Stainless Steel Coil Tube — Fan Coil Unit Heat Exchanger Series
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered tubular component specifically designed for integration into fan coil units (FCUs) and air conditioning heat exchanger assemblies. As a critical element within the hydronic air distribution architecture of modern HVAC (Heating, Ventilation, and Air Conditioning) systems, this coil tube facilitates efficient thermal energy transfer between the circulating refrigerant/water medium and the ambient air stream. The product embodies a rational design philosophy aligned with the principles outlined in the technical study of "Reasonable Selection of Fan Coil Units in Air Conditioning Systems," emphasizing thermal performance optimization, energy efficiency, and long-term operational reliability.
This coil tube is available in seamless and welded configurations, formed into serpentine, zigzag, or spiral geometries to maximize surface area within constrained installation envelopes. The product line is engineered to meet the rigorous demands of commercial, industrial, and institutional air conditioning installations where corrosion resistance, thermal conductivity, and structural integrity are paramount.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, predominantly conforming to AISI 304 and AISI 316 designations, ensuring exceptional resistance to oxidation, pitting, and intergranular corrosion under both wet and dry operational conditions.
- Base Alloy: AISI 304 (UNS S30400) / AISI 316 (UNS S31600) — Chromium-Nickel Austenitic Stainless Steel
- Chromium Content (Cr): 18.0% – 20.0% (AISI 304); 16.0% – 18.0% (AISI 316)
- Nickel Content (Ni): 8.0% – 10.5% (AISI 304); 10.0% – 14.0% (AISI 316)
- Molybdenum Content (Mo): 2.0% – 3.0% (AISI 316 only) — enhances resistance to chloride-induced pitting corrosion
- Carbon Content (C): ≤ 0.08% (AISI 304); ≤ 0.03% (AISI 304L / 316L low-carbon variants)
- Tensile Strength: ≥ 515 MPa (75,000 psi)
- Yield Strength (0.2% Offset): ≥ 205 MPa (30,000 psi)
- Thermal Conductivity: 16.3 W/(m·K) at 25°C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (20–315°C)
- Operating Temperature Range: −196°C to +870°C (continuous service)
- Surface Finish: 2B (cold-rolled, annealed, bright) or No. 4 brushed finish; available in electropolished condition upon request
- Corrosion Resistance: Superior resistance to atmospheric, freshwater, and mildly aggressive chemical environments; AISI 316 grade provides enhanced performance in chloride-rich or marine-adjacent applications
Specifications
| Parameter | Specification |
|---|---|
| Product Designation | Stainless Steel Coil Tube (Coiltube) — FCU Series |
| Item Number | 1107 |
| Material Grade | AISI 304 / AISI 304L / AISI 316 / AISI 316L |
| Outer Diameter (OD) | 6.35 mm (1/4"), 9.52 mm (3/8"), 12.70 mm (1/2") — customizable |
| Wall Thickness (WT) | 0.50 mm – 1.20 mm (standard); 0.30 mm – 2.00 mm (custom range) |
| Tube Length per Row | 0.30 m – 2.40 m (configurable per system design) |
| Row Configuration | 2-row, 3-row, 4-row, 6-row (multi-row serpentine assemblies) |
| Coil Geometry | Serpentine / Zigzag / Spiral / Double-U configurations |
| Fin Type (if finned) | Integral aluminum fins or welded stainless steel fins; fin spacing 2.0 – 3.5 mm |
| Maximum Operating Pressure | 1.6 MPa (232 psi) — standard; 2.5 MPa available for high-pressure applications |
| Hydrostatic Test Pressure | 2.4 MPa (348 psi) — 1.5× maximum working pressure |
| Standard Lengths (Coil) | 5 m, 10 m, 20 m, 30 m, 50 m (continuous coil); custom lengths available |
| Tolerance — OD | ±0.05 mm |
| Tolerance — Wall Thickness | ±0.025 mm |
| End Treatment | Plain cut, beveled, threaded (BSP/NPT), or flanged |
| Applicable Standards | ASTM A269, ASTM A213, EN 10217-7, GB/T 12771 |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd |
Manufacturing Process
The production of this stainless steel coil tube follows a rigorously controlled, multi-stage manufacturing protocol to ensure dimensional accuracy, metallurgical integrity, and consistent performance:
- Raw Material Sourcing and Mill Certification: Hot-rolled stainless steel coils are procured from certified mills, accompanied by mill test certificates (MTC) verifying chemical composition and mechanical properties in accordance with ASTM and EN standards.
- Cold Drawing / Cold Reduction: The hot-rolled precursor coil undergoes precision cold-drawing through calibrated tungsten carbide dies to achieve exact outer diameter and wall thickness tolerances. This process induces beneficial work-hardening, enhancing mechanical strength while maintaining ductility.
- Solution Annealing: Cold-drawn tubes are subjected to controlled solution annealing at temperatures between 1050°C and 1150°C in a protective atmosphere (argon or nitrogen), followed by rapid water quenching. This eliminates cold-work stresses, restores full ductility, and stabilizes the austenitic microstructure.
- Pipe Forming and Bending: Annealed tubes are precisely bent into the required coil geometry (serpentine, zigzag, or spiral) using CNC-controlled tube bending machinery with mandrel support to prevent ovality and wrinkling. Bend radii are engineered to minimize stress concentration at curvature points.
- Tube-to-Tube Joining (if multi-row): Where multi-row configurations are required, individual tube rows are connected via U-bends formed at the coil ends, or joined through precision TIG (Tungsten Inert Gas) welding with full penetration and radiographic inspection.
- Fin Attachment (for finned coil assemblies): Aluminum or stainless steel fins are mechanically crimped or welded onto the tube body using automated fin-rolling or fin-welding equipment, ensuring uniform fin-to-tube contact and minimal thermal contact resistance.
- Surface Cleaning and Passivation: All surfaces are chemically cleaned and passivated using citric or nitric acid solutions to remove scale, oils, and free iron contamination, establishing a stable chromium oxide passive film.
- Quality Inspection and Testing: Each production batch undergoes comprehensive inspection including visual examination, dimensional verification (OD, WT, straightness), hydrostatic pressure testing, and—where applicable—X-ray or ultrasonic flaw detection of weld joints.
- Packaging and Dispatch: Qualified coils are coiled, wrapped in moisture-proof protective film, and packed in export-grade wooden cases or shrink-wrapped bundles for safe transport.
Applications
The stainless steel coil tube from Wenzhou Jixing Metal Materials Co., Ltd serves as a foundational component across a broad spectrum of HVAC and thermal management applications:
- Fan Coil Units (FCUs): Primary application — used as the core heat exchanger element in both constant-volume and variable-volume fan coil units installed in commercial buildings, hotels, hospitals, and office complexes.
- Air Handling Units (AHUs): Integrated into chilled-water and hot-water coil sections of large-capacity air handling units for central air conditioning systems.
- Chilled Water Beam Systems: Employed in radiant cooling and heating systems where stainless steel coil tubes form the primary heat transfer surface.
- Industrial Process Cooling: Utilized in pharmaceutical, food processing, and semiconductor manufacturing facilities where hygienic, corrosion-resistant heat exchangers are mandated.
- Marine and Coastal HVAC: AISI 316-grade coil tubes are specified for air conditioning systems in marine environments, coastal facilities, and desalination plants where chloride exposure is significant.
- Heat Recovery Systems: Applied in enthalpy wheels and plate-type heat recovery units to capture and transfer thermal energy between exhaust and supply air streams.
- Refrigeration Condensers and Evaporators: Used in industrial refrigeration systems requiring stainless steel construction for sanitary or corrosion-resistance reasons.
Design Note: As emphasized in the technical study on the rational selection of fan coil units, proper coil tube specification—including correct material grade, tube diameter, wall thickness, row count, and fin configuration—is essential to achieving optimal part-load efficiency, minimizing pressure drop across the coil, and ensuring adequate dehumidification capacity. Improper coil selection can result in excessive energy consumption, poor indoor air quality, and premature equipment failure.
Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework ensuring full traceability and compliance with international standards:
- ISO 9001:2015 — Quality Management System certification covering the entire product lifecycle from raw material procurement through final inspection and dispatch.
- ISO 14001:2015 — Environmental Management System certification demonstrating commitment to sustainable manufacturing practices and environmental stewardship.
- CE Marking — Conformity with European Union directives for products intended for use in the European Economic Area.
- Mill Test Certificates (MTC / EN 10204 3.1): Provided with every shipment, certifying chemical composition and mechanical properties of the base material.
- Hydrostatic Test Reports: Individual batch-level documentation confirming pressure integrity at 1.5× the maximum working pressure.
- NACE MR0175 / ISO 15156 Compliance (on request): For applications in sour service environments requiring resistance to sulfide stress cracking.
- RoHS / REACH Compliance: Products are free from restricted hazardous substances in accordance with EU regulatory requirements.
Unique Selling Points
- Superior Corrosion Resistance: Austenitic stainless steel construction provides decades of service life without degradation, eliminating the need for chemical treatment or replacement in corrosive environments where carbon steel alternatives would fail within years.
- Hygienic and Non-Toxic: The stainless steel surface is inherently non-toxic, non-reactive, and easily sanitized — critical for pharmaceutical, food-grade, and medical facility applications.
- Precision Engineering: CNC-controlled bending and forming processes ensure consistent geometry, uniform tube-to-tube spacing, and minimal flow maldistribution across multi-row coil assemblies.
- Customization Capability: Wenzhou Jixing offers fully customizable coil configurations — including non-standard tube diameters, wall thicknesses, row counts, and geometries — to match specific system design requirements.
- Energy Efficiency Contribution: Optimized coil design with precise fin spacing and tube arrangement maximizes the surface-area-to-volume ratio, enhancing heat transfer coefficients and reducing overall system energy consumption.
- Full Traceability: Every product batch is accompanied by complete documentation including mill certificates, dimensional inspection reports, and pressure test records, ensuring full supply chain transparency.