Stainless Steel Coil Tube (Fan Coil Heat Exchanger Tube)
1. Product Overview
The Stainless Steel Coil Tube is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd, designed for use in hydronic heating and cooling systems, particularly in fan coil units (FCU) and floor radiant cooling/heating configurations. This product combines the corrosion resistance and hygienic properties of stainless steel with the thermal efficiency of coil geometry, making it an ideal solution for modern HVAC (Heating, Ventilation, and Air Conditioning) applications.
The coil tube is manufactured in continuous helical form, providing an extended heat transfer surface area within a compact footprint. This design is especially suited for applications involving combined cooling systems that integrate floor radiant cooling with fan coil units, as demonstrated in experimental studies on the cooling characteristics of such hybrid systems.
2. Material & Properties
2.1 Base Material
- Material Grade: Austenitic stainless steel conforming to ASTM A213/A213M or equivalent standards
- Common Grades: SUS304 (UNS S30408), SUS316L (UNS S31603), SUS321 (UNS S32100)
- Carbon Equivalent (CE): ≤ 0.03% (for SUS304L/SUS316L variants)
- Chromium Content: 18–20% (minimum)
- Nickel Content: 8–12% (minimum)
2.2 Mechanical Properties
- Tensile Strength: ≥ 520 MPa (75,000 psi)
- Yield Strength: ≥ 205 MPa (29,700 psi)
- Elongation at Break: ≥ 40%
- Hardness: ≤ 92 HRB (annealed condition)
- Impact Strength (Charpy V-Notch): ≥ 27 J at −196°C (liquid nitrogen temperature)
2.3 Physical & Thermal Properties
- Density: 7.93 g/cm³
- Thermal Conductivity: 16.3 W/(m·K) at 20°C
- Specific Heat: 0.50 J/(g·K) at 20°C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (20–100°C)
- Maximum Operating Temperature: 870°C (oxidation limit in continuous air service)
2.4 Corrosion Resistance
- Excellent resistance to atmospheric corrosion, freshwater, and mild alkaline environments
- SUS316L grade provides superior pitting and crevice corrosion resistance due to molybdenum (Mo) content of 2–3%
- Immune to stress corrosion cracking (SCC) in most non-chloride environments
- Passivation layer self-heals under normal oxidizing conditions
3. Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (Fan Coil Heat Exchanger Tube) |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd |
| Item No. | 439 |
| 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 | 0.40 mm – 1.50 mm (customizable) |
| Coil Pitch (Helical Spacing) | 6 mm – 25 mm (adjustable per application) |
| Coil Diameter | 100 mm – 600 mm (customizable) |
| Tube Length per Coil | 3 m – 50 m (continuous) |
| Surface Finish | BA (Bright Annealed), No. 4 Brushed, or Matte |
| End Condition | Plain, Flanged, Threaded, or Soldered |
| Operating Pressure | Up to 1.6 MPa (232 psi) standard; up to 4.0 MPa for thick-wall variants |
| Operating Temperature Range | −40°C to +200°C (hydronic service) |
| Tolerance on OD | ±0.05 mm |
| Tolerance on Wall Thickness | ±10% of nominal |
| Standards Compliance | ASTM A213/A213M, EN 10216-5, GB/T 12771 |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection: Cold-rolled stainless steel strip (coil) is procured from certified mills, with mill test certificates verifying chemical composition and mechanical properties.
- Strip Annealing & Pickling: Cold-rolled strip undergoes controlled annealing to relieve residual stresses, followed by acid pickling and passivation to ensure a clean, corrosion-resistant surface.
- Pipe Forming (ERW or Weldless): The strip is formed into a tubular shape using Electric Resistance Welding (ERW) or seamless extrusion methods. For seamless tubes, hot or cold extrusion is employed.
- Post-Forming Annealing: The formed tube is annealed in a protective atmosphere (nitrogen or hydrogen) to restore ductility and achieve the required mechanical properties.
- Precision Coiling: The straight tube is helically coiled using CNC-controlled coiling equipment, ensuring consistent pitch, uniform curvature, and minimal work-hardening at bend points.
- End Processing: Tube ends are deburred, cut to specified angles, and optionally prepared with threads, flanges, or brazing surfaces.
- Final Inspection & Testing: Each coil undergoes dimensional inspection, visual examination, and pressure testing (hydrostatic or pneumatic) to verify integrity.
4.2 Quality Control Points
- In-line eddy current testing for weld seam integrity (ERW tubes)
- Dimensional verification via laser scanning or ultrasonic measurement
- Hydrostatic pressure testing at 1.5× maximum operating pressure for a minimum of 30 seconds
- Surface quality inspection for scratches, inclusions, or decarburization
- Chemical analysis verification (spectrometry) for each heat batch
5. Applications
5.1 Primary Applications
- Fan Coil Units (FCU): Serves as the heat exchanger tube in commercial and residential fan coil units for both heating and cooling modes.
- Floor Radiant Cooling/Heating: Integrated into floor slab systems where coil tubes are embedded in concrete or screed for radiant heat exchange.
- Combined Cooling Systems: Specifically suited for hybrid systems combining floor radiant cooling with fan coil units, where thermal performance and durability are critical.
- Chilled Water Systems: Used in air handling units (AHU) and terminal units for precise temperature control.
5.2 Industry Applications
- Commercial buildings (offices, hospitals, hotels)
- Residential HVAC systems
- Industrial process cooling
- Food and beverage processing (hygienic environments)
- Pharmaceutical manufacturing facilities
- Marine HVAC systems (corrosion-resistant environments)
5.3 Performance in Combined Cooling Systems
Experimental studies on the combined cooling characteristics of floor radiant and fan coil systems have demonstrated that stainless steel coil tubes offer significant advantages in hybrid cooling configurations. The high thermal conductivity of austenitic stainless steel ensures efficient heat transfer between the working fluid and the surrounding medium. The smooth internal surface finish minimizes flow resistance, reducing pumping energy requirements. Furthermore, the corrosion resistance of stainless steel eliminates concerns about long-term degradation in water-based systems, ensuring consistent performance over extended service life.
6. Quality Certifications & Standards
6.1 Certifications
- ISO 9001:2015 – Quality Management System Certification
- ISO 14001:2015 – Environmental Management System Certification
- CE Marking – Conformity with European health, safety, and environmental protection standards
- EN 10204 3.1 – Material Test Certificate (Manufacturer's Declaration of Compliance)
6.2 Applicable Standards
- ASTM A213/A213M – Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubes for High-temperature Service
- EN 10216-5 – Non-alloy and alloy steel tubes for technical uses – Technical delivery conditions – Part 5: Heat-resistant austenitic stainless steel tubes
- GB/T 12771 – Technical conditions for delivery of welded austenitic stainless steel seamless and welded tubes for general purposes (Chinese National Standard)
- ASME B31.9 – Building Services Piping (for HVAC piping applications)
- ASHRAE 90.1 – Energy Standard for Buildings (relevant for HVAC system efficiency)
6.3 Testing & Compliance
- Chemical composition analysis per ASTM E415 (spark emission spectrometry)
- Mechanical testing per ASTM E8/E8M (tensile) and ASTM E23 (impact)
- Corrosion testing per ASTM G48 (pitting) and ASTM G59 (crevice corrosion)
- Dimensional verification per ASTM A213/A213M tolerances
- Pressure testing per ASME B31.9 Section 9
7. Unique Selling Points
Superior Corrosion Resistance: Unlike carbon steel alternatives, the stainless steel coil tube eliminates concerns about internal and external corrosion, significantly extending service life in water-based HVAC systems. This is particularly important in floor radiant systems where the tube is embedded and difficult to replace.
Hygienic Surface Quality: The bright annealed (BA) or electropolished internal surface provides a smooth, non-porous finish that prevents biofilm formation and maintains water quality integrity, making it suitable for potable water and food-grade applications.
Thermal Efficiency: The combination of stainless steel's inherent thermal conductivity and the helical coil geometry maximizes heat transfer coefficient (U-value), ensuring efficient energy utilization in both heating and cooling modes.
Design Flexibility: Available in multiple diameters, wall thicknesses, coil pitches, and end configurations to accommodate diverse system designs and spatial constraints.
Long Service Life: With proper installation, the stainless steel coil tube offers a service life exceeding 25–30 years without degradation, compared to 10–15 years for carbon steel alternatives in similar applications.
Sustainability: Stainless steel is 100% recyclable, and its long service life contributes to reduced lifecycle environmental impact. The manufacturing process adheres to ISO 14001 environmental management standards.
8. Technical Notes & Recommendations
- Installation: Maintain minimum bend radius of 3× OD during field installation to prevent kinking or work-hardening.
- Welding: Use low-heat-input welding processes (TIG/GTAW preferred) with appropriate filler metals (e.g., ER308L for SUS304, ER316L for SUS316L). Preheating is generally not required but should not exceed 150°C.
- Post-Weld Treatment: Passivation treatment (citric acid or nitric acid) is recommended after welding to restore corrosion resistance in the heat-affected zone (HAZ).
- Storage: Store in dry, well-ventilated areas away from carbon steel to prevent cross-contamination. Use non-ferrous protective wrapping.
- System Compatibility: Compatible with all common HVAC refrigerants and hydronic fluids including water, glycol-water mixtures (up to 60% ethylene glycol), and ammonia-based systems.
Document Reference: Product No. 439 – Stainless Steel Coil Tube Technical Specification | Wenzhou Jixing Metal Materials Co., Ltd