Degradation of Steel 20 during Cathodic Polarization and Hydrogen Embrittlement of the Radiant Section of Steam Boiler Tubes during Operations

The properties in new tubes, tubes artificially saturated with hydrogen, and the radiant section of boiler tubes after long operations are studied. All samples are made of steel 20 according to the same technical conditions and subjected to identical heat treatment modes. The process of embrittlement is evaluated by detecting changes in the microstructural structure and in mechanical properties of the steel revealing the mechanism of hydrogen attack. Artificially hydrogen-saturated tubes do not exhibit decarbonization typical of naturally saturated tubes. These samples also exhibit a decrease in the limit of the rupture strength. Different types of fracturing are observed in tube samples: tubes having artificial hydrogen saturation show transcrystalline fracturing; intercrystalline fractures develop in the naturally saturated samples. At the same time, the fracture parameters (featuring hydrogen embrittlement areas) and the average concentrations of accumulated hydrogen in artificially hydrogen charged tubes and in tubes charged with hydrogen during operations are identical. Significant differences in the physical and mechanical properties are observed in all three types of tubes, making it impossible to apply the results obtained in model samples artificially saturated with hydrogen to real operating components.