Crevice corrosion evaluation

Evaluation of Results After the specimens have been reweighed, they should be examined carefully. LocaHzed attack such as pits, crevice corrosion, stress-acceleratedcorrosion, crackiug, or intergranular corrosion should be measured for depth and area affected. 

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... 

The above considerations show that although considerable advances have been made in developing laboratory controlled potential tests for evaluating crevice corrosion and pitting, the results must be interpreted with caution. 

Recommended practice for examination and evaluation of pitting corrosion Test method for determining susceptibility to stress corrosion cracking of high-strength aluminium alloy products Test method for pitting and crevice corrosion resistance of stainless steels and related alloys by the use of ferric chloride solution Recommended practice for preparation and use of direct tension stress corrosion test specimens... 

For detection of more localized corrosion, such as crevice corrosion or SCC, other ultrasonic inspection techniques may be useful. Baseline data generated at the time of installation will also be helpful in evaluating results. One benefit derived from this type of inspection technique is that it can often be conducted with little or no interference with production. Periodic planned visual inspection of equipment utilized under conditions likely to cause stress cracking is also an effective technique, especially when combined with non-destructive inspection techniques such as dye penetrant inspection. It may be necessary to remove coatings or insulation from the equipment surface to facilitate inspection. 

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],... 

Case Study 7.1—Corrosion Evaluation of Crevice Exposed to Differential Acidity in the Absence of Chlorides or Other Dissolved Oxidizers... 

Pitting and crevice corrosion are associated with the breakdown of passivity [SO]. Electrochemical tests for evaluating the susceptibility of a material to pitting and to crevice corrosion include potentiodynamic, potentiostatic, scratch potentiostatic, potentiostaircase, tribo-eUipsometric methods, pit-propagation rate curves, galvanostatic, and electrochemical noise measurements [80-S2]. 

If susceptibility to specific types of corrosion is of interest, specialized sample configurations can be used. If the corrosion performance of the material in seawater is completely unknown, at a minimum it should be evaluated for general corrosion and pitting, galvanic corrosion, crevice corrosion, and stress corrosion. 

The following standardized test methods describe relevant test procedures or practices for evaluating the pitting and crevice corrosion tendency of a material in a select environment ... 

Corrosion test specimens are used to evaluate average corrosion rate over the exposure period and eire also useful for assessment of crevice corrosion, pitting, and end grain attack, and may be used for metallographic examination of the corrosion test specimen or analysis of any deposits. Special corrosion test specimens may be prepared with welds to assess corrosion problems particular to weld material or heat affected zones. SCC may be monitored with specially mounted and loaded corrosion test specimens. 

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