Crevice corrosion propagation

S9] Kain, R. M., Electrochemical Measurement of the Crevice Corrosion Propagation Resistance of Stainless Steels Effect of Environmental Variables and Alloy Content, Materials Performance, Vol. 23, No. 2, 1984, pp. 24-30. 

Kain, R. M. and BClein, P. A., "Crevice Corrosion Propagation Studies for Alloy N06625 Remote Crevice Assembly Testing in Flowing Natural and Chlorinated Seawater," Paper 158, CORROSION/90, NACE International, Houston TX, 1990. 

The rate of crevice corrosion propagation of stainless steel alloys, such as types 304 and 316, is decreased in natural seawater, when the temperature is increased from ambient to 70°C [8,9]. The tendency for initiation of crevice corrosion is not affected by increase in temperature. The above trend may be attributed to the decreased solubility of oxygen with increased temperature and changes in the nature of the passive film which is formed. 

Since pp of the metal within the crevice is raised by the decrease in pH, the metal is active whereas the outer surface is passive, and this represents the active propagation stage of crevice corrosion there is a significant IR drop between the two zones. 

Polarization techniques have also been used to determine mechanisms by which microorganisms induce localized corrosion in the forms of pitting or crevice corrosion. In most cases itpit was determined in the presence and absence of bacteria, itpit provides data as to the tendency for pitting, but not the rate for pit propagation. Salvarezza et ah " and De Mele... 

Figure 34 The steps involved in determining the depth of container wall penetration under Canadian nuclear waste disposal conditions using data obtained in an electrochemical galvanic coupling experiment. (A) Crevice propagation rate (R cc Ic) as a function of temperature (T) (B) RCc as a function of 02 concentration [02] (C) calculated evolution of container surface temperatures and vault 02 concentrations with time in the vault (D) flux of 02 (Jo2) to the container surface as a function of time (E) predicted evolution of Rcc up to the time of repassivation (i.e., at [02]p) (F) total extent of crevice corrosion damage expressed as the total amount of 02 consumed (Q) up to the time of repassivation (G) experimentally determined maximum depth of wall penetration (Pw) as a function of 02 consumed (Q) (H) predicted maximum value of Pw up to the time of repassivation (fP)-...

The crevice corrosion mechanism is very similar to that of pitting with respect to the autocatalytic propagation. However, the causes of initiation, the morphology and the penetration of pitting are quite different from that of crevice corrosion (Figure 6.21).16... 

The increase in cathodic kinetics due to the action of biofilms on passive alloy surfaces can also increase the propagation rate of galvanic corrosion. Potentiodynamic polarization studies show that cathodic kinetics are increased during biofilm formation on passive alloy surfaces. Tests on crevice corrosion samples of passive alloys S30400 and S31600 revealed that crevice initiation times were reduced when natural marine biofilms were allowed to form on the exposed external cathode surface. (Dexter)5... 

In the experiment shown in Fig. 8.8 the propagating fronts all have their origin at the rim of the unsealed surface. Thus, also crevice corrosion beneath the insulating lacquer and the associated acidification of the chemical environment could have affected our results [24], To exclude this possibility the stainless steel sample was taken out of the electrolyte and imaged ex situ after termination of the experiment and careful removal of the insulating lacquer (see Fig. 8.9). The pits identified by arrows and numbers 1, 2, and 3 are the initial pits which released enough aggressive ions to weaken the oxide layer. It is possible that the first pits nucleated near the... 

Dissolution Reactions The spatial distribution of the metal dissolution within an occluded region defines crevice corrosion. The metal dissolution reactions are those described in Chapter 1.3. The intensity of these reactions varies, but propagation rates for active... 

The propagation of crevice corrosion, cannot he sustained at rates on the order of A cm for long periods of time. Like all corrosion, the anodic reaction, cathodic reaction, or solution properties can control the rate. For example, if the dissolution kinetics in the occluded solution are sluggish, the polarization by the cathodic reaction has a more limited effect. On the other hand, diffusion... 

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