Surface pits

Laser-based profilometry systems have also been adapted for unique applications in nuclear power generating plants. Applications where quantitative information with regard to surface condition for mechanisms such as surface pitting and flow-assisted corrosion are candidates for this NDT method. 

The anodic oxidation of the iron is usually localized in surface pits and crevices which allow the formation of adherent rust over the remaining surface area. Eventually the lateral extension of the anodic area undermines the rust to produce loose flakes. Moreover, once an adherent film of rust has formed, simply painting over gives but poor protection. This is due to the presence of electrolytes such as iron(II) sulfate in the film so that painting merely seals in the ingredients for anodic oxidation. It then only requites the exposure of some other portion of the surface, where cathodic reduction can take place, for rusting beneath the paint to occur. 

If the kick is gained while tripping, the only warning signal we have is an increase in fluid volume at the surface (pit gain). Once it is determined that the pressure overbalance is lost, the well must be closed as quickly as possible. The sequence of operations involved in closing the well is as follows ... 

Pitting and stress corrosion cracking, although usually associated with stainless steels in chloride media, have not been observed on recovered surgical implants. Implants often exhibit cracks and surface pitting, but these are most likely the result of improper manufacture rather than corrosion . 

Surface condition Machined, abraded and pickled surfaces all exhibit much the same behaviour in water, and after exposure of up to about one year at temperatures less than I00°C average attack measures 0 0025-0 0050mm/y. Almost always, however, corrosion of beryllium in water is accompanied by pitting and, on machined surfaces, pits of as much as 0-25mm have been observed in 0-0005M hydrogen peroxide at 85°C. Under similar conditions, annealed material has been found to be somewhat less resistant to attack than either machined or pickled surfaces. 

NOTE A wavy waterline incorporating some deposition is a good indication of surging. Where oxygen is present, metal surface pitting corrosion occurs readily at the steam-water interface or waterline. 

Electron bombardment for longer durations and higher energies led to more severe surface modifications, such as surface pitting and disordered lx reconstructed areas [17]. This means that the introduction of Ob-vacs by electron bom-... 

Fig. 7. The impingement of this jet can create a localized erosion (and even melting) responsible for surface pitting and ultrasonic cleaning (68-70). A second contribution to erosion created by cavitation involves the impact of shock waves generated by cavitational collapse. The magnitude of such shock waves can be as high as 104 atmospheres, which will easily produce plastic deformation of malleable metals (77). The relative magnitudes of these two effects depends heavily on the specific system under consideration.

Asymmetric cavitation bubble collapse in the vicinity of the solid surface leading to the formation of high speed microjets targeted at the solid surface. The microjets can enhance transport rates and also increase surface area through surface pitting. 

Squash such as courgette (zucchini) and cucumber is a chill-sensitive commodity. Exposure to chilling temperatures causes loss of membrane integrity and water redistribution from the cell to the intercellular space. Visible injury symptoms such as surface pitting and dark watery patches eventually develop. Early detection of chill injury is important in order to ascertain the necessity and correct timing of treatments such as heat shock, that can reverse the condition. However, delaying treatment to the point where visible symptoms appear is too late for reversal. 

This effluent is a mixture of produced formation water and brackian dilution water. Presently It is being evaporated in open surface pits. The cuantity of effluent will increase witn increased water cut and surface disposal by evaporation will not he feasible. 

Figure 9-11. Surface pitting of AgBr due to supersaturation of electron holes near the polarized anode [T. Grofle (1991)] and schematic mechanism of surface pitting.

Localized corrosion of passivating metals initiates at local heterogeneities, such as inclusions and second-phase precipitates as well as grain boundaries, dislocations, flaws, or sites of mechanical damage. In the case of stainless steel surfaces, pit initiation occurs at sites of MnS inclusions. Exclusion of inclusions and precipitates, nonequilibrium... 

Collapse of bubbles generated in the proximity of the soiid surface produces high-speed microjets which can raise transport rates and increase the surface area through surface pitting. 

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