A coupling arrangement (15, fig. 3) for restraining two elongate members such as sub-sea pipes (11 or 12) with respect to each other when subjected to hydrostatic end loads, and which is operable remotely by way of an ROV (16), comprises a housing (20) for receiving the pipes containing restraining means axially displaceable by fluid pressure to grip the pipe and also, at the gripping position, the housing wall (25) to prevent pipe retraction unless deliberately released. The restraint means carries on member (33) radially expandable collet means (34) which like the wall is profiled with fine pitch, shallow ridges and grooves provided by a helical screw thread and requiring little axial disturbance of the restraint means from the gripping position to engage. Preferably, the restraint member (33) and collet means (34) are moved further than pipe gripping means (45) to compress spring means (53) which is able thereafter to accommodate changes in hydrostatic end load on the pipe without varying the axial loading at the collet means.