On a methane reactor with a diameter of 29 m and a total height of 16 m, vibrational damage running into millions occurred after three years of operation. It was proved that the damage resulted from vibrations of the stirrer and the surrounding guiding pipe. The reason for the damage was an incorrect calculation of the eigenfrequency of both the stirrer and guiding pipe where the damping of the medium water as well as the effect of the constructive restraints were ignored.