All steel plate and sheet is hot-rolled as a first rolling step, after which it is annealed in order to attain homogeneous material characteristics. Annealing produces an oxide coating on the steel, which is removed by shot blasting and by pickling in an acid bath. As a result of these manufacturing operations, the steel acquires a relatively coarse, matt grey surface with an R_a value in the order of 2-8 µm; the thicker the plate the coarser the surface, and the higher the Ra value. Localised grinding marks may appear on the surface, but have no practical implications for the use of the steel. Hot rolled plate of this finish is mostly used for heavy process equipment and in thickness from around 5 mm and upward.