SPECIALIZED CORROSIONDOE-HDBK-1015/1-93CorrosionCH-02Rev. 0Page 34Figure 15 Austenitic Stainless Steel CausticStressCorrosionCrackingCaustic stress corrosion, or caustic embrittlement, is another form of intergranularcorrosion cracking. The mechanism is similar to that of chloride stress corrosion. Mildsteels (steels with low carbon and low alloy content) and stainless steels will crack if theyare exposed to concentrated caustic (high pH) environments with the metal under atensile stress. In stress cracking that is induced by a caustic environment, the presenceof dissolved oxygen is not necessary for the cracking to occur.Caustic stress corrosion cracking was first encountered in the operation of riveted steamboilers. These boilers were found to fail on occasion along riveted seams. Failure wasattributed to caustic-induced cracking at the highly stressed regions near and under therivets. Boiler water could easily flow into the crevices which existed under the rivets.Radiative heating would cause the water in the crevices to boil. As steam was formed,it would escape from the crevice. More boiler water would then flow into the crevice,boil, and pass from the crevice as steam. The net result of this continuing process wasconcentration of caustic under the rivet. The combination of high stress and high causticconcentrations eventually led to destructive cracking of the boiler vessel.
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