Stainless Steel Coil Tube — Fan Coil Unit (FCU) Application Grade
Product Overview
The Stainless Steel Coil Tube (Product No. 1494) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled tubular product specifically designed for Fan Coil Unit (FCU) air conditioning systems and related HVAC (Heating, Ventilation, and Air Conditioning) applications. This coil tube serves as the core heat exchange element within fan coil systems, facilitating efficient thermal transfer between the circulating refrigerant or heating medium and the ambient air stream. The product is engineered to address the critical challenges of indoor humid environment conditions, including condensation control, corrosion resistance under high-humidity operation, and long-term structural integrity in thermally cyclic service environments.
The coil tube is supplied in continuous coil form, enabling downstream manufacturers to perform automated cutting, forming, and assembly operations with minimal material waste and maximum production efficiency.
Material & Properties
The stainless steel coil tube is fabricated from austenitic stainless steel grades, primarily AISI 304 (UNS S30408) and AISI 316 (UNS S31603), selected for their superior corrosion resistance, formability, and compatibility with HVAC refrigerants and water-based heating media.
Key Material Characteristics
- Corrosion Resistance: The chromium (Cr) content of ≥18% and nickel (Ni) content of ≥8% (Grade 304) or ≥2% molybdenum (Mo) addition (Grade 316) provide excellent resistance to condensation-induced corrosion, chloride pitting, and general atmospheric degradation in high-humidity indoor environments.
- Thermal Conductivity: Austenitic stainless steel offers adequate thermal conductivity (approximately 16.3 W/m·K for Grade 304) to ensure efficient heat transfer across the coil tube wall.
- Mechanical Strength: Tensile strength of ≥520 MPa and yield strength of ≥205 MPa ensure structural integrity under internal pressure cycling and thermal expansion loads.
- Weldability: Excellent cold-forming and welding characteristics facilitate seamless integration into fan coil unit heat exchanger assemblies.
- Hygienic Surface Finish: The smooth internal surface (Ra ≤ 0.8 μm) minimizes fouling, scaling, and microbial biofilm accumulation, maintaining long-term thermal performance.
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 12.7 mm (1/4" – 1/2") | ISO 3505 / ASME B36.19M |
| Wall Thickness (WT) | 0.5 mm – 1.0 mm | ASME B36.19M |
| Coil Inner Diameter (CID) | 300 mm – 600 mm | Manufacturer specification |
| Coil Length | Up to 500 m per coil (continuous) | — |
| Material Grade | AISI 304 / AISI 316 / AISI 321 | ASTM A213 / ASTM A269 |
| Surface Finish | 2B / No. 4 / Electropolished (Ra ≤ 0.8 μm) | ASTM A480 |
| Maximum Working Pressure | 1.6 MPa (standard); 2.5 MPa (reinforced) | EN 10217 / ASME B31.9 |
| Operating Temperature Range | −40 °C to +180 °C | — |
| Tolerance on OD | ±0.1 mm (precision grade); ±0.2 mm (commercial grade) | ISO 1128 / EN 10216 |
| Helix Pitch / Coil Pitch | Customizable, typically 12 mm – 25 mm | Application-specific |
| End Form | Plain / Beveled / Flanged / Threaded | Customer specification |
| Packaging | Wooden pallet with moisture-proof wrapping; coil protected by inner and outer cardboard rings | ISO 4180 |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing workflow designed to ensure dimensional accuracy, metallurgical quality, and surface integrity:
- Raw Material Procurement: Cold-rolled stainless steel strip is sourced from certified mills meeting ASTM A240/A213 chemical composition requirements. Each batch undergoes incoming spectral analysis (OES) to verify alloy content.
- Slitting and Leveling: The strip is slit to the required width and cold-rolled to precise thickness with tension leveling to eliminate residual stresses and ensure flatness.
- Forming (Tube Making): The leveled strip is fed through a series of progressively reducing rollers in a cold-rolled tube-forming machine. The strip is shaped into a semi-circular profile and then closed into a tubular form. The seam is welded using High-Frequency Induction Welding (HF-IW) with argon gas shielding to prevent oxidation of the weld zone.
- Heat Treatment (Optional): For applications requiring stress relief or enhanced corrosion resistance, the welded tube may undergo solution annealing at 1050 °C – 1150 °C followed by rapid quenching.
- Coiling: The formed tube is continuously coiled onto a pay-off reel at controlled tension to maintain dimensional stability. Coil diameter and length are adjusted based on customer requirements.
- Surface Treatment: Optional electropolishing or passivation treatment is applied to enhance surface smoothness, remove work-hardened surface layers, and improve corrosion resistance in humid environments.
- Quality Inspection: Each coil undergoes hydrostatic pressure testing, dimensional verification (OD, WT, straightness), surface defect inspection (eddy current or magnetic particle testing), and chemical composition verification.
- Packaging and Dispatch: Qualified coils are wrapped in moisture-proof material, secured on wooden pallets, and labeled with mill test certificates (MTC) and traceability markings.
Applications
The stainless steel coil tube is engineered for demanding thermal management applications, with particular emphasis on fan coil unit systems operating in high-humidity indoor environments:
- Fan Coil Units (FCU): Primary application — used as the heat exchange coil element in ceiling-mounted, wall-mounted, and concealed fan coil units for commercial and residential HVAC systems.
- Air Handling Units (AHU): Heat exchanger coils in large-capacity air handling units for commercial buildings, hospitals, and cleanrooms.
- Chilled Water Systems: Secondary distribution piping and coil elements in chilled water systems where corrosion resistance under continuous condensation is critical.
- Humidification and Dehumidification Systems: Coil elements in industrial dehumidification equipment operating in high-moisture environments.
- Food and Pharmaceutical Processing: Heat exchange coils in hygienic processing equipment requiring smooth, non-porous, corrosion-resistant surfaces.
- Marine and Coastal HVAC Systems: Fan coil and heat exchanger coils in environments exposed to salt-laden air and high humidity.
Unique Selling Points
- Superior Humid Environment Performance: Engineered specifically for fan coil unit systems operating under sustained condensation conditions. The austenitic stainless steel matrix and optional molybdenum addition (Grade 316) provide outstanding resistance to condensation-induced pitting and crevice corrosion, addressing the core challenges identified in indoor humid environment analyses.
- Continuous Coil Supply: Delivered in continuous coil form, enabling automated downstream processing with minimal cut-off waste (typically < 2% material loss), reducing total cost of ownership for high-volume FCU manufacturers.
- Precision Dimensional Control: Tight tolerance on outer diameter (±0.1 mm) and wall thickness ensures consistent hydraulic performance and reliable fin-tube contact in heat exchanger assemblies.
- Hygienic Surface Quality: Electropolished internal surfaces with Ra ≤ 0.8 μm minimize fouling and biofilm formation, maintaining thermal efficiency over the system's operational life.
- Customizable Configuration: Flexible customization of coil diameter, pitch, length, end form, and surface finish to meet specific application and OEM requirements.
- Full Traceability: Every coil is accompanied by a Mill Test Certificate (MTC) with chemical composition, mechanical properties, and heat treatment records, ensuring complete supply chain traceability.
Quality Certifications and Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and product certifications to ensure compliance with international standards:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System — Certified for design, manufacturing, and supply of stainless steel tube products |
| ISO 14001:2015 | Environmental Management System — Demonstrating commitment to sustainable manufacturing practices |
| ISO 45001:2018 | Occupational Health and Safety Management System |
| CE Marking (EU) | Compliance with European regulatory requirements for pressure equipment and construction products |
| ASTM A213 / A269 | Material compliance for seamless and welded austenitic stainless steel tube |
| EN 10217 / EN 10216 | European standard compliance for welded stainless steel tube |
| GB/T 14976 / GB/T 13296 | Chinese national standard compliance for seamless and welded stainless steel tube |
| TÜV / SGS Testing | Third-party product inspection and verification for international market compliance |
Technical Notes
Note on Humid Environment Performance: In fan coil unit systems operating under conditions of sustained indoor humidity (relative humidity > 60%), condensation on the coil tube surface creates a continuous electrolyte film that accelerates corrosion in carbon steel or improperly specified stainless steel alternatives. The AISI 316 grade with ≥2% molybdenum content is strongly recommended for such applications, as the molybdenum significantly enhances pitting resistance equivalent number (PREN ≥ 24), ensuring a service life exceeding 20 years under continuous condensation exposure. Regular inspection intervals of 12–18 months are advised for systems operating in coastal or industrial humid environments.
Manufacturer Information
Wenzhou Jixing Metal Materials Co., Ltd. is a specialized manufacturer of stainless steel tube products based in Wenzhou, Zhejiang Province, China. The company possesses advanced cold-rolled tube forming capabilities, high-frequency induction welding technology, and comprehensive quality inspection facilities. Product No. 1494 (Stainless Steel Coil Tube) represents a key offering in the company's HVAC and thermal management product portfolio.