Stainless Steel Coil Tube for Low-Temperature Hot Water Radiant Heating Systems
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered continuous coil product specifically designed for low-temperature hot water radiant heating systems. This product series, catalogued under reference number 1000, represents a specialized segment of stainless steel tubing engineered for radiant floor heating, wall heating, and under-slab thermal distribution applications. The coil tube format enables efficient storage, transport, and on-site deployment, minimizing field waste and installation time while maintaining dimensional integrity throughout the supply chain.
Unlike conventional straight-length tubing, the coil tube configuration allows for continuous, joint-free piping runs of significant length—typically ranging from 50 to 300 meters per coil—making it ideal for large-scale radiant heating installations where uninterrupted flow paths are critical for thermal efficiency and system longevity.
Material & Properties
The coil tube is fabricated from austenitic stainless steel grades selected for their superior thermal conductivity, corrosion resistance, and mechanical performance under cyclic thermal loading conditions.
- Primary Grade: SUS304 / AISI 304 (UNS S30400) — Chromium-Nickel austenitic stainless steel providing excellent general corrosion resistance and formability
- Alternative Grade: SUS316 / AISI 316 (UNS S31600) — Molybdenum-enhanced austenitic stainless steel for enhanced resistance to chloride-induced pitting and crevice corrosion in aggressive environments
- Thermal Conductivity: 14.9–16.3 W/(m·K) at 20°C, ensuring efficient heat transfer within radiant heating circuits
- Operating Temperature Range: -40°C to +120°C continuous service; suitable for low-temperature hydronic systems operating at 30–60°C supply temperatures
- Maximum Working Pressure: Up to 1.6 MPa (PN16), with burst pressure exceeding 6.0 MPa
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C (20–100°C), lower than carbon steel, reducing stress accumulation in long pipe runs
- Surface Finish: Electropolished or passivated interior surface with Ra ≤ 0.4 μm, minimizing flow resistance and preventing biofilm accumulation
- Corrosion Resistance: Potentiodynamic polarization testing confirms passivation potential (Epit) exceeding +0.3 V vs. SCE for 316 grade in 3.5% NaCl solution
Specifications
| Parameter | Specification | Standard Reference |
|---|---|---|
| Outer Diameter (OD) | 12.7 mm, 15.8 mm, 19.05 mm, 22.2 mm, 25.4 mm | ASTM A213 / EN 10216-5 |
| Wall Thickness | 1.0 mm – 2.0 mm (±10% tolerance) | ASTM A269 |
| Coil Inner Diameter | 400 mm – 800 mm (configurable) | Manufacturer specification |
| Coil Length per Reel | 50 m – 300 m (typical) | — |
| Material Grade | SUS304 / SUS316 / SUS321 | ASTM A270 / EN 10217-7 |
| Manufacturing Method | Seamless (capillary drawing) or welded (TIG) | ASTM A269 / EN 10217 |
| End Condition | Plain cut, chamfered, or pre-flared | ISO 8035 |
| Surface Treatment | Pickled & Passivated (P&P), electropolished | ASTM A967 |
| Tensile Strength | ≥ 520 MPa (304); ≥ 515 MPa (316) | ASTM A270 |
| Yield Strength | ≥ 205 MPa (0.2% offset) | ASTM A270 |
| Elongation | ≥ 40% (minimum) | ASTM A270 |
| Hydrostatic Test Pressure | 2.0 MPa (minimum, per coil lot) | ASTM A269 |
| Coil Coating (Optional) | PEX cross-linked polyethylene, aluminum foil wrap | ISO 15875 |
| Minimum Bend Radius | 3D (3 × OD) cold bend without kinking | ASTM A269 |
| Packaging | Wooden reel with moisture-proof wrapping, palletized | ISO 4180 |
Manufacturing Process
The production of stainless steel coil tube for radiant heating systems follows a rigorous multi-stage manufacturing sequence designed to ensure dimensional accuracy, metallurgical integrity, and surface quality:
- Strip Preparation & Annealing: Cold-rolled stainless steel strip (coil) is sourced from certified mills and subjected to solution annealing at 1050–1150°C followed by controlled water quenching to achieve a fully austenitic microstructure free of carbide precipitation.
- Forming & Welding: The strip is fed through a multi-roll forming die set to achieve the target OD and wall thickness profile. Welded tube variants undergo high-purity argon-shielded TIG (Tungsten Inert Gas) welding at the longitudinal seam, with internal and external gas protection ensuring a clean, oxide-free weld root.
- Seamless Drawing (Capillary Method): For seamless variants, austenitic bar stock is cold-drawn through tungsten carbide capillary dies with self-lubricating lead-tin alloy coating, producing tubes with uniform wall thickness and no longitudinal weld seam.
- Intermediate Annealing: Tubes undergo stress-relief annealing at 1040–1100°C to restore ductility after cold working and eliminate residual stresses from forming operations.
- Pickling & Passivation: The tube surface is immersed in a mixed acid bath (nitric acid + hydrofluoric acid) to remove mill scale and oxide films, followed by passivation treatment to establish a stable chromium oxide passive layer (Cr₂O₃) on the surface.
- Coiling & Dimensional Inspection: The finished tube is wound onto precision reels while undergoing continuous optical diameter measurement, wall thickness verification via ultrasonic gauging, and leak detection through 100% hydrostatic pressure testing.
- Optional External Coating: For enhanced thermal performance or mechanical protection, the coiled tube may receive a PEX (cross-linked polyethylene) extrusion coating or aluminum foil wrapping, applied under controlled temperature and tension conditions.
- Final Quality Assurance: Each coil lot undergoes chemical composition verification (OES/Spectrometry), mechanical testing (tensile, hardness), dimensional inspection, and surface finish characterization before release.
Applications
The stainless steel coil tube from Wenzhou Jixing Metal Materials Co., Ltd. is engineered for demanding low-temperature hydronic radiant heating applications:
- Radiant Floor Heating Systems: Primary piping medium for under-slab, under-tile, and in-screed floor heating installations in residential, commercial, and industrial buildings. The low-temperature operation (30–60°C supply) leverages the thermal efficiency of radiant systems while exploiting the corrosion resistance of stainless steel for extended service life exceeding 50 years.
- Wall & Ceiling Radiant Panels: Integrated coil tube circuits for radiant wall panels and ceiling heating systems in healthcare facilities, cleanrooms, and high-purity manufacturing environments where floor space is constrained.
- Snow Melting & De-icing Systems: Underground and surface-mounted coil tube networks for parking lot de-icing, walkway snow melting, and rooftop anti-icing applications, leveraging the tube's resistance to freeze-thaw cycling and chemical de-icing agents.
- Greenhouse & Agricultural Heating: Low-temperature radiant heating for controlled-environment agriculture, providing uniform heat distribution with minimal surface temperature to avoid plant damage.
- Solar Thermal Integration: Compatible with solar thermal collector systems for hybrid heating, where the coil tube serves as the distribution medium between solar collectors and radiant emitters.
- Specialty Industrial Processes: Precision temperature control applications in pharmaceutical manufacturing, food processing, and semiconductor fabrication where stainless steel purity and non-contamination characteristics are mandatory.
Quality Certifications & Standards Compliance
The product line adheres to internationally recognized quality and performance standards:
- ISO 9001:2015 — Quality Management System certification for manufacturing operations
- ISO 15875:2017 — Thermoplastic pipes for radiant floor heating systems (applicable to coated variants)
- ASTM A269 — Standard specification for welded austenitic stainless steel tubing
- ASTM A213 — Standard specification for seamless austenitic stainless steel tubing for heat exchangers
- EN 10217-7 — Non-alloy and alloy steel tubes for heat exchangers and similar heat-transfer apparatus
- EN 10216-5 — Heat exchanger and radiator tubes — Seamless austenitic stainless steel tubes
- ASME B31.9 — Pressure Piping, Process Piping (applicable system design reference)
- CE Marking — Conformity with European pressure equipment directives (PED 2014/68/EU)
- Mill Test Certificates (MTC) — EN 10204 3.1 certification provided with each shipment, documenting chemical composition, mechanical properties, and heat treatment history
- NSF/ANSI 61 — Drinking water system components (where applicable for potable water-compatible heating loops)
Unique Selling Points
1. Joint-Free Continuous Coiling: The coil tube format eliminates the need for field welding or mechanical couplings in radiant heating circuits, dramatically reducing leak points and installation labor while ensuring long-term system reliability.
2. Superior Corrosion Resistance vs. Alternatives: Compared to PEX, PERT, and copper alternatives, stainless steel coil tube offers indefinite service life without degradation from UV exposure, oxygen diffusion, or chemical attack—eliminating the 15–20 year replacement cycle associated with polymer piping.
3. Precision Dimensional Tolerance: Tight OD and wall thickness tolerances (±10%) ensure uniform heat emission characteristics and compatibility with automated installation equipment, including robotic coil laying systems.
4. Thermal Cycling Durability: Austenitic stainless steel retains full mechanical properties across the entire operating temperature range without embrittlement, stress corrosion cracking, or fatigue failure—validated through accelerated thermal cycling tests exceeding 100,000 cycles.
5. Low-Flow-Rate Optimization: The electropolished interior surface (Ra ≤ 0.4 μm) reduces friction factor by up to 30% compared to standard finish, enabling efficient operation at low flow rates typical of low-temperature radiant systems while minimizing pump energy consumption.
Technical Notes & Installation Guidelines
Proper installation of stainless steel coil tube in radiant heating systems requires adherence to the following technical parameters:
- Minimum spacing between tube rows: 100–200 mm (dependent on floor load requirements and heat flux calculations)
- Maximum permissible temperature rise across the tube: ΔT ≤ 15°C between supply and return to prevent surface overheating and thermal shock to adjacent materials
- Recommended flow velocity: 0.3–1.0 m/s to ensure uniform heat distribution and prevent stratification
- Cold bending must be performed with a minimum bend radius of 3D (3 × outer diameter) using a hydraulic tube bender with internal mandrel support to prevent ovality exceeding 10% of nominal OD
- All system connections should utilize compression fittings or orbital-welded joints with 100% radiographic or dye penetrant inspection
- System flushing and disinfection per EN 12828 before commissioning to remove manufacturing residues and ensure water quality compliance
Conclusion
The Wenzhou Jixing Metal Materials Co., Ltd. Stainless Steel Coil Tube (Product No. 1000) represents a premium-grade solution for low-temperature hot water radiant heating systems, combining the metallurgical excellence of austenitic stainless steel with the logistical advantages of continuous coil formatting. This product delivers the reliability, longevity, and thermal performance required for next-generation radiant heating installations across residential, commercial, industrial, and agricultural sectors, supported by comprehensive quality documentation and adherence to global standards frameworks.