Failure analysis of a high chromium carbon steel impeller operating in phosphoric acid slurry

Abstract

The aim of this study is to identify the failure mechanism behind the damage found on the impeller of a slurry pump operating in a phosphoric acid production plant. The failure analysis was carried out first by identifying the solid particles found in the slurry, then by analysing the damaged impeller itself. The observed damage was non-uniform throughout the different regions of the impeller, especially in the back shroud. This is why a series of samples was extracted from different regions to perform hardness tests, microhardness profiles along its cross-section as well as cross-sectional microstructure examinations. Slurry erosion and cavitation erosion were the main damage sources and were particularly effective due to the uncharacteristically low surface hardness value. This was due to decarburization and the continuous network of carbides that facilitated crack propagation in the grain-carbide interface in near surface areas.