Stainless Steel Coil Tube — Fan Coil Unit (FCU) System Application
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd.
Product No.: 512
1. Product Overview
The Stainless Steel Coil Tube is a precision-engineered tubular product designed primarily for use in Fan Coil Unit (FCU) systems, heat exchangers, and hydronic heating and cooling applications. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coil tube is produced through advanced cold-rolling and coiling processes that ensure dimensional accuracy, superior thermal conductivity, and long-term corrosion resistance in demanding HVAC (Heating, Ventilation, and Air Conditioning) environments.
Coil tubes in FCU systems serve as the core heat exchange element, facilitating efficient thermal transfer between circulating fluid (water or glycol) and ambient air. The product is engineered to meet the rigorous requirements outlined in user-side overall model simulations for fan coil unit system performance optimization, ensuring reliable operation across varying load conditions and environmental parameters.
2. Material & Properties
2.1 Base Material
- Grade: SUS304 (UNS S30400) / SUS316L (UNS S31603) — austenitic stainless steel conforming to ASTM A269 / ASTM A213 standards.
- Carbon Equivalent (CE): ≤ 0.03% (for 316L grade), ensuring excellent weldability and resistance to intergranular corrosion.
- Chromium (Cr) Content: 18.0–20.0%, providing robust passive oxide layer formation.
- Nickel (Ni) Content: 8.0–11.0%, contributing to ductility and thermal stability.
- Molybdenum (Mo) Content: 2.0–3.0% (316L grade), enhancing resistance to chloride-induced pitting and crevice corrosion.
2.2 Mechanical Properties
- Tensile Strength (UTS): ≥ 520 MPa (SUS304), ≥ 515 MPa (SUS316L)
- Yield Strength (0.2% Offset): ≥ 205 MPa
- Elongation at Break: ≥ 40%
- Hardness (HBW): 140–180 (annealed condition)
- Operating Temperature Range: −196 °C to +870 °C (non-cyclic loading)
2.3 Thermal & Physical Properties
- Thermal Conductivity: 16.3 W/(m·K) at 20 °C
- Specific Heat Capacity: 0.50 J/(g·K) at 20 °C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K (20–100 °C)
- Density: 8.00 g/cm³
- Electrical Resistivity: 7.2 × 10⁻⁷ Ω·m at 20 °C
2.4 Corrosion Resistance
The passive chromium oxide film (Cr₂O₃) self-heals in the presence of oxygen, providing exceptional resistance to atmospheric corrosion, weak acids, alkalis, and non-oxidizing acids. SUS316L grade offers additional protection against chloride environments, making it suitable for coastal and industrial applications.
3. Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 9.52 mm (3/8") / 12.70 mm (1/2") / 15.88 mm (5/8") / Custom | ASTM A269 / EN 10216-5 |
| Wall Thickness | 0.80 mm – 2.00 mm (tolerance ±0.05 mm) | ASTM A269 |
| Coil Length per Spool | 50 m – 300 m (adjustable per customer requirement) | — |
| Coil Inner Diameter (ID) | 300 mm / 400 mm / 600 mm | — |
| Surface Finish | No. 4 Brushed / BA (Bright Annealed) / Mirror (Ra ≤ 0.4 μm) | ASTM A480 |
| Formability | Cold bending radius ≥ 1.5 × OD without cracking | ISO 15497 |
| Hydrostatic Test Pressure | 2.0 × working pressure (minimum 6.0 MPa) | ASTM A269 |
| Welding Suitability | TIG (GTAW) / Orbital / Laser welding — no filler required for thin-wall | ASME BPVC Section IX |
| Maximum Working Pressure | 2.5 MPa (at 150 °C, OD 12.70 mm, WT 1.65 mm) | Calculated per Barlow's Formula |
| Packaging | Wooden reel / steel band / VCI (Vapor Corrosion Inhibitor) wrapped | ISO 4180 |
| Traceability | Heat number, mill certificate, and batch code marked on each coil | ISO 9001:2015 |
4. Manufacturing Process
4.1 Process Flow
- Raw Material Selection: Virgin stainless steel strip or seamless tube blanks procured from certified mills, with full chemical composition analysis (spectrometry) and mechanical property verification.
- Surface Preparation: Acid pickling and descaling to remove mill scale and surface contaminants, followed by passivation treatment to establish the initial passive film.
- Cold Forming / Drawing: Multi-stage cold drawing through precision tungsten carbide dies to achieve target OD and wall thickness with tight dimensional tolerances (±0.05 mm).
- Intermediate Annealing: Solution annealing at 1050–1100 °C in a controlled atmosphere (quenching or furnace cooling) to relieve cold work stresses and restore ductility.
- Coiling / Spooling: Continuous coiling onto precision-machined reels with controlled tension to prevent ovality and residual stress. Coil dimensions are verified by laser diameter measurement systems.
- Surface Finishing: Electropolishing, mechanical polishing, or passivation depending on the required surface finish grade.
- Non-Destructive Testing (NDT): Eddy current testing (ECT) for wall thickness verification, hydrostatic pressure testing for leak integrity, and visual inspection for surface defects.
- Final Inspection & Certification: Dimensional verification, material certification (Mill Test Report / EN 10204 Type 3.1), and packaging for shipment.
4.2 Key Process Controls
- Online diameter monitoring with feedback-controlled roll gap adjustment (±0.02 mm accuracy)
- Atmosphere-controlled annealing furnaces with dew point ≤ −60 °C to prevent decarburization and oxidation
- Automated ECT inspection systems capable of detecting surface defects as small as 0.1 mm²
- Full traceability from raw material heat number through to finished coil identification
5. Applications
5.1 Fan Coil Unit (FCU) Systems
The primary application domain for this coil tube is in the construction of Fan Coil Unit heat exchangers. FCU systems are widely deployed in commercial buildings, hospitals, hotels, and residential complexes for distributed heating and cooling. The stainless steel coil tube provides the following advantages over traditional copper tube alternatives:
- Superior Corrosion Resistance: Eliminates galvanic corrosion when used in systems with varying water chemistry, including treated water, deionized water, and glycol solutions.
- Elimination of Biocide Requirements: Unlike copper tubes, stainless steel does not release biocidal copper ions, making it suitable for potable water-adjacent applications and sensitive environments.
- Long Service Life: Expected operational lifespan exceeds 25 years under normal HVAC operating conditions, significantly outperforming copper alternatives in aggressive water environments.
- Simulation-Validated Performance: Coil tube geometries and thermal parameters have been validated through user-side overall model simulation methods for FCU systems, ensuring accurate prediction of system performance under part-load conditions.
5.2 Additional Applications
- Industrial heat exchangers and condensers
- Refrigeration and cryogenic piping systems
- Pharmaceutical and food-grade process piping
- Chemical processing equipment (non-oxidizing service)
- Solar thermal collector manifolds
- Marine and offshore heat exchange systems
6. Quality Certifications & Compliance
6.1 Quality Management System
- ISO 9001:2015 — Quality Management Systems certification covering the full manufacturing value chain.
- ISO 14001:2015 — Environmental Management Systems certification demonstrating commitment to sustainable manufacturing practices.
- ISO 45001:2018 — Occupational Health and Safety Management Systems certification.
6.2 Product Standards Compliance
| Standard | Scope | Applicability |
|---|---|---|
| ASTM A269 / A269M | Welded Austenitic Stainless Steel Seamless and Welded Tube for High-Pressure Service | Primary product standard |
| ASTM A213 / A213M | Welded Austenitic Stainless Steel Tubing for Heat-Transfer and Exchanger Service | Heat exchanger application |
| EN 10216-5 | Non-alloy and Alloy Steel Tubes for Technical Use — Seamless Tubes for High Temperatures | European market compliance |
| ASME BPVC Section IX | Welding, Brazing, and Fusing Qualifications | Welding procedure qualification |
| EN 10204 Type 3.1 | Inspection Documents — Inspection Certificate | Mill Test Report certification |
| GB/T 12771 | Stainless Steel Seamless Tubes for Fluid Transport | Chinese domestic market |
| GB/T 14976 | Stainless Steel Seamless Tubes for Fluid Transport | Chinese domestic market |
6.3 Testing & Inspection Protocols
- Chemical Analysis: Spectrometric verification of full chemical composition per ASTM E415
- Mechanical Testing: Tensile testing per ASTM E8/E8M with minimum three specimens per heat
- Piezoelectric Impedance Spectroscopy (PIS): Verification of passive film integrity and corrosion resistance
- Pitting Corrosion Testing: ASTM G48 Method A (ferric chloride solution) for 316L grade verification
- Intergranular Corrosion Testing: ASTM A262 Practice E (65 °C, 48-hour exposure) for weld-affected zone verification
- Hydrostatic Testing: 100% inspection at 2.0 × working pressure with minimum 10-second hold time
- Eddy Current Testing: 100% inline inspection for wall thickness uniformity and surface defect detection
7. Unique Selling Points
- Simulation-Validated Design: Product geometry and thermal parameters are validated through user-side overall model simulation methodologies for Fan Coil Unit systems, ensuring predictable performance under real-world operating conditions including part-load and transient scenarios.
- Superior Durability: Austenitic stainless steel construction provides exceptional resistance to both uniform and localized corrosion, eliminating the need for protective coatings or cathodic protection systems.
- Hygienic Surface Finish: Available in electropolished finish (Ra ≤ 0.25 μm) suitable for pharmaceutical, food processing, and medical applications where bioburden control is critical.
- Customizable Dimensions: Flexible manufacturing capability allows customization of OD, wall thickness, coil length, and surface finish to meet specific project requirements.
- Full Traceability: Each coil is traceable to its raw material heat number, ensuring complete quality documentation and compliance with regulatory requirements.
- Thermal Efficiency: Optimized wall thickness and geometry provide high heat transfer coefficients while maintaining structural integrity under cyclic thermal