Cavitation-damage materials

Cavitation damage is a fonn of deterioration associated with materials in rapidly moving liquid environments, due to collapse of cavities (or vapour bubbles) in the liquid at a solid-liquid interface, in the high-pressure regions of high flow. If the liquid in movement is corrosive towards the metal, the damage of the metal may be greatly increased (cavitation corrosion). 

Cavitation may be defined as the instantaneous formation and collapse of vapor bubbles in a liquid subject to rapid, intense localized pressure changes. Cavitation damage refers to the deterioration of a material resulting from its exposure to a cavitating fluid. 

The alternative option for counteracting cavitation damage is the use of a resilient material such as rubber. The mechanical forces attendant on collapse of the bubbles are absorbed by elastic deformation of the resilient material. 

Erickson, H.B., feepalr of Cavitation Damage in Concrete with Epoxy Resin Material in "Epoxies with Concrete," Publication Sp-21, American Concrete Institute, 1968, p. 67. 

Saetre [102] has reported cavitation erosion in GRP pipe bends guiding sea water at around 10ms and at pressures of less than 1 bar. Hammond et aL [103] examined the cavitation damage resistance of FRP before and after sea water immersion using a modified ASTM G32 method. A stationary specimen was placed beneath a Ti-6A1-4V tip oscillated at 20kFIz with an amplitude of 25 pm. The materials studied were ... 

Anonymous (1964). Ripken, John F. Who s who in engineering 9 1555. Lewis New York. Ripken, J.F., Killen, J.M., Crist, S.D. (1965). A new facility for evaluation of materials subject to erosion and cavitation damage. SAF Project Report 77. University of Minnesota Minneapolis. 

Cavitation corrosion is brought about by cavitation damage. It can be seen when the repeated evolution and collapse of tiny air bubbles on material surfaces occurs. Cavitation breaks the stable passive films on materials surfaces, which would easily lead to corrosirMi. 

ASTM G 32-98, Test Method for Cavitation Erosion Using Vibratory Apparatus [13], describes a standard method for performing cavitation tests. Its scope is listed as follows "This test method produces cavitation damage on the face of a specimen vibrated at high iiequency while immersed in a liquid. The vibration induces the formation and collapse of cavities in the liquid, and the coUapsirrg cavities produce the damage to and erosion (material loss) of the specimen. ... 

Cavitation per se is not a form of corrosion however, it is closely related. Cavitation is mechanical in nature. It is the mechanical removal of material resulting from the implosion of vapor bubbles in the liquid. In so doing the protective film is removed which permits corrosion to take place, primarily in the form of pitting. There is also the possibility that corrosion will promote cavitation damage by dissolving a matrix phase that holds hard particles. Once these hard particles are loosened cavitation can take place. 

Cavitation damage It is the degradation of a solid body caused by cavitation. The damage appears in the form of loss of material, change in appearance, surface deformation or changes in properties. It takes place when the velocity becomes so high that its static pressme is lower than the vapor pressure of liquid. 

Selection of materials. Materials, like 18-8 steels and titanium, are resistant to cavitation damage. 

Using materials resistant to cavitation damage (Table 4.17) [116]. 

Cavitation damage This is the damage to a material caused by cavitation. 

General Description. Erosion of a solid surface can take place in a liquid medium even without the presence of solid abrasive particles in that medium. Cavitation, one mechanism of liquid erosion, involves the formation and subsequent collapse of bubbles within the liquid. The process by which material is removed from a surface is called cavitation erosion, and the resulting damage is termed cavitation damage. The collision at high speed of liquid droplets with a solid surface results in a form of liquid erosion called liquid impingement erosion. 

Areas of struetural metals affected by cavitation can be surfaced with welding wire or strip, overlay welding, or eoating with dense high-tensUe materials that resist cavitation damage (e.g. chromium stainless steel 18-8). 

Cavitation is a particular kind of erosion-corrosion caused by the formation and collapse of vapour bubbles in a liquid contacting a metal surface. The resultant shock forces reach high levels in local areas and can tear out jagged chunks of brittle materials or deform soft metals. Where the environment is corrosive, the severity of cavitation damage increases. 

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