Stainless Steel Coil Tube — FP-51WMU Fan Coil Unit Integration
1. Product Overview
The Stainless Steel Coil Tube (Product No. 929) is a precision-engineered tubular component manufactured by Wenzhou Jixing Metal Materials Co., Ltd., designed specifically for integration into high-performance HVAC (Heating, Ventilation, and Air Conditioning) systems, particularly the FP-51WMU Fan Coil Unit (FCU) series. This coil tube serves as the primary heat exchange element within closed-loop thermal transfer systems, leveraging the superior corrosion resistance, thermal conductivity, and mechanical durability inherent to austenitic stainless steel grades.
The product is categorized under the technical literature and engineering reference domain, reflecting its role as a foundational component in building services engineering and industrial process applications. The coil tube is manufactured to meet stringent dimensional tolerances and surface finish requirements, ensuring optimal fluid dynamics and heat transfer efficiency within the FP-51WMU unit assembly.
2. Material & Properties
2.1 Base Material Composition
The coil tube is fabricated from high-quality austenitic stainless steel, primarily conforming to ASTM A269 (Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for General Use) and ASME SA-213 (Standard Specification for Seamless Austenitic Chromium-Nickel Steel Tubing for Heat Exchangers). The preferred alloy grades include:
- 304 (UNS S30400) — Standard general-purpose grade with excellent corrosion resistance and formability
- 316 (UNS S31600) — Enhanced molybdenum-containing grade for aggressive chemical environments
- 316L (UNS S31603) — Low-carbon variant optimized for welding applications and high-temperature service
2.2 Key Physical and Mechanical Properties
- Thermal Conductivity: 16.3 W/(m·K) at 20°C (ASTM A269, Grade 304)
- Specific Heat Capacity: 0.502 kJ/(kg·K) at 20°C
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (20–100°C)
- Yield Strength: ≥ 205 MPa (0.2% offset)
- Tensile Strength: 515–730 MPa
- Elongation: ≥ 40% (in 50 mm gauge length)
- Operating Temperature Range: −196°C to +870°C (continuous service)
2.3 Corrosion Resistance Characteristics
The austenitic stainless steel composition provides exceptional resistance to:
- Atmospheric corrosion (industrial and marine environments)
- Acidic and alkaline solutions (pH range 3–12)
- Chloride-induced pitting (particularly with 316/316L grades, up to 1000 ppm Cl⁻)
- Oxidation and scaling at elevated temperatures
- Intergranular corrosion (when properly stabilized or low-carbon processed)
3. Technical Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Product Designation | Coil Tube for FP-51WMU Fan Coil Unit | — |
| Catalog Number | 929 | Wenzhou Jixing Internal |
| Material Grade | ASTM A269 TP304 / TP316 / TP316L | ASTM A269 / ASME SA-213 |
| Outer Diameter (OD) | 9.52 mm (3/8") / 12.7 mm (1/2") / 15.88 mm (5/8") | ASME B36.19M |
| Wall Thickness | 1.65 mm (18 BWG) / 2.11 mm (16 BWG) / 2.77 mm (14 BWG) | ASME B36.19M |
| Coil Pitch | 25.4 mm (1.0") ± 0.5 mm | Manufacturer Tolerance |
| Tube Length per Coil | 6.0 m ± 0.1 m (standard) / Custom lengths available | — |
| Coil Diameter | 300–600 mm (configurable per unit design) | — |
| Surface Finish | No. 4 Brushed / 2B Annealed / Electropolished (Ra ≤ 0.4 μm) | ASTM A480 |
| Maximum Working Pressure | 1.6 MPa (16 bar) @ 25°C | ASME B31.5 |
| Hydrostatic Test Pressure | 2.4 MPa (24 bar) @ 25°C | ASTM A269 §11 |
| End Forming | Flared / Threaded (M22×1.5) / Grooved / Plain | ASME B31.5 |
| Heat Transfer Coefficient | ≥ 850 W/(m²·K) (water-to-air, turbulent flow) | ASHRAE Handbook |
| Compliance | EN 10216-5 / ISO 14459 / GB/T 14976 | Multi-standard |
| Welding Process | TIG (GTAW) / Orbital Automated | ASME BPV Section IX |
| Heat Treatment | Solution Annealing at 1050–1150°C, Water Quenched | ASTM A269 §8 |
4. Manufacturing Process
4.1 Production Workflow
- Raw Material Inspection: Incoming stainless steel wire rod or seamless tubing undergoes spectroscopic analysis (OES) to verify chemical composition compliance with ASTM A269 requirements. Certificates of Analysis (COA) are cross-referenced with mill test reports.
- Drawing and Forming: High-grade stainless steel wire is cold-drawn through precision tungsten carbide dies to achieve the specified OD and wall thickness. Dimensional accuracy is maintained within ±0.05 mm tolerance.
- Coil Winding: The formed tube is wound onto precision CNC-controlled coil forming machines, ensuring uniform pitch distribution and minimal residual stress. The winding process is performed at controlled speeds to prevent tube ovalization or kinking.
- Welding: U-bend connections between coil passes are fabricated using TIG (Tungsten Inert Gas) welding with high-purity argon (99.99%) shielding gas. Orbital welding equipment ensures consistent weld bead geometry and penetration.
- Heat Treatment: Post-weld solution annealing is conducted at 1050–1150°C followed by rapid water quenching to restore full austenitic microstructure, eliminate residual stresses, and maximize corrosion resistance.
- Surface Finishing: Tubes undergo mechanical polishing or electropolishing to achieve the specified surface roughness (Ra ≤ 0.4 μm for sanitary applications). This process also removes surface contamination and enhances passive film integrity.
- Non-Destructive Testing (NDT): 100% inspection via eddy current testing (ECT) for surface and near-surface defects, supplemented by dye penetrant testing (PT) for weld integrity verification.
- Pressure Testing: Each coil assembly undergoes hydrostatic pressure testing at 1.5× the maximum working pressure for a minimum dwell time of 60 seconds, with no visible leakage or permanent deformation permitted.
- Final Inspection and Packaging: Dimensional verification, visual inspection, and traceability documentation are completed prior to protective packaging in moisture-proof wrapping with desiccant.
4.2 Process Quality Control
Throughout the manufacturing process, statistical process control (SPC) methodologies are applied to critical dimensions including tube OD, wall thickness, coil pitch, and coil diameter. In-process inspections are performed at defined hold points, with full traceability maintained through batch numbering and digital inspection records.
5. Applications
5.1 Primary Application: FP-51WMU Fan Coil Unit
The stainless steel coil tube is the core heat exchange element within the FP-51WMU Fan Coil Unit, a high-efficiency HVAC terminal device used in commercial and institutional buildings. The FP-51WMU unit integrates the coil tube with:
- Forward-curved centrifugal fan assembly (high-static pressure, low-noise operation)
- Aluminum fin-and-tube heat exchanger matrix (fin spacing: 2.1 mm / 12 FPI)
- Stainless steel or galvanized steel water distribution headers
- Integrated condensate drain pan with slope drainage
- Variable speed ECM (Electronically Commutated Motor) or direct-drive motor
5.2 Industry Applications
- Commercial HVAC: Office buildings, hotels, hospitals, retail spaces, and educational facilities
- Industrial Process Cooling: Precision temperature control for manufacturing equipment, electronics, and chemical processes
- Pharmaceutical & Food Processing: Sanitary-grade applications requiring CIP (Clean-In-Place) compatibility and FDA-compliant materials
- Marine & Offshore: Corrosion-resistant HVAC systems for shipboard and offshore platform environments
- Renewable Energy Systems: Thermal loop heat exchange in solar thermal and geothermal installations
- Chilled Beam Systems: Indirect evaporative cooling and radiant cooling applications
6. Quality Certifications & Compliance
| Certification | Scope | Standard |
|---|---|---|
| ISO 9001:2015 | Quality Management System | International Organization for Standardization |
| ISO 14001:2015 | Environmental Management System | International Organization for Standardization |
| CE Marking | EU Conformity — Pressure Equipment Directive (PED 2014/68/EU) | European Union |
| ASME Stamp | Pressure Vessel and Piping Code Compliance | ASME BPV Code Section VIII Div. 1 |
| EN 10204 3.1 | Inspection Certificate — Material Test Report | European Standard |
| NSF/ANSI 61 | Drinking Water System Components — Health Effects | National Sanitation Foundation |
| RoHS Compliance | Restriction of Hazardous Substances | EU Directive 2011/65/EU |
| GB/T 14976 | Chinese National Standard — Seamless Stainless Steel Tubes | Standardization Administration of China (SAC) |
7. Unique Selling Points
- Superior Corrosion Longevity: Austenitic stainless steel construction ensures a design service life exceeding 25 years in aggressive HVAC water treatment environments, significantly outperforming carbon steel alternatives.
- Optimized Heat Transfer Performance: Precision coil geometry with controlled pitch and minimal flow resistance achieves thermal efficiency ratings up to 850 W/(m²·K), reducing energy consumption in terminal HVAC units.
- Multi-Standard Compliance: Simultaneous adherence to ASTM, ASME, EN, and GB standards enables seamless integration into international project specifications without redesign or requalification.
- Full Traceability: Each coil tube is accompanied by a complete material traceability package including mill certificates, heat numbers, and in-process inspection records, supporting audit-ready documentation for regulatory and client requirements.
- Customization Capability: Wenzhou Jixing Metal Materials offers flexible configuration options for OD, wall thickness, coil geometry, end forming, and surface finish to accommodate bespoke FP-51WMU unit designs and specialized application requirements.
- Sanitary-Grade Available: Electropolished variants with Ra ≤ 0.4 μm surface roughness meet pharmaceutical and food-grade hygiene standards, enabling use in GMP (Good Manufacturing Practice) regulated environments.
8. Reference Standards
ASTM A269 — Standard Specification for Seamless and Welded Austenitic Stainless Steel Tubing for General Use
ASME SA-213 — Standard Specification for Seamless Austenitic Chromium-Nickel Steel Tubing for Heat Exchangers and Similar Applications
EN 10216-5 — Non-alloy, Heat Resistant and Stainless Steel Tubes for Pressure Purposes — Technical Delivery Conditions