 304 (UNS S30400) Austenitic Stainless Steel
- Alternative Grade: AISI 316 (UNS S31600) — for enhanced chloride resistance applications
- Material Form: Seamless or welded stainless steel tubing, cold-drawn to final dimensions
- Surface Finish: Mirror polished (Ra ≤ 0.4 μm) or industrial brushed (Ra ≤ 1.6 μm)
2.2 Mechanical Properties
| Property | Grade 304 | Grade 316 | Test Standard |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 515 | ASTM A270 / GB/T 12771 |
| Yield Strength (MPa) | ≥ 205 | ≥ 170 | ASTM A270 / GB/T 12771 |
| Elongation (%) | ≥ 40 | ≥ 40 | ASTM A270 |
| Hardness (HRB) | ≤ 95 | ≤ 92 | ASTM E18 |
| Thermal Conductivity (W/m·K) @ 20°C | 16.3 | 14.6 | ASTM E153 |
| Corrosion Resistance | Excellent | Superior (chloride-resistant) | ASTM G48 / G53 |
2.3 Chemical Composition (Typical)
| Element | Grade 304 (%) | Grade 316 (%) |
|---|---|---|
| Carbon (C) | ≤ 0.08 | ≤ 0.08 |
| Chromium (Cr) | 18.0 – 20.0 | 16.0 – 18.0 |
| Nickel (Ni) | 8.0 – 10.5 | 10.0 – 14.0 |
| Molybdenum (Mo) | — | 2.0 – 3.0 |
| Iron (Fe) | Balance | Balance |
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm (¼"), 9.53 mm (⅜"), 12.7 mm (½"), 15.88 mm (⅝") | ASTM A213 / GB/T 14976 |
| Wall Thickness | 0.5 – 1.5 mm (standard); 0.3 – 0.8 mm (thin-wall FCU grade) | ASTM A270 | Coil Pitch (Row Spacing) | 12.7 mm, 15.88 mm, 19.05 mm, 25.4 mm (configurable) | ASHRAE Standard 90.1 |
| Tube Length per Row | 600 mm – 2,400 mm (custom available) | Manufacturer specification |
| Number of Rows | 2, 3, 4, 6 rows (standard configurations) | ASHRAE / ISO 13373 |
| Coil Configuration | Serpentine, cross-flow, or parallel-flow arrangement | ISO 13373:2019 |
| Operating Temperature | -40°C to +150°C (continuous); +200°C (short-term) | ASME BPV Code |
| Maximum Working Pressure | 1.6 MPa (standard); 2.5 MPa (reinforced) | ASME B31.5 |
| Hydrostatic Test Pressure | 1.5× Working Pressure (minimum 2.5 MPa) | ISO 1127 / EN 10216-5 |
| Dimensional Tolerance (OD) | ±0.05 mm (precision grade) | ASTM A213 |
| Dimensional Tolerance (Wall) | ±10% of nominal | GB/T 14976 |
| Fin Material (if finned) | Aluminum (99.5% Al) or Copper-clad Aluminum | ISO 13373 |
| Fin Density | 10 – 14 fins per inch (FPI) | Manufacturer specification |
| Thread Connection | G½", G¾", G1" BSP or NPT; Flange per ASME B16.5 | ASME B1.20.1 |
4. Manufacturing Process
4.1 Production Workflow
- Material Selection & Inspection: Raw stainless steel coils or bars are verified for chemical composition (spectroscopic analysis) and mechanical properties (tensile testing) prior to processing. Incoming material must conform to ASTM A270 or GB/T 12771 specifications.
- Tube Forming: Precision cold-drawing or cold-rolling of seamless or ERW (Electric Resistance Welded) stainless steel tubing to achieve exact OD and wall thickness tolerances. The cold-working process enhances surface finish and dimensional accuracy critical for FCU heat exchanger performance.
- Coil Bending / Forming: The formed tubes are mechanically bent into serpentine or U-turn configurations using CNC-controlled tube bending machines. Bend radii are carefully controlled (minimum 3× OD) to prevent wall thinning, ovality, or cross-sectional deformation that would compromise flow uniformity across the coil.
- Fin Attachment (for Finned Coil Tubes): Aluminum fins are mechanically bonded to the tube surface using high-frequency brazing (HFR — High Frequency Resistance) or mechanical expansion techniques. This ensures minimal thermal contact resistance between the tube and fin surfaces.
- Header Assembly: Individual coil tubes are connected to inlet and outlet headers (manifolds) using precision TIG (Tungsten Inert Gas) welding with argon shielding. Weld quality is verified through visual inspection and, where applicable, penetrant testing (PT) per ASTM E709.
- Surface Treatment & Cleaning: Final coil assemblies undergo acid pickling and passivation to remove scale, restore the protective chromium oxide layer, and ensure corrosion resistance. Mirror polishing is applied where specified.
- Pressure Testing: Each coil tube assembly undergoes 100% hydrostatic pressure testing at 1.5× the rated working pressure, with a minimum hold time of 30 minutes. Air or nitrogen leak testing is performed for hermetic integrity verification.
- Final Inspection & Packaging: Dimensional verification, surface quality assessment, and performance validation are conducted. Finished products are packaged with protective end caps, desiccant packets, and moisture-barrier wrapping for shipment.
4.2 Process Quality Controls
- Inline optical inspection for surface defects during tube drawing
- CNC bending with real-time radius monitoring and feedback control
- 100% hydrostatic pressure testing (no sampling)
- Weld joint radiography (RT) on 5% of production lots per ASME Section V
- Thermal performance testing on representative samples per ISO 13373
5. Applications
5.1 Fan Coil Unit (FCU) Systems
The primary application domain for this stainless steel coil tube is in Fan Coil Units, which are the terminal air handling devices in central air conditioning systems. The coil tube functions as the heat exchange core, transferring thermal energy between the circulating refrigerant (or chilled/heating water) and the air stream. Key design parameters addressed include:
- Thermal Efficiency: The high thermal conductivity and low fouling resistance of stainless steel ensure optimal heat transfer coefficients (U-values) across varying operating conditions.
- Pressure Drop Optimization: The smooth internal surface finish (Ra ≤ 0.4 μm) minimizes frictional pressure losses, reducing pumping power requirements and improving system COP (Coefficient of Performance).
- Refrigerant Compatibility: Compatible with R-410A, R-32, R-134a, R-407C, ammonia (NH₃), and water-based heat transfer fluids.
- Durability: Resistance to condensation corrosion extends service life to 20+ years in standard HVAC environments.
5.2 Additional Applications
- Commercial and residential HVAC systems (chilled water coils, condensing coils)
- Industrial process cooling and heating heat exchangers
- Food and beverage industry refrigeration systems
- Pharmaceutical cleanroom air handling units
- Marine HVAC and refrigeration systems (Grade 316)
- Automotive air conditioning evaporator and condenser coils
- Chiller and boiler heat exchanger tubes
- Dehumidification and air treatment systems
6. Quality Certifications & Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System — Certified manufacturing processes |
| ISO 14001:2015 | Environmental Management System |
| CE Marking | Compliance with EU Machinery Directive 2006/42/EC and Pressure Equipment Directive 2014/68/EU |
| ASME | American Society of Mechanical Engineers — Pressure Vessel and Piping Code compliance |
| ISO 13373:2019 | Air-Conditioning and Refrigeration — Heat Exchangers (performance testing) |
| ASHRAE Standard 90.1 | Energy efficiency compliance for HVAC equipment |
| EN 10216-5 | European standard for pressure equipment — hydrostatic testing |
| NACE MR0175 / ISO 15156 | Sulfide stress corrosion resistance (for sour service applications) |
| UL / CSA | Safety certification for HVAC components (North American market) |
| NSF/ANSI 61 | Drinking water system components — material safety |
7. Unique Selling Points
- Superior Corrosion Resistance: Stainless steel construction eliminates the corrosion and scaling issues common with copper or carbon steel coils, particularly in high-humidity or chemically aggressive environments. This is a critical advantage in FCU applications where condensation is prevalent.
- Extended Service Life: Designed for 20–25 year operational lifespan with minimal maintenance, significantly reducing total cost of ownership (TCO) compared to conventional materials.
- Hygienic Surface: Mirror-polished interior surfaces prevent biofilm formation and bacterial growth, making this coil tube ideal for pharmaceutical, food processing, and healthcare applications.
- Design Flexibility: Configurable coil pitch, row count, and tube geometry allow customization to match specific FCU design requirements, optimizing thermal performance for each installation scenario.
- Environmental Sustainability: Stainless steel is 100% recyclable, non-toxic, and does not leach harmful substances into refrigerants or water circuits. Compatible with low-GWP (Global Warming Potential) refrigerants.
- Pressure Resistance: Withstanding pressures up to 2.5 MPa, these coil tubes exceed the requirements of standard FCU operating conditions, providing a safety margin for transient pressure events.
- Wenzhou Jixing Manufacturing Excellence: Leveraging the company's expertise in precision metal forming and strict quality control protocols, ensuring dimensional accuracy