The present invention is a method of plugging a pipeline having an exterior surface including the steps of affixing to the exterior of the pipeline first and second spaced apart collars, welding each collar to the pipeline so that an operating space is provided between the collars, positioning a seal with each collar, affixing a containment housing to the opposed collars providing a confined space around the pipeline and surrounding the operating space between the collars, the confined space being accessed by a passageway, cutting and removing a length of pipeline between the collars providing opposed pipeline exterior end surfaces, positioning first and second seal cups between the collars, each seal cup having a forwardly extending circumferential lip of internal diameter greater than the external diameter of the pipeline, and applying force to move the seal cups away from each other, the circumferential lips of the seal cups engaging with the opposed seals to compress them into sealing engagement with the collars and with the pipeline exterior surfaces.