Abstract: A piston pig for pushing pigs from a larger diameter conduit into a smaller diameter conduit, where one embodiment includes a cylindrical body with a first sealing disc attached to the body and adapted to seal against the larger diameter conduit and maintain a pressure differential across the body of the piston pig. The piston pig also includes a second sealing disc attached to the body and capable of sealing against the smaller diameter conduit and maintain a pressure differential across the body. Certain embodiments also include a pressure control device, such as a resilient flapper disc, to limit the differential pressure across the body. Some piston pig embodiments may also include an end cap attached to, and slidable relative to, the body, where the end cap has a closed position in which fluid cannot bypass the end cap and an open position in which fluid can bypass the end cap.

Abstract: A system for supplying pigs to a subsea pig launcher using a system carried and controlled by a remotely operated vehicle. The pigs are carried in racks that hold multiple pigs. The racks are extended and the pigs are allowed to drop into the barrel of the subsea pig launcher. The system is also equipped with a system that retracts the racks if hydraulic and electrical power is lost during the reloading process so that the remotely operated vehicle can be retrieved to the surface safely. The reloading process can be carried out by a remotely operated vehicle support vessel without the need for heavy lifting equipment or a large deck area.