ANALISIS PERAMBATAN RETAK STATIK AKIBAT BEBAN TEKANAN UAP PADA LAST STAGE MOVING BLADE TURBIN UAP MENGGUNAKAN FINITE ELEMENT METHOD (FEM)

Abstract

Steam turbine failure at the last stage moving blade contained in Geothermal Power Plant system occurred after operating for several years. Based on visual observation, initial crack found at trailing edge airfoil cross-section in the connection between blade and the root of moving blade. Cracks that occur due to erosion so the blade thickness will continuously reduced during the turbine operating in this condition. The failure mechanism when the crack widened because of vibrations due to turbine rotor and steam flow in a continuous loading, resulting in high cycle fatigue. This research will be discussed about static crack propagation on the last stage moving blade due to steam turbine pressure loading by giving the initial crack occurs in stress concentration areas and varied crack length. The analysis used based Finite Element Method (FEM) by giving the bending load of the steam pressure and tension loads due to centrifugal force on moving blade. Values obtained from modeling the Von-Misses stress for static failure criteria and Stress Intensity Factor (SIF) mode 1, KI as the main parameters of open crack propagation. Material used in the modeling of moving blade is AISI 403 Stainless Steel with a value of yield strength and fracture toughness respectively 675 MPa and 155 MPa √ m. From the static analysis results can be predicted that at failure zone with stress analysis with static failure criteria through the Von-Misses stress values, the blade motion will fail when the crack length reached 38 mm. Then, in static crack propagation mode 1 analysis with 2 Dimension approach predicted that crack will propagate when the crack length reached 41 mm. The difference results obtained for the geometry factor used in this study.