Stainless Steel Coil Tube (Coiltube) — HVAC Terminal Application Series
Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular component supplied in continuous coil form, designed primarily for use in terminal units of central air conditioning systems in commercial and office buildings. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product series represents a high-performance solution for heat exchange applications where corrosion resistance, thermal conductivity, and long-term operational reliability are critical. The coil tube is formed into compact serpentine or helical configurations that maximize surface area within minimal envelope space, enabling efficient heat transfer in fan coil units (FCUs), air handling units (AHUs), and chilled water terminal coils.
Based on extensive research into the operational regulation of central air conditioning terminal coil tubes in office buildings, this product is engineered to address common challenges such as uneven temperature distribution, excessive pressure drop, scaling accumulation, and premature degradation of heat transfer efficiency. The resulting design prioritizes hydraulic optimization, fouling resistance, and maintainability throughout the service life of the installation.
Material & Properties
The coil tube is fabricated from austenitic stainless steel grades selected for their superior combination of mechanical strength, corrosion resistance, and thermal performance in HVAC environments.
- Primary Alloy Grades: AISI 304 (UNS S30400), AISI 316 (UNS S31600), and AISI 316L (UNS S31603)
- Corrosion Resistance: Excellent resistance to chlorides, condensation water, and atmospheric pollutants; 316/316L grades provide enhanced protection against pitting and crevice corrosion in coastal or high-chloride environments.
- Thermal Conductivity: Approximately 16.3 W/(m·K) at 20°C for 304 grade, providing adequate heat transfer performance for chilled water and hot water circuits.
- Mechanical Properties: Tensile strength ≥ 520 MPa; Yield strength ≥ 205 MPa; Elongation ≥ 40% (annealed condition)
- Operating Temperature Range: −196°C to +870°C (304); −196°C to +870°C (316/316L)
- Surface Finish: Pickled and passivated (2B finish) or electropolished for enhanced sanitary and anti-fouling characteristics
- Hygienic Compliance: Inner surface roughness Ra ≤ 0.4 μm (electropolished variant)
Specifications
| Parameter | Specification |
|---|---|
| Tube Outer Diameter (OD) | 6.35 mm / 8 mm / 9.53 mm / 10 mm / 12.7 mm (custom available) |
| Wall Thickness | 0.5 mm – 1.5 mm |
| Coil Pitch (Center-to-Center Spacing) | 15 mm – 50 mm (configurable) |
| Coil Length (Straight Coil Form) | 5 m – 50 m per coil (standard); up to 200 m on request |
| Number of Rows | 1 – 6 rows (U-bend configurations) |
| U-Bend Diameter | 1.5× OD to 3× OD |
| Maximum Operating Pressure | 1.6 MPa (standard); 2.5 MPa (reinforced) |
| Test Pressure | 1.5× Maximum Operating Pressure (hydrostatic test) |
| Standard Length (Finished Unit) | 500 mm – 1200 mm (per FCU/AHU frame) |
| Fins (if finned) | Aluminum or stainless steel fins; fin density 12–16 FPI |
| Tolerance on OD | ±0.05 mm |
| Tolerance on Wall Thickness | ±10% of nominal |
| Applicable Standards | ASTM A269 / A270, EN 10217-7, GB/T 14976 |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing process to ensure dimensional accuracy, metallurgical integrity, and functional performance:
- Raw Material Selection & Inspection: Cold-rolled stainless steel strip or seamless pipe stock is procured from certified mills. Incoming material undergoes spectroscopic analysis (PMI), visual inspection, and mechanical property verification.
- Tube Forming: Precision roll-forming or drawing processes produce the base tube to specified OD and wall thickness tolerances.
- Coil Winding: The formed tube is wound onto mandrels using CNC-controlled winding machinery to achieve uniform pitch, consistent curvature, and controlled residual stress.
- U-Bend Forming: Where multi-row configurations are required, U-bends are formed using hydraulic bending equipment with calibrated tooling to prevent ovality, kinking, or thinning beyond acceptable limits.
- Welding (if applicable): Butt welds or orbital TIG welds are performed at headers, with full radiographic or dye penetrant inspection (DPI) of critical joints.
- Fin Attachment (if finned): Aluminum or stainless steel fins are mechanically bonded or soldered to the tube using automated finning equipment, ensuring consistent fin-to-tube contact resistance.
- Surface Treatment: Pickling and passivation (HNO₃/HF acid blend) removes scale and oxide layers, followed by thorough water rinsing and drying.
- Hydrostatic Pressure Testing: Each coil tube assembly is pressure-tested at 1.5× the design pressure for a minimum dwell time of 5 minutes to verify leak-tightness.
- Final Inspection & Packing: Dimensional verification, surface quality assessment, and material traceability documentation are completed prior to protective packaging and dispatch.
Applications
- Commercial HVAC Terminal Units: Fan coil units (FCUs), cassette coils, and concealed ceiling coils in office buildings, hotels, hospitals, and retail facilities.
- Air Handling Units (AHUs): Chilled water and hot water coils for large-scale ventilation and climate control systems.
- Cleanroom Systems: Precision temperature and humidity control in pharmaceutical, semiconductor, and laboratory environments where particulate control is critical.
- Marine & Coastal Installations: HVAC systems in offshore platforms, ships, and coastal buildings where chloride-induced corrosion is a concern (316/316L grade).
- Food & Beverage Processing: Heat exchangers and cooling coils in processing plants requiring hygienic-grade stainless steel components.
- Refrigeration Systems: Evaporator and condenser coils in commercial refrigeration equipment.
Quality Certifications & Compliance
- ISO 9001:2015 — Quality Management System certification ensuring consistent manufacturing quality and process control.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices.
- CE Marking — Conformity with European health, safety, and environmental protection standards.
- Material Certification: Each batch is accompanied by a Mill Test Certificate (MTC) per EN 10204 Type 3.1, verifying chemical composition and mechanical properties.
- Third-Party Inspection: Available upon request — SGS, BV, or TÜV inspection services for dimensional accuracy, pressure testing, and material verification.
- NSF/ANSI Standards: Available for potable water contact applications upon specification.
Unique Selling Points
1. Superior Corrosion & Fouling Resistance: Unlike carbon steel alternatives, the austenitic stainless steel construction eliminates internal rust formation, maintaining heat transfer efficiency over extended service intervals (15–25+ years) without the need for chemical descaling.
2. Precision Hydraulic Design: Coil geometry is optimized through computational fluid dynamics (CFD) simulation to minimize pressure drop while maximizing heat exchange capacity, directly addressing the operational regulation challenges identified in HVAC terminal coil research.
3. Full Traceability: Each product is serialized with material batch tracking, ensuring complete traceability from raw steel mill to final installation — critical for warranty claims and regulatory compliance in building safety audits.
4. Customizable Configurations: Wenzhou Jixing Metal Materials offers flexible customization of tube diameter, wall thickness, coil pitch, row count, and fin density to match specific OEM requirements and thermal load calculations.
5. Environmental Sustainability: Stainless steel is 100% recyclable with retained material properties, supporting green building certifications (LEED, BREEAM) and reducing lifecycle environmental impact.