Corrosion Erosion is a term often used to describe the internal erosion of pipe.

In potable water copper lines, corrosion erosion is most prevalent at directional joints. Moreover, when copper systems are installed without properly reaming the ends of the pipe, thus causing turbulence within the pipe, corrosion erosion is probable.

Photo Courtesy of Copper Development Association

Often, when cut cross sectionally (like illustrated above), the direction at which the water flowed can be easily identified.