Abstract
Shallow cracks were infrequently detected at the surface corner of the high-medium-pressure steam turbine inner casing. The objective of this paper is to evaluate the propagation behavior of these cracks. The coefficient of heat transfer on the surface of the casing was evaluated using the equation for a cylinder with an inner column. Thermal and stress analysis during startup operation was performed using steam temperature change that was measured in a power plant. Evaluated stress distribution was used to calculate J-integral at the crack tip. These results were utilized to predict crack propagation behavior at the surface corner of the inner casing together with fatigue crack propagation data of casing material. As a result, it was predicted that more than twenty thousand cycles was necessary for the crack to propagate from 5mm depth to 10mm depth.
