Stainless Steel Coil Tube — Radiant Heating & Fan Coil System Applications
Product Overview
The Stainless Steel Coil Tube (盘管 / Coil Tube) is a precision-engineered tubular product manufactured by Wenzhou Jixing Metal Materials Co., Ltd., specifically designed for use in floor radiant heating systems (地板辐射采暖) and fan coil unit (FCU) heating applications. These coil tubes serve as the primary heat transfer medium within hydronic heating loops, delivering consistent thermal distribution while maintaining long-term structural integrity under cyclic thermal and hydraulic loading conditions. The product is catalogued under reference number 1084 and is classified within the technical literature and application research category, reflecting its integration with comparative thermal environment and energy consumption studies.
Unlike conventional straight-pipe radiant heating systems, coil tubes offer significant advantages in terms of installation flexibility, material economy, and heat exchange efficiency. The continuous helical geometry eliminates the need for frequent pipe fittings and joints, thereby reducing potential leak points and improving system reliability over extended service lives.
Material Composition & Physical Properties
Coil tubes for radiant heating and fan coil applications are typically fabricated from austenitic stainless steel grades that provide an optimal balance of corrosion resistance, thermal conductivity, and mechanical strength. The following materials are commonly specified:
- Grade 304 (UNS S30408 / AISI 304): The most widely used grade for hydronic heating coil tubes, offering excellent general corrosion resistance and weldability. Contains approximately 18% Chromium (Cr) and 8% Nickel (Ni).
- Grade 316 (UNS S31608 / AISI 316): Enhanced pitting and crevice corrosion resistance due to the addition of 2–3% Molybdenum (Mo), making it suitable for aggressive water chemistries or coastal environments.
- Grade 321 (UNS S32103 / AISI 321): Titanium-stabilized variant providing superior resistance to sensitization at elevated operating temperatures, recommended for high-temperature floor heating loops.
Key material properties for Grade 304 stainless steel coil tube include:
- Density: 8.0 g/cm³
- Thermal Conductivity: 16.3 W/(m·K) at 20°C
- Specific Heat Capacity: 500 J/(kg·K)
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /K
- Tensile Strength (Minimum): 515 MPa (annealed condition)
- Yield Strength (0.2% Offset): 205 MPa
- Maximum Service Temperature: 870°C (continuous)
Technical Specifications
| Parameter | Specification | Standard / Reference |
|---|---|---|
| Outer Diameter (OD) | 8 mm, 10 mm, 12 mm, 14 mm, 16 mm (custom sizes available) | ISO 3507 / EN 10217 |
| Wall Thickness | 0.8 mm – 1.5 mm (typical range for radiant heating) | Manufacturer tolerance ±0.05 mm |
| Coil Diameter | 1.0 m – 5.0 m (configurable per installation layout) | Project-specific |
| Coil Length (per Roll) | 50 m – 500 m (standard); up to 1000 m (special order) | ISO 4287 |
| Surface Finish | No. 1 Annealed (bright annealed) or 2B finish | ASTM A270 |
| End Condition | Plain ends, cut square, with protective caps | ISO 261 |
| Operating Pressure (Design) | 0.6 MPa – 1.6 MPa (6 – 16 bar) | EN 12828 |
| Test Pressure | 1.5 × design pressure (hydrostatic) | ISO 11114 |
| Operating Temperature Range | -40°C to +120°C (floor heating); up to +150°C (fan coil) | EN 12828 / EN 1452 |
| Minimum Bend Radius | 3 × OD (cold bending without springback compensation) | ASTM A999 |
| Material Grade | 304 / 316 / 321 Stainless Steel | AISI / ASTM A269 / EN 10216-5 |
| Corrosion Resistance | PV ≤ 1.0 μA/cm² (in potable water at 60°C) | ASTM G5 |
| Service Life | ≥ 50 years (hydronic heating application) | EN 12828 Clause 5 |
| Standards Compliance | ISO 3507, ASTM A269, EN 10217-1, EN 12828 | — |
Manufacturing Process
The production of stainless steel coil tubes for radiant heating and fan coil systems follows a multi-stage manufacturing sequence designed to ensure dimensional accuracy, metallurgical homogeneity, and surface integrity:
- Raw Material Selection: Cold-rolled stainless steel strip (coil) of the specified grade (304/316/321) is procured from certified mills, with each batch accompanied by a mill test certificate (MTC) verifying chemical composition and mechanical properties per ASTM A240 or EN 10088.
- Slitting & Leveling: The master coil is slit to the required strip width and leveled to eliminate coil set, ensuring uniform feed during tube forming.
- Tube Forming (Sewing): The flat strip is fed into a tube-forming machine where it is progressively rolled into a circular cross-section. The longitudinal seam is joined by either high-frequency (HF) induction welding or electron beam (EB) welding, depending on the required weld quality.
- Seam Finishing: The weld seam is trimmed on the inside (ID) and outside (OD) to achieve a flush surface, minimizing flow turbulence and stress concentration at the weld line. For high-pressure applications, the seam may be mechanically rolled or upset.
- Annealing & Pickling: The formed tube undergoes solution annealing (typically at 1050°C in a protective atmosphere) to relieve cold-work stresses, restore full austenitic microstructure, and maximize corrosion resistance. Subsequent pickling and passivation removes scale and oxide layers, establishing a protective chromium oxide film.
- Coiling / Spooling: The annealed and pickled tube is wound into a continuous helical coil of the specified diameter using a precision coiling machine. Tension is carefully controlled to prevent ovality or deformation.
- Quality Inspection: Each coil is subjected to hydrostatic pressure testing (per ISO 11114), dimensional measurement (OD, wall thickness, coil diameter), visual surface inspection, and, where required, eddy current testing (ECT) for weld seam integrity verification.
- Packaging & Dispatch: Coils are wrapped in protective film or paper, secured with strapping, and packed for shipment with accompanying inspection documentation.
Applications
Floor Radiant Heating Systems (地板辐射采暖)
Stainless steel coil tubes are embedded within concrete screeds or installed within dedicated channels beneath floor finishes. The helical coil configuration enables efficient, uniform heat distribution across the entire floor area while minimizing thermal bridging. Key benefits in this application include:
- Superior corrosion resistance compared to PEX or aluminum alternatives, ensuring longevity in alkaline concrete environments.
- Higher thermal conductivity than polymer-based pipes, enabling faster heat-up times and improved thermal responsiveness.
- Resistance to creep deformation under sustained thermal and mechanical loads.
- Compatibility with low-temperature hydronic heating loops (35°C – 60°C supply water temperature).
Fan Coil Unit (FCU) Heating Systems (风机盘管采暖)
In fan coil applications, stainless steel coil tubes serve as the heat exchanger element within the unit's air handling section. Hot water circulates through the coil tubes while a fan forces air across the tube surfaces (often with finned extensions), transferring heat to the conditioned space. Advantages include:
- Resistance to condensation-induced corrosion in humid operating environments.
- Ability to withstand higher operating temperatures (up to 150°C) compared to polymer alternatives.
- Compact coil geometry enabling high heat transfer area within limited installation footprints.
- Long service life with minimal maintenance requirements.
Additional Applications
- Underfloor heating in commercial and industrial facilities
- Radiant heating in greenhouses and agricultural buildings
- Hydronic heating loops in swimming pool deck heating systems
- Industrial process heat tracing
- Domestic hot water (DHW) recirculation loops
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management system and adheres to internationally recognized standards throughout the manufacturing process. The following certifications and standards apply to the Stainless Steel Coil Tube product line:
| Certification / Standard | Scope of Application |
|---|---|
| ISO 9001:2015 | Quality Management System |
| ISO 3507 | Welded stainless steel tubes and pipes — General requirements |
| ASTM A269 | Welded Austenitic Stainless Steel Tubing |
| EN 10217-1 | Welded stainless steel tubes for technical purposes — General requirements |
| EN 12828 | Heating systems in buildings — Design of water-based heating systems |
| EN 1452 | Heating systems in buildings — Design of underfloor heating systems |
| ISO 11114 | Pressure testing of welded stainless steel tubes |
| CE Marking | European Conformity for construction products |
| Mill Test Certificate (MTC) | EN 10204 Type 3.1 — Third-party verified material certification |
| SGS / Intertek Inspection | Independent third-party quality verification |
Unique Selling Points
- Extended Service Life: Stainless steel coil tubes offer a design life exceeding 50 years in hydronic heating applications, significantly outperforming polymer-based alternatives (PEX, PERT) which typically have a rated life of 25 years.
- Zero Leach Risk: Unlike copper or brass piping, austenitic stainless steel does not leach heavy metals into circulating water, making it the preferred material for potable water-compatible heating loops and food-grade facility applications.
- Superior Corrosion Resistance: The passive chromium oxide film provides self-healing corrosion protection even in the presence of chlorides, sulfates, and alkaline concrete environments, eliminating the need for cathodic protection or chemical inhibitors.
- Thermal Efficiency: The high thermal conductivity of stainless steel (16.3 W/m·K for Grade 304) enables faster heat-up times and more responsive temperature control compared to polymer pipes, directly contributing to reduced energy consumption as demonstrated in comparative studies on floor radiant heating vs. fan coil heating thermal environments.
- Continuous Coil Configuration: The absence of joints and fittings in the continuous coil layout minimizes leak risk points and reduces installation labor costs. This is particularly advantageous for large-area floor heating installations where hundreds of meters of piping are required.
- Customizable Geometry: Coil diameter, tube OD, wall thickness, and coil length can be customized to match specific project requirements, enabling optimized hydraulic design and thermal performance for each installation scenario.
- Environmental Sustainability: Stainless steel is 100% recyclable without degradation of material properties, supporting circular economy principles and reducing the environmental footprint of heating system infrastructure.
- Proven Technical Literature: The product benefits from extensive academic research and comparative analysis, including studies on indoor thermal environment quality and energy consumption patterns in floor radiant heating versus fan coil heating systems, providing an evidence-based foundation for engineering design decisions.
Technical Note: When selecting stainless steel coil tubes for radiant heating applications, engineers should consider the thermal conductivity advantage of stainless steel over polymer alternatives. While the initial material cost is higher, the total lifecycle cost (including maintenance, replacement, and energy efficiency) is often more favorable. Comparative studies referenced in the product documentation (文献学习) indicate that proper system design utilizing stainless steel coil tubes can achieve equivalent or superior thermal comfort with lower overall energy consumption compared to conventional fan coil heating systems, particularly in climates with moderate heating demands.
Ordering Information
For detailed quotations, technical drawings, and sample requests, contact Wenzhou Jixing Metal Materials Co., Ltd. with the following information:
- Required material grade (304 / 316 / 321)
- Outer diameter and wall thickness
- Coil diameter and total coil length
- Intended application (floor radiant heating / fan coil / other)
- Applicable standards and required certifications
- Quantity and delivery timeline
Product Reference: Catalog No. 1084 — Stainless Steel Coil Tube (盘管 / Coil Tube)