Since the Kongsberg KG5 gas turbine was introduced into service in 1977 these engines have accumulated more than 100 000 hours of field operation. Apart from an exducer blade vibration problem which was revealed and fixed prior to field introduction, no major operational problems have been encountered.
During test and commissioning of two larger orders, three separate incidents of turbine blade failure occurred, one in March 1982 and two in February 1983. The first incident triggered a number of investigative actions and the resulting conclusion was confirmed by the last two incidents.
The present paper describes the analytical and test methods employed in order to investigate this problem. The blade natural frequencies were determined analytically through a NASTRAN analysis and experimentally with a TV-Speckle Interferometer technique.
It is shown how the influence of an interference fit or dampening joint between the two rotor wheels was actually hiding the possible resonance condition during the initial qualification tests, and how the transient movements of this joint would allow resonance to occur under certain operational conditions.
The possible corrective modifications are discussed and the selected solution is shown. The test set up and the results from the verifying strain gauge test is presented.
