Stainless Steel Coil Tube for HVAC Fan Coil Unit Systems
Product Overview
The Stainless Steel Coil Tube is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd, specifically designed for integration into Fan Coil Unit (FCU) air conditioning systems and thermal exchange applications. This coil tube product represents a critical component in modern demand-response-capable HVAC systems, providing reliable heat transfer performance while maintaining structural integrity under cyclic thermal loading conditions.
Coil tubes are formed through cold-rolling and precision bending processes that produce continuous, tightly wound helical or spiral configurations. These configurations maximize surface area-to-volume ratios, enabling superior thermal exchange efficiency in compact system footprints. The product is engineered to support the adaptability requirements of HVAC systems participating in grid demand response programs, ensuring consistent performance across variable operating conditions.
Material & Properties
The coil tube 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:
- SUS304 (AISI 304 / 1.4301) — Chromium-Nickel austenitic stainless steel offering excellent general corrosion resistance and formability
- SUS316L (AISI 316L / 1.4404) — Low-carbon Chromium-Nickel-Molybdenum austenitic stainless steel providing superior resistance to pitting and crevice corrosion
- SUS321 (AISI 321 / 1.4541) — Titanium-stabilized austenitic stainless steel for enhanced resistance to intergranular corrosion at elevated temperatures
Key Material Properties
- Corrosion Resistance: Passive chromium oxide film (Cr₂O₃) provides self-healing protection against atmospheric, aqueous, and chemical corrosion
- Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C, ensuring efficient heat transfer in refrigerant and water circuits
- Mechanical Strength: Yield strength of 205–310 MPa (annealed condition); tensile strength of 515–720 MPa
- Temperature Range: Operational stability from cryogenic temperatures (−196°C) to 870°C (oxidation limit in air)
- Hygienic Surface Finish: Passivated inner surface with Ra ≤ 0.5 μm available upon request
Technical Specifications
| Parameter | Specification |
|---|---|
| Product Designation | Stainless Steel Coil Tube (SS Coil Tube) |
| Material Grades | SUS304, SUS316L, SUS321, SUS310S (available upon request) |
| Outer Diameter (OD) | 3.0 mm – 25.0 mm (customizable) |
| Wall Thickness (WT) | 0.3 mm – 1.5 mm |
| Coil Winding Diameter | 50 mm – 500 mm |
| Coil Length per Spool | 5 m – 50 m (continuous coil) |
| Tolerance — OD | ±0.1 mm |
| Tolerance — WT | ±10% (minimum) |
| Surface Finish | Mill finish, pickled, polished (2B, BA, #4, mirror) |
| End Condition | Plain cut, deburred, or beveled |
| Operating Pressure | Up to 2.5 MPa (design-dependent) |
| Operating Temperature | −40°C to +150°C (standard); up to +300°C (special grade) |
| Refrigerant Compatibility | R-410A, R-32, R-407C, R-134a, R-404A |
| Welding Compatibility | TIG (GTAW), laser welding, orbital welding |
Manufacturing Process
The production of stainless steel coil tubes follows a rigorous multi-stage manufacturing sequence designed to ensure dimensional precision, metallurgical integrity, and consistent performance:
- Raw Material Selection: Hot-rolled stainless steel strip is sourced from certified mill producers and subjected to incoming inspection per ASTM E10 standard. Chemical composition is verified through Optical Emission Spectrometry (OES) and Positive Material Identification (PMI).
- Slitting & Annealing: Coils are slit to required width specifications and annealed at 1050–1100°C in a protective atmosphere (hydrogen or nitrogen) to achieve full solution treatment and remove cold-work stresses.
- Cold Rolling: Precision cold-rolling reduces strip thickness to target wall thickness specifications with tight tolerance control (±10% minimum wall thickness).
- Tube Forming (Seam Welding): Strip is formed into tubular cross-section through rotary forming rollers, followed by resistance seam welding (RSW) or laser welding to produce a continuous tube body. Weld bead is ground flush for uniform internal diameter.
- Precision Coiling: The formed tube is wound into the required helical or spiral configuration using CNC-controlled coiling equipment. Winding parameters (pitch, diameter, turn count) are programmatically controlled to ensure geometric consistency.
- Post-Weld Annealing & Pickling: Heat-affected zones are stabilized through controlled annealing. The coil tube is then pickled in a mixed acid bath (HNO₃/HF) to remove oxide scale and restore the passive film.
- Passivation: Final passivation treatment using 20–30% citric acid or nitric acid solution ensures maximum corrosion resistance.
- Quality Inspection: Each coil is subjected to dimensional verification, visual inspection, dye penetrant testing (DPT) per ASTM E709, and hydrostatic pressure testing.
Applications
The stainless steel coil tube finds extensive application across multiple industrial and commercial sectors:
- HVAC Fan Coil Units: Primary heat exchanger tubes in air-side heat exchangers for commercial and residential fan coil unit systems. The coil tube geometry enables compact design while maintaining high air-to-water heat transfer coefficients.
- Demand Response HVAC Systems: Integrated into smart building HVAC systems that participate in electrical grid demand response programs. The thermal mass and response characteristics of stainless steel coil tubes support rapid modulation of cooling/heating capacity in response to grid signals.
- Refrigeration & Chilling Systems: Evaporator and condenser coils in commercial refrigeration units, chillers, and heat pump systems.
- Industrial Process Heating & Cooling: Heat exchangers in chemical processing, pharmaceutical manufacturing, and food processing plants.
- Automotive Thermal Management: Engine coolant loops, transmission oil coolers, and electric vehicle battery thermal management systems.
- Water Treatment & Purification: Ultrafiltration membrane housings and reverse osmosis system heat recovery loops.
Demand Response System Integration
In the context of demand response (DR) participation, the stainless steel coil tube's thermal inertia and predictable heat transfer characteristics enable HVAC systems to absorb and release thermal energy strategically. This allows Fan Coil Units to modulate compressor and fan operation in response to utility DR signals, reducing peak electrical demand while maintaining occupant comfort within ASHRAE 55 thermal comfort boundaries.
Quality Certifications & Standards Compliance
All products are manufactured and tested in accordance with the following international standards and certifications:
- ISO 9001:2015 — Quality Management System certification for manufacturing processes
- ISO 14001:2015 — Environmental Management System certification
- ASME B36.19M — Dimensions of stainless steel tubing (welded, seamless, and cold-worked)
- ASTM A213 / A269 — Specifications for austenitic stainless steel tubing for heat transfer
- EN 10217-7 — European standard for cold-worked stainless steel tubes for pressure purposes
- GB/T 14976 — Chinese national standard for seamless stainless steel tubes
- JIS G3446 — Japanese Industrial Standard for cold-rolled stainless steel tubing
- EN 10204 Type 3.1 — Material test certificates provided for all shipments
- CE Marking — Compliance with EU Pressure Equipment Directive (PED 2014/68/EU) for pressure applications
- NSF/ANSI 61 — Available for potable water applications
Unique Selling Points
- Precision Geometry: CNC-controlled coiling ensures dimensional accuracy within ±0.5 mm tolerance on winding diameter, critical for plug-and-play installation in pre-fabricated HVAC assemblies.
- Superior Corrosion Longevity: Austenitic stainless steel construction eliminates concerns of internal corrosion, scale formation, and tube wall thinning — common failure modes of copper and carbon steel alternatives in water-glycol heat transfer fluids.
- Thermal Cycling Resilience: Maintains mechanical and dimensional stability through 100,000+ thermal cycles without fatigue cracking, supporting long-term demand response duty cycles.
- Low Refrigerant Charge: Tight coil winding geometry minimizes internal volume, reducing required refrigerant charge by up to 30% compared to equivalent-capacity finned tube designs — beneficial under Montreal Protocol regulations.
- Hygienic & Food-Grade Compatible: Available in electropolished finish suitable for pharmaceutical and food processing applications requiring FDA-compliant surfaces.
- Custom Engineering: Full customization of coil geometry, material grade, surface finish, and end preparation to meet specific OEM requirements.
Technical Support & Consultation
Wenzhou Jixing Metal Materials Co., Ltd provides comprehensive technical support including thermal performance modeling, pressure drop calculations, and system-level integration guidance. Engineering teams are available to assist with coil tube specification selection for demand response HVAC system design, ensuring optimal balance between thermal capacity, response time, and energy efficiency metrics.