Erosion smooth

Laser-based profilometry systems have also been applied for nondestructive testing and measurement of both smooth-bore and rifled gun tubes. Working through Small Business Innovation Research program, the U.S. Army has developed laser-based profilometry systems for the inspection of the 120mm cannon used on the MI-Al Abrams main battle tank. Systems have also been built to measure the erosion of 25 mm and 155 mm rifled gun tubes. 

Erosion Corrosion. Erosion corrosion is the increase in the rate of metal deterioration from abrasive effects. It can be identified by grooves and rounded holes, which usually are smooth and have a directional pattern. Erosion corrosion is increased by high water velocities and suspended soHds. 

Valve Trim Various alloys are available for valve parts such as seats, disks, and stems which must retain smooth finish For successful operation. The problem in seat materials is fivefold (1) resistance to corrosion by the fluid handled and to oxidation at high temperatures, (2) resistance to erosion by suspended solids in the fluid, (3) prevention of galling (seizure at point of contact) by differences in material or hardness or Both, (4) maintenance of high strength at high temperature, and (5) avoidance of distortion. 

When very high velocities are encountered, metal loss from erosion-corrosion can be general. T ically, however, erosion-corrosion produces localized metal loss in immediate proximity to the disrupted flow. Smooth, rolling, wavelike surface contours are often produced, or distinct, horseshoe-shaped depressions (Fig. 11.1) or comet tails... 

The classic signature of erosion-corrosion is the formation of horseshoeshaped depressions, comet tads, grooves, or sand dunelike surface contours oriented along the direction of fluid flow (Figs. 11.1,11.2,11.3,11.5, and 11.8). Occasionally, erosion-corrosion will produce smooth, almost featureless, surface contours (Fig. 11.15), although even in this case oriented metal loss often exists around the perimeter of the affected region. If erosion-corrosion has been recently active, affected surfaces will be free of accumulated deposits and corrosion products. 

Metal loss of the type illustrated in Fig. 11.14 occurred on the internal surface at the midsection of the tube. Note the erosion grooves oriented in the direction of flow. Metal loss at the inlet end was much more severe and had produced a smooth, relatively featureless contour (Fig. 11.15). Eroded areas were free of corrosion products and deposits. 

Figure 11.7 illustrates the internal surface at the inlet end of the condenser. Approximately 2 in. (5 cm) of the surface is marked by mutually intersecting depressions and grooves. Areas of the internal surface downstream of this zone are smooth and covered with a thin layer of deposits. This typical case of inlet-end erosion can be eliminated by the techniques discussed earlier in this chapter under Elimination. ... 

Exposed ends of the bolts and nuts have also suffered severe localized deterioration, resulting in smooth surface contours. Adjacent areas of each component show no deterioration. Erosion resulting from the impingement of high-velocity slab-cooling spray is the predominant factor in this metal loss. 

Metal loss in these areas had produced a smooth surface, free of deposits and corrosion products. The rest of the internal surface was covered by a thin, uniform layer of soft, black corrosion product. The graphitically corroded surfaces of the pump casing provided soft, friable corrosion products that were relatively easily dislodged by the abrasive effects of high-velocity or turbulent water (erosion-corrosion). 

Attack by erosion-corrosion may be uniform or localised, and in the case of the latter it is characterised by the formation of grooves or rounded depressions that are smooth and free from corrosion products. Frequently the areas of localised attack follow a pattern that is indicative of the direction of movement of the metal or the environment (Fig. 1.61). 

Most mass transfer data is for smooth surfaces . It is well established that as a surface suffers erosion corrosion it will roughen and the mass transfer rate will increase. It has been suggested that when this occurs the roughness becomes more important than the original shape in controlling the mass transfer. 

The life of equipment subjected to corrosive environments can be increased by proper attention to design details. Equipment should be designed to drain freely and completely. The internal surfaces should be smooth and free from crevasses where corrosion products and other solids can accumulate. Butt joints should be used in preference to lap joints. The use of dissimilar metals in contact should be avoided, or care taken to ensure that they are effectively insulated to avoid galvanic corrosion. Fluid velocities and turbulence should be high enough to avoid the deposition of solids, but not so high as to cause erosion-corrosion. 

Gold sulphide had a featureless non-crystalline plain surface with very sharp and smooth edges of the dried mass. However, the smoothness of the surface was destroyed completely with blisters appearing as a result of cavitation, after 30 min of ultrasound irradiation. A closer look at the surface at x 7,500 magnification reveals extensive surface erosion as a result of the micro-jets streaming. 

The cause of ACS in more than 90% of patients is rapture, Assuring, or erosion of an unstable atheromatous plaque. Plaques most susceptible to rupture have an eccentric shape, thin fibrous cap, large fatty core, high content of inflammatory cells such as macrophages and lymphocytes, limited amounts of smooth muscle, and significant compensatory enlargement. 

Between 80 Ma and 50 Ma, the Namib rocks were eroded to a smooth peneplain (the Namib Unconformity). Namib Group Tertiary and Quaternary sedimentary debris was deposited in east-west to southwest trending paleochannels incised into Karibib marbles and schists on that Cretaceous age unconformity. From mid Tertiary to present, the central Namib region has maintained profoundly arid climatic conditions for the last 50 or more million years. Uplift initiated the post African erosion surface that filled valleys and channels with poorly sorted angular... 

Prominent changes in the cells have been revealed after 30 min of irradiation. Besides the oedema of the cytoplasm and nuclei swelUng, crater-like erosions appeared on the luminal surface of the endotheUocytes (Fig. 30.1b). Intercellular spaces became wider, and fibrin thread and single erythrocytes were found in these spaces. In some zones the longitudinal folds of the intima were smoothed, but the endothelial layer remained intact. Such zones may correspond to the sub-endothelial oedema. These changes remained for 6 h after kradiation. One day later the microrelief of the aorta s intima returned to normal. 

An eroded steam nozzle shows no obvious sign of damage. The erosion is quite uniform and the nozzle interior is smooth. The inner diameter of the jet must be checked carefully with a micrometer. Growth in diameter of just 5 to 10 percent is significant. The nozzle is intended to be replaced periodically, much like the wear ring on a centrifugal pump. 

Runoff of pesticides can be increased if sediment in the water reduces infiltration, indicating another important reason to prevent soil erosion. With 1 mg/L of herbicide applied in simulated runoff to smooth bromegrass filter strips, atrazine, cyanazine, and metolachlor losses were reduced 83-85% with no sediment present, but only 53-58% with 10 000 mg/L sediment (Misra, 1994). 

Delayed endothelial healing. In case 1, a smooth, white lesion was detected at three and nine months. In case 2, erosion with a superficial thrombus was seen at three months. At nine months, the erosion had disappeared, although an uncovered stent was observed. In case 3, severe, circumferential erosion with superficial thrombus was detected at three months, with erosion still evident but partly improved at nine months. These results suggest that the healing process was not completed nine months after brachytherapy. Source From Ref. 73. 

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