Probabilistic and Diagnostic methods to determine the multiple failure mechanisms of HPT 1st stage Marine gas turbine blade.

Abstract

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 examination incorporates the exercises like visual review, assurance of material structure, tiny assessment, metallurgical investigation and Mechanical examination.  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 finite element analysis software ANSYS 14.0 has been used to determine the thermal and structural behaviuor of the turbine blades. 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. The root of the blade was affected by LTHC while the areas close to the turbine blade tip were influenced by the HTHC. It is inferred that the multiple failure mechanisms such as hot corrosion & erosion and fatigue might be the reasons for the failure of turbine blade. It is predicted that the weakening of the blade was due to reduction in the thickness of blade material and is attributed to hot corrosion. The fatigue strength is reduced due to decrease in the thickness of the turbine blade which ultimately caused the failure of the turbine blade.

Keywords: Marine gas turbine blade, Super alloy, failure analysis, Metallurgical examination, Mechanical analysis.