Abstract: A method and apparatus for stopping a malfunctioning sealing device which is being propelled inside a pipeline by pneumatic pressure from being expelled out of the pipeline at the laybarge end. The apparatus comprises a plurality of normally retracted gripping jaws and a bumper at its rear end. When impact is made with the bumper by, for example, a sealing device such as a pig being propelled through the pipeline, the gripping jaws which are mechanically linked with the bumper are caused to expand against the inner pipe surface such that the apparatus is secured in place within the pipeline, thereby preventing the pig from being propelled out of the line onto the laybarge.