With weld corrosion,
a welded metallic material in or next to the weld is selectively attacked. The causes could be sediments or segregations, which formed in the welding process in the high temperature
or heat affected zone in or next to the weld.
Often, there are also small crack-like corrosion attacks next to the weld in the heat affected zone, which are called knife-line corrosion
because of their appearance.