Loose flanges (lap weld) are similar in shape to slip on flat flanges, but have a rounded inner edge near the sealing surface to fit tightly to the end weld ring. Flanges of this type are not welded to the pipe, but can rotate freely around it. They are used in frequently dismantled sections of pipelines. Such connections are easy to install, since the fastening holes are easily aligned with the opposite flange. Loose flanges do not come into contact with the medium, so they do not necessarily have to be made of corrosion-resistant steel.