Destructive mechanical erosion

Erosion Erosion of metal is the mechanical destruction of a metal by abrasion or attrition caused by the flow of liquid or gas (with or without suspended solids) in no manner is this metal loss an electrochemical corrosion mechanism (see Velocity Accelerated... 

In a restricted sense, corrosion is considered toconsistof the slow chemical and electrochemical reactions between melals and their environments. From a broader point of view corrosion is the slow destruction of any material by chemical agents and electrochemical reactions. This contrasts with erosion, which is the slow destruction of materials by mechanical agents. The character of the atmospheres to which materials arc exposed may he classified as rural, urban, industrial, urban-marine, industrial-marine, marine, tropical, and tropical-marine. In addition to these general kinds of environments, corrosion is of particular concern in the environments of chemical, petrochemical, and otherprocessing and manufacturing environments where extremely corrosive substances may be encountered. 

Destructive methods involve mechanical and chemical erosion (low resolution) and ion sputtering, which is by far the most widely used of any of the depth profiling techniques. Surface atoms are progressively removed by ion bombardment and are analysed by SIMS. Alternatively, the residual surface may be analysed, generally by AES. The method is universally applicable and in principle is capable of near-atomic depth resolution. In practice, conversion of the observed signal, as a function of time, into concentration as a function of depth may not be easy for a complex system. It should be noted that the information obtained is reliable for the first layer, but for deeper layers the possibility of scrambling of the atomic layers... 

The destructive effects of soil erosion are much in evidence, but the exact mechanisms by which the soil is carried away are much less understood. Heavy rains, running water, and high wind velocities are obviously the causative agents, but when this is stated we have only touched on the more obvious factors or forces. We need to go a little deeper into the phenomena in order to understand better how these destructive forces can be counteracted. 

For the final choice of material in the case of extreme operating conditions or corrosive or erosive media, plant components that are particularly at risk are constructed from the material in question and installed in the plant, monitored during operation of the test plant, and, when the test is finished, subjected to destructive testing. These are the most meaningful tests, since the conditions are closest to those of the industrial plant. Material samples that are to be tested for stress corrosion cracking are best installed in the miniplant under mechanical stress (material samples with welded seams). 

In chemical process engineering, the most important instances of erosion are those where the fluid contains solid particles. If the fluid is a liquid, this type of wear is called hydroabrasive wear or scouring wear, and with gaseous fluids, it is called jet wear. In both types of wear, plowing is active as the essential mechanism, and with steeper angles of impact, there is an additional component causing destruction of the material. Chemical reactions can also occur. 

Simulation in this paper is mainly focused on large deformation of soil particles during destruction stage, whose seepage field was based on the simulation result by SeepAV in the reference A study of water-soil mechanics coupling mechanism and model for loess slope surface erosion on highway, and it was adjusted every ten minutes during the calculation. 

Little information exists on the environmental transport and fate of the dioxin-like-PCBs. However, the available information on the physical/chemical properties of dioxin-like PCBs, coupled with the body of information available on the widespread occurrence and persistence of PCBs in the environment, indicates that these PCBs are likely to be associated primarily with soils and sediments and to be thermally and chemically stable. Soil erosion and sediment transport in water bodies and emissions to the air (via volatilization, dust resuspension, or point source emissions) followed by atmospheric transport and deposition are believed to be the dominant transport mechanisms responsible for the widespread environmental occurrence of PCBs. Photodegradation to less chlorinated congeners followed by slow anaerobic and/or aerobic biodegradation is believed to be the principal path for destruction of PCBs. Similar situations exist for the polybrominated biphenyls (PBBs). 

Rapidly flowing liquids can mechanically wear away or corrode materials surfaces (erosion). This corrosion type is exacerbated by gas bubbles and solid particles in the liquid current (abrasion) and is usually characterised by furrow-like, smooth indentations following the direction of flow of the medium. If this surface corrosion damages or destroys protective covering layers or passivation layers, an aggressive medium can then raise levels of corrosion at these sites. This combination of mechanical surface erosion and corrosion, known as erosion corrosion, involves alternating destruction and repair processes in which the rate of repair of the protective layer is the decisive factor in material resistance. Erosion corrosion is only local in areas where the current is interrupted. 

Corrosion is a physical change in a material brought about by chemical or electrochemical action. Corrosion typically has a deteriorating or destructive effect. Note that erosion is caused by mechanical action. 

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