Stainless Steel Coil Tube — HVAC Fan Coil Unit & Ground Radiation Cooling System
Product Overview
The Stainless Steel Coil Tube (Product No. 280) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed for advanced building thermal management systems. This coil tube is specifically engineered for integration into variable frequency fan coil unit (VFCU) assisted ground radiation cooling systems (GRCS), where it serves as the primary heat transfer medium within hydronic piping networks. The product combines the inherent corrosion resistance and mechanical integrity of austenitic stainless steel with the geometric advantages of a cold-formed coil configuration, enabling superior thermal performance, extended service life, and reduced maintenance requirements in demanding HVAC applications.
The coil tube is manufactured to meet the stringent requirements of modern energy-efficient building systems, where ground source heat exchange and radiant floor cooling technologies are increasingly adopted to minimize operational carbon footprints while maintaining optimal indoor thermal comfort. Wenzhou Jixing Metal Materials Co., Ltd. applies rigorous quality control throughout the production cycle to ensure dimensional accuracy, metallurgical uniformity, and surface integrity that are critical for seamless integration into complex hydronic circuit architectures.
Material & Properties
The stainless steel coil tube is fabricated from premium austenitic stainless steel grades, selected based on application-specific requirements for corrosion resistance, mechanical strength, and thermal conductivity:
- Grade 304 (UNS S30400 / AISI 304): The standard-grade austenitic stainless steel offering excellent general corrosion resistance, good formability, and adequate weldability. Suitable for most indoor HVAC applications where the working fluid is potable water or glycol-based coolant solutions.
- Grade 316 (UNS S31600 / AISI 316): Enhanced molybdenum (Mo) content provides superior resistance to pitting and crevice corrosion in chloride-rich environments. Recommended for ground-source applications where soil chemistry may introduce aggressive ions.
- Grade 321 (UNS S32100 / AISI 321): Titanium-stabilized austenitic grade offering excellent resistance to intergranular corrosion at elevated temperatures. Suitable for high-temperature radiant heating loops.
Mechanical Properties (Annealed Condition, Grade 304):
- Yield Strength (Rp0.2): ≥ 205 MPa
- Tensile Strength (Rm): 515–730 MPa
- Elongation at Break (A): ≥ 40%
- Hardness: ≤ 217 HV
- Density: 8.0 g/cm³
Thermal Properties:
- Thermal Conductivity (at 20°C): 16.3 W/(m·K)
- Specific Heat Capacity (at 20°C): 0.50 J/(g·K)
- Linear Thermal Expansion Coefficient (10–100°C): 17.3 × 10⁻⁶ /K
Corrosion Resistance:
- Excellent resistance to atmospheric, fresh water, and dilute acid corrosion
- Outstanding resistance to scaling and dezincification in hydronic systems
- Resistance to stress corrosion cracking (SCC) under controlled chloride environments (Grade 316)
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Product Name | Stainless Steel Coil Tube | — |
| Product Code | 280 | — |
| Material Grade | SUS 304 / SUS 316 / SUS 321 | ASTM A269 / GB/T 12771 |
| Outer Diameter (OD) | 6.0 mm – 50.8 mm (configurable) | ASTM B563 / EN 10217 |
| Wall Thickness (WT) | 0.5 mm – 3.0 mm | ASTM A269 |
| Diameter Tolerance | ±0.15 mm (standard); ±0.08 mm (precision grade) | GB/T 12771 |
| Wall Thickness Tolerance | ±10% (standard); ±6% (precision grade) | ASTM A269 |
| Coil Length | 50 m – 200 m per coil (custom lengths available) | — |
| Surface Finish | 2B (Cold Rolled & Annealed) / No.4 Brushed / Mirror (8K) | ASTM A480 |
| Weld Seam | Continuous longitudinal TIG (Tungsten Inert Gas) weld; double-sided grinding available | ASME B31.9 |
| Working Pressure | Up to 1.6 MPa (standard); up to 2.5 MPa (heavy-wall) | ASME B31.9 |
| Operating Temperature | −40°C to +250°C | — |
| Hydrostatic Test Pressure | 1.5 × Working Pressure (minimum) | GB/T 24511 |
| End Treatment | Clean-cut, burr-free; optional beveling or flanging | — |
| Coil Packaging | Wooden reel with moisture-proof wrapping; desiccant included | ISO 11607 |
| Maximum Coil Weight | Up to 800 kg per reel | — |
| Standard Lengths | 6 m / 12 m / 24 m (straight-cut options available) | — |
Manufacturing Process
The production of Wenzhou Jixing Metal Materials Co., Ltd. stainless steel coil tubes follows a multi-stage cold-forming process with integrated quality assurance checkpoints at each phase:
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Raw Material Selection & Incoming Inspection:
Hot-rolled stainless steel coils are procured from certified mills and subjected to spectroscopic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition against ASTM A269 or GB/T 12771 requirements. Mechanical property verification includes tensile testing per ASTM A370 and hardness testing per ASTM E10.
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Cold Rolling & Annealing:
The stainless steel strip undergoes controlled cold rolling to achieve the target thickness with uniform grain structure. Subsequent solution annealing in a protective atmosphere furnace (1050–1100°C) relieves residual stresses and restores ductility for subsequent forming operations.
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Pickle & Passivate:
The rolled strip is subjected to acid pickling (hydrochloric/nitric acid blend) to remove scale and surface oxides, followed by passivation to establish a chromium oxide protective layer. Surface cleanliness is verified via contact angle testing.
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Coil Forming (Cold Bending):
Precision-guided rollers progressively bend the flat strip into a circular cross-section. The forming parameters (roller spacing, feed rate, bending angle) are controlled to minimize thickness variation and maintain uniform wall profile throughout the tube circumference.
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Longitudinal Welding:
The formed strip is welded along the longitudinal seam using either:
- TIG (Tungsten Inert Gas) welding: For standard applications, providing a clean, high-integrity weld seam.
- Electrofusion welding: For high-pressure applications requiring homogeneous weld microstructure.
Weld parameters are continuously monitored and recorded for traceability. Internal gas shielding (argon) ensures oxide-free weld surfaces.
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Post-Weld Heat Treatment:
Welded tubes undergo solution heat treatment (1050°C, air or furnace cooling) to homogenize the heat-affected zone (HAZ) microstructure, eliminate residual stresses, and restore full corrosion resistance at the weld seam.
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Surface Finishing:
Depending on the specified finish grade, tubes may undergo internal and external grinding, electropolishing, or mechanical polishing. Internal surface roughness (Ra) is maintained at ≤ 0.8 μm for hydraulic efficiency.
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Dimensional Inspection & Non-Destructive Testing (NDT):
- OD and WT measurement via laser micrometer or ultrasonic thickness gauge (sampling rate: 100% for critical dimensions)
- Eddy current testing (ECT) for weld seam integrity and wall thickness uniformity
- Helium leak testing for pressure integrity verification
- Visual inspection of weld seams for porosity, undercut, or distortion
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Hydrostatic Pressure Testing:
Each coil or cut length undergoes hydrostatic testing at 1.5× the maximum working pressure, held for a minimum of 60 seconds. Any tube exhibiting pressure drop, visible deformation, or weeping is rejected.
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Packaging & Dispatch:
Qualified coils are wound onto wooden reels, wrapped in moisture-barrier film, and sealed with desiccant packs. Each coil is labeled with a unique batch identifier, material grade, dimensional data, and test certificate reference for full traceability.
Applications
The stainless steel coil tube is designed for integration into advanced building thermal systems, with particular suitability for the following applications:
1. Variable Frequency Fan Coil Unit (VFCU) Systems
The coil tube serves as the heat exchange coil within variable frequency fan coil units, where it facilitates efficient heat transfer between the circulating coolant and the conditioned air stream. The variable frequency drive (VFD) adjusts fan speed and pump flow in real-time to match thermal load demands, and the stainless steel coil tube maintains dimensional stability and corrosion resistance under continuous cyclic thermal and hydraulic stress.
2. Ground Radiation Cooling Systems (GRCS)
In ground-source radiant cooling systems, the coil tube is embedded within floor or ceiling assemblies to provide direct radiant heat exchange with building occupants and surfaces. The superior thermal conductivity and long-term durability of stainless steel ensure consistent cooling performance over decades of operation without degradation from corrosion or scaling.
3. Ground-Source Heat Pump (GSHP) Loop Systems
The coil tube is deployed in closed-loop geothermal piping networks, where it circulates through underground boreholes or horizontal trenches to extract or reject thermal energy from the earth. The corrosion resistance of austenitic stainless steel is critical in this application, where exposure to variable soil chemistries and groundwater conditions demands materials immune to pitting, crevice corrosion, and galvanic degradation.
4. Industrial Process Cooling & Heating
Beyond building services, the coil tube finds application in industrial process heat exchangers, food and beverage processing equipment, pharmaceutical manufacturing systems, and chemical processing plants where sanitary-grade materials and high-pressure resistance are required.
5. Marine & Offshore HVAC Systems
Grade 316 stainless steel coil tubes are specified for marine HVAC applications where exposure to salt-laden atmospheres and seawater cooling loops requires maximum corrosion resistance.
Quality Certifications & Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and holds the following certifications and complies with the following standards:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification covering all manufacturing operations |
| ISO 14001:2015 | Environmental Management System certification for sustainable manufacturing practices |
| ISO 45001:2018 | Occupational Health & Safety Management System certification |
| CE Marking (EN 10217-1 / EN 10217-2) | European Conformity marking for pressure equipment and piping applications |
| ASTM A269 | Standard specification for austenitic stainless steel welded, cold-worked, seamless tubing |
| GB/T 12771 | Chinese national standard for welded stainless steel seamless and welded steel tubes |
| ASME B31.9 | Code for heating, cooling, and refrigerating piping systems |
| GB/T 24511 | Chinese national standard for pressure vessel and piping hydrostatic testing procedures |
| NADCAP (if applicable) | Special Process Accreditation for welding and heat treatment operations |
| Mill Test Reports (MTR) | Provided with each shipment, including chemical composition, mechanical properties, and NDT results |
Unique Selling Points
- Integrated Design for VFCU-GRCS Systems: Specifically engineered for seamless integration into variable frequency fan coil unit assisted ground radiation cooling systems, providing optimized thermal performance in hybrid building HVAC architectures.
- Full Traceability: Each coil tube batch is traceable from raw material mill certificate through final dispatch, with complete test data documentation available upon request.
- Precision Dimensional Control: Laser-based inline inspection ensures OD and WT tolerances within ±0.08 mm (precision grade), minimizing fitting waste and installation labor.
- Extended Service Life: Austenitic stainless steel construction provides a design life exceeding 50 years in hydronic service, significantly outperforming carbon steel alternatives (10–20 years) and eliminating repiping costs.
- Sanitary-Grade Internal Surface: Electropolished internal surface (Ra ≤ 0.8 μm) reduces fouling and biofilm formation, maintaining hydraulic efficiency throughout the service life.
- Customization Capability: Flexible manufacturing parameters allow customization of OD, WT, coil length, surface finish, and end treatment to match specific project requirements.
- Environmental Sustainability: Stainless steel is 100% recyclable