Cracking in dissimilar steel points of superheater pipes in TP-100 boiler

To clarify the reasons for cracking of welded joints of pipes manufactured of different steels (12KH1MF and 12KH18N10T), operating in high-pressure boiler superheaters, the, the concentration of residual hydrogen over all butt areas was determined. Alloying element disribution in the areas mentioned was analyzed. It is ascertained that heat-affected zone (HAZ) in pearlitic steel 12Kh1MF has the same composition as the basic metal. HAZ of austenitic steel 12KH18N10T is well stabilized and does not have a tendency for intercrystalline cracking under operation conditions (water vapour, 560 deg C). The assumption is made that hydrogen absorption in HAZ is realized during vapour decomposition in the points of mechanical damage of passivating film and in case of dissociation of other coolant components - hydrazine and ammonium