Microstructural Degradation of Boiler Tubes Due to the Presence of Internal Oxide Layer

Overheating due to the formation of the internal oxide layer has a large influence on the life of boiler components. The aim of this study consisted in assessing the effect of the internal oxide layer on the microstructural degradation in boiler tubes. Three samples of 2.25 Cr-1Mo superheater steel tubes were used. The methodology of the study compared the microstructures of the samples received by optical, scanning electron, and transmission electron microscopy. Tensile and hardness tests were performed. At the end of the tests it was proved the deleterious effect of the internal oxide layer on the life of the component. From the measurements of the internal oxide thickness, the remaining lives of the pipes operating under creep regime were estimated with a methodology established in the literature.