Erosion response

The above discussion clearly brings out certain features of the elevated temperature erosion of metallic materials. Almost all metallic materials exhibit ductile erosion response at room temperature, whereas at elevated temperature both brittle and ductile erosion responses are established [41,46,47]. The velocity exponents for metallic materials are around 2.5 during ambient temperature erosion. At elevated temperatures, the velocity exponents of metals and alloys vary over a wide range from 0.9 to more than 3.0 [41 3]. It is found that the erosion rate at room temperature increases with increase of particle size up to 50 pm, beyond which the particle size has no effect on the erosion rate. The reported literature indicates that the erosion rate increases with increase of particle size at high temperatures [39,40,44,49]. At ambient temperature, changing the particle shape from angular to spherical alters the erosion response from brittle to ductile [60,61], while at elevated temperatures, brittle to ductile response is noted irrespective of the particle shape [39,40, 47]. The particle feed rate has a negligible effect on the room temperature erosion rate [62-64]. A remarkable effect of the particle feed rate has been noted at elevated temperatures [39]. The mechanical properties of the erodent have a nominal influence on room temperature erosion behaviour [65-73]. However, at elevated temperature this aspect has yet to be explored. 

Exploration activities are potentially damaging to the environment. The cutting down of trees in preparation for an onshore seismic survey may result in severe soil erosion in years to come. Offshore, fragile ecological systems such as reefs can be permanently damaged by spills of crude or mud chemicals. Responsible companies will therefore carry out an Environmental Impact Assessment (EIA) prior to activity planning and draw up contingency plans should an accident occur. In Section 4.0 a more detailed description of health, safety and environmental considerations will be provided. 

Figures 11.11 through 11.13 illustrate the type of metal loss responsible for a dozen tube leaks over a 3-month period. Note the highly localized character of the metal loss, as well as the unusual shapes and random orientations of the eroded sites. The sites were located at the inlet end and resulted from the lodgment of debris at the mouth of the tube. Highly localized turbulence created by this debris caused the erosion.

Visually, the sites resemble mechanically induced gouges or indentions in the tube wall. However, examinations of the microstructure at these sites revealed no distortion of the metal, which would certainly occur had the indentions been mechanically induced. The erosive character of the highly localized turbulent flow was the predominant aspect responsible for the metal loss, there being little or perhaps no contribution from corrosion of the metal. 

Erosion. The abrasive is likely to be gas borne (as in catalytic cracking units), liquid borne (as in abrasive slurries), or gravity pulled (as in catalyst transfer lines). Because of the association of velocity and kinetic energy, the severity of erosion may increase as some power (usually up to the 3d) of the velocity. The angle of impingement also influences severity. At supersonic speeds, even water droplets can be seriously erosive. There is some evidence that the response of resisting metals is influenced by whether they are ductile or brittle. Probably most abrasion involved with hydrocarbon processing is of the erosive type. 

Chemical erosion can be suppressed by doping with substitutional elements such as boron. This is demonstrated in Fig. 14 [47] which shows data for undoped pyrolitic graphite and several grades of boron doped graphite. The mechanism responsible for this suppression may include the reduced chemical activity of the boronized material, as demonstrated by the increased oxidation resistance of B doped carbons [48] or the suppressed diffusion caused by the interstitial trapping at boron sites. 

There are a number of basic forms of energy loads or impingement on products to which plastics react in a manner different from other materials. These dynamic stresses include loading due to impact, impulse, puncture, frictional, hydrostatic, and erosion. They have a difference in response and degree of response to other forms of stress. Analyzing these differences provides... 

Where e is the excess acid in mol/L and ionic concentrations are expressed as mol/L. While this more precise definition may apply in some strictly chemical responses such as soil erosion, Biydges and Summers 19) have considered the more complete reactions including biological ionic utilizations and have defined an "acidifying potential" of precipitation as ... 

Cause and effect relationships associated with erosion and river quality can be clearly established for many activities. For example construction activity at a site could be clearly responsible for a resulting landslide into a river. But other activities such as those related to agriculture and forestry may not be so apparent. Spatial and temporal linkages may not be so clearly established. 

The pattern of inflammation in UC is continuous and confluent throughout the affected areas of the GI tract. The inflammation is also superficial and does not typically extend below the submucosal layer of the GI tract (Fig. 16-2). Ulceration or erosion of the GI mucosa may be present and varies with disease severity. The formation of crypt abscesses within the mucosal layers of the GI tract is characteristic of UC and may help to distinguish it from CD. Severe inflammation may also result in areas of hypertrophied GI mucosa, which may manifest as pseudopolyps within the colon.12 The inflammatory response may progress in severity, leading to mucosal friability and significant GI bleeding. 

The ET cover cannot be tested at every landfill site so it is necessary to extrapolate the results from sites of known performance to specific landfill sites. The factors that affect the hydrologic design of ET covers encompass several scientific disciplines and there are numerous interactions between factors. As a consequence, a comprehensive computer model is needed to evaluate the ET cover for a site.48 The model should effectively incorporate soil, plant, and climate variables, and include their interactions and the resultant effect on hydrology and water balance. An important function of the model is to simulate the variability of performance in response to climate variability and to evaluate cover response to extreme events. Because the expected life of the cover is decades, possibly centuries, the model should be capable of estimating long-term performance. In addition to a complete water balance, the model should be capable of estimating long-term plant biomass production, need for fertilizer, wind and water erosion, and possible loss of primary plant nutrients from the ecosystem. 

EPIC is designed to simulate relevant biophysical processes simultaneously and realistically, using readily available input data and accepted methods. It is capable of simulating plant and soil response for hundreds of years, and it is applicable to a wide range of soils, climates, and plants. EPIC also simulates soil erosion and soil chemical and physical property changes over centuries. The time limit for simulation of hydrologic parameters is restricted only by the availability of high-quality climate input data. 

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