Which of the following is NOT a flow-assisted corrosion type?

• A. Erosion-corrosion
• B. Impingement
• C. Cavitation
• D. Pitting

Answer: (D)

Flow-assisted corrosion is damage that is increased by the motion of the fluid. Erosion-corrosion occurs when the flow’s mechanical wear works together with chemical dissolution to remove material faster. Impingement damage comes from high-velocity jets striking a surface, causing direct erosion plus corrosion. Cavitation results from collapsing vapor bubbles in the liquid near the surface, producing shock waves and microjets that eject material. Pitting, by contrast, is a localized electrochemical process driven mainly by chemical conditions (such as chlorides or pH) and protective film breakdown, not by the mechanical action of flowing fluid. While flow can influence pit growth, the initiating mechanism is not flow-assisted, so pitting is not a flow-assisted corrosion type.