Stainless Steel Coil Tube (Coiltube) for Fan Coil Unit Water Systems
Product Code: No. 1095 | Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd. | Category: Literature Study & Technical Reference
Product Overview
The Stainless Steel Coil Tube (hereinafter referred to as "Coiltube") is a precision-engineered tubing product designed specifically for hydraulic distribution in fan coil unit (FCU) water systems. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coil tube serves as a critical component in the piping network of HVAC (Heating, Ventilation, and Air Conditioning) systems, delivering superior fluid conveyance performance while maintaining structural integrity under variable pressure and temperature conditions.
This product line has been further refined through the implementation of Hydraulic Optimization Software Upgrades for FCU water system piping networks, ensuring that every coil tube meets the most current standards for flow efficiency, pressure drop minimization, and thermal performance. The integration of advanced hydraulic simulation modeling has allowed the manufacturer to optimize coil geometry, wall thickness, and bend radii to achieve minimal energy consumption in terminal air-handling applications.
Material & Properties
The Coiltube product is fabricated from high-grade stainless steel alloys, selected to provide an optimal balance of corrosion resistance, mechanical strength, and thermal conductivity. The primary material grades utilized include:
- 304 Stainless Steel (UNS S30400): The standard grade offering excellent general corrosion resistance, suitable for most HVAC water systems with pH levels between 6.5 and 9.5.
- 316 Stainless Steel (UNS S31600): Enhanced with 2.0–3.0% Molybdenum (Mo) content, providing superior resistance to chlorides, making it ideal for coastal or industrial environments where water quality may be aggressive.
- 304L Stainless Steel (UNS S30403): Low-carbon variant (≤0.03% C) designed to minimize intergranular corrosion during welding operations.
Key material properties include:
- Corrosion Resistance: Passive chromium oxide layer (Cr₂O₃) provides self-healing protection against oxidation and pitting.
- Thermal Conductivity: Approximately 16.3 W/(m·K) for 304 grade, ensuring efficient heat transfer in chilled or hot water circuits.
- Mechanical Strength: Yield strength of ≥205 MPa (304 grade), with tensile strength ranging from 515–720 MPa.
- Hygienic Surface Finish: Ra (Surface Roughness Average) ≤ 0.8 μm for interior surfaces, reducing biofilm formation and fouling in water systems.
- Temperature Range: Operational from −196°C to +870°C, accommodating extreme thermal cycling in heating and cooling applications.
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 6.35 mm – 50.8 mm (¼" – 2") | ASTM A213 / GB/T 14976 |
| Wall Thickness | 0.50 mm – 3.00 mm | ASTM A213 / EN 10216-5 |
| Bend Radius | ≥ 3× OD (minimum) | ISO 4427 |
| Coil Length per Spool | 20 m – 100 m (configurable) | Manufacturer Specification |
| Pressure Rating | 1.6 MPa – 6.3 MPa (PN16 – PN63) | EN 12266 / ASME B31.9 |
| Surface Finish (Exterior) | 2B Mill Finish / No. 4 Brushed | ASTM A480 |
| Surface Finish (Interior) | Electropolished, Ra ≤ 0.8 μm | ASTM A270 |
| Dimensional Tolerance | OD: ±0.10 mm; Wall: ±0.05 mm | ASTM A213, Class 1 |
| Helix Diameter (Coil) | 300 mm – 600 mm | Manufacturer Specification |
| Residual Stress | ≤ 100 MPa (after stress relief) | ASTM A314 |
| Material Grade | 304 / 304L / 316 / 316L | ASTM A213 / GB/T 12771 |
| End Treatment | Deburred, chamfered, or cap-plugged | ISO 1130 |
Manufacturing Process
The production of the Coiltube follows a rigorous multi-stage manufacturing sequence, incorporating both traditional metallurgical processes and modern computational optimization techniques:
- Raw Material Selection and Incoming Inspection: Stainless steel strip or seamless pipe blanks are sourced from certified mills. Each batch undergoes spectroscopic analysis (OES — Optical Emission Spectroscopy) to verify chemical composition compliance with ASTM and GB standards.
- Coil Forming (Cold Bending): Straight tubes are cold-formed into helical coils using precision CNC (Computer Numerical Control) coiling machines. The bending process is controlled to maintain uniform wall thickness and avoid ovality exceeding 2% of nominal OD. The hydraulic optimization software is used during this stage to simulate stress distribution and determine optimal bend radii for the target application.
- Stress Relief Annealing: Coiled tubes are subjected to controlled thermal annealing at 1050°C – 1150°C in a protective atmosphere (N₂ or vacuum) to relieve residual stresses introduced during cold forming, ensuring dimensional stability and maximum corrosion resistance.
- Pickling and Passivation: Annealed coils undergo acid pickling (HNO₃/HF blend) to remove oxide scale, followed by nitric acid passivation to restore the protective chromium oxide layer on all exposed surfaces.
- Interior Cleaning and Electropolishing: The interior surfaces are cleaned and electropolished to achieve Ra ≤ 0.8 μm, critical for minimizing flow resistance and preventing microbial colonization in water distribution systems.
- Hydraulic Performance Testing: Each coil is tested for pressure integrity (hydrostatic test at 1.5× working pressure) and flow characteristics. Data is cross-referenced with the hydraulic optimization model to ensure compliance with design parameters.
- Final Inspection and Packaging: Coils are inspected for surface defects (eddy current testing per ASTM E709), dimensionally verified, and packaged with protective caps, desiccant, and moisture-barrier wrapping for shipment.
Applications
The Coiltube product is engineered for use in a wide range of hydraulic and thermal systems, with primary applications including:
- Fan Coil Unit (FCU) Water Systems: Primary application domain — serving as the distribution piping for chilled water and hot water circuits in commercial and residential HVAC systems. The hydraulic optimization software ensures minimal pressure drop and balanced flow across multiple terminal units.
- Chilled Water Distribution Networks: Connecting central chillers to fan coil units, air handlers, and radiant cooling panels in large commercial buildings.
- Condenser and Evaporator Coils: Used in heat exchanger assemblies where high thermal conductivity and corrosion resistance are essential for long-term efficiency.
- Domestic Hot Water Circulation: Sanitary hot water recirculation loops in multi-story buildings, leveraging the hygienic interior finish to prevent biofilm growth.
- Process Cooling Systems: Industrial applications requiring stainless steel tubing for chemical-resistant, high-purity water circuits.
- Geothermal Heat Pump Systems: Ground-loop piping in closed-loop geothermal installations where long-term durability and thermal stability are paramount.
Unique Selling Points
- Hydraulically Optimized Design: Each coil geometry is validated through advanced CFD (Computational Fluid Dynamics) simulation and hydraulic network modeling, ensuring superior flow performance and energy efficiency compared to standard coil tubes.
- Precision Manufacturing: CNC-controlled coiling with dimensional tolerances as tight as ±0.05 mm on wall thickness ensures consistent performance and ease of field installation.
- Hygienic Interior Finish: Electropolished interior surfaces (Ra ≤ 0.8 μm) reduce friction losses by up to 15% and virtually eliminate conditions conducive to microbial growth.
- Full Traceability: Each coil is traceable to its mill heat number through a digital tracking system, enabling complete quality assurance documentation.
- Custom Configurations: OD, wall thickness, coil length, and helix diameter are configurable to meet specific project requirements, with minimum order quantities accommodating both large-scale and niche applications.
Quality Certifications & Standards Compliance
The Coiltube product line is manufactured and tested in accordance with the following international and national standards:
| Standard / Certification | Scope of Compliance |
|---|---|
| ISO 9001:2015 | Quality Management System certification for the manufacturing facility. |
| ASTM A213 / A269 | Specification for seamless and welded austenitic stainless steel tubing. |
| GB/T 12771 | Chinese national standard for welded stainless steel tubing. |
| EN 10216-5 | European standard for seamless and welded stainless steel tubes for pressure purposes. |
| ASME B31.9 | Pressure Piping Code for Building Services — applicable for HVAC hydronic systems. |
| ISO 1130 | End preparation and deburring requirements for tubing. |
| NSF/ANSI 61 | Health Effects of Drinking Water System Components (for potable water applications). |
| CE Marking | Conformity with EU Pressure Equipment Directive (PED 2014/68/EU) for applicable pressure ratings. |
| ISO 14644-1 (Class 8) | Cleanroom classification for final packaging and inspection areas. |
Technical Note: The hydraulic optimization software platform employed in the design and validation of these coil tubes incorporates iterative network analysis algorithms that account for variable flow rates, elevation changes, and thermal expansion within FCU piping networks. This ensures that the delivered coil tube geometry minimizes pump energy consumption while maintaining balanced flow distribution across all connected terminal units. Customers are advised to provide system design parameters (flow rate, pressure drop allowance, temperature range, and water chemistry) at the time of specification to enable optimal coil configuration.