Stainless Steel Coil Tube (Coiltube) for HVAC Fan Coil Terminal Units
Product Code: JX-839 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered heat exchanger component designed specifically for central air conditioning fan coil terminal units. This product represents the core thermal transfer element within HVAC (Heating, Ventilation, and Air Conditioning) systems, where it facilitates efficient heat exchange between refrigerant media and ambient air. The coil tube is manufactured to meet the demanding requirements of networked terminal controllers that govern flow regulation, temperature modulation, and system-wide load balancing in commercial and industrial climate control applications.
As a critical component in fan coil unit assemblies, this coiltube is engineered to withstand cyclic thermal stress, corrosive atmospheric conditions, and continuous mechanical vibration inherent in HVAC operation. The product is supplied in continuous coil form, enabling automated coil winding processes that minimize joint density and maximize thermal performance per unit area.
2. Material & Properties
2.1 Base Material Composition
The coiltube is fabricated from high-grade austenitic stainless steel, selected for its exceptional combination of corrosion resistance, thermal conductivity, and mechanical durability. The primary material grades include:
- AISI 304 (UNS S30400): Standard grade with 18% Chromium (Cr) and 8% Nickel (Ni), offering excellent general corrosion resistance and weldability.
- AISI 316 (UNS S31600): Enhanced grade with 2–3% Molybdenum (Mo) addition for superior resistance to chlorides and aggressive chemical environments.
2.2 Mechanical Properties
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (UTS) | ≥ 520 MPa | ASTM A269 / GB/T 12771 |
| Yield Strength (0.2% offset) | ≥ 205 MPa | ASTM A269 / GB/T 12771 |
| Elongation at Break | ≥ 40% | ASTM A269 |
| Hardness (Rockwell B) | ≤ 95 HRB | ASTM A262 |
| Impact Strength (20°C) | ≥ 40 J | ASTM A370 |
2.3 Physical & Thermal Properties
| Property | Value |
|---|---|
| Density | 7.93 g/cm³ |
| Thermal Conductivity (at 20°C) | 16.3 W/(m·K) |
| Thermal Conductivity (at 100°C) | 21.5 W/(m·K) |
| Specific Heat Capacity | 0.50 J/(g·K) |
| Thermal Expansion Coefficient (20–100°C) | 17.3 × 10⁻⁶ /K |
| Operating Temperature Range | −196°C to +870°C |
2.4 Corrosion Resistance
- Excellent resistance to atmospheric corrosion and industrial atmospheres
- High resistance to oxidation at elevated temperatures up to 870°C
- Outstanding resistance to organic acids, weak inorganic acids, and dilute alkaline solutions
- 316 grade provides exceptional resistance to pitting and crevice corrosion in chloride-containing environments
- Immunity to intergranular corrosion following appropriate solution annealing (1050–1150°C)
3. Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 6.35 mm / 9.52 mm / 12.70 mm / 15.88 mm (1/4" / 3/8" / 1/2" / 5/8") |
| Wall Thickness | 0.50 mm / 0.80 mm / 1.00 mm / 1.20 mm |
| Tolerance on OD | ± 0.05 mm (precision grade) |
| Tolerance on Wall Thickness | ± 0.05 mm |
| Coil Length (per spool) | Up to 1,000 m (continuous, joint-free) |
| Coil Inner Diameter (ID) | 200 mm – 600 mm (configurable) |
| Surface Finish | Mirror polish (Ra ≤ 0.2 μm) / Brushed (Ra ≤ 0.8 μm) / Annealed matte |
| Pressure Rating | Up to 1.6 MPa (standard) / 3.2 MPa (heavy-wall) |
| End Preparation | Plain end / Beveled end / Flanged (custom) |
| Heat Treatment Condition | Solution annealed and pickled (SA) |
3.1 Dimensional Tolerances
| OD Range (mm) | OD Tolerance (mm) | Wall Thickness Tolerance (mm) |
|---|---|---|
| ≤ 10.0 | ± 0.05 | ± 0.05 |
| 10.1 – 20.0 | ± 0.08 | ± 0.05 |
| 20.1 – 32.0 | ± 0.10 | ± 0.08 |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection: Hot-rolled stainless steel strip/sheet from certified mills, verified via spectroscopic analysis (OES) for chemical composition compliance.
- Cold Rolling & Annealing: Strip is cold-rolled to precise gauge thickness, followed by continuous annealing in protective atmosphere (95% N₂ + 5% H₂) at 1050–1150°C to achieve fully austenitic microstructure.
- Pickling & Passivation: Acid pickling removes scale and oxidation; passivation treatment forms a stable chromium oxide passive film on the surface.
- Tube Forming (Cold Drawing): Strip is formed into tubular cross-section using precision CNC forming stations with calibrated tooling to ensure dimensional accuracy.
- Continuous Annealing: Formed tubes undergo continuous furnace annealing to relieve cold-work stresses and restore ductility.
- Surface Finishing: Mechanical polishing, electrolytic polishing, or brushing operations achieve specified surface roughness values.
- Coil Winding: Continuous tubes are wound onto spools using automated coil-winding systems to maintain uniform tension and prevent deformation.
- Non-Destructive Testing (NDT): 100% eddy current inspection (per ASTM E309) and hydrostatic pressure testing (per ASTM A269) on all production lots.
4.2 Quality Control Measures
- Online dimensional monitoring via laser micrometers at each forming station
- Automated eddy current flaw detection at line speed (minimum 30 m/min)
- Hydrostatic testing at 1.5× maximum working pressure, held for minimum 5 seconds per tube segment
- Chemical composition verification via portable XRF analyzer on each incoming coil
- Hardness testing (Rockwell/Brinell) on every production lot
5. Applications
5.1 Primary Applications
- Central Air Conditioning Fan Coil Units (FCUs): Primary heat exchanger coils in terminal air-handling units for commercial buildings, hospitals, and industrial facilities.
- Networked HVAC Terminal Controllers: Integration with computerized networked control systems that monitor and regulate coil performance parameters including water flow rate, supply/return temperature differential, and valve actuator positions.
- VAV (Variable Air Volume) Systems: Coils within variable air volume terminal units that modulate cooling/heating capacity based on zone demand signals.
5.2 Secondary Applications
- Heat recovery and heat exchange systems in energy-efficient building HVAC
- Condensers and evaporators in refrigeration and chiller systems
- Process heating and cooling in pharmaceutical, food and beverage, and chemical industries
- Water treatment and desalination plant heat exchangers
- Automotive and marine HVAC systems requiring corrosion-resistant components
6. Quality Certifications & Standards Compliance
| Certification / Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 14001:2015 | Environmental Management System |
| ISO 45001:2018 | Occupational Health & Safety Management |
| ASTM A269 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing |
| ASTM A270 | Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Chemical and Allied Lines |
| GB/T 12771 | Chinese National Standard for Stainless Steel Tubes for General Purposes |
| EN 10217-7 | European Standard for Stainless Steel Tubes — General Requirements |
| JIS G3459 | Japanese Industrial Standard for Stainless Steel Tubes for General Purposes |
| PED 2014/68/EU | European Pressure Equipment Directive (Category I–IV) |
| NACE MR0175 / ISO 15156 | Resistance to Sulfide Stress Cracking (for oil/gas HVAC applications) |
7. Unique Selling Points
- Continuous Joint-Free Construction: Supplied as continuous coil up to 1,000 m per spool, eliminating butt-weld joints that represent potential failure points and thermal bottlenecks in heat exchanger assemblies.
- Precision Dimensional Control: ± 0.05 mm tolerance on outer diameter ensures perfect fit within automated coil-winding and brazing equipment used in FCU manufacturing.
- Superior Surface Integrity: Mirror-polished finish (Ra ≤ 0.2 μm) minimizes fouling and biofilm accumulation, maintaining heat transfer efficiency over extended service life.
- Networked Controller Compatibility: Designed with consistent hydraulic resistance characteristics that enable accurate pressure-flow modeling in networked terminal unit control algorithms.
- Extended Service Life: Austenitic stainless steel construction provides 25+ year design life under normal HVAC operating conditions without corrosion-related degradation.
- Energy Efficiency: Low thermal resistance and high thermal conductivity contribute to reduced fan power consumption and improved COP (Coefficient of Performance) in fan coil systems.
- Environmental Sustainability: 100% recyclable material; production process incorporates closed-loop water recycling and zero-chlorine pickling options.
8. Packaging & Delivery
Coiltubes are supplied wound on heavy-duty steel spools, wrapped in anti-corrosion VCI (Vapor Corrosion Inhibitor) film, and secured with tension bands. Each spool is labeled with material grade, heat number, dimensions, and traceability code. Export packaging complies with ISPM 15 (International Standards for Phytosanitary Measures) for wooden spool components. Standard lead time is 15–20 working days from order confirmation.
Note: This product is specifically engineered for integration with networked controller systems in central air conditioning fan coil terminal units, as detailed in the technical design literature "Design of Networked Controller for Central Air Conditioning Fan Coil Terminal Units." All performance parameters are validated for compatibility with digital communication protocols (Modbus RTU/TCP, BACnet) employed in modern building management systems.