Stainless Steel Coil Tube for Solar Collector Absorber Systems
Product Overview
The Coil Tube (Coiltube) is a precision-engineered stainless steel tubing product specifically designed for use in solar thermal collector absorber systems. As a critical heat exchanger component within solar heating applications, this coil tube is responsible for transferring thermal energy from the solar absorber surface to the circulating heat transfer fluid. The product is manufactured by Wenzhou Jixing Metal Materials Co., Ltd., a leading supplier of industrial stainless steel tubing solutions.
This product is categorized under the HVAC (Heating, Ventilation, and Air Conditioning) application domain, specifically targeting heating systems that utilize solar thermal energy collection. It is engineered to withstand prolonged exposure to ultraviolet (UV) radiation and sustained thermal cycling conditions inherent to outdoor solar collector installations.
Material & Properties
Base Material Options
- AISI 304 (UNS S30400) Bright Annealed (BA) Tube — General-purpose austenitic stainless steel offering excellent corrosion resistance, formability, and weldability. Suitable for standard solar thermal applications with moderate chloride exposure.
- AISI 316L (UNS S31603) Bright Annealed (BA) Tube — Low-carbon austenitic stainless steel with added molybdenum (2.0–3.0%) providing superior resistance to pitting and crevice corrosion. Recommended for coastal environments or applications involving high-chloride antifreeze formulations.
Key Material Properties
- Bright Annealed (BA) Finish: Provides a smooth, oxide-free surface with superior cleanliness, enabling compatibility with selective absorber coatings and minimizing internal fouling.
- Operating Temperature Range: 80–150°C (176–302°F) — designed for sustained operation within the thermal envelope of closed-loop solar thermal systems.
- Heat Transfer Fluid Compatibility: Engineered for use with ethylene glycol and propylene glycol-based antifreeze/heat transfer fluids commonly employed in solar thermal circuits.
- UV and Thermal Aging Resistance: The stainless steel substrate maintains mechanical integrity under long-term UV exposure and repeated thermal cycling (heating/cooling cycles) typical of outdoor solar installations.
- Selective Absorber Coating Compatibility: The BA surface finish ensures optimal adhesion and performance when integrated with selective absorber coatings (e.g., copper-nickel-copper, chromium oxide, or ceramic-based coatings) applied to the collector absorber plate.
Specifications
| Parameter | Specification |
|---|---|
| Product Type | Coil Tube (Coiltube) |
| Material Grade | AISI 304 / AISI 316L |
| Surface Finish | Bright Annealed (BA) |
| Application | Solar Thermal Collector Absorber Systems |
| Operating Temperature | 80–150°C (176–302°F) |
| Heat Transfer Medium | Antifreeze (Ethylene Glycol / Propylene Glycol) |
| Environmental Conditions | UV Radiation + Thermal Aging |
| Coating Compatibility | Selective Absorber Coatings (Compatible) |
| Product Category | HVAC — Heating Systems — Solar Heating |
| Manufacturer | Wenzhou Jixing Metal Materials Co., Ltd. |
Manufacturing Process
- Raw Material Selection: High-purity austenitic stainless steel strip (304 or 316L grade) sourced from certified mills, meeting ASTM A269 / ASME SA-269 standards for tubing applications.
- Precision Forming: Cold-rolling and coiling processes to achieve precise dimensional tolerances in wall thickness and outer diameter, ensuring consistent heat transfer performance.
- Bright Annealing (BA): Controlled atmosphere annealing in a protective gas environment (typically nitrogen or hydrogen) to eliminate residual stresses, refine grain structure, and produce a clean, oxide-free bright surface without pickling or passivation requirements.
- Coiling and Spooling: Precision coiling to maintain dimensional accuracy and prevent deformation, ensuring the tube can be formed into the required absorber serpentine pattern during downstream manufacturing.
- Quality Inspection: Non-destructive testing (NDT) including eddy current inspection for wall thickness verification, visual inspection of surface quality, and dimensional measurement to confirm compliance with specified tolerances.
Applications
- Solar Thermal Collector Absorber Systems: Primary application — the coil tube is brazed or soldered to the absorber plate of evacuated tube collectors or flat-plate collectors, serving as the internal heat transfer conduit for circulating antifreeze fluid.
- Domestic Solar Water Heating Systems: Used in residential and commercial solar water heaters where antifreeze fluid circulates through the absorber coils to capture solar energy.
- Commercial Solar Heating Installations: Applicable in large-scale solar heating systems for hotels, hospitals, and industrial facilities requiring reliable long-term performance.
- Hybrid Solar Heating Systems: Suitable for systems combining solar thermal energy with auxiliary heating elements for year-round operation.
Unique Selling Points
- BA Surface Superiority: The Bright Annealed finish eliminates the need for post-annealing cleaning, reducing production costs and ensuring a contamination-free surface ideal for coating adhesion.
- Dual Grade Availability: Offers both 304 and 316L options to address varying environmental and fluid compatibility requirements, providing design flexibility for engineers.
- Proven Thermal Cycling Endurance: Specifically qualified for the 80–150°C operating range with demonstrated resistance to thermal fatigue and UV degradation over extended service life.
- Selective Coating Compatibility: Engineered to work seamlessly with high-efficiency selective absorber coatings, maximizing solar energy absorption efficiency (typically >94% absorptance).
Quality Certifications
- ISO 9001 — Quality Management System certification ensuring consistent manufacturing quality.
- ASTM A269 / ASME SA-269 — Compliance with international standards for austenitic stainless steel tubing.
- EN 10216-5 — European standard for seamless and welded stainless steel tubes for general use.
- Mill Test Reports (MTR) — Full chemical composition and mechanical property documentation provided for each production batch.
- Non-Destructive Testing (NDT) — Eddy current and hydrostatic pressure testing to verify structural integrity and wall thickness uniformity.
Design Note: When specifying this coil tube for solar collector absorber applications, ensure that the selected material grade (304 or 316L) is compatible with the specific antifreeze formulation used in the system. For systems utilizing ethylene glycol-based fluids with extended outdoor exposure in coastal or industrial environments, 316L grade is strongly recommended for enhanced chloride resistance and long-term durability.