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4.2. Turbine unit 6in Thermal Power Plant ′′Kakanj′′
Turbine unit 6 of 110 MW had been inspected in July 2001. Following tests were
applied for inspection of medium pressure turbine rotor:
•visual inspection,
•magnetic particles testingof blades, stiffenersand rivets, of rotor axes body, discs,
shafts and couplings,
• ultrasonic testing of shafts and coupling front side,of disc fang on regulation wheel,
of contact surfaceof discs and axes body on last four pressed discs,
• hardness measurement on the location of replication,
• testing by videoscope of central hole.
By magnetic particles testing linear indications of net type had been detected on
transition radiuses, discs 17, 18 and 19 (forgings. material ČSN 15.320.9) (200 to 300
indications), 1 to 10 mm long,in the regions 500 mm long and 40 mm wide (Figs. 9, 10).
Figure 9: Distribution of discontinuities of medium turbine rotor
After rotor machining on the turning lathe for 1.8 mm in diameter, new testing
revealed reduced number of indications for 10 to 15%. This was not accepted and the
discs were replaced by new discs.