Abstract: Apparatus and method for electrically heating a segment of a subsea pipeline are provided. Electrical power may be supplied about midpoint between the ends of concentric pipes. The annulus between the pipes electrically isolates the pipes, but at the ends of the segment the concentric pipes are electrically connected. The pipes may be electrically connected by bulkheads or by an insulating joint. A toroidal transformer may be placed in the annulus for extracting power at a selected location along the pipeline. An insulating joint allows power to be extracted from the ends of the heated segment. Extracted power may be used for pumps, other devices or for heating jumpers or other short segments of the pipeline. Contiguous segments of a pipeline may be heated, each segment having an electrical connection to the inner and the outer pipe intermediate the ends of the segment. A riser or segment of a riser having a pipe-in-pipe configuration may also be heated.

Abstract: A pipelay apparatus and method comprising a steel turntable and a stinger pipe guide which can be supported on the construction deck of a repair vessel or drill ship are provided. The turntable is framed so that loads from two hanging pipes can be securely supported. The table-supported framing members can be moved so the load centerline for each pipeline can be placed an appropriate distance from the center of turntable rotation, which is useful where the two pipelines are of different diameters. This apparatus permits a vessel to simultaneously handle different sizes of pipe and pass large diameter appurtenances without modifying the stinger pipe guide.

Abstract: A deep trench is excavated into a sea bottom. The trench is filled with a slurry, e.g. clay and water, to maintain trench integrity for a period of time. A pipeline is subsequently lowered to the trench bottom by either gravity settlement, jet down using water jets, or vibration.

Abstract: One construction method for burying offshore pipelines utilizes a segmented excavation shield for forming a trench in the seafloor. The present invention provides a propulsion method for advancing the shield which eliminates the need to pull the shield. This is done by advancing skin plates which are attached to the shield, then advancing the shield by transmitting soil reaction through the skin plates, which remain stationary, to the shield.