Which of the following is NOT a form of Stress Corrosion Cracking (SCC)?

The correct choice indicates that acidic stress corrosion cracking is not commonly classified as a specific form of stress corrosion cracking (SCC). Stress corrosion cracking typically occurs in metals that are under tensile stress in the presence of specific corrosive environments that can include chlorides, sulfides, or caustic agents.

Chloride SCC arises in environments where chlorides are present and can lead to cracking in a variety of metals, particularly stainless steels. Sulphide SCC occurs in the presence of hydrogen sulfide, affecting certain metals known to be susceptible to this form of corrosion. Caustic embrittlement, although related to corrosion processes, is typically due to the presence of caustic environments (high pH) and is recognized as a separate mechanism that leads to failure, often occurring in boiler tubes or pressure vessels.

While acidic environments can also contribute to corrosion, the term "acidic SCC" is not widely recognized as a distinct category in the same manner as the others listed. This distinction is crucial in understanding SCC, as recognizing the specific environmental factors is key in preventing and managing such failures.