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Uszkodzenia rur ekranowych kotła wodnego WP 120

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Wiele kotłów wodnych eksploatowanych w ciepłowniach posiada zabudowany układ szczelny ekranów komory paleniskowej. Rury ekranowe są elementem kotła wpływającym na jego niezawodność. Z tego też względu ustalenie przyczyn zaistniałych awarii tych elementów ma szczególnie istotne znaczenie. W artykule zrelacjonowano wyniki badań materiałowych wycinków rur ekranu szczelnego z kotła wodnego WP 12[...]

Assessment of pearlite degradation in power industry cast steel after long-term exploitation DOI:10.15199/28.2017.5.2


  Changes of the metals and alloys microstructure under heat activation are caused by the tendency to reduce the free energy. McLean [1] defines this behaviour as internal instability of the system. The result of this instability are processes such as grain growth, spheroidization, particle coarsening, coalescence, discontinuous thickening etc. Knowledge of these processes from the point of view of their mechanisms and kinetics is very important in cognitive terms, but primarily in utilitarian. This is the basis for analysis of the morphological stability of microstructure. As regards the lamellar microstructure such as perlite morphological destabilization is above all the result of the spheroidization and particle coarsening. The process of pearlite spheroidization consists in a change of the shape of the cementite plates into the shape which is approximately spherical, with the preservation of the constant phase volume, while is can be accompanied by diffusion growth [2]. The first stage of the process is fragmentation, i.e. division of the plates into smaller ones. Next, gradual rounding of the plates is observed, until a semi-spherical shape is obtained. In the further stages, coarsening of the spheroidized particles may occur. The complexity of the processes taking place during spheroidization has its source in the substructure of ferrite and cementite, the geometrical characteristics of the phases (deviations from the plate morphology), the properties of the interface boundaries etc. Particle coarsening, in alloys with disperse phase, is the process of particles growth, consisting in a diffusive growth of larger particles at the expense of dissolution of the smaller in the matrix, at a constant volume fraction of the disperse phase (e.g. cementite). Particle coarsening results in increasing of mean particle size, as well as changes in the particles size distribution [3]. Many power plants use ferritic-pearlitic steels form[...]

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