Stainless Steel Coil Tube for HVAC Fan Coil Units
Product Overview
The Stainless Steel Coil Tube is a precision-engineered tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd, specifically designed for integration into Fan Coil Units (FCU) and air-handling systems within Heating, Ventilation, and Air Conditioning (HVAC) applications. This coil tube serves as the core heat exchange medium, enabling efficient transfer of thermal energy between circulating refrigerant or hot water and ambient air. The product is manufactured to meet the rigorous requirements outlined in the Simplified Calculation Method for Measurement Uncertainty of Cooling and Heating Capacity of Fan Coil Units, ensuring that capacity performance remains within acceptable uncertainty bounds under standardized test conditions.
As a coiled form of stainless steel tubing, this product offers superior flexibility in installation geometry, resistance to corrosion in humid and chemically aggressive environments, and long-term structural integrity under cyclic thermal loading. The coil configuration maximizes heat transfer surface area within a compact envelope, making it indispensable for high-efficiency HVAC systems in commercial, industrial, and residential settings.
Material and Properties
Base Material
The coil tube is fabricated from high-grade austenitic stainless steel, with SAE 304 (UNS S30400) and SAE 316L (UNS S31603) being the primary grades employed. Grade 316L is selected for applications involving chloride-rich environments or marine HVAC systems, providing enhanced resistance to pitting and crevice corrosion due to its molybdenum content (2.0%–3.0% Mo).
Mechanical Properties
- Tensile Strength: 515–720 MPa (depending on grade and heat treatment condition)
- Yield Strength (0.2% offset): 205–310 MPa
- Elongation at Break: ≥35% (minimum)
- Hardness: 137–207 HB (annealed condition)
Thermal Properties
- Thermal Conductivity: 14.9 W/(m·K) at 25°C (Grade 304); 14.2 W/(m·K) at 25°C (Grade 316L)
- Specific Heat Capacity: 0.50 J/(g·K) at 20°C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (20–100°C)
- Maximum Operating Temperature: 870°C (continuous); 1100°C (intermittent)
Corrosion Resistance
Both grades exhibit excellent resistance to atmospheric corrosion, weak organic and inorganic acids, and alkaline solutions. Grade 316L demonstrates superior performance in environments containing chlorides, sulfides, and other aggressive ions commonly encountered in coastal HVAC installations or industrial process cooling loops. The passive chromium oxide film (Cr₂O₃) self-repairs in the presence of oxygen, providing sustained protection against localized corrosion attack.
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Product Name | Stainless Steel Coil Tube (盘管) | — |
| Material Grade | SAE 304 / 316L / 321 (upon request) | ASTM A213 / GB/T 12771 |
| Outer Diameter (OD) | Φ6.0 mm – Φ12.7 mm (standard); custom available | ISO 6520 |
| Wall Thickness | 0.5 mm – 1.5 mm (standard range) | ASTM A269 |
| Coil Diameter | 50 mm – 300 mm (configurable per FCU design) | Manufacturer specification |
| Tube Length per Coil | 1.0 m – 10.0 m (variable) | — |
| Surface Finish | Pickled & Passivated (P&P); Ra ≤ 0.8 μm | ASTM A967 |
| Winding Tolerance | ±0.5 mm on coil diameter; ±1.0 mm on pitch | Internal QC standard |
| Pressure Rating | 1.6 MPa (design); 3.2 MPa (test) | GB/T 12771 |
| Operating Temperature Range | −50°C to +250°C (continuous) | — |
| Refrigerant / Fluid Compatibility | R-22, R-410A, R-32, R-134a, hot water, glycol mixtures | ASHRAE Standard 34 |
| Fin Configuration (if finned) | Aluminum or stainless steel fins; 6–12 fins per inch | Manufacturer specification |
| Packaging | Wooden pallet with VCI (Vapor Corrosion Inhibitor) wrapping | ISO 11607 |
Manufacturing Process
Step 1: Raw Material Inspection and Certification
Stainless steel seamless or welded tubes are sourced from certified mills with full mill test certificates (MTC) conforming to EN 10204 Type 3.1. Incoming material undergoes visual inspection, dimensional verification, and spectroscopic chemical composition analysis to confirm compliance with the specified grade requirements (e.g., ASTM A213 TP304/TP316L).
Step 2: Cutting and End Preparation
Tubes are cut to the required length using precision sawing or laser cutting equipment. Cut ends are deburred and chamfered to prevent fluid turbulence and ensure proper welding or brazing during assembly. End surfaces are inspected for squareness and cleanliness.
Step 3: Coiling and Winding
The straight tube segments are fed into a CNC-controlled coiling machine that winds the tube into the predetermined coil geometry. The coiling process is executed under controlled bending force to avoid work hardening, ovalization, or micro-cracking of the tube wall. The coil diameter, pitch (spacing between adjacent turns), and total number of turns are precisely controlled to meet the thermal performance requirements of the target FCU design.
Step 4: Welding and Brazing of Headers
Tube ends are connected to stainless steel or copper headers (inlet and outlet manifolds) using TIG (Tungsten Inert Gas) welding with argon shielding gas, or high-temperature silver brazing. The welding parameters (current, voltage, travel speed, gas flow rate) are optimized to ensure full penetration, minimal distortion, and a hermetic seal capable of withstanding the specified pressure rating.
Step 5: Heat Treatment and Stress Relief
Following welding, the coil assembly undergoes stress-relief annealing at 650–800°C (for 304) or 850–900°C (for 316L), followed by controlled cooling. This process eliminates residual stresses introduced during coiling and welding, restores full temper ductility, and stabilizes the microstructure for consistent mechanical performance.
Step 6: Pickling and Passivation
The completed coil tube assembly is subjected to acid pickling (using a mixture of nitric and hydrofluoric acid) to remove weld scale, oxidation, and surface contaminants. This is followed by passivation treatment to re-establish the protective chromium oxide film. The process conforms to ASTM A967 and ASTM A380 standards. Post-passivation, the surface is rinsed with deionized water and dried to prevent water-spot staining.
Step 7: Pressure Testing and Leak Detection
Each coil tube assembly undergoes hydrostatic pressure testing at 1.5 times the design pressure (typically 2.4 MPa for a 1.6 MPa design rating) for a minimum hold time of 30 minutes. Any pressure drop exceeding 0.1% indicates a defect requiring rework. Additionally, helium leak detection or bubble testing may be employed for critical applications to verify weld integrity at the micron level.
Step 8: Dimensional and Performance Verification
Final inspection includes verification of coil diameter, pitch uniformity, tube straightness, and surface finish quality. Thermal performance is validated through reference calculations in accordance with the Simplified Calculation Method for Measurement Uncertainty of Cooling and Heating Capacity of Fan Coil Units, ensuring that the uncertainty in cooling and heating capacity measurements remains within the specified tolerance (typically ±5% or better, depending on the application class).
Applications
HVAC Fan Coil Units (FCU)
The primary application domain is in commercial and residential FCUs, where the coil tube serves as the heat exchange core for air conditioning and heating. These units are installed in offices, hotels, hospitals, retail spaces, and multi-story residential buildings to provide precise indoor climate control.
Chilled Water and Hot Water Distribution Systems
The coil tube is employed in secondary-loop distribution systems where chilled water (typically 6–12°C) or hot water (typically 40–70°C) circulates through the coil to cool or heat supply air. The stainless steel construction ensures long-term resistance to scaling, biofilm formation, and chemical degradation in closed-loop hydronic systems.
Industrial Process Cooling
In industrial environments—such as pharmaceutical manufacturing, food processing, and electronics fabrication—stainless steel coil tubes are used in process chillers and heat exchangers where hygienic standards and corrosion resistance are paramount. The non-reactive nature of austenitic stainless steel prevents product contamination and facilitates cleaning-in-place (CIP) procedures.
Marine and Coastal HVAC Systems
Grade 316L coil tubes are specifically recommended for HVAC installations in marine environments, coastal regions, and offshore platforms where high chloride concentrations in the ambient air can cause severe pitting corrosion in lower-grade materials. The molybdenum addition in 316L provides the necessary resistance to maintain structural and functional integrity over extended service life.
Refrigerant Circuit Heat Exchangers
In direct-expansion (DX) air conditioning systems, the coil tube functions as the evaporator coil through which refrigerant (e.g., R-410A, R-32) absorbs heat from passing air. The stainless steel construction offers an alternative to traditional copper tubing in applications where copper contamination is unacceptable (e.g., semiconductor cleanrooms, aerospace manufacturing).
Quality Certifications and Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management system aligned with international standards. The following certifications and compliance frameworks apply to the Stainless Steel Coil Tube product:
- ISO 9001:2015 — Quality Management Systems (QMS), ensuring consistent product quality and continuous improvement across all manufacturing processes.
- ISO 14001:2015 — Environmental Management Systems, demonstrating commitment to minimizing environmental impact through responsible material sourcing, energy-efficient manufacturing, and waste reduction.
- ISO 45001:2018 — Occupational Health and Safety Management Systems, ensuring a safe working environment for all personnel involved in production.
- CE Marking (EU) — Conformity with European health, safety, and environmental protection standards, enabling market access within the European Economic Area (EEA).
- EN 10204 Type 3.1 — Mill Test Certificate providing verified chemical composition and mechanical property data for each production batch.
- ASTM A213 / A269 — Compliance with American Society for Testing and Materials (ASTM) standards for stainless steel tubes used in heat exchangers and heat transfer applications.
- GB/T 12771 — Compliance with the Chinese national standard for stainless steel seamless and welded tubes for general purposes.
- ASHRAE Standard 34 — Safety classification compliance for refrigerants used in conjunction with the coil tube in HVAC systems.
- NSF/ANSI 61 (where applicable) — Certification for potable water contact applications, ensuring the material does not leach harmful substances into water systems.
Unique Selling Points
- Enhanced Corrosion Resistance: The use of SAE 316L stainless steel provides superior resistance to pitting and crevice corrosion compared to conventional copper or carbon steel coil tubes, significantly extending service life in aggressive environments.
- Thermal Performance Optimization: Coil geometry is engineered in accordance with the Simplified Calculation Method for Measurement Uncertainty of Cooling and Heating Capacity of Fan Coil Units, ensuring that thermal capacity is predictable, repeatable, and within tight uncertainty bounds.
- Hygienic and Non-Contaminating: The passive oxide surface of stainless steel is non-toxic, non-reactive, and resistant to biofilm formation, making it ideal for pharmaceutical, food-grade, and semiconductor manufacturing HVAC applications.
- Full Traceability: Each coil tube batch is accompanied by a comprehensive Mill Test Certificate (EN 10204 Type 3.1) with spectroscopic verification, enabling complete material traceability from raw material to finished product.
- Customizable Geometry: Coil diameter, pitch, tube length, and fin configuration can be tailored to specific FCU design requirements, allowing OEMs to achieve optimal thermal performance within constrained installation footprints.
- Rigorous Quality Assurance: Multi-stage quality control—including incoming material inspection, in-process dimensional verification, pressure testing, and final performance validation—ensures zero-defect delivery.
- Sustainability: Stainless steel is 100% recyclable with no loss of material properties, and the manufacturing process adheres to ISO 14001 environmental management standards, supporting sustainable building practices and green certification programs (LEED, BREEAM).
Note: All specifications referenced in this document are subject to revision based on evolving industry standards and customer-specific requirements. For the most current technical data, material certifications, and application-specific guidance, please contact Wenzhou Jixing Metal Materials Co., Ltd directly.