Probabilistic and diagnostic methods to determine the multiple failure mechanisms of HPT 1st stage marine gas turbine blade

Abstract

The failure analysis of high pressure turbine (HPT) blade belonging to 30 MW gas turbine used in marine applications is presented. Before failure, the turbine blade under evaluation was operated for about 10000 hours while its service life was expected to be around 15000 hours. The gas turbine blade was made of Nickel based super alloy and was manufactured by investment casting method. An attempt has been made to analyze the causes and modes of failure of a gas turbine blade. During operation, the turbine blade is subjected to large centrifugal forces and operated at elevated temperatures in corrosive environmental attack such as oxidation, hot corrosion and sulphidation etc. The investigation includes the activities like visual inspection, determination of material composition, microscopic examination, metallurgical analysis and Mechanical analysis. Metallurgical examination was carried out to diagnose the possible causes of blade failure of micro structural damage due to blade operation at elevated temperatures. The thermal-structural finite element analysis was performed on the turbine blades using ANSYS 14.0 software. From the results it was observed that, the temperatures are below the melting point of blade material. It was also observed that the blade might have suffered both corrosion (including HTHC & LTHC) and erosion. LTHC was prominent at the root of the blade while the regions near the tip of the blade were affected by the HTHC. It is concluded that the turbine blade failure might be caused by multiple failure mechanisms such as hot corrosion & erosion and fatigue. Hot corrosion could have been reduced the thickness of the blade material and thus weaken the blade. This reduction of the blade thickness reduces the fatigue strength which ultimately led to the failure of the turbine blade.