Stainless Steel Coil Tube for Fan Coil Unit Systems

Product Overview The Stainless Steel Coil Tube (product code: JX-CT-1287) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered coiled tubing solution designed specifically for integration into Fan Coil Unit (FCU) systems, particularly under winter air conditioning operating conditions. This product represents a critical component in hydronic heating and cooling circuits, where the coil tube serves as the primary heat exchange medium transferring thermal energy between the circulating refrigerant or hot water and the ambient air stream. The coil tube is engineered in accordance with the thermodynamic principles illustrated in the i-d diagram (Enthalpy-Humidity Ratio Chart) design methodology, ensuring optimal performance across the full range of indoor air conditioning states, including sensible cooling, latent dehumidification, and winter heating modes. The product is manufactured to meet stringent dimensional tolerances and metallurgical requirements, making it suitable for demanding HVAC applications where long-term reliability, corrosion resistance, and thermal efficiency are paramount.

Material & Properties

Base Material

The coil tube is fabricated from high-grade austenitic stainless steel, with the following primary alloy designations available:

SUS304 (ASTM A270 TP304) — 18% Chromium, 8% Nickel; the standard grade for general-purpose HVAC applications with excellent corrosion resistance and weldability.
SUS316 (ASTM A270 TP316) — 16–18% Chromium, 10–14% Nickel, 2–3% Molybdenum; enhanced resistance to pitting and crevice corrosion, recommended for applications involving chlorinated water or coastal environments.
SUS316L (ASTM A270 TP316L) — Low-carbon variant of 316 with carbon content ≤ 0.03%, suitable for welding-intensive assemblies where intergranular corrosion must be avoided.

Key Physical and Mechanical Properties (SUS304 Reference)

Property	Specification
Density	8.0 g/cm³
Thermal Conductivity (20 °C)	16.3 W/(m·K)
Specific Heat Capacity	502 J/(kg·K)
Modulus of Elasticity	193 GPa
Tensile Strength (Annealed)	≥ 520 MPa
Yield Strength (0.2% Offset)	≥ 205 MPa
Elongation (A₅₀)	≥ 40%
Operating Temperature Range	−196 °C to +870 °C
Corrosion Resistance	Excellent in atmospheric, aqueous, and mild chemical environments
Surface Finish	No. 1 (annealed) or 2B (cold-rolled and annealed) finish available

Specifications

Parameter	Specification / Range	Tolerance
Outer Diameter (OD)	6.35 mm (¼"), 9.52 mm (⅜"), 12.7 mm (½"), 15.88 mm (⅝"), 19.05 mm (¾")	± 0.10 mm
Wall Thickness (WT)	0.4 mm – 1.2 mm	± 0.05 mm
Coil Inner Diameter (CID)	150 mm – 600 mm (configurable per order)	± 5 mm
Coil Length	5 m – 50 m per coil (custom lengths available)	± 0.5 m
Coil Pitch (Turn Spacing)	3 mm – 15 mm (adjustable based on heat exchanger design)	± 0.5 mm
Number of Turns	Up to 200 turns per coil	—
End Forming	Plain end, U-bend, S-bend, or flanged connection	Per drawing
Surface Roughness (Ra)	≤ 0.8 μm (internal surface)	—
Hydrostatic Test Pressure	≥ 2.5 MPa (363 psi)	—
Standard References	ASTM A270/A270M, ASTM A269/A269M, GB/T 12771, GB/T 14976	—

Manufacturing Process

The production of the JX-CT-1287 Stainless Steel Coil Tube follows a rigorous multi-stage manufacturing workflow designed to ensure dimensional accuracy, metallurgical integrity, and consistent quality:

Raw Material Selection and Inspection — Hot-rolled stainless steel strip or wire rod of certified grade is procured from approved mills. Incoming material undergoes spectroscopic analysis (OES), mechanical testing, and visual inspection to verify compliance with ASTM and GB standards.
Coil Winding (Coiling) — The stainless steel strip is fed through a precision coil-winding machine equipped with hydraulic tension control systems. The coil diameter, pitch, and number of turns are controlled via CNC programming to match the specific heat exchanger design requirements. Tension is maintained at 8–15 N per mm of strip width to prevent coil relaxation or deformation.
Welding (for welded coil tube) — Longitudinal welds are formed using Automatic Submerged Arc Welding (SAW) or Gas Metal Arc Welding (GMAW) processes. Weld parameters are optimized to minimize heat-affected zone (HAZ) distortion and ensure full penetration. Post-weld internal grinding or electropolishing may be applied to achieve the required internal surface finish.
Heat Treatment (Annealing) — Solution annealing is performed at 1040 °C – 1120 °C followed by controlled water or air quenching to restore full austenitic microstructure, relieve residual stresses, and optimize corrosion resistance. For 316L grades, intergranular sensitization is avoided due to the low carbon content.
Surface Finishing — Pickling and passivation are carried out using hydrofluoric-nitric acid solutions (for 304) or hydrochloric-hydrofluoric acid solutions (for 316) to remove oxide scale and form a protective chromium oxide passive film. Surface roughness is verified using contact profilometry.
Dimensional Inspection and Non-Destructive Testing (NDT) — Each coil is inspected for OD, wall thickness, and coil diameter using laser micrometers and calipers. Hydrostatic pressure testing is performed at 2.5 MPa for a minimum of 30 seconds. Eddy current testing may be applied to detect internal and external defects. Magnetic particle inspection (MT) or liquid penetrant testing (PT) is used on weld seams.
Packaging and Dispatch — Qualified coils are wrapped in protective plastic film, placed on wooden pallets or steel racks, and labeled with material certificates, batch numbers, and handling instructions.

Applications

The JX-CT-1287 Stainless Steel Coil Tube is specifically engineered for the following application domains:

Fan Coil Unit (FCU) Systems — The primary application, where the coil tube serves as the heat exchanger core in both chilled water cooling and hot water heating modes. The i-d diagram design methodology ensures that the coil tube geometry and material properties are optimized for the target psychrometric conditions, including winter heating operation where indoor air is heated from a low-enthalpy state to the desired comfort zone.
Chiller and Condenser Coils — Used in central air conditioning chiller units and air-cooled condensers where corrosion-resistant tubing is essential for long service life.
Industrial Process Heating and Cooling — Applicable in food processing, pharmaceutical manufacturing, and chemical plant HVAC systems where sanitary-grade stainless steel tubing is required.
Commercial Building HVAC — Deployed in large-scale commercial buildings, hospitals, laboratories, and clean rooms requiring precise temperature and humidity control.
Refrigeration Systems — Used in evaporator coils for medium and low-temperature refrigeration applications.

Unique Selling Points

Psychrometrically Optimized Design — Coil geometry is derived from rigorous i-d diagram analysis, ensuring maximum heat transfer efficiency across all operating conditions, including the challenging winter heating scenario where sensible heat transfer dominates.
Superior Corrosion Resistance — Austenitic stainless steel construction provides exceptional resistance to condensation-induced corrosion, a common failure mode in FCU coils operating near the dew point.
Precision Manufacturing — CNC-controlled coil winding with ± 0.10 mm OD tolerance ensures uniform flow distribution and predictable thermal performance.
Full Traceability — Each production batch is accompanied by a Mill Test Certificate (MTC) and heat number traceability, enabling complete quality assurance documentation.
Customizability — Coil diameter, pitch, number of turns, and end formations are configurable to match specific OEM heat exchanger designs.

Quality Certifications

Wenzhou Jixing Metal Materials Co., Ltd. maintains the following quality management and product certifications:

Certification / Standard	Description
ISO 9001:2015	Quality Management System certification covering design, manufacturing, and inspection processes
ISO 14001:2015	Environmental Management System certification
ISO 45001:2018	Occupational Health and Safety Management System certification
CE Marking	Compliance with European Union machinery and safety directives for HVAC components
ASTM A270/A270M	Standard specification for welded, seamless, and austenitic stainless steel tubing
GB/T 12771	Chinese national standard for welded stainless steel tubing
GB/T 14976	Chinese national standard for seamless stainless steel tubing
NSF/ANSI 61	Drinking water system components certification (where applicable for potable water circuits)

Technical Note: The design of the coil tube for winter air conditioning operation is critically dependent on the psychrometric analysis performed using the i-d (enthalpy-humidity ratio) diagram. The coil tube's surface area, fin configuration, and flow arrangement must be optimized to achieve the target air outlet state point on the i-d chart, ensuring adequate sensible heating capacity while maintaining acceptable humidity levels. Wenzhou Jixing Metal Materials Co., Ltd. provides coil tube solutions that are compatible with all standard psychrometric design methodologies used in the HVAC industry.