A roll assembly and a pipe extrusion plant for producing pipes with a variable diameter, includes an extruder, an adjustable calibration device, and a cooling device, whereby a pipe to be produced is guided at least in part during the production process. In order to be able to provide a guide that is suited to different pipe diameters, a roll assembly is provided to include a row of rolls which are placed one behind the other in a take-off direction, with each roll mounted in a bracket and supported to allow vertical positioning thereof in dependence on the pipe diameter.