This newsletter is to inform users of problems associated with General Electric Steam Turbines that utilise 40in Titanium last stage buckets with finger dovetails.
Unit type
General Electric A10 and D11 Steam Turbines with 40in Ti L-0 buckets.
History
There have been at least six rows of 40in Ti L-0 buckets with severe cracking present on General Electric steam turbines. One case of a bucket liberation was documented in Korea, in which a total failure was the result. The OEM recommendation in TIL 1795 requires a minimum four week outage to remove and inspect the affected components. This inspection is required on all units, having greater than 650 start/stop cycles.
Advanced Turbine Support has worked with General Electric Inspection Technologies to develop and patent a probe to allow for the inspection of these components while still in the unit. This in-situ inspection only requires a 12 hour shift for each row being inspected. The photo in this newsletter highlights the area of known cracking in the transition from the top to centre portions of the dovetail fingers.
Recommendation
TIL 1795 requires inspections to be performed until the affected components can be replaced with the new acceptable design. Due to a limited supply of new components, it is suggested to inspect affected assets in-situ to allow for optimum prioritisation of component replacement and to screen units for continued operation, while minimising downtime. At this time we recommend not exceeding 100 start/stop cycles between inspections until more data can be gathered with regards to crack propagation rates.