Diagnostics of steam turbine disks

Fig.1,a shows the typical field Нр distribution in SC zone detected on the disk rim of a solid-forged part of the rotor. Stepwise field Hp distribution in a SC zone characterizes a fault of the blades fit density in the disk slot. Over a long period of exploitation there is possible fatigue failure of the rim in this zone as is presented by fig.1,b. It should be noted that the field Нр distribution in SC zone presented on fig.1,a is possible also on disks of relatively new rotors. At disk rim inspection by the TSC-type instrument with recording and scanning devices the method of SC zones and Kin determination is simplified essentially.

Fig.1. The typical distribution of residual magnetization field Нр in stress concentration (SC) zone: 1 – SC zone.

Fig.2 presents the example of the testing results of the disk rim of the stage №30 of the turbine PT-60 of Dyagilevskaya heat power plant. Fig.2,a shows the field Нр distribution registered along the disk rim, on fig.2,b – the fragment of the field Нр distribution in the crack zone.

Fig.2a. The field Нр distribution along the disk rim.

Fig.2b. The fragment of the field Нр distribution in the crack zone.

Fig.2c. The location of revealed crack and SC zone – a potential crack: 1 – SC zone, potential crack; 2 – crack; 3 – examination zone.

Fig.2,c shows the revealed crack location as well as location of SC zone – a potential crack. In order to avert the mentioned damages it is recommended to examine riveted joint state by MMM during rotor repairs. Fig.2,c shows the zones recommended for intensity field Нр measurement on rivet faces and the adjacent part of disk.