Boiler tube failures are the major causes of forced shut downs in thermoelectric units. The thickness of the oxide layer formed on the inner wall of these tubes is the main cause of failure due to overheating. From the measured values of the inner oxide layer, it is possible to estimate the residual life of the component via correlations with parameters established in the scientific community. Cepel has been developing methodologies for estimating the residual life of boiler components for power plants, following the world trends and the needs of its customers in Brazil. With the recent acquisition of ultrasonic equipment for detecting defects and to perform thickness measurements it has become possible to perform both operations at the same time. This article presents a comparison between the results of measurements of oxide layer thickness in tubes by the non-destructive ultrasonic technique and the destructive metallographic technique associated with optical microscopy. Oxide layers with different thicknesses were used to perform the analysis. Also, the effect of surface preparation was evaluated for the reliability of results by ultrasonic testing. Finally, the study examines, in a critical way, the remaining life results obtained from the measured oxide layer thickness. To perform this analysis, two tubes with different oxide scale thicknesses were taken from a generation unit, both of them operated for the same amount of time.
Ultrasonic technique; Oxide scale thickness; Remaining life
