Stainless Steel Coil Tube for Fan Coil Unit Heat Exchangers
Product Overview
The Stainless Steel Coil Tube (product code: 1594) is a precision-engineered tubular component designed specifically for use in fan coil unit (FCU) air conditioning heat exchangers. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coil tube delivers exceptional thermal transfer efficiency, corrosion resistance, and mechanical integrity under continuous cyclic thermal loading conditions. The product represents a specialized segment of the literature-driven engineering study on the structural design and thermodynamic performance optimization of fan coil unit heat exchangers, translating academic research findings into high-performance industrial components.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, predominantly conforming to grades such as SUS304 (UNS S30400) and SUS316L (UNS S31603), selected for their superior resistance to condensation-induced corrosion and thermal fatigue. Key material properties include:
- Chemical Composition: Chromium (Cr) content ≥ 18%, Nickel (Ni) content ≥ 8% for SUS304; Mo (Molybdenum) addition ≥ 2% for SUS316L to enhance pitting corrosion resistance
- Thermal Conductivity: 16.3 W/(m·K) at 20°C, ensuring efficient heat exchange between refrigerant and air streams
- Maximum Operating Temperature: Up to 870°C in oxidizing atmospheres; sustained performance at HVAC operating ranges of -20°C to +120°C
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, condensate water, and common HVAC refrigerants
- Mechanical Strength: Yield strength ≥ 205 MPa; tensile strength ≥ 515 MPa (as-rolled condition)
- Surface Finish: Mill finish or electropolished surface with Ra ≤ 0.8 μm to minimize fouling and pressure drop
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | Φ6.0 mm / Φ7.0 mm / Φ8.0 mm (customizable) | ISO 4287 |
| Wall Thickness | 0.4 mm – 1.0 mm (±10% tolerance) | ASTM A269 / ASTM A270 |
| Coil Length | Up to 50 m per continuous coil | — |
| Coil Winding Diameter | 300 mm – 600 mm (adjustable per application) | — |
| Surface Treatment | Pickled & Passivated / Electropolished | ASTM A967 |
| Heat Treatment Condition | Solution Annealed (1010°C – 1120°C, water quench) | ASTM A473 |
| Hydrostatic Test Pressure | 2.0 MPa minimum, no leakage permitted | ASTM A269 |
| Dimensional Tolerance | OD: ±0.1 mm; Wall thickness: ±0.05 mm | ISO 4287 |
| Maximum Bending Radius | ≥ 3× OD (cold forming) | — |
| Operating Pressure Range | Up to 1.6 MPa (16 bar) continuous | — |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing sequence designed to ensure dimensional accuracy, metallurgical uniformity, and surface integrity:
- Raw Material Selection: Hot-rolled stainless steel strip is sourced from certified mills and subjected to spectroscopic analysis (OES) to verify chemical composition compliance.
- Cold Drawing & Sizing: The strip is fed through precision tungsten carbide (WC) die sets in a multi-pass cold drawing process to achieve the target outer diameter and wall thickness with tight tolerances.
- Coil Winding: The drawn tube is wound onto precision mandrels using CNC-controlled winding machines to achieve uniform coil geometry and consistent inter-pass spacing.
- Solution Annealing: Coiled tubes undergo continuous annealing in a protective nitrogen atmosphere at 1010°C – 1120°C followed by controlled cooling to eliminate cold-work stresses and restore full austenitic microstructure.
- Pickling & Passivation: Surface scale and oxide films are removed via nitric-hydrofluoric acid pickling, followed by passivation treatment to restore the protective chromium oxide layer.
- Quality Inspection: Each batch undergoes dimensional verification (CMM), hydrostatic pressure testing, surface roughness measurement, and visual inspection for defects.
Applications
The stainless steel coil tube is engineered for demanding applications in HVAC (Heating, Ventilation, and Air Conditioning) systems, with primary use in:
- Fan Coil Unit Heat Exchangers: As the core heat transfer element in air-side and water-side heat exchangers, facilitating efficient thermal exchange between chilled/hot water and air streams in commercial and residential HVAC systems.
- Chilled Water Systems: Resistant to corrosion from treated water containing inhibitors, suitable for long-term immersion in glycol-water mixtures.
- Condensing Coils: Withstands condensate formation and associated corrosion in cooling coil applications.
- Industrial Process Cooling: Applicable in food processing, pharmaceutical, and laboratory HVAC systems where hygiene and corrosion resistance are critical.
- Refrigerant Side Tubes: Compatible with ammonia (NH₃), R-134a, R-410A, and other common refrigerants without risk of stress corrosion cracking.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality assurance systems and holds the following certifications and compliance standards:
- ISO 9001:2015 — Quality Management System certification for manufacturing operations
- ISO 14001:2015 — Environmental Management System certification
- ASTM A269 / ASTM A270 — Compliance with standard specifications for welded austenitic stainless steel tubing
- EN 10217-7 — European standard compliance for austenitic stainless steel tubes and pipes
- GB/T 14976 — Chinese national standard for cold-rolled stainless steel seamless tubes
- CE Marking — Conformity with European Economic Area safety directives
- Mill Test Certificates (MTC) — Available per batch with full chemical and mechanical test data
Unique Selling Points
The coil tube product from Wenzhou Jixing Metal Materials Co., Ltd. distinguishes itself in the competitive HVAC component market through several key advantages:
Academic-Driven Engineering: The product design incorporates findings from systematic research on fan coil unit heat exchanger structural optimization and thermodynamic performance, ensuring that empirical knowledge is translated into measurable performance gains.
- Superior Corrosion Longevity: The austenitic stainless steel construction provides a service life exceeding 25 years in aggressive condensate environments, significantly outperforming copper and aluminum alternatives.
- Low-Fouling Surface: The electropolished finish with Ra ≤ 0.8 μm minimizes biological fouling and scale deposition, maintaining thermal efficiency over extended operating cycles.
- Thermal Fatigue Resistance: Engineered to withstand thousands of thermal cycling events without degradation, critical for fan coil units operating in variable-load conditions.
- Customization Capability: Flexible manufacturing allows tailoring of OD, wall thickness, coil winding diameter, and length to match specific heat exchanger designs.
- Environmental Compliance: Fully recyclable stainless steel material with zero lead, nickel leaching below regulatory thresholds, and compliance with RoHS and REACH directives.