A centralizer system is provided for use in a marine riser system, the centralizer being preferably heat-shrink fitted to an upset portion of a keel joint, the upset portion having tapered sections on the upper and lower ends that gradually blend into the outer diameter of the pipe used as the keel joint, the centralizer preferably comprising axially extending annular grooves in surrounding relationship to the upset portion, the grooves serving to permit forces acting on the centralizer to be redirected or dissipated to thereby prevent excessive buildup on a selected region of the upset portion adjacent the radial grooves.