Pump impeller failures — a compendium of case studies

Abstract

This paper presents a collection of pump impeller failures that have been encountered during the consulting activities at the University of the Witwatersrand and the Plant Infrastructure and Pipelines Centre at the Council for Scienti®c and Industrial Research. 7

Novel forging technology of a magnesium alloy impeller with twisted blades of micro-thickness

“…1 shows the impeller produced by 5-axis machining center and model considered in this work. To date, the impeller has been manufactured by casting [7] or machining process [8] due to the very complicated blades. However, the mechanical properties or manufacturing cost or production rate is not sufficient for industrial requirements.…”

Wear analysis of centrifugal slurry pump impellers

“…The process of bubbles formation is exceedingly rapid and is enhanced by turbulence (which can be caused by high flow rates or surface irregularities of the components). Damage is caused when the bubbles makes contact with the surface and collapse due to a localized increase in the pressure (Van Bennekom et al , 1999), or in other word when the cavities collapse in a high – pressure zone, shocks will be generated causing localized deformation or pitting damage on the surface (Wilson et al , 1997).…”

“…The mechanical shock induced by cavitation is similar to that of liquid impingement erosion causing direct localized damage of the surface or by inducing fatigue. Cavitation damage can be divided into four stages, namely: bubbles form due to velocity or turbulence effects (pressure different), bubbles make contact with the material surface, then bubbles implode on the surface, setting up shock waves thereby damaging or removing some surface material and finally repetition of the above processes (Van Bennekom et al , 1999). Cavitation damage is often observed at the high pressure side of a pump (outlet) due to the bubbles collapsing under the influence of the higher pressure in this region (Van Bennekom et al , 1999).…”

“…General corrosion is the name given to the uniform removal of metal from the surface of a metallic component over a period of time. Since, the corrosion is uniform, damage of this type manifests itself over a period of time and is usually detected by a gradual decline in pump efficiency (Van Bennekom et al , 1999). In a corrosive slurry system, corrosion occurs when two or more electrochemical reactions take place on a wearing surface.…”

“…When the fluid velocity exceeds some critical value, the film of corrosion product on the substrate is stripped mechanically from it. Mechanical stripping of the film of corrosion products results from the transfer of kinetic energy from the fluid to the swept surface and when there are solid particles present in the fluid/slurry this can occur at much lower velocities (Van Bennekom et al , 1999).…”