The correct answers are A, D, and E because these conditions are associated with higher corrosion risk and degradation mechanisms , making wall thickness inspection necessary under the Mechanical Integrity element.

Option A is correct because piping under insulation is susceptible to corrosion under insulation (CUI) , a well-known and often hidden damage mechanism. Moisture trapped beneath insulation can lead to significant metal loss without visible external signs.

Option D is correct because buried piping at soil-to-air interfaces is particularly vulnerable to corrosion. This transition zone is prone to moisture accumulation, oxygen gradients, and coating breakdown , making it a critical inspection location.

Option E is also correct because stagnant liquids can promote internal corrosion, especially if they contain water, corrosive chemicals, or allow for sediment buildup. Lack of flow can accelerate localized corrosion such as pitting.

Option B (drinking water) and C (nitrogen) are generally less corrosive services and typically present lower risk , though inspections may still occur depending on conditions.

CCPS emphasizes that inspection programs should be risk-based , focusing on areas where degradation is most likely, ensuring early detection of wall thinning and prevention of loss of containment.