For critical service and/or severe duty piping systems, directional changes are usually made by use of a manufactured elbow, such as ANSI B16.9 elbows for butt welding or ANSI B16.11 elbows for socket welding; or by shop or field bending of a length of straight pipe.Prior to the availability of butt welding elbows, mitred bends were often used.Because such joints require considerable time to cut and fit so that a more-or-less adequate juncture-weld can be made, mitred bends are seldom economical as compared to use of butt welding elbows; provided a butt welding elbow is available when needed.