Stainless Steel Coil Tube (Coiltube) — Fan Coil Unit Integration Series
Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered tubular product designed for integration into fan coil unit (FCU) systems and related HVAC (Heating, Ventilation, and Air Conditioning) applications. The coil tube is formed into a compact helical or serpentine configuration, providing an optimized surface-area-to-volume ratio that maximizes thermal exchange efficiency within constrained installation footprints. This product line is particularly suited for intelligent control system integration, where consistent geometric tolerances and material homogeneity are critical to the performance of automated temperature regulation algorithms.
The Coiltube is supplied in continuous coil form, enabling downstream manufacturers to cut and shape the tubing to precise specifications without introducing additional weld joints or stress concentrations. The seamless nature of the coil winding process ensures uniform wall thickness distribution along the entire tube length, which is a prerequisite for reliable heat transfer coefficient calculations in intelligent control system modeling.
Material & Properties
The Coiltube is fabricated from austenitic stainless steel grades, with the primary production grade being SAE/AISI 304 (UNS S30400), supplemented by SAE/AISI 316 (UNS S31600) for applications requiring enhanced corrosion resistance in marine or chemically aggressive environments.
- Chemical Composition (304 Grade): Chromium (Cr) 18–20%, Nickel (Ni) 8–10.5%, Manganese (Mn) ≤2.0%, Carbon (C) ≤0.08%, Silicon (Si) ≤1.0%, Phosphorus (P) ≤0.045%, Sulfur (S) ≤0.030%
- Chemical Composition (316 Grade): Chromium (Cr) 16–18%, Nickel (Ni) 10–14%, Molybdenum (Mo) 2.0–3.0%, Carbon (C) ≤0.08%, Silicon (Si) ≤1.0%
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (304 grade); 16.3 W/(m·K) at 20°C (316 grade)
- Specific Heat Capacity: 0.502 kJ/(kg·K) at 20°C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (20–100°C)
- Yield Strength (Annealed): ≥205 MPa (304); ≥170 MPa (316)
- Tensile Strength: 515–730 MPa (304); 485–620 MPa (316)
- Operating Temperature Range: −196°C to +870°C (304); −196°C to +870°C (316)
- Corrosion Resistance: Excellent resistance to atmospheric, aqueous, and mild chemical corrosion; 316 grade offers superior resistance to pitting and crevice corrosion due to molybdenum addition
Specifications
| Parameter | Specification / Range |
|---|---|
| Outer Diameter (OD) | 6.0 mm – 25.4 mm (1/4" – 1") |
| Wall Thickness (WT) | 0.5 mm – 1.5 mm |
| Coil Winding Diameter | 50 mm – 200 mm (configurable per application) |
| Coil Length (Continuous) | Up to 500 meters per coil |
| Surface Finish | Pickled & Passivated (2B); Electropolished (EP); Brushed (No. 4) |
| Surface Roughness (Ra) | ≤ 0.8 μm (electropolished); ≤ 1.6 μm (2B finish) |
| Tolerance on OD | ±0.05 mm |
| Tolerance on Wall Thickness | ±10% of nominal |
| End Condition | Plain cut; Beveled; Flared; Threaded (per customer specification) |
| Coating (Optional) | None (bare stainless); PTFE (Polytetrafluoroethylene) inner lining for enhanced flow characteristics |
| Standard Conformity | ASTM A269 / A270; EN 10216-5; ISO 3505; JIS G3459 |
| Pressure Rating | Up to 6.0 MPa (60 bar) at 20°C, dependent on OD and WT combination |
Manufacturing Process
The production of the Stainless Steel Coil Tube at Wenzhou Jixing Metal Materials Co., Ltd follows a rigorous multi-stage process designed to ensure dimensional precision, metallurgical integrity, and surface quality suitable for high-performance HVAC integration:
- Raw Material Selection: Cold-rolled stainless steel strip (coil) is procured from certified mills and subjected to incoming inspection, including spectroscopic chemical analysis (OES — Optical Emission Spectroscopy) and mechanical property verification.
- Tube Forming (Cold Rolling): The flat strip is passed through a series of progressively reducing rollers in a cold tube-forming machine, where it is progressively rolled into a tubular cross-section. This process induces controlled work hardening, improving mechanical strength while maintaining ductility.
- Longitudinal Welding: The formed tube is subjected to high-frequency induction welding (HFW) or TIG (Tungsten Inert Gas) welding to create the longitudinal seam. Weld parameters are monitored in real time via closed-loop temperature and current feedback systems to ensure weld integrity.
- Pipe Milling & OD Trimming: The welded tube undergoes external and internal pipe milling to achieve precise outer diameter and wall thickness tolerances, removing any weld protrusion and ensuring uniform cross-sectional geometry.
- Pickling & Passivation: The tube is immersed in a nitric-hydrofluoric acid pickling bath to remove mill scale and oxidation. Subsequently, a passivation treatment using dilute nitric acid (HNO₃) or citric acid forms a protective chromium oxide layer on the surface, enhancing corrosion resistance.
- Coil Winding: The finished straight tube is wound onto a precision winding mandrel at controlled tension to produce the final coil tube configuration. Winding tension is regulated to prevent kinking, ovality, or springback.
- Final Quality Inspection: Each coil undergoes dimensional verification (OD, wall thickness, coil diameter), surface finish measurement (profilometry), hydrostatic pressure testing, and optional eddy current testing for weld seam defect detection.
Applications
The Stainless Steel Coil Tube is deployed across a broad spectrum of thermal management and fluid conveyance applications:
- Fan Coil Units (FCU): The primary application domain, where the coil tube serves as the heat exchange element within air handling units for commercial and residential HVAC systems. The compact coil geometry enables efficient air-side and water-side heat transfer within space-constrained installation environments.
- Intelligent HVAC Control Systems: The geometric consistency and material uniformity of the Coiltube facilitate accurate modeling of heat transfer coefficients, enabling reliable performance of automated temperature control algorithms, predictive maintenance systems, and energy management platforms.
- Refrigeration & Air Conditioning: Used as evaporator and condenser coils in split-system air conditioners, chiller units, and refrigeration condensers where corrosion resistance and long service life are paramount.
- Heat Exchangers: Integrated into shell-and-coil heat exchangers, plate-fin coils, and air-to-water heat exchangers for industrial process heating and cooling.
- Automotive Thermal Management: Application in automotive radiator cores, intercoolers, and HVAC evaporator assemblies where lightweight, corrosion-resistant tubing is required.
- Food & Pharmaceutical Processing: Utilized in sanitary-grade heat exchangers for pasteurization, sterilization, and process fluid temperature control, leveraging the hygienic surface finish and non-reactive properties of austenitic stainless steel.
- Domestic Water Heaters & Boilers: Employed as internal heating coils in domestic hot water systems and electric boiler heating elements.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management framework aligned with international standards:
- ISO 9001:2015 — Quality Management Systems certification ensuring consistent product quality and customer satisfaction
- ISO 14001:2015 — Environmental Management Systems certification covering sustainable manufacturing practices
- ISO 45001:2018 — Occupational Health and Safety Management Systems certification
- EN 10204-3.1 — Material Test Certificate compliance for each production batch
- CE Marking — Conformity with European Union health, safety, and environmental protection standards
- RoHS Compliance — Restriction of Hazardous Substances directive compliance (EU Directive 2011/65/EU)
- Mill Test Reports (MTR): Available upon request, providing full chemical composition, mechanical properties, and traceability data for each heat number
Unique Selling Points
1. Intelligent Control System Compatibility: The dimensional precision (±0.05 mm OD tolerance) and material homogeneity of this Coiltube product enable accurate thermal modeling, which is essential for the reliable operation of intelligent control algorithms in modern FCU systems. This directly supports the research objectives outlined in the study on intelligent control system optimization for fan coil units.
2. Seamless Continuous Coil Supply: Delivery in continuous coil form eliminates the need for field welding of short tube segments, reducing installation labor, minimizing potential leak points, and improving overall system reliability.
3. Customizable Coil Geometry: Coil winding diameter and pitch can be tailored to specific application requirements, enabling optimization of air-side velocity, pressure drop, and heat transfer performance for each installation scenario.
4. Superior Corrosion Resistance: The austenitic stainless steel matrix, combined with the protective passivated surface layer, provides exceptional longevity in humid, corrosive, and chemically aggressive environments — significantly outperforming carbon steel alternatives in total cost of ownership.
5. Full Traceability: Every production coil is accompanied by comprehensive material certification documentation, ensuring complete traceability from raw steel mill heat number to final product delivery.
Conclusion
The Stainless Steel Coil Tube from Wenzhou Jixing Metal Materials Co., Ltd represents a convergence of precision manufacturing capability and material science expertise, delivering a product that meets the exacting requirements of modern intelligent HVAC systems. Its compatibility with automated control architectures, combined with proven corrosion resistance and thermal performance, positions it as a preferred component for next-generation fan coil unit designs and broader thermal management applications.