FAILURE ANALYSIS OF A STORAGE PUMP SHAFT

Abstract

The shaft is an important component in hydraulic pumps used to transmit power from electrical motor to the pump impeller. The paper presents failure analysis of a shaft, from a double suction hydraulic pump in operation of approximately 30 years, in a storage station. The shaft material is a Romanian steel, equivalent after their chemical composition and mechanical characteristics with American SAE 4340 steel for which in literature are available necessary data for failure analysis. The paper is structured in two parts: finite element analysis of the pump shaft and an analytical failure analysis for a circumferential crack type, using the failure assessment diagram (FAD). In a modeling program for stress and strain analysis the 3D shaft was loaded in torsion. The numerical results show the maximum stress zones, the stress concentration effect, and the possibility of crack occurrence. For circumferential crack type the failure assessment diagram for Mode III loading were plotted using the stress intensity factor solution. The results indicate the unsafe zone respectively the critical circumferential crack depth, where the shaft cannot operate with defects. This study presents an opportunity related to safe operation condition and remaining life estimation for a storage pump.