Question 336Steam Plants - 1st Asst/Chief

The correct answer is D) vibration generated by the rotor. The Babbitt lining in a turbine journal bearing is susceptible to cracking due to excessive vibration from the rotor. Vibrations can cause fatigue and wear in the Babbitt lining, leading to cracking over time. This is a common failure mode for turbine bearings. The other options are incorrect because: A) low-speed operation would not directly cause Babbitt cracking, B) full-speed operation alone does not necessarily lead to Babbitt failure, and C) excessive thrust bearing wear, while problematic, does not directly impact the journal bearing Babbitt lining.