An improved length compensating joint suitable for use in repairing pipelines includes an inner tubular member (12), an outer tubular member (14) which receives the inner member in close fitting engagement, seals disposed radially and axially between the inner and outer members define annular piston areas for providing selective relative between the inner and outer members, a pressure responsive locking piston (40) with a camming surface (82) for urging gripping elements (58) into locking engagement with the inner member, a metal-to-metal seal (148, 154) between the inner and outer members which can be deenergized during extension or retraction operations and a test port (128) for verifying the integrity of the metal-to-metal seal after installation. Additionally, a second embodiment provides an alternative metal-to-metal seal configuration which can also be deenergized during extension and retraction operations.