2024

Resumo: The petrochemical industry heavily relies on steam reforming furnaces for large-scale hydrogen production. Centrifugally cast HP stainless-steel tubes constitute the majority of components in these furnaces, enduring temperatures ranging from 600 to 1000 ºC for extended periods. These tubes manifest distinct aging states, characterized by specific microstructural markers linked to the exposed wall temperature. Given their significant cost and importance, monitoring the service life of these tubes is crucial. The current aging state is particularly relevant due to the correlation between creep damage and advanced aging stages. Hence, this study aims to assist in assessing the remaining life of HP stainless-steel tubes by employing a portable Eddy Current Testing (ECT) inspection system, coupled with real-time Support Vector Machine (SVM) classification of aging states. Two 12.6-meter-long tubes, aged for 160,000 hours, underwent inspection using the portable ECT inspection system to evaluate the progression of aging states along their height, considering the expected vertical temperature gradient. Results underscore the efficacy of the SVM classification in identifying the various aging states present along the studied tubes, highlighting promising in situ applications.

Resumo: In this study, cellular spacing, porosity and corrosion of 1050 aluminum alloy subjected to the different levels of Gamma radiation was examined using a Gammacell Co-60 type irradiator, with activity of 16.13 TBq and dose rate around 6.98 Gy/min. Samples were extracted from an aluminum ingot, which was obtained with directional solidification apparatus. This upward directional solidification technique allowed obtaining of aluminum samples under different conditions of cooling rates. Firstly, cooling rates were determined during solidification experiment and then correlated to the cellular spacings and porosity content. The experimental results pointed out that cooling rates exerts a strong effect on the microstructural patterns and porosity formation. Laws have been determined, indicating that increase in cooling rates favored a refinement effect on as-cast microstructure and a decrease in porosity content. Furthermore, measurable effects of different levels of the Gamma radiation on the microstructure, porosity and corrosion for samples of 1050 aluminum alloy, were determined. The experimental results show that Gamma radiation has favored changes in cellular spacings, porosity formation and corrosion behavior. From this results, one can conclude that coarser microstructures, porosity formation and corrosion are favored by prolonged thermal annealing caused by temperature field generated during Gamma radiation exposure. On the other hand, even after the exposure to different levels of Gamma radiation, the microstructure and porosity observed in as-cast samples are still strongly dependent of the cooling conditions.

Resumo: The new extreme faces strain gauges (XFS) technique, when compared to the direct current potential drop (DCPD) and back face strain gauge (BFS) methods, has shown superior accuracy and reliability in studying corrosion fatigue in high pressure. The XFS method serves a dual purpose by accurately measuring the crack length and acting as a mechanical load transducer. The results indicate that all three techniques can predict the final crack length effectively. However, BFS is unsuitable for high-pressure environments, and the current DCPD method can affect the crack propagation rate. The developed XFS methodology shows excellent performance in accurately evaluating corrosion fatigue studies.

Resumo: This paper presents the evaluation of hydrogen degradation in AISI 4340 steel based on the multispectral analysis of magnetic Barkhausen noise. Previous studies using acoustic and magnetic response of the Barkhausen effect have shown a large change in the course of the phenomenon as a result of the progression of hydrogen destruction of steel, and the applied time-frequency analysis has been limited to aggregated data in a few frequency bands. Thus, due to the complex nature of changes in the Barkhausen noise course, this study uses the analysis of the multi-domain representation of the measured signals, enabling a broad characterization of various aspect of obtained signal distributions by multiple feature assessment.