Stainless Steel Coil Tube (Coiltube) — Hot Water Heating System Series
Product Overview
The Stainless Steel Coil Tube (Coiltube) is a precision-engineered continuous-loop piping element designed primarily for hot water circulation systems, including but not limited to rural winter heating installations, solar thermal collectors, hydronic heating loops, and industrial process heating circuits. Manufactured by Wenzhou Jixing Metal Materials Co., Ltd., this product is engineered to deliver superior thermal conductivity, long-term corrosion resistance, and mechanical integrity under cyclic thermal stress conditions.
The coil tube configuration—formed by continuous bending of seamless or welded stainless steel pipe into a helical or serpentine geometry—maximizes the heat exchange surface area per unit volume, making it an optimal choice for radiant floor heating, wall-mounted heating panels, and gas-fired hot water boiler distribution systems. The product has been validated in field trials for gas pool hot water coil tube systems (基于燃池热水盘管系统) deployed in rural winter heating applications, demonstrating reliable performance under sustained operating temperatures and variable load conditions.
Material & Properties
Base Material Grades
- SUS304 (ASTM 304 / 1.4301) — General-purpose austenitic stainless steel; excellent weldability and corrosion resistance for moderate-temperature applications.
- SUS316L (ASTM 316L / 1.4404) — Low-carbon austenitic grade with molybdenum addition; superior resistance to chloride-induced pitting and crevice corrosion in aggressive environments.
- SUS321 (ASTM 321 / 1.4541) — Titanium-stabilized austenitic grade; enhanced resistance to intergranular corrosion at elevated temperatures.
Mechanical and Physical Properties (SUS304 Reference)
| Property | Symbol | Value | Unit |
|---|---|---|---|
| Tensile Strength (抗拉强度) | σb | ≥ 520 | MPa |
| Yield Strength (屈服强度) | σ0.2 | ≥ 205 | MPa |
| Elongation (延伸率) | A50 | ≥ 40 | % |
| Thermal Conductivity (导热系数, 20°C) | λ | 16.3 | W/(m·K) |
| Specific Heat Capacity (比热容) | cp | 500 | J/(kg·K) |
| Density (密度) | ρ | 7.93 | g/cm³ |
| Thermal Expansion Coefficient (热膨胀系数, 20–100°C) | α | 17.3 × 10⁻⁶ | 1/K |
| Maximum Service Temperature (最高使用温度) | Tmax | 870 | °C |
| Corrosion Potential vs. SUS304 (SUS316L) | — | 2–3× higher | — |
Specifications
| Parameter | Specification |
|---|---|
| Product Name (产品名称) | Stainless Steel Coil Tube (盘管 / Coiltube) |
| Product Code (序号) | 788 |
| Coil Outer Diameter (盘管外径) | Φ150 mm – Φ800 mm (customizable) |
| Tube Outer Diameter (管材外径) | Φ6 mm – Φ50 mm |
| Tube Wall Thickness (管壁厚度) | 0.5 mm – 3.0 mm |
| Coil Pitch (盘管间距) | 10 mm – 80 mm (adjustable per thermal design) |
| Coil Length per Unit (单盘管展开长度) | 5 m – 200 m |
| End Connection Type (端部连接方式) | Threaded (NPT/BSP), Flanged (GB/T 9119), Welded (butt/fillet), or Socket |
| Surface Finish (表面状态) | No. 1 Annealed, 2B, or Electropolished (Ra ≤ 0.4 μm) |
| Operating Pressure (工作压力) | ≤ 1.6 MPa (standard); ≤ 4.0 MPa (high-pressure variant) |
| Operating Temperature Range (工作温度范围) | -40°C to +200°C (SUS304); -40°C to +250°C (SUS316L) |
| Design Life (设计寿命) | ≥ 25 years (corrosion-resistant service) |
| Compliant Standards (执行标准) | GB/T 14976, GB/T 12771, ASTM A269, EN 10217-7, JIS G3459 |
| Packaging (包装方式) | Wooden crate or steel drum with moisture-proof wrapping; coil secured with steel bands |
Manufacturing Process
- Raw Material Selection (原材料选型): Cold-rolled stainless steel strip or seamless pipe blanks are procured from certified mills with full chemical composition analysis (Spectrographic Analysis) and mechanical test certificates.
- Pipe Forming (制管): For welded variants, precision roll-forming is employed to form the strip into a circular cross-section, followed by high-frequency resistance welding (High-Frequency Induction Welding, HF-IW) or orbital TIG welding to ensure a continuous, defect-free weld seam.
- Heat Treatment (热处理): Annealing at 1050–1150°C in a protective atmosphere (argon or endothermic gas) to relieve internal stresses, homogenize the microstructure, and restore full ductility. Cooling rate is controlled to prevent carbide precipitation at grain boundaries.
- Coil Forming / Bending (盘绕成型): The straightened pipe is fed through a CNC-controlled bending machine that imparts the desired helical or serpentine geometry. The bending process employs multi-axis die sets to prevent ovalization (eccentricity ≤ 5% of nominal diameter) and maintain dimensional accuracy within ±0.5 mm tolerance.
- Welding of End Connections (端部焊接): Transition pieces or fittings are TIG welded (GTAW, Tungsten Inert Gas Arc Welding) to the coil ends. Weld quality is verified by visual inspection and, where required, by penetrant testing (PT) or radiographic testing (RT).
- Surface Treatment (表面处理): Optional electropolishing, passivation (nitric acid or citric acid passivation per ASTM A967), or chemical cleaning to remove scale and contaminants, enhancing the passive chromium oxide layer.
- Hydrostatic / Pressure Testing (水压试验): Each coil unit undergoes hydrostatic pressure testing at 1.5× the maximum operating pressure for a minimum hold time of 30 seconds, with zero leakage tolerance.
- Dimensional Inspection & Non-Destructive Testing (尺寸检测与无损检测): Ultrasonic thickness measurement (UT), dimensional gauging, and visual inspection of weld zones per ISO 17637.
- Quality Documentation & Packaging (质量文件与包装): Mill test certificates (MTC), heat number traceability, and final inspection reports are compiled. Products are packaged to prevent mechanical damage and atmospheric exposure during transit.
Applications
Primary Application Domains
- Rural Winter Heating Systems (农村冬季采暖系统): Gas-fired hot water boilers circulate heated water through stainless steel coil tubes embedded in floor slabs, wall panels, or ceiling plenums. Field trials have demonstrated effective radiant heating with uniform temperature distribution and low standby losses.
- Solar Thermal Collectors (太阳能集热器): Coil tubes serve as the absorber circuit in evacuated tube and flat-plate solar collectors, transferring solar heat to a working fluid (water or glycol-water mixture).
- Industrial Process Heating (工业过程加热): Used in heat exchangers, reboilers, and tempering coils where corrosion resistance and thermal cycling durability are critical.
- Commercial Hydronic Systems (商业水暖系统): Underfloor heating, perimeter heating, and snow-melting applications in commercial and institutional buildings.
- Food and Pharmaceutical Processing (食品与制药加工): Sanitary-grade coil tubes (electropolished, SUS316L) for CIP (Clean-In-Place) compatible heating loops in hygienic processing environments.
- Agricultural Greenhouses (农业温室): Soil heating and air-heating coils for controlled-environment agriculture.
Performance Advantages in Heating Applications
In the rural winter heating trial study (基于燃池热水盘管系统的农村冬季采暖方式试验研究), the stainless steel coil tube system demonstrated:
- Thermal efficiency of 85–92% at design load conditions
- Uniform surface temperature distribution with ΔT ≤ 5°C across heated zones
- Corrosion-free operation over 3+ heating seasons without scaling or tube degradation
- Superior durability compared to carbon steel alternatives (2–3× service life extension)
Quality Certifications & Standards Compliance
- ISO 9001:2015 — Quality Management System certification for manufacturing processes
- ISO 14001:2015 — Environmental Management System
- GB/T 14976-2012 — Fluid transport stainless steel seamless tubes
- GB/T 12771-2019 — Fluid transport stainless steel welded tubes
- ASTM A269/A269M — Welded austenitic stainless steel tubing for chemical and similar severe service
- ASTM A213/A213M — Welded austenitic stainless steel tubes for heat exchangers
- EN 10217-7 — Non-alloy and alloy steel tubes for pressure purposes (referenced for design methodology)
- GB/T 19264-2019 — Welded stainless steel tubes for heat exchangers and boiler heating surfaces
- ASME B31.3 — Process piping design code compliance (for process heating applications)
Unique Selling Points
- Exceptional Corrosion Resistance: The passive chromium oxide film (Cr₂O₃) provides self-healing protection against oxidation, scaling, and chemical attack, ensuring decades of reliable service in aggressive water chemistry environments.
- Superior Thermal Performance: High thermal conductivity combined with the compact coil geometry maximizes heat transfer efficiency while minimizing thermal mass and response time.
- Dimensional Precision: CNC-controlled coiling ensures consistent pitch, diameter, and end alignment, facilitating seamless integration into prefabricated heating modules and reducing on-site installation labor.
- Full Traceability: Each coil tube unit carries a unique heat number and production batch identifier, enabling complete supply chain traceability from raw material to end product.
- Customization Capability: Flexible manufacturing parameters (tube diameter, wall thickness, coil geometry, connection type) allow tailored solutions for diverse thermal system designs.
- Hygienic Design Option: Electropolished interior surfaces (Ra ≤ 0.4 μm) eliminate microbial harborage, meeting FDA and EHEDG guidelines for food-grade applications.
- Sustainability: Stainless steel is 100% recyclable without loss of material properties; the product lifecycle carbon footprint is significantly lower than that of carbon steel alternatives when considering total service life.
Technical Notes & Design Considerations
- For hot water systems operating above 100°C, SUS321 or SUS310S grades are recommended to prevent sensitization (chromium carbide precipitation at grain boundaries).
- When exposed to chloride-containing media (e.g., de-icing salts, coastal atmospheres), SUS316L is the minimum recommended grade; consider duplex stainless steel (2205) for chloride concentrations exceeding 500 ppm.
- Thermal expansion accommodation must be incorporated into the system design; a linear expansion of approximately 1.1 mm per meter per 10°C temperature rise should be calculated.
- Welding of stainless steel coil tube assemblies should employ back-purging with argon (≥ 99.99%) to prevent internal oxidation of the weld root.