Crevice corrosion description

General description. In incomplete fusion, complete melting and fusion between the base metal and the weld metal or between individual weld beads does not occur (Fig. 15.8). Incomplete fusion that produces crevices or notches at surfaces can combine with environmental factors to induce corrosion fatigue (Chap. 10), stress-corrosion cracking (Chap. 9), or crevice corrosion (Chap. 2). See Fig. 15.9. 

The phosphoric acid-anodized process provides markedly improved stressed-bond joint durability and retards bond-line crevice corrosion (started at an edge) in severely corrosive environments when compared to chromic acid-anodized and FPL etched. (See Chapter 9 for description.)... 

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. ... 

General Description. Crevice corrosion is a form of localized attack that occurs at narrow openings or spaces (gaps) between metal-to-metal or nonmetal-to-metal components. This type of attack results from a concentration cell formed between the electrolyte within the crevice, which is oxygen starved, and the electrolyte outside the crevice, where oxygen is more plentiful. The material within the crevice acts as the anode, and the exterior material becomes the cathode. 

Description and corrosion resistance. This alloy s high critical pitting crevice temperatures provide more resistance to pitting and crevice corrosion than lesser-alloyed materials. The very high yield strength of this alloy combined with good ductihty allows lower wall thickness in process equipment. 

Description and corrosion resistance. Incoloy 825 is a nickel-iron-chromium alloy with additions of molybdenum and copper. It has excellent resistance to both reducing and oxidizing acids, stress-corrosion cracking, and localized attack such as pitting and crevice corrosion. The alloy is especially resistant to sulfuric and phosphoric acids. 

The initiation of crevice corrosion by pitting inside the crevice gap is mainly invoked for stainless steels. Indeed, several investigators [23,46,63,64] have observed pitting and further coalescence of the pits inside stainless steel crevices. Eklund [64] showed that pitting on MnS inclusions near the mouth of the crevice may be the initial stage of crevice corrosion of stainless steels. Oldfield and Sutton [46] have given a detailed description of... 

The description of the crevice solution chemistry is probably the most difficult step (at least from the corrosion or chemistry standpoint if not the computer programming) as a result of the lack of reliable data. The main problems are ... 

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