Specific erosion

To illustrate I return to the example of deforestation (Fig. XI. 1). There are a number of peasant plots around a lake. I shall tell three stories about different choices the peasants could be facing. In the first story, deforestation has occurred and erosion is underway. It can be stopped, however, if new trees are planted. Specifically, erosion can be stopped on an individual plot such as A if and only if trees are planted on that plot and on both the adjoining plots, B and C There are two equilibria. In one, no trees are planted and the land is lost to the lake. No individual peasant can do anything to stop it. In the other, trees are planted on all plots and erosion is halted. Given that others cooperate in reforestation, it is in the interest of each to go along. This equilibrium, although better for all than the first, may not be realized. The peasants may not know that their... 

Which type of deagglomeration prevails—erosion, firagmentation, or shattering Such knowledge can be used to select the dispersion techniques according to the product specification. Erosion, for instance, is less favourable when coarse particle fractions should be avoided. 

In extreme cases of wear, parts inside the feed zone are hard surfaced or specific erosion resistant components are used. Hard surfacing is often used on the accelerator plate, particularly on leading edges and the tips of the vanes, where most wear takes place. Some shaped accelerators have been made completely of urethane rubber. 

Later studies by Mills and Mason (1977) considered the effect of particle concentration on erosion in bends. It was found by these investigators that the effect of particle concentration on erosion is slight, however, the depth of penetration of the particles into the bend surface material increases significantly with increase in particle concentration. The specific erosion measured as the mass of material eroded from the bend per unit mass of product conveyed is related to the solids loading as... 

Further tests with various metals having different types of crystalline domains will have to be conducted before this electrolytic erosion can be definitely verified. However, past studies by various investigators tend to indicate that some erosive action other than high intensity mechanical forces are necessary to produce the high rate of deterioration and specific erosion patterns observed in hydraulic pumps and other equipment subject to severe cavitation. 

We wish to point out that Mills and Mason s time-to-failure studies reveal a dependency of bend failure upon velocity that is not the same as the dependency of specific erosion (mass or volmne of material eroded per miit mass or volume of impacting solids) upon velocity. The specific erosion typically varies only as the 2" to power of velocity. Thus Mills and Mason s results indicate that the mass eroded from the bends at the point of failure is more sensitive to velocity than that foimd in more coimnonly reported specific erosion tests. 

For settling and deposition, mechanistic theories based on discrete particle interactions have been developed and fit to experimental data. For erosion, however, mechanistic modeling is less well developed, and reliance has been placed instead on site-specific erosion studies. Site-specific studies are especially important when dealing with erosion of fine-grained sediments, which involves the disintegration of a cohesive sediment matrix into discrete suspended particles. The quantitative effects of bulk properties of sediments on erosion have been inferred from these experiments, rather than from well-established general principles. 

Estimates of the nitrogen lost in eroded soil are even more uncertain. A global soil erosion mean of 20 t/ha implies annual removal of about 30 Gt of soil, a conservative total given the high erosion rates in parts of Africa, Latin America, and Asia. A disaggregated calculation using specific erosion means for continents ended up with about 35 Gt. With at least V4 of this soil redeposited on adjacent cropland or on more distant alluvia, the loss would be 22-25 Gt/year. 

The mechanical performance of equipment is likely to deteriorate with use due to wear, corrosion, erosion, vibration, contamination and fracture, which may lead to failure. Since this would threaten a typical production objective of meeting quality and quantity specifications, maintenance engineering provide a service which helps to safely achieve the production objective. 

Most metals are subject to erosion-corrosion in some specific environment. Soft metals, such as copper and some copper-base alloys, are especially susceptible. Erosion-corrosion is accelerated by, and frequently involves, a dilute dispersion of hard particles or gas bubbles entrained in the fluid. 

Occasionally, tubes affected by erosion-corrosion or erosion processes may be confined to specific regions of the equipment. In this case, only the metallurgy of affected tubes needs to be altered. For example,... 

The inlet and exhaust systems in gas turbines are described. The inlet and exhaust systems consist of an inlet filter, silencers, ducting, and expansion joints. The design of these systems can be critical to the overall design of a gas turbine. Proper filtration is a must, otherwise problems of blade contamination and erosion ensue. The standards are minimal for specifications. 

Pipe, valve, and fittings tables must specify which size of each class of pipe is threaded, flanged, or socket welded. ANSI B31.3 provides no specific guidance except that it suggests that threads be avoided where corrosion, severe erosion, or cyclic loading is anticipated. 

Refractory quality. Refractory lining was first developed mainly for use in the iron and steel industries. It was not until the refractory manufacturers began developing products specifically designed for FCC applications that tremendous improvements in erosion and insulating properties were realized. 

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