Definition - What does Honeycomb Corrosion mean?
Honeycomb corrosion is a type of non-uniform corrosion in which the metal is deeply destroyed. This type of corrosion is severe, because even an insignificant loss of metal may cause equipment failure.
Honeycomb corrosion is a transitory state between early stage crystallographic pitting and general corrosion. The electrochemical conditions for honeycomb-like appearance (and crystallographic pitting) are those of low pH and low oxygen content, as can be found at the tip of a deep crevice.
Corrosionpedia explains Honeycomb Corrosion
Honeycomb corrosion refers to a cell-like cavities resembling a honeycomb on the corroded surface. Intergranular pits may extend in a honeycomb shape like the complicated caves of a limestone region. This type of corrosion can be disastrous — for example, on horizontal and vertical stabilizers of an aircraft made from a metal honeycomb with a metal skin, once water gets into the honeycomb, corrosion takes place, resulting in the skin-honeycomb bonding being weakened to the extent that it can peel away during flight.
Cavitation erosion is the loss of material caused by exposure to cavitation, which is the formation and collapse of vapor bubbles at a dynamic metal-liquid interface — for example, in rotors of pumps or on trailing faces of propellers. This type of corrosion causes a sequence of pits, sometimes appearing as a honeycomb of small, relatively deep fissures. The surface becomes deeply pitted and appears to be spongy, or honeycomb-like.