Gouging

In summary, it has become quite clear that contact between two surfaces is limited to a small fraction of the apparent area, and, as one consequence of this, rather high local temperatures can develop during rubbing. Another consequence, discussed in more detail later, is that there are also rather high local pressures. Finally, there is direct evidence [7,8] that the two surfaces do not remain intact when sliding past each other. Microscopic examination of the track left by the slider shows gouges and irregular pits left in the softer metal... 

Caustic corrosion (gouging) occurs when caustic is concentrated and dissolves the protective magnetite (Fe O layer. Iron, in contact with the boiler water, forms magnetite and the protective layer is continuously restored. However, as long as a high caustic concentration exists, the magnetite is constantiy dissolved, causing a loss of base metal and eventual failure (Fig. 4). 

Fig. 4. Caustic gouging caused failure of this boiler tube.

Porous metal oxide deposits also permit the development of high boiler water concentrations. Water flows into the deposit and heat appHed to the tube causes the water to evaporate, leaving a concentrated solution. Again, corrosion may occur. Caustic attack creates irregular patterns, often referred to as gouges. Deposition may or may not be found in the affected area. 

In wet ball milling the grinding rate increases with sohds content up to 70 wt % (35 vol%), as Fig. 20-33 shows, due to pulp rheology. Examination of gouge marks indicated that most breakage was by impact of balls on particles rather than by abrasion. 

Figure 11.7 Metal loss on the internal surface at an inlet end (equally spaced circumferential gouges near the tube end were created during tube removal).

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. 

Severe, highly localized gouging of the internal surface of the type shown in Fig. 11.21 perforated a total of 100 tubes over a 4-year period. Visual inspections disclosed numerous additional gouged but, as yet, imperforated tubes. The gouging was confined to the first 8 in. (20 cm) of the inlet end of the tubes. 

The gouge sites had a bright metallic luster and various shapes (Figs. 11.22 and 11.23). Microstructural examinations of the gouged regions revealed that plastic deformation of the metal had not occurred. 

The rust-colored concrete chips shown in Fig. 11.24 were removed from the tube ends. Inspection of the water box revealed large quantities of debris adhering to the tube sheet. The gouging was caused by the lodgement of this hard debris at tbe inlet end of the tubes. Intense turbulence by the lodged debris was sufficient to cause highly localized erosion. 

Although not illustrated in Figs. 11.21 through 11.23, each erosion site was composed of two or more gouged areas. This is characteristic of erosion due to lodged debris since at least two points of contact with the tube wall are required for a particle to remain in place. 

Figure 11.22 Close-up of perforated gouge shown in Fig. 11.21. (Magnification 7.5x.)...

Gouges. Gouges are usually elongated grooves in the tube wall caused by mechanical removal of metal during tube fabrication. 

The various forms of defects on the internal surface of this tube could be overlooked in a casual, visual examination. Closer observation, however, would disclose several forms of discontinuities, such as shallow gouges (Fig. 14.7) and particles of smeared metal (Fig. 14.8). These features are prominent in a distinct longitudinal zone (Fig. 14.9). 

Figure 14.7 Shallow, aligned gouges on the internal surface. (Magnification 6.5x.)...

Gouging. Whenever a velocity over about 1.6 km/s is anticipated, the projectile must be designed to prevent any contact of metal projectile components with the gun barrel. Only plastic components of the projectile should touch the barrel. Metal sliding against metal at velocities over 1.6 km/s can result in serious or even disastrous gouging of the gun barrel in a single shot (Barker et al., 1989). 

Often contain defects (hydrogen cracks, slag inclusions, stop-start marks). Help initiate fatigue cracks. Critical welds must be tested non-destructively and defects must be gouged out. 

Along with the sounds, evidence and signs of cavitation, there is a broad range of other information and signals available to the maintenance mechanic. Almost all mechanics have seen the gouge and scratch marks, and signs of heat on the pump when disassembled in the shop. Sadly, most mechanics are never trained to interpret these marks. 

You might sec gouge or wear marks all around the circumferences of close tolerances on the rotary elements, and a corresponding wear spot at approximately 60° from the cutwater on the stationary elements. 

You may see the same evidenee all around the eireumferenee of the elose toleranee rotary elements, with gouge or wear spots on the stationary elements at about 240° from the pump cutwater. 

If you see the same evidence, gouge and wear marks around the circumference of close tolerance rotary elements, and spots or arcs on the close tolerance stationary elements at about 180° from the cutwater, or straight down ... 

You may even see the same evidence of gouges and wear around the cireumferenee of strict tolerance rotary elements, leaving a corresponding spot on the stationary elements at any other point around the volute circle of the pump. 

Next we ll discuss evidence marks and prints that are different, but to the untrained eye, they may appear the same. You may see a spot or arc of wear and gouging on the rotary elements, and a eireumferential wear circle on the bore of the close tolerance stationary elements. This is a maintenanee-indueed problem, d his is the sign of a physically bent shaft, or a shaft that is not round, or a dynamic imbalance in the shaff-sleeve-impeller assembly. The solution is to put the shaft on a lathe or dynamic balancer, verify its condition, and correct before the next installation. 

The next condition and physical evidence we ll mention is rare, but we need to cover it in ease you should ever see it. You might see scratch and gouge marks all around the cireumferenee of strict tolerance rotary element ODs, and stationary element bores alike. This condition and marks is evidence of a Lack of Control . It could be from any of the... 

Avoid rust, scratches, gouges, creases, indentations, hammer blows and dirt. 

Abrasive wear can be classified into three types. Gouging abrasion is a high stress phenomenon that is likely to be accomplished by high comprehensive stress and impact. Grinding abrasion is a high stress abrasion that pulverizes fragments of the abrasive that become sandwiched between metal faces. And erosion is a low-stress scratching abrasion. 

The Heeva brasiliensis may be tapped for latex by gouging the bark with a tapping knife. The composition of the Hevea latex varies quite widely but the following may be considered to be a typical composition ... 

The investigation following the accident showed that the pipeline rupture was due to stresses induced in, and possibly by damage to, the pipeline resulting from its repositioning three months before. This work had occurred in conjunction with road work on the highway adjacent to the accident site. The pipeline had been dented and gouged. 

Besteck, n. ease, set (of instruments) cover (at table), tableware, bestecken,r.t.stick (with) plant (with), Besteg, m. (Mining) gouge, flucan. bestehen, c.t, consist exist persist, insist.— v.r. resist encounter pass. — —aus, consist of. 

---