Electrochemical tests crevice corrosion

Lee, T. S., A Method for Quantifying the Initiation and Propagation Stages of Crevice Corrosion, Electrochemical Corrosion Testing, ASTM STP 727, F. Mansfield and U. Bertocci, Eds., ASTM International, West Conshohocken, PA, 1981, pp. 43-68. 

Evidence of localized corrosion can be obtained from polarization methods such as potentiodynamic polarization, EIS, and electrochemical noise measurements, which are particularly well suited to providing data on localized corrosion. When evidence of localized attack is obtained, the engineer needs to perform a careful analysis of the conditions that may lead to such attack. Correlation with process conditions can provide additional data about the susceptibility of the equipment to locaHzed attack and can potentially help prevent failures due to pitting or crevice corrosion. Since pitting may have a delayed initiation phase, careful consideration of the cause of the localized attack is critical. Laboratory testing and involvement of an... 

Wilde, B. E. and Williams, E., The Relevance of Accelerated Electrochemical Pitting Tests to the Long Term Pitting and Crevice Corrosion Behaviour of Stainless Steels in Marine Environments , J. Electrochem. Soc., 118, 1056 (1971)... 

Although important contributions in the use of electrical measurements in testing have been made by numerous workers it is appropriate here to refer to the work of Stern and his co-workerswho have developed the important concept of linear polarisation, which led to a rapid electrochemical method for determining corrosion rates, both in the laboratory and in plant. Pourbaix and his co-workers on the basis of a purely thermodynamic approach to corrosion constructed potential-pH diagrams for the majority of metal-HjO systems, and by means of a combined thermodynamic and kinetic approach developed a method of predicting the conditions under which a metal will (a) corrode uniformly, (b) pit, (c) passivate or (d) remain immune. Laboratory tests for crevice corrosion and pitting, in which electrochemical measurements are used, are discussed later. 

FIG. 25-14 Schematic diagram of the electrochemical cell used for crevice corrosion testing. Not shown are three hold-down screws, gas inlet tube, and external thermocouple tube. 

In 1980 Bemhardsson et introduced an automated electrochemical method for CPT determination. The specimen is mounted as described in Section IV.2 (ii) using a stream of argon to avoid crevice corrosion and 0.02-5% sodium chloride as electrolyte. The CPT is determined by a potentiostatic test method using an instrument called the Santron CDT 400 for potential control, temperature control, and current measurements. 

Fig. 2.9 Electrochemical cell with separated creviced anode and cathode for crevice corrosion testing [20].

Ijsseling FP. Electrochemical methods in crevice corrosion testing. British Corrosion Journal, 15, 1980 1 51-69. 

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]. 

Pitting and crevice corrosion tendencies of a material in a select environment may be determined by immersion testing or by electrochemical techniques. Immersion testing generally involves visual examination and dimensional analysis after exposure of a test specimen to a select environment. Electrochemical methods usually involve exposure of a test specimen to a select environment and graphical interpretation of data. 

The tests can be classified into three general categories (i) non-electrochemical tests, (ii) electrochemical tests under open-circuit conditions, and (iii) electrochemical tests under controlled potential or current conditions. Brief descriptions of the more established methods for evaluating crevice corrosion appear in Table 1 along with comments concerning limits of applicability. Details of each method can be found in the literature cited. The reader is also advised to consider one or more of the excellent reviews on test techniques for crevice corrosion [40-45,76,114. ... 

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