Stainless Steel Coil Tube (Coiltube) — Floor Heating System Application
Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered piping solution designed specifically for hydronic floor heating systems, with particular emphasis on wet-area applications such as bathrooms. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product combines the inherent corrosion resistance of austenitic stainless steel with a continuous coil geometry that facilitates efficient thermal distribution and simplified on-site installation. The coil tube is supplied in a pre-formed helical configuration, minimizing field cutting and reducing the risk of joint-related leakage—a critical consideration in waterproofed floor assemblies.
Material & Properties
The coil tube is fabricated from high-grade austenitic stainless steel, typically conforming to ASTM A269 / ASTM A312 specifications. The material selection ensures exceptional resistance to chloride-induced pitting corrosion, thermal cycling fatigue, and long-term mechanical stress within the floor slab environment.
- Primary Alloy Grade: 304 (UNS S30400) or 316 (UNS S31600) stainless steel, selected based on the corrosive exposure conditions of the installation environment.
- Chemical Composition (304): Carbon (C) ≤ 0.08%, Chromium (Cr) 18.0–20.0%, Nickel (Ni) 8.0–10.5%, Manganese (Mn) ≤ 2.0%, Silicon (Si) ≤ 1.0%, Phosphorus (P) ≤ 0.045%, Sulfur (S) ≤ 0.030%.
- Mechanical Properties: Tensile Strength (UTS) ≥ 515 MPa, Yield Strength (0.2% offset) ≥ 205 MPa, Elongation ≥ 40%, Hardness (HB) ≤ 187.
- Surface Finish: Mill finish or electropolished interior surface to minimize flow resistance and prevent biofilm accumulation within the heating circuit.
- Temperature Resistance Range: Continuous operation from −196°C to +870°C, well exceeding the typical 35–60°C operating range of domestic floor heating systems.
- Corrosion Resistance: Excellent resistance to atmospheric, freshwater, and moderate chloride environments; 316 grade offers superior pitting resistance for aggressive bathroom conditions.
Specifications
| Parameter | Specification |
|---|---|
| Product Name | Stainless Steel Coil Tube (Coiltube) |
| Material Grade | 304 / 316 Stainless Steel (ASTM A269 / A312) |
| Outer Diameter (OD) | 12 mm, 14 mm, 16 mm, 18 mm, 20 mm (custom sizes available) |
| Wall Thickness | 0.8 mm – 2.0 mm (standard range for floor heating applications) |
| Coil Inner Diameter | 300 mm – 500 mm (adjustable per project layout requirements) |
| Coil Length per Roll | 50 m – 200 m (configurable based on installation area) |
| Tube End Condition | Deburred, chamfered, or threaded per customer specification |
| Weld Type | Continuous TIG (Tungsten Inert Gas) welded seam or seamless |
| Surface Treatment | Passivated interior; mill finish or polished exterior |
| Working Pressure | ≥ 0.6 MPa (standard floor heating system rating) |
| Hydrostatic Test Pressure | ≥ 1.5 MPa (factory acceptance test) |
| Operating Temperature | −20°C to +90°C (typical hydronic heating range) |
| Design Service Life | ≥ 50 years under normal operating conditions |
| Standard Reference | ASTM A269, ASTM A312, EN 10217, GB/T 12771 |
Manufacturing Process
The production of the stainless steel coil tube follows a rigorous multi-stage manufacturing protocol to ensure dimensional accuracy, weld integrity, and consistent material properties throughout the product life cycle.
- Material Selection & Incoming Inspection: Stainless steel strip or round bar is sourced from certified mills with full material traceability documentation (Mill Test Certificates per EN 10204 3.1). Incoming material undergoes chemical composition verification via optical emission spectrometry (OES) and mechanical property confirmation through tensile and hardness testing.
- Coil Forming / Pipe Drawing: The raw material is cold-formed into the required tube cross-section using precision roll-forming dies or drawn through calibrated mandrels. The helical coil geometry is achieved through CNC-controlled coiling equipment that maintains uniform curvature and prevents localized plastic deformation or work-hardening.
- Welding (if applicable): Longitudinal seams are welded using automated TIG (GTAW — Gas Tungsten Arc Welding) with argon shielding gas. The welding parameters (current, voltage, travel speed, gas flow rate) are calibrated to produce a fully fused, defect-free weld bead with penetration integrity verified by radiographic testing (RT) or ultrasonic testing (UT).
- Heat Treatment & Stress Relief: Post-weld annealing is performed at 1050°C ± 50°C with water quenching to restore full austenitic microstructure, eliminate residual welding stresses, and ensure uniform corrosion resistance. For seamless tubes, a solution annealing cycle is applied to relieve cold-work hardening.
- Passivation & Cleaning: The interior and exterior surfaces undergo acid pickling and passivation treatment to remove mill scale, welding discoloration, and free iron contamination. This establishes a stable chromium oxide passive film essential for long-term corrosion protection.
- Dimensional Inspection & Non-Destructive Testing (NDT): Each coil is inspected for dimensional compliance (OD, wall thickness, coil diameter) using laser micrometers and ultrasonic thickness gauges. Weld integrity is verified through 100% visual inspection and periodic radiographic or eddy current testing per ASME V or EN ISO 9712 standards.
- Hydrostatic Pressure Testing: Every coil undergoes a hydrostatic pressure test at ≥ 1.5 MPa held for a minimum of 60 seconds to confirm zero leakage and structural integrity prior to packaging.
- Coil Packaging & Shipping: Coils are wrapped in protective film or paper, secured with steel strapping, and palletized for transport. Protective end caps are installed to prevent mechanical damage to tube openings during handling and storage.
Applications
The stainless steel coil tube is engineered for demanding hydronic heating installations where reliability, corrosion resistance, and long-term performance are paramount. Key application domains include:
- Residential & Commercial Floor Heating Systems: The primary application, where coil tubes are embedded within screed or concrete slabs to provide radiant heat distribution. The coil geometry enables efficient serpentine or spiral layout patterns that maximize heat exchange surface area while minimizing installation time.
- Bathroom & Wet-Area Heating: Specifically suited for bathroom floor heating installations where exposure to moisture, cleaning chemicals, and potential chloride contamination necessitates superior corrosion resistance. The seamless or continuously welded construction eliminates joint failure points—a critical requirement for waterproofed floor assemblies where leakage could compromise the waterproofing membrane and structural integrity.
- Underfloor Heating in Swimming Pools & Spa Areas: The 316-grade variant provides exceptional resistance to chlorinated water environments, making it ideal for pool deck heating applications.
- Commercial Building Heating Systems: Hotels, hospitals, and office buildings where long service life and minimal maintenance are required to avoid costly floor slab disruption for repairs.
- Specialty Industrial Heating: Process heating circuits requiring stainless steel piping in coil configuration for space-constrained installations.
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework to ensure product conformity and traceability:
- ISO 9001:2015 — Quality Management System certification covering the full production cycle from raw material procurement to finished goods delivery.
- ISO 3834-2 — Quality requirements for welding of metallic materials (if welded coil tubes are specified).
- CE Marking — Conformity with European Construction Products Regulation (CPR) for structural and safety-critical building applications.
- Mill Test Certificates (MTC) — Provided per EN 10204 Type 3.1 for every production lot, documenting chemical composition, mechanical properties, and heat treatment parameters.
- ASME / ASTM Compliance — Product specifications aligned with ASTM A269 (welded austenitic stainless steel tube) and ASTM A312 (seamless austenitic stainless steel tube) standards.
- Hydrostatic Test Certification — Each coil is accompanied by a test report confirming pressure test results, ensuring zero-defect delivery.
- Third-Party Inspection (TPI) — Available upon request for independent verification of manufacturing processes and product conformity.
Unique Selling Points
- Leak-Free Continuous Construction: The coil tube's continuous geometry minimizes or eliminates field joints, dramatically reducing the probability of leakage—a decisive advantage for waterproofed floor heating installations where even minor failures can compromise structural waterproofing membranes.
- Exceptional Corrosion Resistance: Austenitic stainless steel provides inherent immunity to the corrosive agents commonly encountered in bathroom and wet-area environments, including cleaning agents, chlorides, and prolonged moisture exposure.
- Extended Service Life: A design life exceeding 50 years eliminates the need for replacement during the typical building lifecycle, reducing total cost of ownership and avoiding the high expense of floor slab demolition and reconstruction.
- Superior Thermal Performance: Stainless steel's thermal conductivity and the coil's high surface-area-to-volume ratio ensure rapid heat response and uniform temperature distribution across the heated floor area.
- Hygienic Interior Surface: The passivated, smooth interior surface prevents scale buildup and biofilm formation, maintaining consistent hydraulic performance and heat transfer efficiency throughout the service life.
- Full Traceability & Quality Assurance: Every product lot is accompanied by comprehensive test documentation, enabling complete supply chain traceability and facilitating compliance with building code and inspection requirements.
Technical Note: When integrating stainless steel coil tubes into waterproofed bathroom floor heating systems, strict adherence to waterproofing construction protocols is essential. The coil tube installation must be completed and pressure-tested prior to the application of the waterproofing membrane layer. All tube-to-manifold connections must be verified for watertight integrity, and the entire system must undergo a sustained pressure test (≥ 0.6 MPa for 24 hours) before any covering layer is applied. This sequential construction methodology ensures that the waterproofing system remains uncompromised and that any potential tube defects are identified and rectified before permanent encapsulation within the floor structure.