US Patent 7380589 Subsea coiled tubing injector with pressure compensation

A pressure compensated tubing injector for injecting coiled tubing into a subsea wellhead or flowline. A traction device including grippers carried on respective opposing chain loops provides gripping engagement with the coiled tubing to longitudinally move the coiled tubing. A plurality of sealed outboard bearing assemblies guide movement of the chain loops. A drive unit powers the chain loops and includes a sealed gear case. One or more pressure compensators are placed in communication with the sealed gear case and one or more of the bearing assemblies, to compensate for subsea pressure and prevent intrusion of seawater. The bearing assemblies may include self-contained pressure compensators.