Pitting depth

Evaluation of attack if other than general, such as crevice corrosion under suppoi t rod, pit depth and distribution, and results of microscopic examination or bend tests... 

Fig. 6. Penetration of a liquid into (a) a cylindrical and (b) a re-entrant pit (after de Bruyne [41 ]). Pit depth 100 pm, diameter at mouth 1 pm, re-entrant angle 45°.

Finley, H. F., An Extreme-value Statistical Analysis of Maximum Pit Depths and Time to First Perforation , Corrosion, 23, 83 (1%7)... 

Stainless steels have not been widely used in applications where they are buried in soil, but some applications have involved underground service. Various stainless steels from the 13% Cr to the molybdenum-bearing austenitic types were included in the comprehensive series of tests in a variety of soils reported by Romanoff . High-chloride poorly-aerated soils proved most aggressive, but even here the austenitic types proved superior to the other metals commonly used unprotected. Of special interest is the fact that though corrosion was by pitting there was little or no increase in pit depth after the first few years. 

In atmospheric exposure 18% Ni maraging steel corrodes in a uniform manner , and becomes completely rust covered. Pit depths tend to be more shallow than for the low-alloy high-strength steels. Atmospheric corrosion rates in industrial (Bayonne, New Jersey) and marine (Kute Beach, North Carolina) atmospheres are compared with those for low-alloy steel in Figs. 3.29, 3.30 and 3.31. The corrosion rates drop substantially after the first year or two and in all cases the rates for maraging steel are about half the corrosion rate for HY80 and AISI 4340 steels. 

Alloy composition n t. loss Range of pit depth (mm) Wt. loss Range of pit depth (mm) ... 

A portion of the original surface should be protected so as to provide a datum line for the measurement of pit depths. 

For the profile (length from 0.5 to 3 km, point interval of 50 m) sampling, both small hand-dug test pits (depth about 50 cm) and percussion drilling (sampling depth 1 to 1.5 m) have been used. Measurements were made using the ScanMobile system which is a moving... 

Young et al. (2002a) showed that ultraviolet laser ablation combined with MC-ICPMS (LA-MC-ICPMS) can offer advantages over other methods of spatially resolved Mg isotopic analysis of meteorite materials. They collected data for chondrules and a CAI from the Allende meteorite. Each datum in that study represents approximately 2.8 pg of material (based on a laser spot diameter of 100 pm and laser pit depth of 30 pm depths are uncertain to + 20%). 

Figure 19,23 Critical pit depth, D, which will just allow the unlimited growth of a...

Figure 22 Maximum pitting depth as a function of time for (a) AA3003-H14 and (b) AA6061-T6 exposed to natural seawater at Halifax, Nova Scotia. The pit penetration rate can be estimated from the slope of the line. While the initial pit penetration rate is rapid, it decreases substantially after the first year. (Data from H. P. Godard et al., The Corrosion of Light Metals, John Wiley, New York (1967).

Maximum Pitting Depth (mils) S Maximum Pitting Depth (mils)... 

A source of doubt in such analyses is whether the depths of the pits grown electrochemically are representative of those expected under natural conditions and therefore appropriate to extrapolate to longer times in predictive models. The data shown for pitting of carbon steel, sketched in Fig. 28, show that they are not. Clearly, growth is accelerated under potentiostatic electrochemical conditions, and the extrapolation of pit depths seriously overestimates the predicted pit depths after long exposure times. This is not surprising, since the use of a... 

Figure 28 Illustration of the problems encountered when trying to produce a database of pit depths in an accelerated electrochemical experiment. The shaded area shows the range of pit depths on naturally corroded steel specimens in a range of soil types. (1) Predicted pit depth evolution based on potentiostatically grown pits. (Data schematically reproduced from Ref. 50.)...

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