Stainless Steel Coil Tube — HVAC Fan Coil Unit Application (Model: JX-409)
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. (温州吉兴金属材料有限公司)
Product Category: Stainless Steel Coil Tube for HVAC Fan Coil Unit (FCU) Heat Exchanger Applications
Product Code: JX-409
Product Overview
The JX-409 Stainless Steel Coil Tube is a precision-engineered continuous coil tubing product specifically designed for integration into Fan Coil Units (FCU) and other HVAC (Heating, Ventilation, and Air Conditioning) heat exchanger assemblies. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coil tube is formed into serpentine or spiral configurations to maximize surface area and thermal exchange efficiency within compact unitary equipment.
This product represents a critical component in modern air handling systems, where it serves as the primary heat transfer medium, circulating chilled water or hot water through its lumen to achieve precise temperature regulation in commercial and residential environments. The coil tube is engineered to withstand the thermal cycling, chemical exposure, and mechanical stress inherent in continuous HVAC operation.
Material Composition & Physical Properties
Base Material Grades
- Primary Grade: Austenitic Stainless Steel AISI 304 (UNS S30400) — Chromium-Nickel austenitic stainless steel
- Alternative Grade: AISI 316L (UNS S31603) — Low-carbon Chromium-Nickel-Molybdenum austenitic stainless steel, for enhanced corrosion resistance
- Economic Grade: Ferritic Stainless Steel AISI 430 (UNS S43000) — Chromium ferritic stainless steel, for cost-sensitive applications
Chemical Composition (Typical — AISI 304)
| Element | Specification (%) | Element | Specification (%) |
|---|---|---|---|
| Carbon (C) | ≤ 0.08 | Chromium (Cr) | 18.00 – 20.00 |
| Manganese (Mn) | ≤ 2.00 | Nickel (Ni) | 8.00 – 10.50 |
| Silicon (Si) | ≤ 1.00 | Nitrogen (N) | ≤ 0.10 |
| Phosphorus (P) | ≤ 0.045 | Sulfur (S) | ≤ 0.030 |
| Sulfur (S) | ≤ 0.030 | Iron (Fe) | Balance |
Mechanical Properties (Annealed Condition)
| Property | Specification | Test Standard |
|---|---|---|
| Tensile Strength (Rm) | ≥ 520 MPa (75,400 psi) | ASTM A269 / GB/T 12771 |
| Yield Strength (Rp0.2) | ≥ 205 MPa (29,700 psi) | ASTM A269 / GB/T 12771 |
| Elongation (% Elt.) | ≥ 40% | ASTM A269 |
| Hardness (HBW) | ≤ 187 | ASTM A269 |
| Thermal Conductivity (20°C) | 16.3 W/(m·K) | ASM Handbook |
| Operating Temperature Range | −196°C to +870°C | — |
Surface Finish Options
- No. 4 Finish: Brushed, satin appearance (Ra ≤ 0.4 μm) — standard for visible applications
- 2B Finish: Cold-rolled, annealed, pickled, and bright-passed (Ra ≤ 0.25 μm)
- BA (Bright Annealed): Mirror-quality surface (Ra ≤ 0.1 μm) — for food-grade or pharmaceutical FCU systems
- Polished: Mechanical polishing to specified Ra values (Ra ≤ 0.05 μm for sanitary grade)
Dimensional Specifications
| Parameter | Specification | Tolerance | Standard Reference |
|---|---|---|---|
| Outer Diameter (OD) | 9.52 mm (3/8") / 12.70 mm (1/2") / 15.88 mm (5/8") | ±0.10 mm | ASTM A269 |
| Wall Thickness (WT) | 0.50 mm / 0.65 mm / 0.80 mm / 1.00 mm | ±0.05 mm | ASTM A269 |
| Inner Diameter (ID) | Calculated: OD − 2 × WT | Derived | — |
| Coil Length (per roll) | Up to 500 m (continuous coil) | ±2% | ISO 4955 |
| Coil Inner Diameter (reel) | 200 mm / 300 mm / 400 mm (standard reel sizes) | ±5 mm | ISO 4955 |
| Coil Weight (typical) | 200 – 500 kg per coil | — | — |
| Surface Roughness (Ra) | ≤ 0.8 μm (standard) / ≤ 0.4 μm (premium) | — | ASTM A269 |
| Roundness | ≤ 0.5% of OD | — | ASTM A269 |
| Maximum Allowable Pressure | 2.5 MPa (365 psi) at 90°C | — | EN 10217 |
Manufacturing Process
Process Flow Diagram
- Raw Material Procurement: Selection of certified stainless steel strip (coil) from approved mills (e.g., POSCO, Outokumpu, Taigang), verified by mill test certificates (MTC) in accordance with EN 10204 Type 3.1.
- Incoming Quality Inspection: Verification of chemical composition via Optical Emission Spectroscopy (OES), dimensional measurement, and surface quality assessment.
- Slitting: Precision slitting of wide strip coil into tube-forming strips of required width and thickness, with controlled edge quality to prevent defects during roll-forming.
- Tube Forming (Roll-Pipe Method): Continuous roll-forming of flat strip into seamless tube geometry using a multi-stand roll-forming mill. This process eliminates weld seams, ensuring uniform wall thickness and superior corrosion resistance throughout the entire tube length.
- Welding (if welded tube): For welded variants, Transverse Resistance Welding (TRW) or High-Frequency Resistance Welding (HFRW) is applied with precise heat input control to minimize sensitization and maintain mechanical properties.
- Heat Treatment (Annealing): Solution annealing at 1050–1150°C followed by rapid air or water quenching to restore full austenitic microstructure, eliminate residual stresses from forming, and achieve maximum corrosion resistance and ductility.
- Pickling and Passivation: Chemical treatment using mixed acid (HNO₃ + HF) solution to remove oxide scale and form a protective chromium oxide passive layer on the surface, enhancing long-term corrosion resistance.
- Surface Finishing: Mechanical polishing or electropolishing to achieve specified surface roughness values, depending on application requirements.
- Coil Winding: Finished tube is wound onto standard-diameter reels with controlled tension to prevent deformation, kinking, or surface damage during storage and transportation.
- Final Quality Control: 100% inspection including dimensional verification, visual surface examination, pressure testing (hydrostatic at 1.5× working pressure), and sampling for chemical and mechanical testing.
Applications
Primary Application — HVAC Fan Coil Units
The JX-409 Coil Tube is specifically engineered for use in Fan Coil Units (FCU), which are terminal air distribution devices in commercial HVAC systems. The coil tube is formed into serpentine configurations and integrated with aluminum fins to create high-efficiency air-to-water heat exchangers. Key performance parameters derived from temperature time-period control studies demonstrate:
- Temperature regulation accuracy of ±0.5°C within the controlled zone
- Optimal thermal exchange efficiency through maximized coil surface area in compact geometries
- Time-period control capability enabling energy-efficient operation schedules aligned with occupancy patterns
- Reduced temperature overshoot and undershoot through optimized coil geometry and flow dynamics
Additional Applications
- Commercial Air Handling Units (AHU): Heating and cooling coils in centralized air handling systems
- Industrial Process Cooling: Heat exchangers in food processing, pharmaceutical, and chemical manufacturing
- Refrigeration Systems: Evaporator and condenser coils in commercial refrigeration equipment
- Domestic Water Heating: Immersion coils for water heaters and boilers
- Heat Recovery Systems: Air-to-air and air-to-water heat recovery units
- Condensers and Chillers: Water-cooled condenser tubing in chiller plants
Quality Certifications & Compliance
| Certification / Standard | Scope | Applicability |
|---|---|---|
| ISO 9001:2015 | Quality Management System | Manufacturing Process |
| ISO 14001:2015 | Environmental Management System | Production & Operations |
| GB/T 12771 | Seamless Stainless Steel Tubes for General Purposes | Product Specification (China) |
| ASTM A269/A269M | Welded Austenitic Stainless Steel Tubing | Material & Testing |
| EN 10217-7 | Non-ferrous Metal Tubes — Stainless Steel Tubes | European Standard Compliance |
| EN 10204-3.1 | Inspection Documents — Test Reports | Mill Test Certification |
| GB/T 21832 | Stainless Steel Tubes for Heat Exchangers | HVAC Heat Exchanger Application |
| ASME B31.5 | Process Piping | Pressure Vessel & Piping Applications |
| NSF/ANSI 61 | Drinking Water System Components | Water Contact Compliance (upon request) |
Unique Selling Points
- Seamless Construction: Roll-formed seamless tube eliminates weld-induced corrosion initiation sites, extending service life beyond 25 years in HVAC applications.
- Superior Corrosion Resistance: Austenitic stainless steel composition provides exceptional resistance to condensate corrosion, chloride-induced pitting, and chemical degradation from HVAC refrigerants and additives.
- Continuous Coil Supply: Delivered as a continuous coil up to 500 meters, enabling uninterrupted production in downstream coil-forming operations without splicing losses.
- Precision Dimensional Control: Tight tolerances (±0.05 mm wall thickness, ±0.10 mm OD) ensure optimal fit within heat exchanger headers and fin-tube assemblies, maximizing thermal contact efficiency.
- Thermal Cycling Durability: Engineered to withstand over 100,000 thermal cycles between −40°C and +120°C without cracking, fatigue failure, or significant property degradation.
- Temperature Time-Period Control Compatibility: Coil geometry and flow characteristics optimized for advanced time-period temperature control strategies in smart building HVAC systems, achieving energy savings of 15–25% compared to conventional controls.
- Food-Grade Option Available: BA finish and sanitary polishing options available for applications requiring compliance with FDA 21 CFR Part 178 and EC 1935/2004 regulations.
- Full Traceability: Each coil is marked with heat number, production date, and chemical composition reference, enabling complete material traceability throughout the supply chain.
Technical Notes & Recommendations
Installation Guidance: When forming the coil tube into serpentine configurations for fan coil unit heat exchangers, a minimum bending radius of 3× the outer diameter (3D) should be maintained to prevent wall thinning, ovalization, or material fatigue at bend locations. Cold forming is recommended over hot forming to preserve the passive oxide layer and avoid sensitization of the austenitic microstructure.
Storage Requirements: Store coils in a dry, indoor environment at temperatures between 5°C and 35°C, away from corrosive atmospheres. Coils should be protected from mechanical impact and UV radiation. Maximum storage duration without re-inspection: 12 months.
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