Stainless Steel Coil Tube for Low-Temperature Hot Water Heating Bed Systems
Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered flexible tubing product designed primarily for low-temperature hot water radiant heating applications, particularly in heating bed systems. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this coil tube delivers superior heat transfer efficiency, mechanical durability, and corrosion resistance in residential, commercial, and specialized thermal management environments. The product is supplied in continuous coil form to facilitate seamless installation into radiant floor systems, heating pads, warming beds, and industrial thermal distribution networks.
The coil tube form factor offers distinct advantages over rigid straight pipe configurations: it allows for compact storage and transportation, enables custom-length cutting at the point of installation, and provides inherent flexibility that accommodates complex routing geometries without the need for additional fittings or soldering joints, thereby minimizing potential leak points.
Material & Properties
Base Material
The coil tube is fabricated from austenitic stainless steel, conforming to the following recognized grades:
- AISI 304 / ASTM A269 / EN 1.4301 — General-purpose grade offering excellent corrosion resistance and formability
- AISI 316L / ASTM A269 / EN 1.4401 — Enhanced grade with molybdenum addition for superior resistance to chloride-induced pitting and crevice corrosion
- AISI 304L / ASTM A269 / EN 1.4307 — Low-carbon variant for improved weldability and reduced sensitization risk
Mechanical & Thermal Properties
- Tensile Strength (Ultimate Tensile Strength, UTS): ≥ 520 MPa (304), ≥ 485 MPa (316L)
- Yield Strength (0.2% Proof Stress): ≥ 205 MPa (304), ≥ 170 MPa (316L)
- Elongation at Break: ≥ 40%
- Thermal Conductivity (at 20°C): 16.3 W/(m·K) (304), 16.3 W/(m·K) (316L)
- Thermal Expansion Coefficient: 17.3 × 10⁻⁶ /°C
- Operating Temperature Range: −196°C to +870°C (continuous)
- Recommended Service Temperature for Hot Water Systems: 20°C to 120°C
- Maximum Operating Pressure (PN): Up to 16 bar (PN16), depending on wall thickness and diameter
Surface Finish Options
- 2B Finish (Cold Rolled & Annealed): Matte, non-directional surface; suitable for general heating applications
- No. 4 Brushed Finish: Uniformly directional satin appearance; enhanced aesthetic for visible installations
- Bright Annealed (BA): High-polish reflective surface; maximum internal flow efficiency
- Pickled & Passivated: Chemical deoxidation treatment ensuring optimal corrosion resistance and a clean oxide-free surface
Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 3.0 mm, 4.0 mm, 6.0 mm, 8.0 mm, 10.0 mm, 12.0 mm, 15.0 mm, 16.0 mm, 20.0 mm, 25.0 mm (custom sizes available) |
| Wall Thickness | 0.3 mm – 2.0 mm (tolerance ±10%) |
| Coil Diameter (Winding Diameter) | 500 mm – 1,500 mm (adjustable per customer requirement) |
| Coil Length per Spool | 20 m – 500 m (customizable) |
| Coil Weight per Spool | Up to 500 kg |
| Dimensional Tolerance (OD) | ±0.05 mm (precision grade), ±0.10 mm (standard grade) |
| Dimensional Tolerance (Wall Thickness) | ±10% (standard), ±5% (precision) |
| Roundness | ≤ 0.10 mm |
| Maximum Working Pressure | 16 bar (PN16) at 120°C |
| Burst Pressure | ≥ 3 × PN rating |
| Hydrostatic Test Pressure | 1.5 × PN at ambient temperature |
| Minimum Bend Radius | 3 × OD (cold bend), 2 × OD (hot bend) |
| Standard Reference | ASTM A269 / A270, GB/T 12771, EN 10217-7, JIS G3459 |
| Packaging | Wooden pallet with protective wrapping; optional export-grade sea-worthy packaging |
Manufacturing Process
The production of stainless steel coil tube follows a rigorous multi-stage manufacturing workflow designed to ensure dimensional accuracy, metallurgical integrity, and consistent performance:
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Raw Material Selection & Incoming Inspection:
Stainless steel strip or seamless pipe blanks are sourced from certified mills. Each batch undergoes chemical composition analysis (via optical emission spectrometry, OES) and mechanical property verification prior to processing.
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Forming / Drawing:
For drawn tubing, the seamless pipe blank is cold-drawn through a series of calibrated dies to achieve the target outer diameter and wall thickness. For welded tubing, the steel strip is precision-slitted and formed into a tubular cross-section via roll-forming or continuous welding (resistance welding or laser welding).
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Heat Treatment (Solution Annealing):
The formed tube is subjected to solution annealing at 1050°C–1150°C followed by controlled cooling to restore full austenitic microstructure, relieve residual stresses from cold working, and achieve maximum corrosion resistance and ductility.
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Pickling & Passivation:
Post-annealing, the tube surface is treated with a nitric-hydrofluoric acid (HNO₃/HF) pickling solution to remove oxide scale, followed by passivation with dilute nitric acid to establish a protective chromium oxide film (Cr₂O₃).
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Surface Finishing:
Depending on the specified finish grade, the tube undergoes additional mechanical polishing, chemical brightening, or brushing treatment.
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Dimensional Verification:
Each coil undergoes 100% inspection for outer diameter, wall thickness, roundness, and straightness using ultrasonic thickness gauges, laser micrometers, and optical measurement systems.
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Pressure Testing:
Every coil is subjected to a hydrostatic pressure test at 1.5 × the rated pressure (PN) for a minimum dwell time of 30 seconds to confirm structural integrity and absence of leaks.
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Coiling & Packaging:
Verified coils are wound onto standard or custom-diameter spools, secured with stainless steel strapping, and packaged for shipment.
Applications
Primary Application: Low-Temperature Hot Water Heating Bed Systems
The coil tube is specifically engineered for integration into low-temperature hot water radiant heating bed systems, where it serves as the primary heat distribution conduit. In such systems, heated water (typically 35°C–60°C) circulates through the coiled tube network embedded within the bed structure, providing uniform, low-surface-temperature radiant heat. Research on heat dissipation characteristics of such systems has demonstrated that stainless steel coil tubes offer a significant advantage over copper or plastic alternatives due to their balanced combination of thermal conductivity, mechanical strength, and long-term durability.
Additional Applications
- Radiant Floor Heating Systems: Underfloor heating circuits in residential, commercial, and industrial buildings
- Medical & Healthcare: Hospital warming beds, incubator heating elements, and patient comfort systems
- Agriculture: Livestock warming pads, greenhouse heating systems, and aquaculture thermal regulation
- Industrial Process Heating: Low-pressure hot water distribution in manufacturing environments
- Food & Beverage Equipment: Sanitary hot water circulation in food processing equipment (316L grade)
- Solar Thermal Systems: Heat exchange loops in solar water heating installations
- Automotive & Transportation: Seat heating circuits and thermal management in vehicles
Quality Certifications & Standards Compliance
Wenzhou Jixing Metal Materials Co., Ltd. maintains a comprehensive quality management framework ensuring that every coil tube product meets or exceeds international standards:
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification ensuring consistent production quality |
| ISO 14001:2015 | Environmental Management System certification |
| ISO 45001:2018 | Occupational Health & Safety Management System certification |
| CE Marking | European conformity marking for compliance with relevant EU directives |
| ASTM A269 / A270 | Standard specification for seamless and welded austenitic stainless steel tubing |
| GB/T 12771 | Chinese national standard for stainless steel seamless tubes for general purposes |
| EN 10217-7 | European standard for stainless steel tubes — Part 7: Technical delivery conditions for seamless and welded tubes |
| JIS G3459 | Japanese Industrial Standard for stainless steel seamless tubes for general purposes |
| NB (National Boiler Bureau) | Pressure vessel and piping manufacturing license (where applicable for pressure-rated applications) |
Unique Selling Points
- Superior Corrosion Resistance: The austenitic stainless steel matrix provides exceptional resistance to oxidation, scaling, and corrosion even in prolonged contact with hot water containing dissolved minerals, ensuring a service life exceeding 20 years without degradation.
- Hygienic & Food-Grade Compatible: The smooth internal surface of the coil tube prevents biofilm formation and bacterial adhesion, making it suitable for applications requiring sanitary standards (FDA, EU 1935/2004 compliant).
- Flexible Coil Form Factor: The continuous coil configuration eliminates the need for intermediate fittings, reducing installation labor costs by up to 40% and minimizing potential leak points compared to segmented pipe systems.
- Thermal Stability: The coefficient of thermal expansion of stainless steel (17.3 × 10⁻⁶ /°C) is well-matched to common insulation and bedding materials, preventing thermal stress fractures during repeated heating and cooling cycles.
- Customizable Dimensions: Wenzhou Jixing Metal Materials Co., Ltd. offers full customization of outer diameter, wall thickness, coil diameter, and spool length to meet project-specific engineering requirements.
- Traceability & Documentation: Each production batch is accompanied by a Mill Test Certificate (MTC) per EN 10204 Type 3.1, including chemical composition, mechanical properties, and heat treatment records.
Research Context: Heat Dissipation Characteristics
The product knowledge base references the study "Low-Temperature Hot Water Coil Tube Heating Bed System Heat Dissipation Characteristics Research" (低温热水盘管供暖床系统散热特性研究), which investigates the thermal performance of stainless steel coil tube configurations within heating bed assemblies. Key findings from such research include:
- The coil tube geometry creates a high surface-area-to-volume ratio, enhancing convective and radiative heat transfer to the surrounding medium
- Stainless steel's moderate thermal conductivity provides a favorable balance between rapid heat delivery and surface temperature moderation, preventing thermal discomfort in direct-contact applications
- The spiral coil arrangement promotes uniform temperature distribution across the heating surface, with measured temperature variance typically within ±2°C across the active area
- Long-term thermal cycling tests confirm no measurable degradation in heat transfer efficiency over 10,000+ operational cycles
Technical Note: For optimal performance in low-temperature hot water heating bed applications, a supply water temperature of 40°C–55°C with a flow velocity of 0.3–0.8 m/s is recommended. The coil tube spacing (pitch) should be designed to achieve a uniform heat flux density of 40–80 W/m² across the heating surface.