Stainless Steel Coil Tube (Coiltube) for Three-Constant System Ceiling Applications
Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd is a precision-engineered cold-formed stainless steel tube supplied in continuous coil form, specifically designed for integration into Three-Constant System (恒温、恒湿、恒氧 — Constant Temperature, Constant Humidity, Constant Oxygen) ceiling radiant cooling and heating installations. These coil tubes are embedded within structural floor slabs or suspended ceiling assemblies to provide uniform, high-efficiency thermal regulation across large indoor spaces, including commercial buildings, hospitals, laboratories, and premium residential complexes.
Unlike conventional heating and cooling systems that rely on forced-air distribution, the Three-Constant System utilizes the thermal mass of the building structure combined with coil tubes to achieve superior indoor environmental control. The stainless steel coil tubes serve as the primary heat exchange medium, circulating chilled or heated water through the embedded tube network to maintain precise indoor climate conditions with minimal energy consumption.
Material & Properties
The coil tubes are fabricated from high-grade austenitic stainless steel, selected for exceptional corrosion resistance, mechanical strength, and thermal conductivity. The material composition and performance characteristics are as follows:
- Base Material: Austenitic stainless steel conforming to AISI 304 (UNS S30400) or AISI 316L (UNS S31603) grades
- Chromium Content (Cr): 18.0–20.0% (provides passive oxide film for corrosion resistance)
- Nickel Content (Ni): 8.0–10.5% (stabilizes austenitic microstructure)
- Molybdenum Content (Mo): 2.0–3.0% (in 316L grade; enhances pitting and crevice corrosion resistance)
- Tensile Strength (Rm): ≥ 520 MPa (AISI 304); ≥ 485 MPa (AISI 316L)
- Yield Strength (Rp0.2): ≥ 205 MPa
- Elongation (A50): ≥ 40%
- Thermal Conductivity (λ): 14.6–16.3 W/(m·K) at 25°C
- Operating Temperature Range: −196°C to +870°C (non-oxidizing atmosphere)
- Corrosion Resistance: Excellent resistance to atmospheric, chemical, and chloride-induced corrosion; suitable for long-term exposure to dehumidified air and condensate within ceiling cavities
- Surface Finish: 2B mill finish or BA (Bright Annealed) finish; surface roughness Ra ≤ 0.8 μm
Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Tube Outer Diameter (OD) | 8.0 mm / 10.0 mm / 12.0 mm / 15.0 mm / 16.0 mm | Customizable per project requirements |
| Wall Thickness (t) | 0.5 mm / 0.8 mm / 1.0 mm / 1.2 mm | EN 10217-7; GB/T 12771 |
| Coil Width | Up to 1500 mm (flat-rolled configuration) | — |
| Coil Length | Up to 200 m per coil (continuous) | — |
| Coil Inner Diameter (ID) | 508 mm (20 inches) standard; 610 mm optional | ISO 4892 |
| Dimensional Tolerance (OD) | ±0.1 mm | EN 10217-7 Class A |
| Dimensional Tolerance (Wall Thickness) | ±0.05 mm | EN 10217-7 Class A |
| Hydrostatic Test Pressure | ≥ 3.0 MPa (minimum burst pressure ≥ 1.5 × working pressure) | GB/T 24511 |
| Operating Pressure (Design) | 0.3–0.6 MPa (typical for radiant ceiling systems) | ASHRAE 90.1; GB 50736 |
| Design Flow Velocity | 0.5–2.0 m/s | ASHRAE Guideline 17 |
| Tube Spacing (Center-to-Center) | 150 mm / 200 mm / 250 mm / 300 mm | Project-specific layout |
| Heat Transfer Coefficient | 150–350 W/(m²·K) (water-to-air, typical radiant ceiling) | ASHRAE Handbook—HVAC Systems |
| Design Service Life | ≥ 25 years (embedded application) | GB 50736-2012 |
Manufacturing Process
The production of stainless steel coil tubes at Wenzhou Jixing Metal Materials Co., Ltd follows a rigorously controlled multi-stage manufacturing workflow to ensure dimensional accuracy, metallurgical integrity, and long-term structural reliability:
- Raw Material Procurement and Incoming Inspection: Cold-rolled stainless steel strip is sourced from certified mills (e.g., Taigang, Baowu) and subjected to chemical composition analysis (OES), mechanical testing, and surface quality inspection per EN 10204 Type 3.1 certification.
- Slitting and Leveling: The strip is slit to the required width and passed through a precision leveling line to eliminate coil set and ensure flatness within 0.15 mm/m.
- Forming (Cold Rolling into Tube): The leveled strip is fed through a multi-stand roll-forming mill (typically 8–12 forming stations) where progressive rollers incrementally bend the flat strip into a circular tube cross-section. Laser weld heads or induction welding systems may be employed to create a seamless or single-weld-seam tube.
- Weld Seam Inspection (if applicable): Welded tubes undergo 100% inline eddy current testing (ECT) and/or ultrasonic testing (UT) to detect seam defects, porosity, and lack of fusion.
- Heat Treatment (if required): Tubes that have undergone significant cold working may be solution-annealed at 1050–1100°C in a protective atmosphere (argon or vacuum) followed by controlled cooling to restore full austenitic microstructure and eliminate residual stresses.
- Pickling and Passivation: The tube surface is acid-pickled (nitric/hydrofluoric acid blend) to remove oxide scale, followed by passivation treatment to re-establish the protective chromium oxide film (Cr₂O₃).
- Hydrostatic Pressure Testing: Every coil is subjected to 100% hydrostatic pressure testing at ≥ 3.0 MPa with a minimum hold time of 30 seconds to verify weld integrity and dimensional conformance.
- Coiling and Packaging: The finished tube is coiled around a standard core, wrapped with protective film (PE or PP), secured with steel strapping, and labeled with heat number, dimensions, grade, and certificate reference.
Applications
Primary Application: Three-Constant System (三恒系统) Radiant Ceiling
The Three-Constant System is an advanced integrated building environmental control technology that maintains constant indoor temperature (恒温), constant humidity (恒湿), and constant oxygen/air quality (恒氧) throughout the occupied zone. The stainless steel coil tubes are the core heat exchange element, installed within the ceiling void or embedded in the structural slab as follows:
- Radiant Ceiling Panels: Coil tubes are laid in serpentine or meander patterns within suspended ceiling modules, connected to a manifold system that distributes chilled water (6–12°C for cooling) or heated water (25–35°C for heating). The large surface area of the ceiling provides efficient radiant heat exchange, reducing the effective room temperature by 2–3°C compared to air temperature.
- Structural Slab Integration: In high-performance building designs, coil tubes are embedded directly into reinforced concrete floor slabs during construction. The thermal mass of the slab acts as a heat sink, enabling thermal buffering and reduced peak loads.
- Dehumidification Integration: The low-temperature chilled water circulated through the coil tubes condenses moisture from the supply air, achieving latent load removal (恒湿) without overcooling the space.
Secondary Applications
- Underfloor Heating Systems: Coil tubes embedded in screed or concrete slabs for hydronic radiant floor heating in residential and commercial buildings.
- Industrial Process Heating/Cooling: Custom coil tube configurations for heat exchangers, condensers, and evaporators in chemical, pharmaceutical, and food processing industries.
- Heat Pump Systems: Coil tubes used as evaporator or condenser coils in ground-source and air-source heat pump installations.
- Building Energy Storage: Phase-change material (PCM) encapsulated coil tube assemblies for thermal energy storage in smart buildings.
Quality Certifications and Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd maintains a comprehensive quality management system and ensures product compliance with the following international and national standards:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification covering design, manufacturing, and supply chain |
| EN 10204 Type 3.1 | Inspection certificate issued by an authorized inspector independent of the manufacturer |
| EN 10217-7 | European standard for cold-drawn seamless and welded stainless steel tubes for pressure purposes |
| GB/T 12771 | Chinese national standard for welded austenitic stainless steel tubes for general purposes |
| GB/T 24511 | Chinese national standard for pressure piping and components |
| GB 50736-2012 | Chinese code for design of radiant floor and ceiling heating systems |
| ASTM A269 / A270 | American standards for welded and seamless austenitic stainless steel tubes |
| ISO 14692 | European standard for stainless steel tubes for pressure purposes — technical delivery conditions |
| CE Marking (PED 2014/68/EU) | European Pressure Equipment Directive compliance for pressure-rated applications |
| RoHS / REACH | Compliance with EU restrictions on hazardous substances and chemical registration |
Unique Selling Points
1. Purpose-Built for Three-Constant System Integration: Unlike generic stainless steel tubing, these coil tubes are engineered specifically for the thermal and hydraulic demands of Three-Constant System radiant ceilings, with optimized wall thickness-to-diameter ratios that maximize heat transfer while maintaining structural integrity under long-term cyclic thermal loading.
2. Superior Corrosion Resistance in Humid Environments: The austenitic stainless steel construction provides exceptional resistance to condensation-induced corrosion, a critical failure mode in radiant ceiling systems where low-temperature surfaces are continuously exposed to moisture-laden air. This eliminates the need for galvanization or protective coatings that would otherwise degrade heat transfer performance.
3. Continuous Coil Supply for Rapid Installation: The coil tube format eliminates the need for on-site cutting, threading, and welding of individual pipe segments, dramatically reducing installation time and labor costs. A single coil of 200 meters can serve an entire ceiling zone, minimizing connection points and potential leak sources.
4. Dimensional Precision for Automated Laying: Tight dimensional tolerances (±0.1 mm OD, ±0.05 mm wall thickness) enable compatibility with automated coil tube laying machines, ensuring consistent tube spacing and optimal heat distribution across the ceiling plane.
5. Full Traceability and Documentation: Every coil is accompanied by a complete material traceability package including heat number, chemical analysis, mechanical test results, hydrostatic test records, and dimensional inspection data, facilitating seamless integration into building energy performance verification and commissioning processes.
6. Energy Efficiency Contribution: By enabling radiant cooling/heating at higher water temperatures (compared to forced-air systems), these coil tubes reduce the coefficient of performance (COP) penalty of chiller and boiler plants, contributing to overall building energy efficiency improvements of 20–40% as documented in ASHRAE and IEA research on radiant HVAC systems.