Question 582Steam Plants - Assistant Engineer

The correct answer is D) vibration generated by the rotor. Babbitt linings in turbine journal bearings are prone to cracking due to excessive vibration from the rotor. Vibration can cause the Babbitt material to become fatigued and crack over time, leading to bearing failure. The other answer choices are not the primary causes of Babbitt lining cracking - excessive thrust bearing wear, prolonged low-speed operation, or prolonged full-speed operation do not directly lead to the cracking of the Babbitt material in the same way that rotor vibration does. Proper balancing and alignment of the rotor is crucial to prevent this issue and ensure the longevity of the turbine journal bearings.