Corrosion average rate

A test water box was installed during a 2-week trial to monitor corrosion and fouling in a utility cooling water system. A baffle plate from the test box was removed after the test. Small, hollow incipient tubercles dotted surfaces (Fig. 3.28). Small amounts of carbonate were present atop and around each tubercle. Each tubercle capped a small depression no deeper than 0.005 in. (0.013 cm) (Fig. 3.29). This indicated local average corrosion rates were as high as 130 mihy (3.3 mm/y). 

Figure 5.2 Schematic of carbon steel corrosion rate versus exposure time in a typical oxygenated cooling water. Note how the average corrosion rate decreases with time and converges to CR at t (the minimum exposure time to get reproducible results).

Figure 5.3 As in Fig. 5.2. Note that the average corrosion rate (CR average) is always larger than the instantaneous corrosion rate (CR instantaneous) and that this difference is largest at small exposure times.

It is often found that wet corrosion attacks metals selectively as well as, or instead of, uniformly, and this can lead to component failure much more rapidly and insidiously than one might infer from average corrosion rates (Fig. 23.7). Stress and corrosion... 

Exposure time Average corrosion rate for period (mm/y) ... 

In extended exposure periods of up to 16 years in tropical sea water, Southwell and Alexander obtained an average corrosion rate for steel of 0-18 mm/y in the first year, falling off to a constant rate after 4 years at 0-025 mm/y. They also quote pitting rates as 1 mm/y in the first year falling... 

Nickel-iron alloys fully immersed in sea-water may suffer localised corrosion which can be severe under conditions where oxygen is constantly renewed at the surface and the formation of protective corrosion products is hindered, e.g. in fully-aerated flowing sea-water. In quieter, less oxygenated conditions, average corrosion rates of Fe-36Ni are low and well below those for mild steel, as exemplified in the data given in Table 3.33 . However the resistance to localised attack is not improved to the same extent. 

Fig. 3.72 Average corrosion rates of amorphous Fe-10Cr-10B-7A and Fe-10Cr-13P-7A alloys in 0 -1 N H2SO4 at 30°C, where X is one of the metalloids indicated on the abscissa ...

Fig. 3.73 Average corrosion rates of amorphous Ni-P alloys measured in 1 n HCl at 30°C. Included are average corrosion rates of crystalline nickel and nickel-base alloys ...

Maximum corrosion rates used by Du Pont for various alloys are given in Table 19.4, and most users of the test consider average corrosion rates of 0-46-0-61 mm/y and 0-76 mm/y to represent the upper limits for satisfactory resistance for wrought austenitic alloys and cast austenitic alloys, respectively. Streicher considers that if the corrosion rate for each period increases over that for the previous period the alloy is susceptible. 

Estimating an average corrosion rate, the sewer life expectancy can be calculated assuming the thickness of an allowable concrete loss. 

By considering that the average corrosion rate is influenced principally by the deposition rates of chloride and S02 and adding the effect of cleansing of the metallic surface caused by rain the following empirical model was proposed ... 

Figure 6.Average corrosion rate (g/m2a) depending on exposure condition and type of atmosphere for test stations located in the western part of the Cuban Isle...

Figure 11. Annual average corrosion rate of carbon steel at Campeche, Veracruz and Puerto Morelos as function of distance to the shoreline.

Table VII. Average corrosion rate of steel, standard deviation, average Chloride deposition rate, standard deviation and aerage TOW-... 

Discontinuities in the corrosion product film result in differential aeration cells, leading to pitting corrosion. A pitting rate of 0.25-0.38 mm/yr on bare steel and 0.5 mm/yr on steel with mill scale has been observed. Assuming the average corrosion rate of 0.125 mm/yr, the pitting factor works out to be 2 to 3 for... 

Table 4.81 Average corrosion rate of zinc coating inside concrete in marine environmentsa...

Solution Temperature (°C) Duration of test (days) Average corrosion rate (mils/yr)b ... 

The corrosion rate in aqueous systems such as cooling water may be assessed by using a side stream line containing pre-weighed metal coupons. The coupons are removed at intervals, cleaned, and re-weighed. Their weight loss, area, and time of immersion are used to calculate the average corrosion rate. 

Average corrosion rates — high-temperature sulfur corrosion in hydrogen-free environment. 21... 

Figure 1.11 Average corrosion rates of high temperature sulfur corrosion in a hydrogen free environment as compiled from 1961 A.P.I. questionnaire data from industry-desulfurizing processes and published or reported data—npndesulfurizing processes,9...

Experimental studies usually yield good agreement between the rates of corrosion obtained from polarization resistance measurements and those derived from weight-loss data, particularly if we recall that the Tafel slopes for the anodic and the cathodic processes may not be known very accurately. It cannot be overemphasized, however, that both methods yield the average rate of corrosion of the sample, which may not be the most critical aspect when localized corrosion occurs. In particular it should be noted that at the open-circuit corrosion potential, the total anodic and cathodic currents must be equal, while the local current densities on the surface can be quite different. This could be a serious problem when most of the surface acts as the cathode and small spots (e.g., pits or crevices) act as the anodic regions. The rate of anodic dissolution inside a pit can, under these circumstances, be hundreds or even thousands of times faster than the average corrosion rate obtained from micro polarization or weight-loss measurements. 

IQR=Q3-Q , where Q3 is the third quartile and Qj is the first quar-tile, when the median divides the experimental sample into two parts. Outliers were found in experiments No 1, 3 and 6 and may be rejected but we did not find enough good reason for that and they were used in calculations of the average corrosion rate value and its standard deviation. 

Table I shows the average corrosion rates observed for Cor-Ten A, zinc, and copper in 1-month, 3-month, and 1-year exposures. The corrosion rates for copper and zinc were lowest at the Washington, DC, site, while the Cor-Ten A corrosion rate was lowest at the New York site. The corrosion rates for galvanized steel and for Galvalume were less than 1 m/y in exposures up to 1 year. The corrosion rate for aluminum, as expected, was low (less than 0.1 ym/y).

Table I. Average corrosion rates at four field sites...

Bronze data is sparse. An alloy of 92% Cu exposed from 1931 1951 showed no corrosion in the desert environment and very little at the rural sites. Coincident zinc data indicates that over the 20 year period the average corrosion rates were higher for bronze at marine sites but much lower for bronze than for zinc at rural sites (Figure 2). 

City Corrosion Rate Average Corrosion Rate... 

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