Abstract
The paper presents a case history of failure of a gas turbine, which was manifested in high vibrations, loud noise, and, eventually, damaged parts, such as impellers, bearings, and probes were discovered. The turbine features a bearing with floating sleeve design, originally intended to reduce lubricant relative speeds within the bearing (that is, decreasing journal to bearing speed gradient throughout the lubricant circumferential flow, breaking the flow in two sections, at both surfaces of the floating sleeve).
In this turbine, the floating sleeve bearing was the major cause of the failure. It contributed to restraining the oil supply from the journal/thrust bearing assembly, which resulted in high amplitude lateral subsynchronous 1/3X vibrations. The event was accompanied by oil charring in the bearing and, due to overheating, melting of the brass thrust washer, which was in addition to mechanical deterioration.
In the paper, several disadvantages of a floating sleeve bearing are discussed, such as:
• Floating ring lateral instability.
• Floating ring axial instability, unusual for other types of journal bearings.
As a consequence, inevitable metal-to-metal surface friction occurs within the bearing in axial and lateral directions, thus increasing tendency to oil charring.
The major objective for using the floating sleeve, the reduction of relative speeds within the bearing, is not achieved: The sleeve does not prevent lubricant from high speed rotation and creates further potentially severe malfunctions of the turbine.
