Stainless Steel Coil Tube — Fan Coil Unit & HVAC Application Series
Product Overview
The Stainless Steel Coil Tube (Coiltube) produced by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered continuous-length tubular product specifically designed for integration into Fan Coil Unit (FCU) plus Fresh Air Systems and other Heating, Ventilation, and Air Conditioning (HVAC) applications. This coil tube is manufactured in a continuous helical or serpentine configuration that maximizes heat transfer surface area within a compact volumetric envelope, making it an ideal component for energy-efficient thermal exchange systems.
As a critical component in modern building climate control infrastructure, this stainless steel coil tube delivers superior thermal conductivity, corrosion resistance, and long-term structural integrity under cyclic thermal loading conditions. The product aligns with current research findings on energy-saving measures for fan coil unit systems, where material selection and coil geometry directly influence system efficiency and operational longevity.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, selected for its outstanding combination of mechanical strength, corrosion resistance, and thermal performance characteristics.
Material Grades
- SUS304 (ASTM A213 TP304): General-purpose austenitic stainless steel with excellent corrosion resistance in moderate environments. Chromium (Cr) content: 18–20%; Nickel (Ni) content: 8–10.5%.
- SUS316L (ASTM A213 TP316L): Enhanced grade with added Molybdenum (Mo: 2–3%) for superior resistance to chlorides, acidic environments, and marine atmospheres. Low-carbon variant (C ≤ 0.03%) to prevent intergranular corrosion during welding.
- SUS321 (ASTM A213 TP321): Titanium-stabilized austenitic stainless steel (Ti ≥ 5×C) suitable for elevated-temperature applications up to 870°C, offering excellent resistance to stress corrosion cracking.
Key Physical & Mechanical Properties
- Density: 7.93 g/cm³ (SUS304/316L)
- Thermal Conductivity: 16.3 W/(m·K) at 25°C (SUS304)
- Specific Heat Capacity: 0.50 J/(g·K)
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (25–300°C)
- Tensile Strength (UTS): ≥ 520 MPa (SUS304, annealed condition)
- Yield Strength (0.2% offset): ≥ 205 MPa
- Elongation at Fracture: ≥ 40%
- Operating Temperature Range: −196°C to +870°C (SUS321)
- Surface Roughness (Ra): ≤ 0.8 μm (electropolished finish)
Specifications
| Parameter | Specification / Range | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm – 31.75 mm (¼" – 1¼") | ASTM A213 / ASME B36.19M |
| Wall Thickness | 0.5 mm – 3.0 mm | ASTM A213 |
| Coil Pitch (Helical Spacing) | 3 mm – 25 mm (adjustable per design) | Manufacturer Specification |
| Bund Diameter | 50 mm – 400 mm | Manufacturer Specification |
| Tube Length (per coil) | 3 m – 30 m (continuous) | — |
| Surface Finish | Mill finish / Electropolished / Passivated | ASTM A967 / ASTM A380 |
| Surface Roughness (Ra) | 0.4 – 1.6 μm | ISO 1302 |
| Heat Transfer Efficiency | Enhanced by 15–25% vs. straight tube (per unit volume) | ASHRAE Standard 90.1 |
| Maximum Operating Pressure | 1.6 – 4.0 MPa (gauge) | ASME BPV Code Section I |
| Corrosion Resistance | Passive film stable in pH 3–12 aqueous environments | ASTM G48 (Pitting Resistance) |
| End Connections | Flanged / Threaded / Soldered / Brazed | ASME B16.5 / ISO 7 |
| Welding Suitability | Full range (TIG, MIG, Orbital, Resistance) | ASME BPV Code Section IX |
Manufacturing Process
The production of stainless steel coil tubes involves a multi-stage precision manufacturing sequence designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection & Inspection: Hot-rolled stainless steel strip is procured from certified mills and subjected to spectrographic analysis (OES) to verify chemical composition compliance with specified grade requirements.
- Slitting & Leveling: The strip is slit to precise width tolerances (±0.05 mm) and leveled through a roller train to eliminate coil set and ensure flatness.
- Pipe Forming (Cold Roll Forming): The leveled strip passes through a progressive die set with calibrated roll stations that gradually form the flat strip into a tubular cross-section. The forming process is controlled to maintain wall thickness uniformity within ±10% of nominal.
- Seam Welding: A high-frequency induction seam welding (HF) process or TIG (Tungsten Inert Gas) welding is applied to create a continuous, leak-tight seam. Weld bead geometry is optimized for fatigue resistance under cyclic thermal loading.
- Heat Treatment (Annealing): Where required, the formed tube undergoes solution annealing at 1050–1150°C followed by controlled cooling to restore full austenitic microstructure, relieve residual stresses, and achieve the specified soft and bright (S&B) or annealed condition.
- Coil Winding (Helical Coiling): The continuous straight tube is wound into a helical or serpentine coil configuration using CNC-controlled coiling equipment. Pitch, bund diameter, and coil geometry are precisely controlled per engineering drawings.
- Pickling & Passivation: The coil tube is immersed in an acid pickling bath (HNO₃/HF mixture) to remove heat scale and oxidation, followed by nitric acid passivation to establish a chromium-rich passive film (Cr₂O₃) on the surface for enhanced corrosion protection.
- Quality Inspection & Testing: Every production lot undergoes non-destructive testing (NDT) including eddy current inspection (ECI) for wall thickness and seam integrity, hydrostatic pressure testing at 1.5× working pressure, and dimensional verification using laser micrometry.
- Packaging & Dispatch: Finished coil tubes are wrapped in protective VCI (Vapor Corrosion Inhibitor) film, secured in wooden or steel crates, and shipped with mill test certificates (MTC) per EN 10204 Type 3.1.
Applications
The stainless steel coil tube is employed across a broad spectrum of industrial and commercial applications where high thermal efficiency, corrosion resistance, and hygienic requirements are paramount:
Primary Applications
- Fan Coil Units (FCU): Integral heat exchange coils in commercial HVAC systems for air conditioning, heating, and dehumidification in office buildings, hospitals, and hotels.
- Fresh Air Systems: Heat recovery coils in dedicated outdoor air systems (DOAS) for energy-efficient ventilation.
- Chilled Water Systems: Primary and secondary loops in central air handling units (AHU).
- Refrigeration Coils: Evaporator and condenser coils in commercial refrigeration equipment.
Secondary Applications
- Food & Beverage Processing: Sanitary heat exchangers in dairy, brewing, and pharmaceutical production lines (SUS316L, electropolished Ra ≤ 0.4 μm).
- Marine & Offshore: Seawater cooling coils in marine HVAC and power generation systems (SUS316L with Mo-enhanced chloride resistance).
- Chemical Processing: Condensers, reboilers, and heat recovery coils in petrochemical and chemical plants.
- Power Generation: Economizer coils and feedwater heaters in combined cycle power plants.
- Automotive Thermal Management: Battery thermal management coils in electric vehicle (EV) cooling systems.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains rigorous quality management systems ensuring full traceability and compliance with international standards:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification for manufacturing operations |
| ISO 14001:2015 | Environmental Management System for sustainable production practices |
| ISO 45001:2018 | Occupational Health & Safety Management System |
| EN 10204 Type 3.1 | Mill Test Certificate (MTC) with specific inspection results for each lot |
| ASTM A213 | Standard specification for seamless austenitic stainless steel boiler, heat exchanger, and heat-transfer tubing |
| ASME BPV Code Section I | Pressure vessel and heat exchanger design and fabrication compliance |
| CE Marking (EU) | Conformity with European Pressure Equipment Directive (PED 2014/68/EU) |
| TÜV / DNV | Third-party inspection and verification for marine and offshore applications |
| NSF/ANSI 61 | Drinking water system components safety certification (SUS304/316L) |
| 3-A Sanitary Standards | Food-grade hygienic design certification for dairy and pharmaceutical applications |
Unique Selling Points
- Energy Efficiency Enhancement: The helical coil geometry increases heat transfer surface area by up to 40% compared to equivalent-length straight tubing, directly contributing to energy savings of 15–25% in fan coil unit systems as validated by research on FCU plus fresh air system optimization.
- Extended Service Life: Austenitic stainless steel provides corrosion resistance exceeding 50 years in indoor HVAC environments, significantly outperforming copper and carbon steel alternatives in chloride-containing atmospheres.
- Hygienic Design: Electropolished surfaces (Ra ≤ 0.4 μm) minimize biofilm formation and facilitate CIP (Clean-In-Place) protocols, essential for pharmaceutical and food-grade applications.
- Thermal Cycling Durability: The austenitic microstructure accommodates repeated thermal expansion/contraction cycles without fatigue failure, ensuring reliable performance over millions of operating cycles.
- Full Traceability: Each coil tube lot is accompanied by a complete material passport including chemical analysis, mechanical test results, and heat treatment records per EN 10204 Type 3.1.
- Customizable Geometry: CNC-controlled coiling enables precise customization of pitch, bund diameter, and coil configuration to match specific system design requirements and space constraints.
Note: This product specification is based on industry-standard engineering principles and applicable international codes. Specific product parameters should be confirmed with the manufacturer for each order, as configurations may vary based on end-use requirements and applicable jurisdictional regulations.