Stainless Steel Coil Tube for Fan Coil Unit Heat Exchange Systems

Product Overview

The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product designed specifically for heat exchange applications within fan coil unit (FCU) air conditioning systems. This product represents a critical component in modern HVAC (Heating, Ventilation, and Air Conditioning) infrastructure, where efficient thermal transfer between working fluids and ambient air is paramount to system performance.

Unlike conventional straight-segment heat exchanger tubes, the coil tube configuration provides a significantly increased surface-area-to-volume ratio, enabling superior convective and conductive heat exchange characteristics. The coiled geometry facilitates compact assembly within confined mechanical housings while maximizing thermal contact efficiency — a principle extensively validated in comparative studies of fan coil unit heat exchange performance.

Material & Properties

Base Material Composition

The coil tube is fabricated from austenitic stainless steel grades conforming to international metallurgical standards. The primary alloy grades utilized include:

Key Mechanical and Physical Properties

Microstructural Characteristics

The fully austenitic (face-centered cubic, FCC) crystal structure provides exceptional ductility and work hardening capability during the cold coiling process. The absence of martensitic transformation ensures dimensional stability across the operational temperature spectrum, eliminating the risk of thermal fatigue cracking in cyclic heating and cooling service typical of fan coil unit operation.

Specifications

Parameter Specification Standard Reference
Outer Diameter (OD) 6.35 mm (1/4"), 9.52 mm (3/8"), 12.7 mm (1/2") ASTM A213 / ASTM A269
Wall Thickness 0.5 mm – 1.5 mm ISO 4287
Coil Pitch 10 mm – 30 mm (configurable) Custom engineering specification
Coil Diameter 150 mm – 400 mm Custom engineering specification
Tube Length per Coil 1.5 m – 6.0 m Customer-specific requirement
Surface Finish Baer (2B) / Pickled & Passivated / Mirror Polished (Ra ≤ 0.4 μm) ASTM A480 / ASTM A666
End Condition Plain ends / Flared ends / Welded caps / Fitted connectors ASME B16.9
Pressure Rating Up to 2.5 MPa (design pressure, dependent on geometry) ASME BPV Section I
Applicable Media Water, glycol-water mixtures, refrigerant condensate ASHRAE Standard 15
Delivery Form Coiled on spool / Bundled with protective packaging ISO 4180

Manufacturing Process

Step 1: Raw Material Preparation

High-purity stainless steel wire rod, conforming to ASTM A580 or equivalent specifications, is supplied as the starting material. Incoming material undergoes rigorous chemical composition verification via Optical Emission Spectrometry (OES) and mechanical property testing to ensure compliance with the specified grade requirements.

Step 2: Wire Drawing

The wire rod is cold-drawn through a series of progressively reducing dies to achieve the target outer diameter and wall thickness. This process imparts beneficial work hardening, enhancing the final product's mechanical strength while maintaining adequate ductility for subsequent forming operations.

Step 3: Annealing and Pickling

Intermediate annealing cycles are conducted in a controlled atmosphere furnace (protective nitrogen or vacuum environment) to relieve accumulated cold-work stresses and restore formability. Subsequent pickling and passivation treatment removes surface oxides and contaminants, establishing a stable chromium oxide passive film critical for long-term corrosion resistance.

Step 4: Precision Coiling

The drawn and annealed tube is cold-coiled using numerically controlled (CNC) coiling equipment to achieve precise geometric parameters — including consistent coil pitch, uniform coil diameter, and smooth curvature transitions. The coiling process is monitored for dimensional accuracy within ±0.5 mm tolerance on pitch and ±1 mm on coil diameter.

Step 5: Surface Treatment and Quality Inspection

Finished coil tubes undergo final surface finishing (mechanical polishing or electrolytic polishing as required), followed by comprehensive quality assurance inspection including:

Step 6: Packaging and Dispatch

Inspected and approved coil tubes are individually wrapped in moisture-resistant protective film, bundled with corrosion-inhibiting desiccant packs, and secured on wooden spools or steel pallets for safe transport and storage.

Applications

Primary Application: Fan Coil Unit (FCU) Heat Exchangers

The stainless steel coil tube serves as the core heat transfer element within fan coil units — modular air conditioning devices widely deployed in commercial buildings, hospitality facilities, and institutional structures. The coiled configuration maximizes heat exchange surface area within the compact footprint of the FCU housing, enabling efficient sensible and latent heat transfer between the working fluid (typically chilled water or hot water) and the forced air stream.

Research comparing heat exchange characteristics of fan coil units has demonstrated that the geometric parameters of the coil tube — including coil pitch, tube diameter, and material thermal conductivity — directly influence the overall unit efficiency, pressure drop, and noise performance. The stainless steel construction offers a significant advantage over traditional copper tubing in terms of:

Secondary Applications

Quality Certifications and Standards Compliance

Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring product conformity to international and national standards:

Unique Selling Points

1. Superior Thermal Performance: The austenitic stainless steel coil tube delivers consistent and reliable heat transfer coefficients across the full operational temperature range, with minimal degradation over extended service life. Comparative studies confirm that properly designed stainless steel coil configurations achieve thermal efficiency within 3–5% of copper alternatives, while offering dramatically superior corrosion longevity.

2. Precision Manufacturing Capability: CNC-controlled coiling ensures geometric uniformity critical for optimal airflow distribution and pressure balance within fan coil unit assemblies. Tight manufacturing tolerances reduce turbulence-induced noise and ensure uniform heat distribution.

3. Extended Service Life: With proper installation and maintenance, stainless steel coil tubes provide 25–30 years of reliable service in standard HVAC applications — significantly exceeding the 10–15 year typical lifespan of copper tube alternatives in aggressive environments.

4. Customization Flexibility: Full configurability of coil geometry (pitch, diameter, length) and surface finish enables optimization for specific application requirements, from ultra-compact residential units to high-capacity commercial installations.

5. Sustainability Advantage: Austenitic stainless steel is 100% recyclable with no loss of inherent material properties. The extended service life and corrosion resistance result in reduced lifecycle carbon footprint compared to copper alternatives requiring more frequent replacement.

Technical Advisory Note

For optimal fan coil unit performance, the selection of stainless steel coil tube geometry should be evaluated in conjunction with the specific thermal load requirements, available installation space, and environmental conditions. Wenzhou Jixing Metal Materials Co., Ltd. provides comprehensive engineering consultation services to assist customers in selecting the appropriate tube specification, material grade, and coil configuration for their particular application. Technical data sheets, material test certificates, and dimensional drawings are available upon request for each production batch.