Stainless Steel Radiant Floor Heating Double-Layer Coil Tube System
Product Overview
The Stainless Steel Double-Layer Coil Tube (Product Code No. 593) is a precision-engineered radiant floor heating coil tube system manufactured by Wenzhou Jixing Metal Materials Co., Ltd. This product is designed specifically for hydronic underfloor heating applications where thermal efficiency, long-term durability, and uniform heat distribution are critical performance parameters. The double-layer coil tube architecture represents an advanced configuration in which two concentric stainless steel tubes are arranged to form a dual-circuit flow path, enabling optimized thermal exchange between the circulating heating medium and the floor slab structure.
Unlike conventional single-tube coil systems, the double-layer design leverages numerical simulation and computational fluid dynamics (CFD) optimization to achieve superior thermal performance, reduced thermal stratification, and improved flow uniformity across the heated zone. The system has been validated through rigorous finite element analysis (FEA) and numerical simulation studies to ensure consistent temperature distribution with minimal thermal gradients at the floor surface.
Material & Properties
Base Material
The coil tube is fabricated from austenitic stainless steel conforming to international standards, with the following material designations:
- Primary Grade: AISI 304 / EN 1.4301 / SUS 304 (Standard Austenitic Stainless Steel)
- High-Performance Grade: AISI 316L / EN 1.4404 / SUS 316L (Low-Carbon, Molybdenum-Alloyed for Enhanced Corrosion Resistance)
- Alternative Grade: AISI 321 / EN 1.4541 (Stabilized with Titanium for Elevated Temperature Service)
Mechanical Properties (AISI 304 Reference)
- Tensile Strength (Ultimate): 515–730 MPa
- Yield Strength (0.2% Offset): ≥ 205 MPa
- Elongation at Break: ≥ 40%
- Hardness (HB): 137–201
- Density: 7.93 g/cm³
Thermal Properties
- Thermal Conductivity (at 20°C): 16.3 W/(m·K)
- Thermal Conductivity (at 100°C): 17.0 W/(m·K)
- Specific Heat Capacity: 500 J/(kg·K)
- Linear Thermal Expansion Coefficient (20–100°C): 16.0 × 10⁻⁶ /K
- Operating Temperature Range: −196°C to +450°C
Corrosion Resistance
The austenitic stainless steel composition provides excellent resistance to:
- General atmospheric corrosion and oxidation
- Chloride-induced pitting corrosion (especially 316L grade)
- Intergranular corrosion (stabilized grades)
- Scaling and fouling in hydronic heating circuits
- Chemical attack from water treatment agents and inhibitors
Specifications
| Parameter | Specification |
|---|---|
| Product Code | No. 593 |
| Product Type | Double-Layer Coil Tube (盘管) |
| Material Grade | AISI 304 / 316L / 321 (Customizable) |
| Outer Diameter (OD) | Φ15.0 mm / Φ16.0 mm / Φ20.0 mm / Φ22.0 mm (Standard) |
| Wall Thickness | 0.8 mm / 1.0 mm / 1.2 mm / 1.5 mm |
| Inner Diameter (ID) | Φ12.0 mm / Φ13.0 mm / Φ14.0 mm (Dependent on OD & Wall) |
| Coil Diameter | Φ600 mm – Φ1200 mm (Configurable) |
| Tube Length per Coil | 15 m – 60 m (Standard); Custom lengths available |
| Surface Finish | 2B (Cold-Rolled Annealed) / BA (Bright Annealed) / Mirror Polished |
| Surface Roughness (Ra) | ≤ 0.8 μm (Standard); ≤ 0.4 μm (Polished) |
| Maximum Operating Pressure | 1.6 MPa (Standard); 2.5 MPa (Reinforced) |
| Hydrostatic Test Pressure | 2.4 MPa (1.5× Operating Pressure) |
| Maximum Flow Velocity | 2.0 m/s (Recommended); 3.0 m/s (Maximum) |
| Recommended Flow Rate | 0.2 – 1.5 L/min per tube |
| Spacing Configuration | 150 mm / 200 mm / 250 mm / 300 mm (Center-to-Center) |
| Design Service Life | ≥ 50 Years |
| Compliance Standards | ASTM A213 / ASTM A269 / EN 10217-7 / GB/T 14976 |
| Heat Transfer Coefficient | 350–600 W/(m²·K) (Double-Layer Configuration) |
| Thermal Efficiency | ≥ 92% (Optimized Double-Layer System) |
Manufacturing Process
1. Raw Material Procurement & Inspection
Stainless steel strip or seamless tube blanks are procured from certified mill suppliers with full chemical composition analysis (Spectrographic Testing) and mechanical property verification. Each batch undergoes incoming quality inspection (IQC) including visual examination, dimensional verification, and material traceability documentation.
2. Seamless Tube Forming
The coil tube is manufactured via one of the following processes depending on the required dimensions:
- Swaging Process: For seamless tubes with OD ≤ 22 mm. A heated mandrel is drawn through a die, reducing the diameter of the tube while maintaining wall thickness uniformity.
- Piercing & Rolling: For larger OD tubes. A solid billet is heated and pierced, then cold-rolled to final dimensions.
- Welded Tube (ERW): For specific configurations. Strip steel is formed into a tube shape and welded using Electric Resistance Welding (ERW), followed by post-weld annealing.
3. Cold Drawing & Sizing
The formed tube undergoes cold drawing through a series of precision dies to achieve the exact final dimensions with tight tolerances (±0.05 mm on OD, ±10% on wall thickness). This process also imparts beneficial strain hardening, improving mechanical properties.
4. Solution Annealing
The drawn tube is solution annealed at 1050–1150°C followed by rapid quenching (air or water) to:
- Eliminate cold work stresses
- Restore full austenitic microstructure
- Maximize corrosion resistance
- Ensure ductility for subsequent coiling operations
5. Surface Treatment
Depending on the application requirements, the tube surface is finished through:
- Acid Pickling: Removal of oxide scale using mixed acid solutions (HNO₃ + HF)
- Pickling & Passivation: Followed by passivation treatment to restore chromium oxide passive film
- Mechanical Polishing: For mirror finish applications (Ra ≤ 0.4 μm)
- Electropolishing: For critical applications requiring ultra-smooth internal surfaces
6. Coiling & Double-Layer Configuration
The straight tube is coiled into the required coil diameter using precision coiling equipment. For the double-layer configuration:
- Two concentric tubes are assembled with appropriate clearance
- Thermal separation is achieved through the annular space between layers
- End connections are made using welded joints or compression fittings
- The double-layer assembly undergoes numerical simulation validation for optimal flow and heat distribution
7. Quality Control & Testing
- Dimensional Inspection: OD, ID, wall thickness measured at multiple points along tube length
- Hydrostatic Pressure Test: All tubes tested at 1.5× maximum operating pressure for minimum 10 seconds
- Helium Leak Testing: For high-integrity applications
- Visual Inspection: Internal and external surfaces examined for defects
- Chemical Composition Analysis: Spectrographic verification of alloy composition
- Corrosion Testing: Salt spray testing (ASTM B117) for 316L grade verification
- Heat Transfer Performance Testing: Thermal conductivity measurement under operating conditions
8. Numerical Simulation & Optimization
A distinguishing feature of this product line is the integration of numerical simulation in the design and validation process. The double-layer coil tube system undergoes:
- Computational Fluid Dynamics (CFD) Analysis: Simulating fluid flow patterns, pressure drop, and heat transfer within the double-layer configuration
- Finite Element Thermal Analysis: Evaluating temperature distribution across the floor slab, identifying hot spots and cold zones
- Optimization of Tube Spacing: Determining the optimal center-to-center spacing for uniform floor surface temperature
- Flow Rate Optimization: Calculating the recommended flow velocity for minimum energy consumption while maintaining thermal performance
- Thermal Response Simulation: Modeling the system's dynamic behavior during startup, steady-state, and shutdown conditions
Applications
Primary Applications
- Residential Radiant Floor Heating: Single-family homes, apartments, and condominiums requiring efficient, low-maintenance underfloor heating systems
- Commercial Floor Heating: Retail spaces, offices, and hospitality facilities where uniform comfort temperatures are essential
- Industrial Floor Heating: Clean rooms, laboratories, and manufacturing facilities requiring precise temperature control
- Greenhouse Heating: Agricultural applications where controlled root-zone temperatures improve crop yield
- Aquaculture Heating: Fish farming and aquaculture facilities requiring stable water temperature maintenance
Specialized Applications
- Food Processing Facilities: Where corrosion resistance and hygiene are paramount
- Pharmaceutical Clean Rooms: Meeting GMP (Good Manufacturing Practice) requirements
- Marine & Coastal Environments: Where 316L grade provides superior chloride corrosion resistance
- High-Rise Building Heating Systems: Where lightweight, space-efficient coil tubes are advantageous
- Geothermal Heating Integration: Compatible with low-temperature geothermal heat sources
Quality Certifications & Compliance
Product Certifications
- ISO 9001:2015 — Quality Management System Certification
- ISO 14001:2015 — Environmental Management System Certification
- CE Marking — European Conformity for construction products
- EN 10217-7 — Technical delivery conditions for austenitic stainless steel tubes for pressure purposes
- ASTM A213 — Standard specification for seamless austenitic stainless steel tubes
- ASTM A269 — Standard specification for seamless austenitic stainless steel tube for chemical and similar severe service
- GB/T 14976 — Chinese National Standard for stainless steel seamless tubes
- JIS G3459 — Japanese Industrial Standard for stainless steel tubes
Testing & Compliance Standards
- EN 12828 — Heating systems in buildings: design of low-temperature systems
- EN 1264 — Floor heating systems: performance rating
- ASTM B117 — Salt spray (fog) testing for corrosion resistance verification
- ASTM E290 — Surface roughness measurement standards
- ASME B31.9 — Building services piping code for hydronic heating systems
Material Certifications
- Mill Test Certificate (MTC / EN 10204 3.1): Provided with every shipment, documenting chemical composition, mechanical properties, and heat treatment history