Steady-state corrosion rate

Non-steady state corrosion rate behavior appears to be a general phenomenon and is associated with polymerization reactions. The latter, which results in formation of a film on the sorbed monolayer, provides a smaller increment of protection than does adsorption and occurs at the expense of inhibitor loss from the solution. In some cases, however, the increased protection provided by the film is substantial and merits further investigation. 

By determining the steady-state corrosion rate, we can predict the life of the battery, provided the latter is limited by the corrosion rate of the positive grid. 

The data in Fig. 2.39 indicate that the corrosion process proceeds in two stages non-stationary and stationary [114]. Bullock and Butler established that the corrosion rate is controlled by the rate of oxygen transport [122]. When the flux of oxygen to the Pb tet-PbO interface equals the flux of oxygen to the tet-Pb0 a-Pb02 interface, a steady-state corrosion rate is reached (Fig. 2.39). The thickness of the tet-PbO film will then remain constant Under these conditions, the corrosion rate will be independent of potential and relatively insensitive to temperature. 

Plot the data in Table 8.1 (the two data columns to the left) in a diagram showing steady-state corrosion rate as a function of the SO2 deposition rate, under which you assume that the lowest and the highest corrosion rate in a deposition interval correspond, respectively, to the lowest and highest deposition rate in the same interval. 

According to ISO 9224 (steady-state corrosion rate derived from long-term exposures). 

Rural atmosphere < urban atmosphere < industrial atmosphere We also observe that the average corrosion rate (given by the slope of the curves) is not constant. It is highest at the start of the experiments, then it decreases with time, finally reaching a constant value after a period of several years. The initial period, corresponding to a non-steady-state corrosion rate, shortens with increasing degree of atmospheric pollution. 

Figure 8.16 Corroded mass of a steel sample (a) exposed to a rural atmosphere (b) to an nrban atmosphere and to (c) an industrial atmosphere for a period of several years. The dashed lines indicate the time required to reach the steady-state corrosion rate [14],...

Note ST = average corrosion rate during the first ten years of exposure. LT = steady state corrosion rate for long-term exposures. 

In the near neutral pH range, corrosion rate is nonlinear with respect to time. Almost any clean carbon steel surface in contact with aerated water will corrode at a rapid rate for the first few hours. The rate decreases with time, eventually reaching a steady state. This steady state corrosion rate is the rate of practical interest in water systems. 

The degrees of protection were determined on the basis of the steady state corrosion rates obtained at the end of the test run determined from differential iron counts. 

From a practical point of view it is only necessary to assess the level of the inhibited corrosion rate. The degree of inhibition is immaterial, once one has decided that inhibition is required. In order to answer these questions, it is necessary to establish a valid steady state corrosion rate that is predictive of field conditions. This is actually a rather demanding task because... 

The following immersion test results relate to multilayer undiluted gas tungsten arc deposits. N/L represents an initial corrosion rate of greater than 50 mpy (1.27 mm/year) and a steady state corrosion rate of less than 5 mpy (0.13 mm/year). 

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