Abstract: A pipe joint seal comprises an insert (10) adapted to be mounted around the joint and the pipe sections adjacent thereto and having in its inner side dovetailed grooves (11) or the like which are filled with a plastic sealing compound. The insert (10) can be clamped around the pipes and the joint by means of a sheet-metal union piece (21) having bent edges (22) to form a channel within which said insert (10) is mounted. When insert (10) is tightened around the pipes, the sealing compound urges the insert portions defining the dovetailed grooves (11) tightly against the pipes so that a satisfactory seal is obtained also on uneven pipe surfaces. By designing one bent longitudinal edge (22) of the union piece (21) with a height greater than that of said insert, and by causing said bent edge to engage with a groove in one of said pipes, the seal can be simply and conveniently held in nondisplaceable engagement with said pipe, while the other pipe is displaceable in the seal.