Failure Analysis of the L-0 Steam Turbine Blade

The main objective of the paper is to present an analysis that leads to detect the most possible cause of the L-0 blade fracture. Recently, several L-0 blades 28.5 inches long of a steam turbine have fractured. The fracture appeared 5 inches from the blade root platform, Fig. 1-“C”, causing the forced outage of the turbine. Previously, in the beginning of the last decade a finite element analysis of the blade was carried out calculating the natural frequencies and the vibratory stresses, and also, a telemetry test was carried out on these blades. These were published several years ago [1]. The analysis results gathered then were very precious to find a root cause of the present failure. To find out the causes of the blade fracture the following activities were carried out: analysis of the operational data during the last two years, analysis of the previous investigations, metallurgical investigations, identification of the mechanical and metallurgical modes of the failure. Apart from that, the turbine was overloaded by certain period of time. In this paper the results of the investigations indicated a miswelding process of the stubs as a principal cause of the blade fracture.