Restoration of metal of steam generating boiler tubes after their hydrogen cracking

Relevance. The increase in the number of damages to the screen tubes of industrial power boilers due to the development of hydrogen embrittlement. This phenomenon is a serious problem in ensuring the safe and uninterrupted operation of power plants, leads to premature failure of equipment and creates potentially dangerous situations. Aim. To develop a comprehensive heat treatment that allows healing cracks caused by hydrogen embrittlement and restoring the original ferrite-pearlite microstructure. Methods. Optical and scanning microscopy, optical emission spectral analysis of chemical composition, vacuum heating method using a mass spectrometric analyzer for hydrogen analysis, mass spectrometric analysis of metal gases. Results and conclusions. The article considers operational hydrogen embrittlement of metal of steam-generating boiler tubes (steel 20) with no external signs of methane disease (swelling, bulging). Cracks formed as a result of hydrogen attack originated and grew along grain boundaries during decarburization of the microstructure, which was accompanied by a significant decrease in cementite (pearlite grains) and an increase in the amount of ferrite grains without methane formation. Complex heat treatment was used to close hydrogen cracks in the heating surface tubes screening the boiler combustion space. The results revealed microstructural improvements such as coalescence of relatively small cracks, filling of the tips of large cracks with material, restoration of the two-phase ferrite-pearlite microstructure. The paper discusses healing mechanism and the applicability limits of the identified mode of restorative heat treatment, the level of improvement of the specified characteristics. Subsequent studies of the capabilities of various heat treatment modes should be aimed at assessing the level of restoration of the mechanical properties and performance characteristics of steam-generating tubes of power boilers. However, even now the obtained results seem promising in terms of extending the service life of the equipment.