One method of measuring the abrasiveness of slurries is the Miller Test (standardised in ASTM G75-15). For example, iron oxide slurries often have a solids content of more than 50% but wear from abrasion is low because the particle sizes are small (generally less than a 10 -3mm). However, particle size and hardness play a more important role. If the fluid contains a high percentage of solids, a pump will generally experience greater wear. When the diameter of the solids exceeds the clearances within the pump, extreme wear can occur even at low concentrations. In addition to hardness, the shape and size of entrained solids are important factors in determining wear. Abrasion and pump wear becomes a serious problem with solids greater than 6 on the Mohs hardness scale. For example, aluminium has a rating of 2.5, iron 4.5 and hardened steel 8. This ranges from 1 (talc) to 10 (diamond). The hardness or scratch resistance of solids is measured using the Mohs scale. Which Solids Cause Abrasion?Ĭlearly, the harder the solid, the greater the risk of pump wear. The wear experienced by a pump is determined by the characteristics of the solids, their concentration, the viscosity of the liquid, the materials used in the construction of the pump, and the operating conditions – in particular the pump speed and pressure. The main concern regarding pump selection is identifying a system suitable for transporting the medium efficiently while minimizing pump wear, maintenance costs and downtime. For example, solids carried in water will abrade corroded metallic surfaces within a pump, exposing metal surfaces for further corrosion.Īlthough chemical processes must be taken into account, an abrasive liquid is considered to be one carrying a finely divided, refractory material such as lime-scale, clay, paint pigments, carbon, or metal fines. In many cases, both physical and chemical processes will occur simultaneously. The simplest example is that of water, which will cause iron or steel components to rust. Many pumped liquids contain solid matter either as contaminants (such as lime-scale), as components of a slurry (sewage treatment) or in a suspension for transfer or transportation purposes (mining and paint applications).Ĭhemical effects are the result of reactions between the pumped medium and the components of the pump. Physical erosion arises from the action of entrained solids carried by and within the pumped fluid. Useful information on pumping abrasive liquid What is an Abrasive Liquid?Īn abrasive liquid is one that causes increased wear to a pump either by eroding surfaces through physical force or by chemical reaction.
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