Failure analysis of a steam turbine casing

In case of turbine components the fluctuation of operational parameters are less compared to boiler components. Even then, the turbine compo¬nents often fail due to thermal fatigue, corrosion, erosion, stress corrosion cracking, fretting fatigue and corrosion fatigue. The failure analysis data of a failed component is necessaryfor safe operation of plant and for the prevention of further failure. In this paper, failure of a lower casing of high pressure turbine stage, has been analysed. The lower casing was weld repaired after detecting cracks which was found after 30 years of service. But after 5 years of operation the repaired casing showed forma¬tion of cracks in the weld region. It was shown that the cracks were origi¬nated in the weld region due to improper choice of the welding electrodes. It has been suggested that using proper weld electrodes and proper weld process the casing may operate safely for another few years.