Force Analysis on Flexible Pipe Connectors of Parabolic Trough Solar Collectors

Abstract

Concentrating Solar Power (CSP) enables renewable energy with thermal storage and high grid stability. Parabolic Trough Collectors (PTCs) are an established technology in commercial solar power plants. A critical component of these systems are the flexible pipe connectors, which connect the solar field with the absorber tubes of the collectors and are exposed to high mechanical loads due to daily tracking movements and thermal expansion. Due to their function, these components are referred to as Rotation and Expansion Performing Assemblies (REPAs). REPAs are dynamic seal systems subject to wear, making their long-term durability a key reliability concern. A failure of these components can lead to leaks, potentially causing fires and unplanned power plant shutdowns. This study investigates the long-term behavior of REPAs through accelerated lifespan testing and force analyses to understand how stresses evolve and enable predictive maintenance. The two main types of REPAs, Rotary Flex Hose Assemblies (RFHA) and Ball Joint Assemblies (BJA), are tested on a specially developed test rig. A full daily tracking cycle is simulated in 2.5 minutes, resulting in 10,000 cycles over one month, equivalent to a 30-year operational lifetime. The tests are conducted under realistic conditions, with a heat transfer fluid (HTF) at 393 °C and 34 bar pressure. In the RFHA test campaign, 24,240 cycles were carried out until the test was terminated due to a leak. The analysis reveals that the forces on RFHAs remain stable throughout the lifecycle, but 1,000 cycles before a critical leak show early increases in forces and torques, with 150 cycles before the failure, significant force spikes can be observed. These findings enable the development of a condition monitoring system where force measurements and vibration analyses for both REPA types and optical angle monitoring, especially for BJAs, could serve as cost-effective monitoring methods. Only the first test series has been completed in the BJA test campaign, with 2,700 cycles performed. As no leaks or failures have occurred, no definitive conclusions regarding predictive maintenance can be drawn; however, load behavior similarities suggest that early failure indicators may emerge. In ongoing testing, these sensor approaches will be further investigated to develop a reliable and practical early fault detection strategy.