A method for assembly of a fitting with a pipe piece using a flange connection disposes centering elements on the fitting at a distance from one another on the circumference, and centering bolts are inserted into centering openings of the centering elements and into accommodation openings of the fitting. A collar surface of the pipe piece is aligned on alignment surfaces of the centering elements. Subsequently, a loose flange ring is aligned on the centering bolts via its passage openings. The fitting and the pipe piece, which are aligned with one another, are connected with one another by the flange ring as well as connection elements, and in this regard, the centering elements and centering bolts are removed. Also a method having a similar effect, for assembly of two pipe pieces uses a flange connection, as does a centering apparatus for assembly.