Abstract: The invention relates to a device and a method for determining the quality of the corrosion on the inside of a wall manufactured from non-corrosion-resistant material of a space in which corrosive conditions prevail, wherein at least one part of the wall is removable from the wall without destructive operations and is available after removal for examination outside the space. This measure has the advantage that an element to be removed without destructive operations can be removed easily and can be replaced. Although in the first instance a screw is envisaged, other embodiments are in no way precluded, such as a pin or a prop onto which another fixation device is arranged, for instance a bayonet fitting.