Lengths of pipe larger than about 2 in. (50 mm) are usually connected by flanges or by welding. Flanges are matching disks or rings of metal bolted together compressing a ket between their faces. The flanges themselves are attached to the pipe by screwing them on or by welding or brazing. A flange with no opening, used to close a pipe, called a blind flange or a blank flange. For joining pieces of large steel process piping, especially for high-pressure service, welding has become the standard method. Welding makes stronger joints than do, and since it does not weaken the pipe wall, lighter pipe can be used for a given pressure. Properly made welded joints are leakproof, whereas other types of joints environmental protection legislation considers flanged and screwed joints to not. volatile materials. be sources of emission of Almost the only disadvantage of a a welded joint is that it cannot be opened without destroying it.