Stainless Steel Coil Tube (Coiltube) – HVAC Fan Coil Unit Application Series
Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product specifically designed for integration into Fan Coil Unit (FCU) systems within Heating, Ventilation, and Air Conditioning (HVAC) applications. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coiltube product combines the superior corrosion resistance of austenitic stainless steel with the geometric flexibility required for compact heat exchanger configurations. The coiltube is supplied in continuous coil form to facilitate automated manufacturing processes, reducing waste and ensuring consistent dimensional accuracy throughout production runs.
This product represents a critical component in modern building HVAC infrastructure, where efficient thermal transfer, long service life, and resistance to environmental degradation are paramount. The coil configuration enables maximum heat exchange surface area within a minimized footprint, making it ideal for ceiling-mounted and concealed fan coil unit installations in commercial, residential, and industrial settings.
Material & Properties
The stainless steel coil tube is fabricated from high-grade austenitic stainless steel, with the primary material grade conforming to industry standards for HVAC heat exchanger applications.
- Primary Alloy Grade: AISI 304 (UNS S30400) / AISI 316 (UNS S31600) for enhanced chloride resistance applications
- Carbon Equivalent (CE): ≤ 0.04% (AISI 304), ≤ 0.03% (AISI 316)
- Chromium (Cr) Content: 18.0–20.0% (AISI 304), 16.0–18.0% (AISI 316)
- Nickel (Ni) Content: 8.0–10.5% (AISI 304), 10.0–14.0% (AISI 316)
- Molybdenum (Mo) Content: ≤ 0.08% (AISI 304), 2.0–3.0% (AISI 316)
- Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C
- Thermal Expansion Coefficient: 16–18 × 10⁻⁶ /°C (20–100°C)
- Tensile Strength (UTS): ≥ 515 MPa (annealed condition)
- Yield Strength (0.2% Offset): ≥ 205 MPa
- Elongation at Break: ≥ 40% (ASTM A270)
- Operating Temperature Range: −196°C to +870°C (continuous service)
- Corrosion Resistance: Excellent resistance to atmospheric corrosion, mild acids, and organic compounds; superior pitting resistance with Mo-bearing grades
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 12.7 mm (1/4" – 1/2") | ASTM A270 / GB/T 14976 |
| Wall Thickness | 0.4 mm – 1.0 mm | ASTM A270 / GB/T 14976 |
| Coil Bundle Length | 1.5 m – 6.0 m (configurable) | Custom / OEM Specification |
| Coil Pitch | 10 mm – 25 mm (center-to-center) | Design-Specific |
| Surface Finish | Mirror polish (Ra ≤ 0.4 μm) / Brushed (Ra ≤ 1.6 μm) | ASTM A480 |
| Delivery Condition | Full Annealed (Solution Treated) | ASTM A270 |
| End Treatment | Flared / Rolled / Buttwelded / Brazed (per application) | ISO 15493 |
| Coil Form | Continuous spiral coil / U-bend bank / Serpentine | OEM Specification |
| Working Pressure | ≤ 1.6 MPa (standard), ≤ 2.5 MPa (reinforced) | ASME B31.9 |
| Design Life | ≥ 25 years (indoor HVAC service) | ISO 15510 |
| Maximum Design Temperature | +120°C (hot water), +150°C (steam) | ASME B31.9 |
| Refrigerant Compatibility | R-22, R-410A, R-407C, R-134a, R-32 | ASHRAE Standard 34 |
Manufacturing Process
The production of stainless steel coil tubes for FCU applications follows a rigorously controlled multi-stage manufacturing sequence to ensure dimensional precision, metallurgical integrity, and functional reliability:
- Raw Material Selection and Inspection: Hot-rolled stainless steel strip is procured from certified mills, subjected to spectrographic analysis (OES/XRF) to verify chemical composition, and tested for mechanical properties prior to acceptance.
- Cold Rolling and Annealing: Strip is cold-rolled to target thickness with controlled reduction ratios (typically 40–60% per pass) to achieve desired grain structure and mechanical properties. Interpass annealing at 1050–1100°C in a protective atmosphere furnace ensures full recrystallization and elimination of work-hardening effects.
- Slitting and Edge Preparation: The annealed strip is slit to precise widths with deburred edges to ensure uniform tube formation and minimize surface defects.
- Tube Forming: Precision roll-forming or extrusion processes shape the strip into seamless tubes with tight tolerances on OD and wall thickness (±5% per ASTM A270). The forming process maintains the austenitic microstructure without inducing detrimental martensitic transformation.
- Heat Treatment (Solution Annealing): Final solution treatment at 1040–1120°C followed by rapid water quenching ensures uniform carbide dissolution, maximum corrosion resistance, and optimal ductility for subsequent bending operations.
- Coil Bending and Forming: Computer Numerically Controlled (CNC) bending machines form the straight tube into the specified coil geometry (serpentine, U-bank, or spiral). Bend radii are calculated to prevent wall thinning below 85% of original thickness and to avoid ovality exceeding 5%.
- Fin Attachment (if applicable): Aluminum or copper fins are mechanically or brazed onto the coil tube to enhance heat transfer coefficients, with fin density typically ranging from 10–16 fins per inch (FPI).
- Surface Treatment: Electropolishing or mechanical polishing achieves the specified surface roughness, reducing fouling resistance and facilitating cleaning maintenance.
- Pressure Testing and Leak Detection: Each coil assembly undergoes hydrostatic pressure testing at 1.5× working pressure for a minimum of 15 minutes, followed by helium or nitrogen leak detection to verify weld integrity.
- Final Inspection and Packaging: Dimensional verification, visual inspection, and material traceability documentation are completed. Coils are packaged in protective film with desiccant to prevent corrosion during storage and transit.
Applications
The stainless steel coil tube product is specifically engineered for the following application domains:
- Fan Coil Units (FCUs): Primary application in both supply-air and return-air configurations for commercial and residential HVAC systems. The coil tube serves as the refrigerant or hot/cold water circuit within the FCU heat exchanger.
- Chilled Water Systems: Integration into secondary chilled water loops where corrosion resistance and thermal efficiency are critical for maintaining system COP (Coefficient of Performance).
- Hot Water Heating Circuits: Utilization in radiant floor heating and wall-mounted radiator systems requiring long-term resistance to water-side scaling and corrosion.
- Commercial Refrigeration: Evaporator and condenser coil construction for supermarket display cases, walk-in coolers, and cold storage facilities operating with ammonia or fluorocarbon refrigerants.
- Food and Pharmaceutical Processing: Heat exchange components in sanitary processing lines where CIP (Clean-In-Place) compatibility and FDA/USDA compliance are mandated.
- Marine and Coastal Environments: HVAC installations on vessels, offshore platforms, and coastal facilities where chloride-induced pitting corrosion is a primary degradation mechanism (AISI 316 grade recommended).
- Clean Room and Hospital Environments: Precision temperature and humidity control systems requiring non-shedding, antimicrobial, and easily sanitized heat exchange surfaces.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring that every coil tube product meets or exceeds international standards:
- ISO 9001:2015 – Quality Management System certification covering all manufacturing and inspection processes
- ISO 14001:2015 – Environmental Management System demonstrating sustainable manufacturing practices
- ISO 45001:2018 – Occupational Health and Safety Management System
- CE Marking – Compliance with European Union directives for pressure equipment (PED 2014/68/EU)
- ASME Stamp – Authorization for fabrication of pressure-containing components per ASME BPV Code
- TÜV Certification – Third-party verification of product safety and performance compliance
- EN 10204 3.1 – Mill test certificates with independent inspection body verification for material conformity
- NSF/ANSI 61 – Drinking water system components certification (where applicable for potable water heating circuits)
Unique Selling Points
Superior Corrosion Resistance: The austenitic stainless steel construction provides exceptional resistance to corrosion in humid, chemically aggressive, and marine environments—significantly outperforming conventional carbon steel or copper alternatives in terms of service life and maintenance intervals.
Thermal Efficiency Optimization: The precision-manufactured coil geometry, combined with the inherently high thermal conductivity of stainless steel, ensures optimal heat transfer coefficients while minimizing pressure drop across the coil circuit.
Design Flexibility: Available in multiple OD, wall thickness, coil pitch, and end-treatment configurations to accommodate diverse OEM specifications and custom engineering requirements for FCU manufacturers.
Long Service Life: With a design life exceeding 25 years under normal indoor HVAC operating conditions, the stainless steel coil tube eliminates the need for frequent replacement and reduces total cost of ownership (TCO) over the system lifecycle.
Sanitary and Hygienic: Mirror-polished surfaces (Ra ≤ 0.4 μm) inhibit bacterial adhesion and facilitate routine cleaning, making these products ideal for food-grade, pharmaceutical, and medical HVAC applications.
Environmental Sustainability: Stainless steel is 100% recyclable without degradation of material properties, supporting circular economy principles and reducing the environmental footprint of HVAC system replacements.
Design Considerations for FCU Integration
When selecting stainless steel coil tubes for Fan Coil Unit design, the following engineering parameters must be evaluated:
- Heat Transfer Coefficient (U-value): Calculated based on tube material conductivity, fin geometry, flow velocity, and fouling factors per ASHRAE Handbook – HVAC Systems and Equipment.
- Pressure Drop (ΔP): Must be minimized to reduce fan energy consumption; Darcy-Weisbach equation applied with stainless steel roughness factor (ε = 0.015 mm).
- Flow Distribution: Coil tube arrangement (counter-flow, cross-flow, or mixed-flow) directly impacts FCU performance characteristics and must be optimized for the specific load profile.
- Condensate Management: Surface finish and coil slope must prevent water retention and promote efficient condensate drainage to avoid microbial growth.
- Freezing Protection: Material ductility at low temperatures ensures resistance to thermal stress cracking during winter operation or defrost cycles.
Wenzhou Jixing Metal Materials Co., Ltd. provides full technical support including thermal performance modeling, flow simulation (CFD), and material selection guidance to ensure optimal integration of stainless steel coil tubes into FCU and broader HVAC system designs.