Stainless Steel Coil Tube for Fan Coil Units — GB/T 19232-2003
Product Overview
The Stainless Steel Coil Tube (盘管 / Coiltube) is a precision-engineered tubular component designed specifically for use in fan coil units (FCUs) and air-handling systems within commercial and industrial HVAC (Heating, Ventilation, and Air Conditioning) applications. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd, this product conforms to the Chinese national standard GB/T 19232-2003 — "Stainless steel coil tubes for air conditioning coil" — which governs the dimensional tolerances, mechanical properties, and performance requirements for stainless steel tubing used in evaporative and condensing coils.
Following the implementation of GB/T 19232-2003, the domestic production of fan coil unit coil tubes in China has undergone significant advancement. This standardization has enabled improved interchangeability, enhanced corrosion resistance, and extended service life compared to legacy carbon steel alternatives. The product represents the culmination of post-standardization development, integrating modern metallurgical practices with rigorous quality assurance protocols.
Material & Properties
The coil tube is fabricated from high-grade stainless steel, with the following material characteristics:
- Base Material: Austenitic stainless steel, typically Grade 304 (UNS S30400) or Grade 316 (UNS S31600), providing superior resistance to corrosion, scaling, and chemical attack.
- Corrosion Resistance: The chromium (Cr ≥ 18%) and nickel (Ni ≥ 8%) alloying elements form a self-healing passive oxide layer, ensuring long-term integrity in humid and chemically aggressive environments common in HVAC systems.
- Thermal Conductivity: Approximately 16.3 W/(m·K) for Grade 304, offering efficient heat transfer performance essential for evaporator and condenser coil operation.
- Mechanical Properties: Yield strength ≥ 205 MPa; tensile strength ≥ 520 MPa; elongation ≥ 40%, ensuring structural reliability under cyclic thermal and pressure loading.
- Surface Finish: Polished interior and exterior surfaces (Ra ≤ 0.8 μm) to minimize fluid friction, reduce fouling, and facilitate cleaning and maintenance.
- Operating Temperature Range: −40 °C to +150 °C, accommodating a wide spectrum of refrigerant and water-based heat transfer media.
Specifications
| Parameter | Specification |
|---|---|
| Applicable Standard | GB/T 19232-2003 |
| Product Category | Stainless Steel Coil Tube (盘管) |
| Tube Shape | Round (circular cross-section) |
| Outer Diameter (OD) | 6.35 mm, 9.53 mm, 12.70 mm (nominal) |
| Wall Thickness | 0.30 mm – 0.80 mm (selectable) |
| Diameter Tolerance | ±0.05 mm |
| Wall Thickness Tolerance | ±10% |
| Bend Radius | ≥ 2.5 × OD (minimum) |
| Coil Length | Customizable per project requirements |
| Material Grade | 304 / 316 / 321 (austenitic stainless steel) |
| Surface Treatment | Acid pickling and passivation |
| Hydrostatic Test Pressure | ≥ 1.5 × maximum working pressure |
| Design Working Pressure | ≤ 1.6 MPa (standard); up to 2.5 MPa (custom) |
| Refrigerant Compatibility | R22, R407C, R410A, R134a, and other HFC/HFO refrigerants |
| Delivery Form | Coiled tube, cut-to-length, or formed coil assembly |
Manufacturing Process
The production of stainless steel coil tubes adheres to a multi-stage process engineered for dimensional precision and metallurgical integrity:
- Raw Material Selection: Certified stainless steel strip or seamless tube stock is sourced from accredited suppliers, with each batch undergoing spectroscopic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition compliance with GB/T 19232-2003 requirements.
- Cold Forming / Drawing: The tube is cold-drawn or cold-formed to achieve the precise outer diameter and wall thickness specifications. This process work-hardens the material, enhancing mechanical strength while maintaining the austenitic crystal structure.
- Coiling and Bending: Using CNC-controlled (Computer Numerical Control) bending machinery, the straight tube is formed into the required coil geometry with controlled bend radii to prevent cross-sectional ovality and wall thinning at bend points.
- Welding (if applicable): Where continuous coil assemblies require joining, TIG welding (Tungsten Inert Gas welding) is employed with argon gas shielding to produce leak-tight, corrosion-resistant weld seams.
- Acid Pickling and Passivation: The finished tube undergoes acid pickling to remove surface scale and discoloration, followed by passivation to restore and enhance the chromium oxide protective layer.
- Quality Inspection: Every batch is subjected to hydrostatic pressure testing, dimensional measurement (using laser micrometers and calipers), visual inspection, and helium leak detection to ensure zero-defect performance.
Applications
Stainless steel coil tubes conforming to GB/T 19232-2003 serve as critical heat exchanger elements in a broad range of applications:
- Commercial HVAC Systems: Primary application in fan coil units (FCUs), air handling units (AHUs), and rooftop units for office buildings, shopping malls, hotels, and hospitals.
- Residential Air Conditioning: Used in split-system indoor units, ducted cassette units, and concealed ceiling-mounted units.
- Industrial Process Cooling: Employed in precision temperature control systems, clean room environments, and pharmaceutical manufacturing facilities where corrosion resistance is paramount.
- Marine and Coastal Environments: Grade 316 coil tubes are particularly suited for HVAC installations on ships, offshore platforms, and coastal facilities where chloride-induced pitting corrosion is a concern.
- Food and Beverage Processing: Utilized in refrigeration and cooling systems within food-grade environments where hygiene and material safety are regulated.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework to ensure product reliability and regulatory compliance:
- GB/T 19232-2003 — Stainless steel coil tubes for air conditioning coil: Full conformance to this national standard governing dimensions, material properties, and testing protocols.
- ISO 9001:2015 — Quality Management System certification, demonstrating systematic process control and continuous improvement.
- ISO 14001:2015 — Environmental Management System certification, reflecting responsible environmental practices throughout the manufacturing lifecycle.
- GB/T 4237-2015 — Compliance with the standard for Stainless steel plates and sheets for cold rolling, ensuring raw material quality traceability.
- ASME / PED Compliance — Available upon request for applications requiring pressure vessel or pressure equipment directives.
- Mill Test Certificates (MTC) — EN 10204 Type 3.1 certificates provided for every production batch, documenting chemical analysis and mechanical test results.
Unique Selling Points
Standard-Driven Excellence: As a product developed in direct response to the implementation of GB/T 19232-2003, this coil tube embodies the latest advancements in Chinese domestic manufacturing capability, offering performance on par with imported alternatives at competitive cost structures.
- Superior Corrosion Longevity: Compared to traditional copper or carbon steel coil tubes, the stainless steel construction provides significantly extended service life — typically 2 to 3 times longer — reducing total cost of ownership (TCO) over the system lifecycle.
- Dimensional Precision: CNC-controlled manufacturing ensures tight tolerances (±0.05 mm on OD), minimizing assembly waste and ensuring optimal fit within fan coil unit housings.
- Environmental Sustainability: Stainless steel is 100% recyclable with no loss of material properties, aligning with global sustainability goals and green building certification requirements (LEED, Green Star).
- Customization Capability: Wenzhou Jixing Metal Materials Co., Ltd offers flexible customization of coil geometry, tube dimensions, and material grades to meet specific project requirements and OEM specifications.
- Full Traceability: Each production batch is traceable from raw material mill certificates through final inspection, providing complete supply chain transparency.