Temperature critical pitting

The critical pitting temperature (CPT) is widely used as a measure of the resistance of stainless steel against pitting attack. Various methods for determination of the CPT are described here, special attention being given to the choice of test potential for the control of stainless steel quality. 

In the early 1970s, Brigham and Tozer were the first to make a systematic study, using temperature as the variable, of the connection between potential, temperature, and pitting corrosion (Fig. 12). They argued that in principle a critical pitting temperature should exist, but the data obtained showed a transition over a range of temperatures. The sharp transition was demonstrated experimentally by Quarfort in 1989. 

Figure 12. The limits of pitting as a function of potential and temperature according to the experimental results of Brigham and Tozer. CPT, critical pitting temperature.

Using this method, it takes many days to determine a single reliable CPT value. Salinas-Bravo and Newman published in 1994 what they called An alternative Method to Determine Critical Pitting Temperature of Stainless Steels in Ferric Chloride solution. ... 

Moayed, M.H., Laycock, N.J. Newman, R.C., Dependence of the critical pitting temperature on surface roughness, corrosion science, 45, pp 1203-1216, 2003. 

Crevice corrosion is, of course, dependent on temperature. No crevice corrosion is found to occur below a certain temperature called the critical crevice corrosion temperature, which is similar to the critical pitting temperature mentioned earlier. The critical crevice corrosion temperature has been used as a measure to evaluate metallic materials for the susceptibility to crevice corrosion [63],... 

Effects of Temperature on Pitting the Critical Pitting Temperature... 

Fig. 7.22 Correlation between the critical pitting temperature and critical pitting potential of 1 7 high-performance alloys. The alloys are ...

ASTM G150 is a new standard for the determination of critical pitting temperature (GPT) [4]. That standard describes a flushed port cell, in which the sample is pressed against an o-ring attached to a cell. 

G150-99, Standard test method for electrochemical critical pitting temperature of stainless steel. Annual Book of ASTM Standards, ASTM International, Philadelphia, Pa., 2000, p. 638, Vol. 3.02. 

V.M. Sahnas-Bravo, R.C. Newman, An alternative method to determine critical pitting temperature of stainless steek in ferric chloride solution, Corros. Sci. 36 (1994) 67—77. 

R. Qvarfort, Critical pitting temperature measurements of stainless steek with an improved electrochemical method, Corros. Sci. 29 (1989) 987—993. 

M.H. Moayed, R.C. Newman, Evolution of current transients and morphology of metastable and stable pitting on stainless steel near critical pitting temperature, Corros. Sci. 48 (2006) 1004—1018. 

Figure 10.4 Critical pitting temperature (CPT) and critical crevice corrosion temperature (CCT) for various stainless steels in 6% FeCb solution [10.9]. The figures below the columns show the contents of Cr, Ni and Mo, respectively (compare Tables 10.5 and 10.6).

Lower critical pitting temperature as compared to the high-molybdenum superaustenitic stainless steels such as Alloy 926 [13]. 

Pitting tendency increases with increasing temperature, with the result that the critical pitting potential decreases as temperature increases. The critical pitting temperature (CPT) is defined as the temperature below which an alloy does not... 

In addition to the critical pitting potential (CPP) (noble to which pits initiate), critical pitting temperatures (CPT) have been measured. Stable pitting occurs at temperatures above the CPT [42]. Below this temperature, stable pitting does not take place at any potential. The CPT has been explained as the... 

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