A pipe clamp for reinforcing a welded joint between two pipes, having a plurality of circumferential clamp segments that are bolted together around the joint. One axial end of the clamp has circumferentially extended ridges that project inward and seat in corresponding circumferential grooves in a pipe on one side of the joint. The other axial end of the clamp has circumferentially spaced fingers that extend inward and fit into corresponding pockets on the other side of the weld joint. Either or both the ridges or the fingers have a taper whose cross-section reduces in an inward direction and fits in complimentary grooves or pockets on either side of the joint. The taper forces the opposite sides of the weld joint toward each other as the clamp segments are tightened together.