Stainless Steel Coil Tube for Floor Radiant Heating Systems
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered tubular product specifically designed for ground-coil floor radiant heating applications. This product represents a critical component in modern hydronic radiant floor heating systems, where continuous, uniform heat distribution is paramount to occupant comfort and energy efficiency. The coil tube is supplied in factory-wound coil configurations to facilitate rapid installation, minimize on-site welding joints, and reduce the risk of thermal bridging at connection points.
Unlike conventional straight-length stainless steel piping that requires field bending and joining, the coil tube form factor eliminates the need for intermediate fittings in continuous runs, thereby enhancing system integrity, reducing pressure drop, and improving long-term hydraulic performance. This product is particularly suited for residential, commercial, and industrial radiant heating installations where corrosion resistance, thermal conductivity, and mechanical durability are essential design criteria.
2. Material & Properties
2.1 Base Material
The coil tube is fabricated from austenitic stainless steel conforming to internationally recognized standards. The primary grades utilized include:
- 304 (UNS S30408) — General-purpose grade with excellent corrosion resistance, suitable for potable water and low-chloride environments.
- 316 (UNS S31608) — Enhanced pitting and crevice corrosion resistance due to molybdenum addition (2–3% Mo), ideal for high-chloride or aggressive service environments.
- 321 (UNS S32108) — Stabilized grade with titanium addition, suitable for elevated-temperature applications and resistance to sensitization.
2.2 Mechanical Properties
| Property | 304 Grade | 316 Grade | 321 Grade |
|---|---|---|---|
| Tensile Strength (MPa) | ≥ 520 | ≥ 515 | ≥ 520 |
| Yield Strength (MPa) | ≥ 205 | ≥ 170 | ≥ 205 |
| Elongation (%) | ≥ 40 | ≥ 40 | ≥ 40 |
| Thermal Conductivity (W/m·K) at 20°C | 16.3 | 14.6 | 16.3 |
| Thermal Expansion Coefficient (×10⁻⁶/K) | 17.3 | 16.0 | 17.3 |
| Density (kg/m³) | 8.00 | 8.00 | 8.00 |
2.3 Chemical Composition (Typical, wt%)
| Element | 304 | 316 | 321 |
|---|---|---|---|
| Carbon (C) max | 0.08 | 0.08 | 0.07 |
| Chromium (Cr) | 18.0–20.0 | 16.5–18.5 | 17.0–19.0 |
| Nickel (Ni) | 8.0–10.5 | 10.0–14.0 | 9.0–12.0 |
| Molybdenum (Mo) | — | 2.0–3.0 | — |
| Titanium (Ti) | — | — | 5×C–0.70 |
3. Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 6.0 mm, 8.0 mm, 10.0 mm, 12.0 mm, 15.0 mm, 16.0 mm, 20.0 mm |
| Wall Thickness (WT) | 0.8 mm, 1.0 mm, 1.2 mm, 1.5 mm, 1.8 mm, 2.0 mm |
| OD Tolerance | ±0.1 mm (per ASTM A269 / GB/T 12771) |
| Wall Thickness Tolerance | ±10% of nominal |
| Coil Length | 50 m, 100 m, 150 m, 200 m (custom available) |
| Coil Inner Diameter | 300 mm – 500 mm (standard) |
| Surface Finish | BA (Bright Annealed), 2B, or No. 4 Brushed |
| Maximum Operating Temperature | −196 °C to +800 °C (grade-dependent) |
| Maximum Working Pressure | Up to 1.6 MPa (PN16) at 95 °C |
| Minimum Bend Radius | 3× OD (cold bending without mandrel) |
| Standard Compliance | ASTM A269/A269M, GB/T 12771, EN 10217-7, JIS G3446 |
| End Condition | Plain cut, beveled, or threaded (upon request) |
4. Manufacturing Process
4.1 Seamless Tube Production
The coil tube is produced via the seamless tube manufacturing route, ensuring a homogeneous microstructure free of weld seams that could act as preferential corrosion sites. The process comprises the following stages:
- Hot Rolling & Pipe Making — Steel billets are heated to approximately 1,150 °C and pierced to form hollow tubes.
- Hot Finishing — Tubes are rolled to approximate dimensions and scaled.
- Pickling & Descaling — Oxide scale is removed via acid pickling to reveal a clean metal surface.
- Cold Drawing / Cold Rolling — Tubes are drawn through precision dies to achieve exact dimensional tolerances and smooth surface finishes.
- Intermediate Annealing — Stress relief annealing at 1,050–1,100 °C followed by rapid quenching to restore ductility and achieve solution-treated condition.
- Coil Winding — Finished tubes are wound into coils on precision mandrels under controlled tension to prevent kinking, ovality, or deformation.
- Final Inspection & Packaging — Each coil undergoes dimensional verification, pressure testing, and visual inspection prior to protective packaging.
4.2 Quality Control Measures
- 100% hydrostatic pressure testing at 1.5× working pressure
- Ultrasonic flaw detection (UT) for internal and external defects
- Dimensional verification via laser measurement systems
- Surface roughness measurement (Ra ≤ 0.8 μm for BA finish)
- Chemical composition verification via spark OES or wet chemical analysis
5. Applications
5.1 Floor Radiant Heating (Underfloor Heating)
The primary application domain for this coil tube is hydronic floor radiant heating systems. The continuous coil configuration allows installers to deploy long, unbroken runs of piping through floor screeds or under concrete slabs, ensuring uniform heat emission and eliminating thermal losses at joint connections. Simulation and design methodologies for ground-coil floor radiant heating systems demonstrate that stainless steel coil tubes offer superior thermal performance compared to polymer alternatives due to their higher thermal conductivity, enabling faster heat-up times and more responsive temperature control.
5.2 Additional Applications
- Domestic Hot Water Distribution — Corrosion-resistant piping for potable water supply networks.
- Industrial Process Heating — Heat exchanger tubing in chemical, pharmaceutical, and food processing plants.
- Geothermal Systems — Ground-source heat exchanger loops for geothermal heating and cooling.
- Marine & Offshore Systems — Seawater-resistant piping in shipboard and offshore platform installations.
- Solar Thermal Systems — Heat transfer fluid circuits in concentrated solar thermal installations.
6. Quality Certifications
Wenzhou Jixing Metal Materials Co., Ltd. maintains comprehensive quality management systems and product certifications that assure conformity to international standards:
- ISO 9001:2015 — Quality Management System certification for consistent manufacturing quality.
- ISO 14001:2015 — Environmental Management System certification.
- EN 10204 3.1 — European material certificates confirming compliance with specified standards.
- CE Marking — Conformity with European regulatory requirements for construction products.
- PED 2014/68/EU — Pressure Equipment Directive compliance for pressurized applications.
- NSF/ANSI 61 — Drinking water system components certification (where applicable).
- GB/T 12771 — Chinese national standard for seamless stainless steel tubes for fluid transport.
7. Unique Selling Points
Seamless Construction: The absence of longitudinal or circumferential weld seams eliminates potential failure points, ensuring superior corrosion resistance and structural integrity over the service life of the installation.
- Continuous Coil Supply: Factory-wound coils of up to 200 meters eliminate the need for field joining in long runs, reducing installation time by up to 40% and minimizing leak risk.
- Exceptional Corrosion Resistance: Austenitic stainless steel chemistry provides decades of service life in aggressive aqueous environments without degradation.
- High Thermal Conductivity: Superior heat transfer characteristics compared to PEX or PERT alternatives, enabling lower supply temperatures and improved system efficiency (COP enhancement of 8–12%).
- Dimensional Precision: Tight tolerances on OD and wall thickness ensure consistent hydraulic performance and compatibility with standard fittings and manifolds.
- Design Flexibility: Available in multiple diameters, wall thicknesses, and coil lengths to accommodate diverse radiant heating design loads and floor constructions.
- Simulation-Validated Performance: Product performance is validated through CFD (Computational Fluid Dynamics) and finite element thermal simulations aligned with ISO 13370-2 and ISO 13373 standards for radiant heating system design.
8. Design Considerations for Radiant Heating Applications
When specifying stainless steel coil tube for floor radiant heating systems, the following engineering parameters should be considered in accordance with ISO 13370-2 (Design) and ISO 13373 (Performance):
- Tube Spacing: Typically 100–300 mm center-to-center, depending on heat load requirements and floor finish type.
- Embedment Depth: Recommended minimum 50 mm of concrete screed above tube centerline for uniform heat distribution.
- Flow Velocity: Maintained between 0.3–0.5 m/s to prevent sedimentation and minimize noise.
- Supply/Return Temperature Differential: Typically 5–10 K for low-temperature radiant systems.
- Expansion Accommodation: Stainless steel thermal expansion (17.3 × 10⁻⁶/K) must be accommodated through flexible loops or expansion joints at system boundaries.
This product represents a premium solution for engineering-grade floor radiant heating systems where long-term reliability, thermal efficiency, and corrosion-free operation are non-negotiable requirements.