Critical crevice temperature

The variability of critical crevice temperature measurement was origintdly addressed by Brigham [63], The round... 

Hibner, E. L., Modification of Critical Crevice Temperature Test Procedures for Nickel Alloys in a Ferric Chloride Environment, Materials Performance, Vol. 26, No. 3, 1987, pp. 37-40. 

Steinsmo, U., Rogne, T., Dmgli, J. A., and Gartltind P. O., High Alloyed Stainless Steels for Chlorinated Seawater Applications—Critical Crevice Temperatures, Engineering Solutions to Industrial Corrosion Problems, NACE International, Sandefjord, Norway, 1993. 

Determination of the critical pitting or critical crevice temperature is often used as an alternative to comparing the severity of attack on several samples [2f-23], Procedures for this testing are described in Methods C and D of ASTM G 48. Specimens are immersed for a given period (e.g., 72 h) at a temperature that is not expected to cause attack. Fresh specimens are then exposed at 5°C increments for the same duration until the temperature at which attack occurs (critical temperature) is determined. For many materials, the critical temperatures of replicate specimens fall within a 5°C variation. Retesting of the same specimen can affect the critical temperature [24]. Testing may be initiated just below the critical temperature, if it can be estimated. If not, this technique can require many specimens and a few weeks to find the critical temperature. 

Figure 1-11. Critical crevice temperatures of stainless steels and nickel alloys in 10% FeClj solution (Heubner,...

AOD argon-oxygen decarburization CCT critical crevice temperature... 

The alloy offers excellent resistance to pitting and crevice corrosion, having a PREN of 47.45. The critical pitting temperature for alloy 25-6Mo is 140°F (60°C) or higher while the critical crevice temperature for alloy 25-6Mo is 90°F (32.5°C). 

Performance in the area of pitting and crevice corrosion is often measured using critical pitting temperature (CPT), critical crevice temperature (CCT), and pitting resistance equivalent number (PREN). As a general rule, the higher the PREN, the better the resistance. The PREN is determined by the chromium, molybdenum, and nitrogen contents PREN=%Cr-l-3.3 (%Mo)-l-30(%N). Table 1.4 lists the PRENs for various austenitic stainless steels. 

Critical pitting temperature test Potentiostatic 200 mV (°C) Potentiostatic 350 mV (°C) Critical crevice temperature test Potentiostatic 200 mV (°C) Potentiostatic 350 mV (°C)... 

A critical crevice temperature obtained by periodically increasing the temperature by steps of 2.5 or 5°C until passivity breakdown occurs in the crevice. However, because the passive film becomes more stable widi increasing exposme time, the critical temperature may depend to some extent on the temperature selected to start the test. 

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