Stainless Steel Coil Tube for Fan Coil Unit Systems (Coiltube)
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered, cold-drawn stainless steel tubing formed into a helical coil configuration. This product is specifically designed for integration into Fan Coil Unit (FCU) Systems, where it serves as the primary heat exchange element responsible for thermal energy transfer between circulating refrigerant (or hot water) and ambient air.
The coil tube is engineered to address critical performance challenges observed in HVAC (Heating, Ventilation, and Air Conditioning) installations, particularly the issue of ceiling water leakage caused by inadequate condensate drainage, improper coil tube geometry, or material degradation over extended service cycles. By leveraging superior corrosion resistance and dimensional precision, this product ensures long-term reliability and eliminates common failure modes associated with conventional carbon steel or copper coil alternatives.
As a key component in commercial and residential HVAC systems, the coil tube must maintain structural integrity under cyclic thermal stress, resist scaling and biofilm formation, and facilitate efficient airflow through its helical arrangement. Wenzhou Jixing Metal Materials Co., Ltd. delivers this product with rigorous adherence to international manufacturing standards, ensuring consistent performance across diverse operating environments.
Material & Properties
Material Composition
The coil tube is fabricated from high-grade austenitic stainless steel, conforming to the following material specifications:
- Primary Grade: SUS 304 / ASTM A269 TP304 (18/8 Stainless Steel)
- Alternative Grade: SUS 316 / ASTM A269 TP316 (for enhanced chlorided corrosion resistance in coastal or chemically aggressive environments)
- Chromium (Cr) Content: 18.0% – 20.0% (SUS 304) / 16.0% – 18.0% (SUS 316)
- Nickel (Ni) Content: 8.0% – 10.5% (SUS 304) / 10.0% – 14.0% (SUS 316)
- Molybdenum (Mo) Content: < 0.08% (SUS 304) / 2.0% – 3.0% (SUS 316)
- Carbon (C) Content: ≤ 0.08% (SUS 304) / ≤ 0.08% (SUS 316)
Mechanical Properties
| Property | Specification | Test Method |
|---|---|---|
| Tensile Strength (Ultimate) | ≥ 520 MPa (SUS 304) / ≥ 550 MPa (SUS 316) | ASTM A370 |
| Yield Strength (0.2% Offset) | ≥ 205 MPa (SUS 304) / ≥ 240 MPa (SUS 316) | ASTM A370 |
| Elongation at Break | ≥ 40% | ASTM A370 |
| Hardness (Rockwell B) | ≤ 95 HRB (annealed condition) | ASTM E18 |
| Thermal Conductivity | 16.3 W/(m·K) at 20°C (SUS 304) / 16.0 W/(m·K) at 20°C (SUS 316) | ASTM E153 |
| Thermal Expansion Coefficient | 17.3 × 10⁻⁶ /°C (20–100°C) | ASTM E228 |
| Maximum Service Temperature | 870°C (SUS 304) / 870°C (SUS 316) | — |
| Minimum Service Temperature | -196°C (cryogenic compatible) | — |
Corrosion Resistance
- Pitting Corrosion Resistance: SUS 316 grade exhibits superior resistance in chloride-containing environments (e.g., coastal HVAC installations), with a Critical Pitting Temperature (CPT) of ≥ 30°C in 3.5% NaCl solution.
- Intergranular Corrosion Resistance: All grades are supplied in solution-annealed (SA) condition to prevent sensitization; verified by ASTM A269 Section VIII intergranular corrosion testing.
- Biofilm Resistance: The smooth, non-porous surface finish (Ra ≤ 0.4 μm) minimizes microbial adhesion and condensate film formation, directly mitigating the ceiling water leakage issues documented in FCU system failure analyses.
Specifications
| Parameter | Specification | Remarks |
|---|---|---|
| Outer Diameter (OD) | 9.52 mm (3/8"), 12.70 mm (1/2"), 15.88 mm (5/8") | Standard HVAC coil tube sizes |
| Wall Thickness | 0.81 mm (32 AWG) / 1.02 mm (30 AWG) / 1.24 mm (28 AWG) | Tolerance: ± 0.13 mm |
| Coil Diameter (Pitch) | 150 mm – 300 mm (adjustable per system design) | Helical coil configuration |
| Coil Length (Total) | Up to 6,000 mm (customizable) | Continuous seamless coil |
| Number of Turns | 20 – 120 turns (configurable) | Optimized for heat transfer area |
| Surface Finish | Mirror polished (Ra ≤ 0.4 μm) or standard pickled & passivated (Ra ≤ 0.8 μm) | Anti-condensate adhesion |
| End Preparation | Deburred, chamfered, or threaded (G1/2, G3/4, NPT) | Per customer specification |
| Pressure Rating | Up to 1.6 MPa (232 psi) working pressure | Hydrostatic test at 2.4 MPa |
| Heat Transfer Coefficient (U-value) | 150 – 350 W/(m²·K) (depending on airflow velocity and fluid conditions) | Optimized helical geometry |
| Refrigerant / Fluid Compatibility | R-22, R-410A, R-32, Hot Water (≤ 90°C), Glycol Solutions | Non-reactive with all standard HVAC fluids |
| Operating Humidity Range | 0% – 100% RH (condensate-resistant) | Key advantage over carbon steel alternatives |
| Weight | Approximately 0.4 – 2.5 kg (depending on dimensions) | Lightweight installation |
Manufacturing Process
The production of the stainless steel coil tube follows a meticulously controlled multi-stage manufacturing process to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Raw Material Selection: High-purity stainless steel strip or seamless tube stock is sourced from certified mills, with full chemical composition analysis (via Optical Emission Spectroscopy, OES) and mechanical property verification prior to acceptance.
- Cold Drawing / Cold Forming: The stainless steel tube is cold-drawn through precision tungsten carbide dies to achieve exact outer diameter and wall thickness tolerances (± 0.13 mm). This process induces beneficial work hardening, increasing yield strength by approximately 20–30% without compromising ductility.
- Intermediate Annealing: Where multiple drawing passes are required, intermediate solution annealing at 1050°C – 1100°C in a protective atmosphere (argon or nitrogen) prevents work hardening accumulation and maintains corrosion resistance by dissolving carbide precipitates.
- Coil Forming: The drawn tube is helically coiled using CNC-controlled forming equipment to achieve precise pitch, coil diameter, and turn count. Forming parameters are optimized to prevent ovalization (ovality ≤ 2%) and surface deformation.
- Final Solution Annealing: The formed coil is subjected to a final solution heat treatment at 1050°C – 1100°C followed by rapid water quenching to restore full austenitic structure, eliminate residual stresses from forming, and maximize corrosion resistance.
- Pickling and Passivation: The annealed coil undergoes acid pickling (HNO₃ / HF blend) to remove oxide scale, followed by passivation treatment to establish a stable chromium oxide (Cr₂O₃) protective layer. This step is critical for preventing the corrosion-induced condensate leakage documented in field failure analyses.
- Surface Polishing (Optional): For applications requiring mirror finish (Ra ≤ 0.4 μm), the coil undergoes mechanical polishing followed by electropolishing to achieve a chemically smooth, biofilm-resistant surface.
- End Preparation: Tube ends are cut, deburred, chamfered, or threaded to customer specifications using automated CNC end-processing stations.
- Quality Inspection: Every coil tube undergoes 100% hydrostatic pressure testing (at 1.5× working pressure), dimensional verification via ultrasonic wall thickness gauging, visual surface inspection, and random chemical spot testing.
- Packaging and Traceability: Each unit is individually packaged with protective end caps, accompanied by a material certificate (Mill Test Report, MTR) and a unique batch traceability code linking to full production records.
Applications
The stainless steel coil tube is deployed across a broad spectrum of HVAC applications where reliability, corrosion resistance, and thermal efficiency are paramount:
- Commercial HVAC Systems: Primary heat exchange coils in fan coil units installed in office buildings, shopping centers, hospitals, and educational facilities.
- Residential HVAC Systems: Compact coil assemblies in wall-mounted or ceiling-cassette fan coil units for residential apartments and villas.
- Industrial Process Cooling: Temperature control coils in manufacturing facilities requiring non-corrosive, food-grade compatible heat exchange elements.
- Cleanroom Environments: HVAC coils in pharmaceutical, semiconductor, and laboratory facilities where particulate generation and chemical resistance are critical.
- Marine and Coastal Applications: HVAC systems in offshore platforms, marine vessels, and coastal buildings where chloride-induced corrosion is a dominant failure mechanism.
- Refrigeration Systems: Evaporator and condenser coils in commercial refrigeration units where stainless steel provides superior longevity over copper alternatives.
- Condensate-Prone Environments: Specifically engineered to address the ceiling water leakage problem identified in fan coil unit system analyses, where conventional materials fail due to corrosion-induced wall thinning and structural degradation.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management and product certification systems to ensure international compliance:
- ISO 9001:2015 — Quality Management System certification covering all manufacturing processes, from raw material procurement through final dispatch.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices and waste minimization.
- CE Marking (EU Conformity) — Product conformity with European health, safety, and environmental protection standards, including compliance with Pressure Equipment Directive (PED 2014/68/EU) where applicable.
- ASME / ASTM Compliance — Manufacturing processes and material properties verified against ASTM A269 (Specification for Seamless and Welded Austenitic Stainless Steel Tubing for Boiler, Heat Exchanger, and Similar Heat Transfer Applications) and ASTM A270 (Specification for Seamless and Welded Austenitic Stainless Steel Tubing for General Applications).
- EN 10217-7 Compliance — European standard for seamless and welded austenitic stainless steel tubes for pressure purposes.
- JIS G3446 / JIS G3459 Compliance — Japanese Industrial Standards for seamless and welded austenitic stainless steel tubes for heat exchange applications.
- Mill Test Reports (MTR) — Full chemical analysis (OES), mechanical testing (tensile, hardness), and dimensional verification data provided with every shipment.
- NDT (Non-Destructive Testing) — 100% hydrostatic pressure testing supplemented by random ultrasonic (UT) and eddy current (ET) inspection for internal defect detection.
- Third-Party Inspection — Available upon request through recognized inspection bodies (e.g., SGS, Bureau Veritas, TÜV) for independent verification of product conformity.
Unique Selling Points
1. Superior Corrosion Resistance Eliminating Ceiling Leakage: The austenitic stainless steel construction provides inherent resistance to condensate-induced corrosion, directly addressing the root cause of ceiling water leakage in FCU systems identified in field failure analyses. Unlike carbon steel or copper coils, the stainless steel coil tube maintains wall thickness integrity over decades of service, preventing perforation and structural failure.
2. Mirror-Polished Surface for Condensate Management: The optional Ra ≤ 0.4 μm surface finish minimizes condensate adhesion and promotes uniform water sheet formation, ensuring efficient drainage and preventing the localized water pooling that leads to ceiling saturation.
3. Precision Helical Geometry for Optimized Heat Transfer: CNC-controlled coil forming ensures consistent pitch and turn geometry, maximizing the heat transfer surface area while maintaining laminar airflow through the coil assembly, resulting in improved system efficiency (COP enhancement of 5–12% compared to irregularly formed alternatives).
4. Full Traceability and Documentation: Each coil tube is accompanied by a complete Mill Test Report (MTR) and batch traceability code, enabling full lifecycle quality assurance and compliance documentation for building inspection and warranty purposes.
5. Customizable Specifications: Flexible manufacturing capabilities allow customization of coil diameter, turn count, tube dimensions, surface finish, and end preparation to match specific system design requirements, ensuring optimal integration into diverse FCU configurations.