Stainless Steel Coil Tube (Coiltube) for Fan Coil Unit Systems

Product Overview

The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd (Wenzhou Jixing), specifically designed for integration into Fan Coil Units (FCUs) as defined under the national standard GB/T 19232—2019 "Fan Coil Units". This coil tube serves as the primary heat exchange element within chilled water and hot water distribution systems, facilitating efficient thermal energy transfer between the circulating fluid and ambient air.

Compliant with the revised provisions of GB/T 19232—2019, this product addresses critical performance requirements including improved thermal efficiency, enhanced corrosion resistance, reduced pressure drop, and extended service life under continuous operational conditions. The coil tube is supplied in a pre-formed coil configuration, enabling rapid installation and minimizing on-site fabrication requirements.

Material & Properties

The coil tube is fabricated from high-grade austenitic stainless steel, ensuring superior resistance to corrosion, scaling, and thermal degradation. The following material specifications are maintained throughout production:

• Base Alloy: Austenitic Stainless Steel — Grades 304 (UNS S30400), 304L (UNS S30403), and 316L (UNS S31603)
• Chromium (Cr) Content: ≥ 18.0% (Grade 304/304L); ≥ 16.5% (Grade 316L)
• Nickel (Ni) Content: ≥ 8.0% (Grade 304/304L); ≥ 10.0% (Grade 316L)
• Molybdenum (Mo) Content: 0.0% (Grade 304/304L); 2.0–3.0% (Grade 316L)
• Carbon (C) Content: ≤ 0.08% (Grade 304); ≤ 0.03% (Grade 304L/316L)
• Surface Finish: Bright Annealed (BA) or No. 4 Brushed Finish
• Thermal Conductivity: 14.5–16.5 W/(m·K) at 20°C
• Operating Temperature Range: −196°C to +870°C
• Maximum Working Pressure: Up to 1.6 MPa (gauge)

Specifications

Parameter	Specification	Standard Reference
Tube Outer Diameter (OD)	9.52 mm / 12.70 mm (3/8" / 1/2")	GB/T 14976
Tube Wall Thickness	0.50 mm – 1.20 mm	GB/T 14976
Coil Diameter (CD)	200 mm – 500 mm (configurable)	Manufacturer Standard
Coil Height (CH)	150 mm – 600 mm (configurable)	Manufacturer Standard
Tube Length (Total Development)	15 m – 120 m (per coil)	Project-Specific
Fin Pitch (if finned)	2.0 mm – 3.5 mm	GB/T 19232—2019
Fin Material	Aluminum (Al 1060-H14) or Stainless Steel (304)	ASTM B209
Number of Rows	1-Row, 2-Row, 3-Row, 4-Row configurations	GB/T 19232—2019
Flow Rate Capacity	0.5 m³/h – 8.0 m³/h (per unit)	GB/T 19232—2019
Cooling Capacity	1.2 kW – 12.0 kW	GB/T 19232—2019
Heating Capacity	1.5 kW – 15.0 kW	GB/T 19232—2019
Pressure Drop (Water Side)	≤ 30 kPa (at rated flow)	GB/T 19232—2019
Air Side Pressure Drop	≤ 80 Pa (at rated airflow)	GB/T 19232—2019
Welding Method	Orbital TIG (GTAW) / Laser Welding	GB/T 12469
Hydrostatic Test Pressure	1.5× Maximum Working Pressure (≥ 2.4 MPa)	GB/T 24237
Corrosion Resistance (Salt Spray)	≥ 500 hours (ASTM B117, 5% NaCl)	ASTM B117
Service Life	≥ 20 years (continuous operation)	Manufacturer Guarantee

Manufacturing Process

The production of the stainless steel coil tube follows a rigorous, multi-stage manufacturing workflow adhering to international best practices and the technical requirements specified in GB/T 19232—2019:

1. Raw Material Procurement & Incoming Inspection:

   Stainless steel strip or seamless tube stock is sourced from certified mills (e.g., POSCO, Outokumpu, Taigang). Each batch undergoes spectroscopic analysis (OES) to verify chemical composition compliance with ASTM A240 / GB/T 4237 specifications. Mill Test Reports (MTRs) are retained for traceability.

2. Dimensional Forming & Coil Bending:

   Flat strip material is cold-formed into round or oval cross-section tubes using precision roll-forming equipment. The formed tube is then coiled onto a mandrel using CNC-controlled bending machinery to achieve exact coil diameter (CD) and coil height (CH) dimensions with a tolerance of ±0.5 mm.

3. Fin Attachment (if finned configuration):

   Aluminum or stainless steel fins are attached to the coiled tube via a high-frequency mechanical pressing process (roll-bonding) or brazing. The fin-to-tube bond strength exceeds 50 N/mm to ensure thermal contact integrity and prevent vibration-induced separation.

4. Header Assembly & Welding:

   Tube ends are welded to stainless steel headers (manifolds) using orbital TIG (GTAW) welding with argon shielding gas. Weld seams are ground flush and inspected via dye penetrant testing (PT) per ASTM E709 to confirm weld integrity and absence of porosity or cracks.

5. Surface Treatment & Passivation:

   The assembled coil tube undergoes acid pickling and passivation treatment (HNO₃/HF solution) to remove mill scale, weld discoloration, and free iron contamination. This restores the protective chromium oxide layer, enhancing corrosion resistance.

6. Hydrostatic Pressure Testing:

   Each coil tube assembly is subjected to a hydrostatic pressure test at 1.5 times the maximum working pressure (minimum 2.4 MPa) for a hold time of 30 minutes. Zero leakage is required for acceptance. Test results are documented and archived.

7. Final Inspection & Packaging:

   Dimensional verification (OD, wall thickness, coil geometry), visual inspection, and surface quality assessment are performed. Units are protected with plastic caps, wrapped in moisture-barrier film, and packed in export-grade wooden crates for shipment.

Applications

The stainless steel coil tube manufactured by Wenzhou Jixing Metal Materials Co., Ltd is integral to a broad spectrum of HVAC (Heating, Ventilation, and Air Conditioning) and industrial thermal management applications:

• Commercial HVAC Systems: Primary heat exchange component in ceiling-mounted, floor-standing, and concealed fan coil units for office buildings, shopping malls, and hospitality facilities.
• Residential Climate Control: Used in ducted and ductless mini-split systems for precise temperature regulation in residential and light commercial spaces.
• Industrial Process Cooling: Applied in chemical processing, pharmaceutical manufacturing, and food processing plants where corrosion-resistant heat exchangers are mandatory.
• Cleanroom Environments: Suitable for pharmaceutical and semiconductor cleanrooms requiring hygienic, non-contaminating heat exchange surfaces.
• Marine & Offshore Applications: Grade 316L coil tubes provide exceptional resistance to chloride-induced pitting in marine HVAC systems.
• Energy Recovery Systems: Integrated into air-to-air and air-to-water heat recovery units for energy-efficient building operation.

Quality Certifications & Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework ensuring full traceability and compliance with international and national standards:

• GB/T 19232—2019: "Fan Coil Units" — Primary product standard governing performance, safety, and testing requirements for fan coil unit assemblies.
• GB/T 14976: "Seamless Stainless Steel Tubes for General Purposes" — Governs tube dimensional tolerances and mechanical properties.
• GB/T 4237: "Cold-Rolled Stainless Steel Plates and Sheets" — Material specification for raw strip stock.
• ASTM A240: Standard Specification for Chromium and Chromium-Nickel Stainless Steel Plates, Sheets, and Strips.
• ISO 9001:2015: Quality Management System certification ensuring consistent production quality and continuous improvement.
• ISO 14001:2015: Environmental Management System certification demonstrating environmental stewardship in manufacturing operations.
• CE Marking: Conformity with European Union directives including the Pressure Equipment Directive (PED 2014/68/EU) and Machinery Directive (2006/42/EC).
• TÜV / SGS Inspection: Third-party certification for material composition, dimensional accuracy, and pressure test performance.
• Mill Test Reports (MTRs): Provided for every production batch, documenting chemical analysis, mechanical test results, and heat treatment records.

Unique Selling Points

• Enhanced Corrosion Resistance: The use of austenitic stainless steel grades (304/304L/316L) provides superior resistance to scaling, pitting, and general corrosion compared to carbon steel alternatives, extending service life to over 20 years without replacement.
• Hygienic Design: Bright annealed surface finish with low roughness (Ra ≤ 0.8 μm) prevents biofilm accumulation, making the coil tube suitable for food-grade and pharmaceutical applications.
• High Thermal Efficiency: Precision manufacturing of coil geometry and fin attachment ensures optimal air-to-water heat transfer coefficients (U-value), achieving energy savings of 15–25% compared to conventional designs.
• Low Pressure Drop: Smooth internal tube surfaces and optimized flow path design minimize hydraulic resistance, reducing pumping energy consumption in distribution systems.
• Full Traceability: Every coil tube is serialized with batch-specific Mill Test Reports, pressure test records, and dimensional inspection data, ensuring complete quality traceability from raw material to final installation.
• Customizability: Flexible manufacturing capability allows customization of coil diameter, height, number of rows, tube dimensions, and material grade to meet specific project requirements.
• Regulatory Compliance: Full adherence to GB/T 19232—2019 ensures the coil tube meets the latest national requirements for fan coil unit performance, noise levels, and safety standards.

Technical Reference: GB/T 19232—2019 Key Revisions

The 2019 revision of GB/T 19232 introduced several critical updates relevant to coil tube design and performance:

• Revised thermal performance rating methodology incorporating steady-state and part-load efficiency metrics (COP at part-load conditions).
• Enhanced noise level requirements — maximum sound pressure level reduced to ≤ 32 dBA at low-speed operation for residential applications.
• Mandatory energy efficiency classification (EEI — Energy Efficiency Index) with minimum thresholds of EEI ≤ 1.15 for cooling and EEI ≤ 1.25 for heating.
• Updated safety requirements including electrical insulation resistance (≥ 2 MΩ), leakage current limits (≤ 0.25 mA), and temperature rise restrictions for electrical components.
• Incorporation of environmental impact assessment requirements, including refrigerant charge limits and greenhouse gas potential evaluation.

Manufacturer: Wenzhou Jixing Metal Materials Co.,