Erosion Environments8212;This test method may be used for evaluating the erosion resistance of materials for service environments where solid surfaces are subjected to repeated impacts by liquid drops or jets. Occasionally, liquid impact tests have also been used to evaluate materials exposed to a cavitating liquid environment. The test method is not intended nor applicable for evaluating or predicting the resistance of materials against erosion due to solid particle impingement, due to “impingement corrosion” in bubbly flows, due to liquids or slurries “washing” over a surface, or due to continuous high-velocity liquid jets aimed at a surface. For background on various forms of erosion and erosion tests, see Refs (1) through (7). Ref (6) is an excellent comprehensive treatise.
Discussion of Erosion Resistance8212;Liquid impingement erosion and cavitation erosion are, broadly speaking, similar processes and the relative resistance of materials to them is similar. In both, the damage is associated with repeated, small-scale, high-intensity pressure pulses acting on the solid surface. The precise failure mechanisms in the solid have been shown to differ depending on the material, and on the detailed nature, scale, and intensity of the fluid-solid interactions (Note 1). Thus, “erosion resistance” should not be regarded as one precisely-definable property of a material, but rather as a complex of properties whose relative importance may differ depending on the variables just mentioned. (It has not yet been possible to successfully correlate erosion resistance with any independently measurable material property.) For these reasons, the consistency between relative erosion resistance as measured in different facilities or under different conditions is not very good. Differences between two materials of say 20 % or less are probably not significant: another test might well show them ranked in reverse order. For bulk materials such as metals and structural plastics, the range of erosion resistances is much greater than that of typical strength properties: On a normalized scale on which Type 316 stainless steel is given a value of unity, the most resistant materials (some Stellites and tool steels) may have values greater than 10, and the least resistant (soft aluminum, some plastics) values less than 0.1 (see Refs (7) and (8)).
Note 18212;On failure mechanisms in particular, see in Ref (6) under “The Mechanics of Liquid Impact” by W. F. Adler, “Erosion of Solid Surfaces by the Impact of Liquid Drops” by J. H. Brunton and M. C. Rochester, and “Cavitation Erosion” by C. M. Preece.
Significance of the Variation of Erosion Rate with Time:
The rate of erosion due to liquid impact or cavitation is not constant with time, but exhibits one of several “erosion rate-time patterns” discussed more fully in 10.3.3. The most common pattern consists of an “incubation p......