Many high performance alloys, originally destined for service in high temperature applications (aircraft, aerospace) are becoming widely used in various chemical, petrochemical, pulp and paper, and pollution control equipment[1, 2]. The changes in processing (higher temperatures, higher pressures, new catalyst systems, and more aggressive chemicals) make it such that the use of conventional stainless steels is no longer applicable; thus highly alloyed materials are needed[1-5]. However, despite their high nickel, chromium, and molybdenum contents, several of these high performance alloys appear to be susceptible to localized corrosive attack in the forms of “pitting” corrosion, “crevice” corrosion, “underdeposit” corrosion, “hot wall” corrosion, and “gas-liquid” interface corrosion. The unpredictable occurrences of these localized corrosive attacks make it difficult to take them into consideration in practical engineering designs. Furthermore, these forms of material degradation are among the most dangerous, yet the most common, types of corrosion encountered in aqueous environments[6, 7]. They cause many service failures in the chemical industry[8] and account for about 32 corrosion failure cases, within a two-year period, at a “typical” chemical company[9]. Also, localized corrosion is stated to be responsible for at least 90 percent of metal failure by corrosion[10].
