No, eccentric reducers are also used for line size reductions in pipeways in order to keep the bottom of pipe (BOP) the same and in proper contact with the pipe supports.
It is also used in other cases. Eccentric reducers are used on both the inlet and outlet piping to some other equipment. The equipment in question had connections that were very close together and the flange sizes for the equipment nozzles were one or more sizes smaller than the inlet and outlet line sizes and I needed to use the eccentric reducer to off-set the centerline of the two pipes to provide proper line spacing as they increased in size.
This text is an extract from questions gathered from numerous queries of anonymous people in the Piping Engineering and Design profesion. The answers or discussions of the topics were provided by James O. Pennock.