Study onWeld Failure Mechanism of Diffuser for Long Distance Oil DeliveryPump

Abstract

Centrifugal pump is an important tool for pipeline transportation，and its safety and service life will greatly restrict the cost of pipeline transportation.The centrifugal pump is composed of internal rotor and external diffuser，among which，the external diffuser is welded from steel plates，the weld between the steel plates as the weak link of the diffuser，is a main failure part of the centrifugal pump.Therefore，in this paper，a failed diffuser of an oil transmission station was used as the raw material，scanning electron microscopy (SEM)，energy dispersive spectroscopy (EDS)，and electron back scatter diffraction (EBSD) detection for the welds of the diffuser were conducted，and the failure mechanism of the welds of the diffuser was analyzed from the perspective of microstructure，combining the three detection results and the working environment of the diffuser.Based on EBSD test results，the critical dislocation density ρGND of weld，heat affected zone and substrate was calculated and the strength and toughness of the three positions were quantitatively compared.Results showed that the heat affected zone had the highest strength and toughness，followed by the substrate，and the weld was the lowest.Defects such as slag inclusion，scratch and residual austenite created the initial condition for weld corrosion and cracking.Micro cracks rapidly expanded under the combined action of cyclic stress and corrosive medium，and eventually leading to weld failure of diffuser.The results of this study could provide some reference for the use and manufacture of centrifugal pumps.

Keywords

• long distance oil delivery pump；failure analysis；sem；eds；ebds；corrosion of metals；weld failure