Condition Monitoring of Flexible Pipe Connectors in Parabolic Trough Solar Collectors

Abstract

Parabolic Trough Collectors are the most commonly used type of Concentrating Solar Power technology, providing renewable energy. They concentrate solar radiation onto a receiver tube, from which heat is transported via a Heat Transfer Fluid to a turbine generating electricity. At the ends of the collectors, flexible pipe connectors accommodate the rotational sun-tracking movement and thermal expansion of materials. Methods for condition monitoring of these connectors are currently under research to enable preventive maintenance. Several sensors monitor Ball Joint Assemblies at a test rig during accelerated lifetime experiments. In this study, three cameras and a laser sensor are implemented to detect geometrical transformations of the connectors. Additionally, a gas concentration sensor setup measures leakage of evaporated Heat Transfer Fluid from the ball joints. The cycling phase of the experiment comprises 2,700 cycles, representing approximately seven years of plant operation. Throughout the cycling, no trend of geometric transformation is observed. The angle between the connector tubes varies from cycle to cycle around 1.5 degrees, with an estimated accuracy of 0.5 degrees. Gas concentration measured near one of the ball joints remains low, between 0 ppb to 4 ppb. However, during heat-up of the test rig and at low ambient temperatures, higher gas concentrations of 36.5 ppb and above are observed. The implemented methods did not indicate a need for maintenance, however, observed outgassing after movement stopped suggests that maintenance was necessary. Nonetheless, it remains unclear whether a complete failure could have been anticipated.