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Rotors for Reaction Turbines 103

higher are not unusual. With these large rotors the welded disk
design has a very important advantage. The individual rotor compo-
nents still have moderate weights, and the relatively small cross
sections allow the material to be thoroughly forged. Thus high met-
allurgical quality is guaranteed with reduced risk of rejection. Figure
5.17 shows welding of the low-pressure rotor of a 1000 MW turbine for
a nuclear power plant, and Fig. 5.18 depicts the same rotor after weld-
ing and annealing.
Figure 5.19 shows the various stages of development of the weld
preparation during four decades. The deep weld technique adopted for
today’s rotors has been used by qualified manufacturers since about
1958 (Fig. 5.19d). Using this procedure and advanced welding meth-
ods, a rotor is produced where the stress values in the welded areas are
similar to those in the base material of the forged disks. Regular tests
on rotor welds provide a solid statistical background to the welded
rotor design. Microsections through rotor welds (Fig. 5.20) are pre-
pared to determine the quality of the weld, the extent to which the base
material has been affected by the welding procedure, and the mechan-
ical properties of the weld material.
Ultrasonic testing is now largely automated and enables flaws as
small as 1 to 2 mm to be detected. If any weld is faulty, it is cut out,
rewelded, and once again subjected to the heat treatment process.

Figure 5.17 Utility steam turbine
rotor being welded. (Asea Brown-
Boveri, Baden, Switzerland)