The run-out report for a compressor rotor showed an almost continuous
bow between the two bearings. The maximum run-out of 0.03 mm (0.0012 i
n.) occurred at the inlet to the fourth stage impeller. The steel comp
ressor rotor was just over 3 m in length. It had been removed from ser
vice for maintenance. Each of the seven compressor stages was mounted
on the rotor at the time of the stress measurement. An evaluation of t
he residual stress at the inlet locations in the shaft using criticall
y refracted longitudinal, L-CR, ultrasonic waves showed compressive st
ress on the bowed side of the rotor, supporting the conclusion that re
sidual stress is the cause of the bow.