A one-dimensional mathematical model is presented which describes the acoustic behaviour of thick-walled liquid-filled pipes. The model is based on conventional water-hammer and beam theories. Fluid–structure interaction (FSI) is taken into account. The equations governing straight pipes are derived by the cross-sectional integration of axisymmetric two-dimensional basic equations. The resulting FSI four-equation model has small correction terms and factors accounting for the wall thickness. Exact solutions of this model show that these corrections are important only for very thick pipes, with, say, a radius/thickness ratio smaller than 2.