Abstract: An expansion lance assembly for an expansion of a hollow profile by the exertion of a fluidic high internal pressure. The expansion lance assembly includes a rod-shaped seal carrier detachably connected to a carrier holder and having a seal arrangement including at least two sealing rings. At least one spacer sleeve is situated between the at least two sealing rings and is arranged on the seal carrier. The seal carrier has an axial inflow bore connected to a fluid high-pressure source and at least one transverse bore branching off from the axial inflow bore. To provide that the lance can be used for long periods of time with a reliable seal of the seal arrangement, the expansion lance assembly includes that each of the sealing rings includes a first component and a second component. The first component includes a low-abrasion high-pressure-resistant elastomer ring which bears against a circumferential surface of the seal carrier such that it is elastically deformable axially by high internal pressure.