Which damage mechanism creates sub-surface cracking?

Which damage mechanism creates sub-surface cracking?

• A. Carbon dioxide corrosion
• B. Caustic stress corrosion cracking
• C. Mechanical fatigue
• D. Wet hydrogen sulfide cracking

Answer: (D)

Wet hydrogen sulfide cracking, also known as hydrogen-induced cracking (HIC), is the damage mechanism that is particularly associated with sub-surface cracking in pressure vessels. This form of cracking occurs in environments containing hydrogen sulfide, and the presence of this compound can lead to the absorption of hydrogen into the metal. As hydrogen diffuses through the material, it can create internal pressures, resulting in cracks that initiate beneath the surface. This phenomenon is critical for inspectors to understand since it can lead to severe structural integrity issues in pressure vessels, often advancing unnoticed until they manifest into significant failures. Wet hydrogen sulfide cracking is most prevalent in certain carbon steels and can compromise the vessel's integrity without visible signs on the exterior, which means that thorough inspection and monitoring are required to detect and address it. In contrast, the other damage mechanisms listed, while potentially harmful, do not primarily create sub-surface cracking. For example, carbon dioxide corrosion typically leads to uniform or localized surface corrosion rather than subsurface issues. Caustic stress corrosion cracking involves the interaction between caustic environments and tensile stress but typically manifests on the surface. Mechanical fatigue is associated with cyclic loading and generally leads to surface cracking rather than subsurface failures.

Wet hydrogen sulfide cracking, also known as hydrogen-induced cracking (HIC), is the damage mechanism that is particularly associated with sub-surface cracking in pressure vessels. This form of cracking occurs in environments containing hydrogen sulfide, and the presence of this compound can lead to the absorption of hydrogen into the metal. As hydrogen diffuses through the material, it can create internal pressures, resulting in cracks that initiate beneath the surface.

This phenomenon is critical for inspectors to understand since it can lead to severe structural integrity issues in pressure vessels, often advancing unnoticed until they manifest into significant failures. Wet hydrogen sulfide cracking is most prevalent in certain carbon steels and can compromise the vessel's integrity without visible signs on the exterior, which means that thorough inspection and monitoring are required to detect and address it.

In contrast, the other damage mechanisms listed, while potentially harmful, do not primarily create sub-surface cracking. For example, carbon dioxide corrosion typically leads to uniform or localized surface corrosion rather than subsurface issues. Caustic stress corrosion cracking involves the interaction between caustic environments and tensile stress but typically manifests on the surface. Mechanical fatigue is associated with cyclic loading and generally leads to surface cracking rather than subsurface failures.