Crack Propagation in a 500 MW LP Turbine in Service

A 500 MW turbine generator set that operated through a rigorous two shift regime had developed a crack whilst in service. The shaft line was regularly subjected to multiple starts with oil whirl manifesting on load during certain operational conditions. First observations on generator no. 11 bearing showed an increase in the 1× component over a period of time, with changes through the critical speed during run-down triggering close monitoring. Further observations over time revealed that the Low Pressure turbine three, 1× and 2× components increased during steady state in conjunction with changes in phase angles and critical speed during transient conditions. Early indications showed that the likelihood of a crack in the main turbine shaft was high. Further observations over time revealed that the 1× and 2× steady state trends continued to increase up to the ISO limits set for the turbine generator set. The unit was shut down and qualitative inspections undertaken. The findings revealed that a crack had developed on the main rotor body in the pencil shaft.