Abstract: An expansion seal for use with a product pipeline which extends through a larger casing is disclosed. The seal may also be adapted to function as a coupling if a leak occurs in the product pipeline. The device comprises a cap having an axial opening to receive a sleeve which then surrounds the pipeline. The periphery of the cap is adapted to be welded to the casing end. The sleeve defines an internal circumferential recess which contains packing, and the sleeve carries means for compressing the packing into sealing engagement between the pipeline and sleeve. The device may function as a coupling by welding the sleeve to the pipeline.