Abstract: Apparatus (200) for detecting corrosion of a coating (250) of an object (216), the apparatus comprising: an electrically conductive body (202) defining a cavity (204) for containing an electrolyte (206), the body (202) arranged to be, in use, in electrically conductive contact with the object (216) and arranged to isolate, in use, the electrolyte (206) from the object; and a first electrode (208) within the cavity (204), the first electrode (208) for electrical connection to a potentiostat (402) or to a galvanostat and arranged to be, in use, in electrical contact with the electrolyte (206) in the cavity (204); wherein the body (202) comprises a first part (222) and a second part (224), the second part (224) being slidably movable relative to the first part (222) between a retracted position and an extended position.