Stainless Steel Coil Tube (Coiltube) – Fan Coil Unit Heat Exchanger Grade

Product Overview

The Stainless Steel Coil Tube (Coiltube) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd, specifically designed for use in fan coil unit (FCU) heat exchangers and dynamic heat transfer systems. This coil tube product integrates advanced metallurgical composition with high-precision forming technology to deliver superior thermal conductivity, corrosion resistance, and mechanical durability under continuous cycling thermal loads. The product is engineered in accordance with the principles of dynamic heat transfer modeling and computer simulation, ensuring optimized performance in HVAC (Heating, Ventilation, and Air Conditioning) applications where thermal efficiency and long-term reliability are critical.

The coil tube is available in a continuous coil configuration, enabling seamless integration into automated heat exchanger assembly lines. Its geometry—characterized by a uniform helical winding—maximizes the surface-area-to-volume ratio, thereby enhancing convective and conductive heat exchange efficiency within compact heat exchanger cores.

Material & Properties

The coil tube is fabricated from high-grade austenitic stainless steel, with the following material characteristics:

Base Alloy: Austenitic stainless steel (e.g., AISI 304, AISI 316, or equivalent grades such as SUS304, SUS316L)
Chromium (Cr) Content: 18–20%, providing excellent passive film formation and oxidation resistance
Nickel (Ni) Content: 8–10.5%, ensuring stable austenitic microstructure and ductility
Molybdenum (Mo) Content: 2–3% (in 316/316L grades), enhancing resistance to pitting and crevice corrosion
Carbon (C) Content: ≤0.08% (standard grade) or ≤0.03% (low-carbon grade such as 304L/316L), minimizing sensitization risk during welding
Thermal Conductivity: 14–16 W/(m·K) at 25°C, ensuring efficient heat transfer performance
Operating Temperature Range: −196°C to +870°C (grade-dependent)
Corrosion Resistance: Excellent resistance to atmospheric corrosion, mild acids, alkaline solutions, and chlorinated water
Mechanical Properties: Tensile strength ≥515 MPa; Yield strength ≥205 MPa; Elongation ≥40% (as per ASTM A269/A270)
Surface Finish: No. 4 brushed finish, BA (Bright Annealed), or electropolished surface (Ra ≤0.4 μm) available upon request

Specifications

Parameter	Specification	Standard / Reference
Product Name	Stainless Steel Coil Tube (Coiltube)	—
Product Catalog No.	1218	Wenzhou Jixing Internal Catalog
Material Grade	AISI 304 / 304L / 316 / 316L / 321 / 310S (customizable)	ASTM A269 / ASTM A270 / EN 10216-5
Outer Diameter (OD)	6.0 mm – 32.0 mm (typical); custom sizes available	ASTM A269 Table 11
Wall Thickness (WT)	0.3 mm – 2.0 mm (typical); custom tolerances available	ASTM A269 / GB/T 12771
Coil Winding Diameter	50 mm – 300 mm (customizable per application)	—
Coil Length	Continuous coil; standard lengths of 50 m, 100 m, 200 m, or custom	—
Dimensional Tolerance	OD: ±0.05 mm; WT: ±0.03 mm	ASTM A270 Class 1 / Class 2
Surface Treatment	BA (Bright Annealed), No. 4 Brushed, Electropolished, or Passivated	ASTM A967 (Passivation)
End Condition	Plain end, beveled end, or flanged (upon request)	—
Heat Treatment	Solution annealed (1010°C – 1150°C) + water quench	ASTM A269 / ASTM A270
Delivery Condition	Hot-rolled + cold-drawn + annealed (HR + CD + A)	—
Applicable Standards	ASTM A269, ASTM A270, GB/T 12771, EN 10216-5, JIS G3459	Multi-standard compliance
Coil Packaging	Wooden crate with moisture-proof wrapping; or export-grade palletized coil	ISO 4180 (Packaging for Transport)

Manufacturing Process

The production of the Stainless Steel Coil Tube follows a rigorous multi-stage manufacturing process to ensure dimensional accuracy, metallurgical integrity, and surface quality:

Raw Material Selection: High-purity stainless steel billets or strip stock sourced from certified mills (e.g., POSCO, Outokumpu, or domestic Chinese producers meeting GB standards). Incoming material undergoes spectroscopic verification (PMI – Positive Material Identification) to confirm chemical composition compliance.
Hot Rolling (HR): Steel billets are heated to 1200°C–1300°C and hot-rolled into seamless tube blanks or welded tube strips, depending on the production route.
Cold Drawing / Cold Forming (CD): The tube blanks are cold-drawn through precision dies to achieve the target OD and wall thickness with tight tolerances (±0.05 mm). This step refines grain structure and enhances mechanical properties.
Solution Annealing: The cold-worked tubes are solution-annealed at 1010°C–1150°C followed by rapid water quenching. This restores ductility, relieves residual stresses, and dissolves precipitates to ensure a uniform austenitic microstructure.
Surface Treatment: Depending on application requirements, tubes undergo Bright Annealing (BA) in a controlled hydrogen atmosphere, mechanical brushing (No. 4 finish), or electropolishing (Ra ≤0.4 μm) for hygienic or high-conductivity applications.
Passivation: A citric acid or nitric acid passivation treatment is applied per ASTM A967 to remove free iron from the surface and promote the formation of a stable chromium oxide passive film.
Coil Winding: The finished straight tubes are precision-wound into helical coils using automated winding machines with CNC (Computer Numerical Control) tension control to prevent deformation or kinking.
Quality Inspection: Each coil lot undergoes hydrostatic testing (per ASTM A270), dimensional verification (OD, WT, coil diameter), surface inspection (visual + dye penetrant testing), and chemical analysis. Non-destructive testing (NDT) methods such as eddy current testing (ECT) are employed to detect internal or surface defects.
Packaging & Dispatch: Coils are wrapped in moisture-proof PE film, secured on wooden pallets or crated, and labeled with mill certificates (MTC – Material Test Certificate) in accordance with EN 10204 3.1 or 3.2.

Applications

The Stainless Steel Coil Tube is designed for demanding applications where thermal efficiency, corrosion resistance, and long service life are paramount:

Fan Coil Unit (FCU) Heat Exchangers: Primary application domain. The coil tube forms the core heat transfer element in FCU units used in commercial and residential HVAC systems. Its helical geometry maximizes air-side and water-side heat exchange efficiency, as validated by dynamic heat transfer modeling and CFD (Computational Fluid Dynamics) simulation studies.
Air Conditioner Evaporators & Condensers: Used in split-type and central air conditioning systems where corrosion resistance to condensation water and refrigerant compatibility are critical.
Refrigeration & Cryogenic Systems: Suitable for evaporator and condenser coils operating at low temperatures (down to −196°C), where austenitic stainless steel maintains ductility and mechanical integrity.
Heat Recovery Systems: Deployed in energy recovery ventilators (ERV) and heat recovery chillers (HRC) for efficient thermal energy transfer between air streams.
Industrial Process Heat Exchangers: Used in chemical processing, food and beverage (F&B) pasteurization, pharmaceutical cleanroom HVAC, and power generation applications requiring hygienic or corrosion-resistant heat transfer surfaces.
Automotive HVAC Components: Precision coil tubes for automotive air conditioning evaporators and heater cores, where compactness and corrosion resistance are essential.
Marine & Offshore HVAC: 316/316L grade coil tubes resist chloride-induced pitting corrosion in high-salinity marine environments.

Quality Certifications & Compliance

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

ISO 9001:2015 – Quality Management System certification
ISO 14001:2015 – Environmental Management System certification
ISO/TS 22163 – Railway industry quality management (for specialized applications)
EN 10204 3.1 / 3.2 – Material Test Certificates (MTC) provided with each shipment
ASTM A269 / A270 – Compliance with American Society for Testing and Materials standards for stainless steel tube
GB/T 12771 – Chinese national standard for cold-rolled stainless steel seamless tubes
EN 10216-5 – European standard for welded stainless steel tubes
JIS G3459 – Japanese Industrial Standard for stainless steel tubes
SGS / Bureau Veritas – Third-party inspection and testing reports available upon request
RoHS / REACH Compliance – Ensuring environmental and regulatory compliance for EU and international markets

Unique Selling Points

Simulation-Validated Thermal Performance: The coil tube geometry and dimensional parameters are optimized based on dynamic heat transfer modeling and computer simulation (CFD), ensuring peak thermal efficiency in fan coil unit heat exchangers. This data-driven design approach minimizes energy consumption and maximizes COP (Coefficient of Performance).
Tight Dimensional Tolerances: With OD tolerance of ±0.05 mm and wall thickness tolerance of ±0.03 mm, the coil tube ensures precise fit within heat exchanger headers and brazing joints, reducing assembly defects and improving long-term leak resistance.
Multi-Grade Material Flexibility: Availability across AISI 304, 304L, 316, 316L, 321, and 310S grades allows customers to select the optimal material for their specific corrosion, temperature, and mechanical requirements.
Continuous Coil Format: The coil configuration eliminates tube joining requirements, reducing potential leak points and enabling high-speed automated heat exchanger production. This translates to lower manufacturing costs and higher throughput for OEM customers.
Superior Surface Quality: BA and electropolished finishes provide low-surface-roughness surfaces (Ra ≤0.4 μm) that minimize fouling, enhance heat transfer coefficients, and facilitate cleaning in hygienic applications.
Full Traceability & Documentation: Every coil lot is accompanied by a comprehensive MTC with chemical composition, mechanical test results, and dimensional inspection data, ensuring complete supply chain traceability.
Custom Engineering Capability: Wenzhou Jixing offers OEM/ODM (Original Equipment Manufacturing / Original Design Manufacturing) services, including custom OD, wall thickness, coil winding diameter, and surface treatment configurations tailored to specific heat exchanger designs.

Note: The dynamic heat transfer performance of the coil tube in fan coil unit applications has been validated through computational simulation, demonstrating that the helical coil geometry achieves superior air-side heat transfer coefficients compared to traditional straight-tube configurations, particularly under turbulent flow conditions (Reynolds number > 4000). Customers are encouraged to provide specific operating parameters for customized thermal performance analysis.