Patent ID: 7964041

Claim:
A method for driving a scraper through a subsea pipe that is designed to be laid on the seabed which is at a given hydrostatic pressure, wherein said subsea pipe has two opposite ends, and a sole fluid connection between said opposite ends is within the subsea pipe, the method comprising providing a launch device at one end of said subsea pipe and a receiver trap device at the other end of said subsea pipe, providing said scraper to slide inside said subsea pipe to therein delimit two watertight chambers, including an upstream chamber between said launch device and said scraper and a downstream chamber between said receiver trap device and said scraper, providing said scraper able to be launched into said pipe from said launch device toward said receiver trap device, bringing said subsea pipe to an internal pressure lower than said hydrostatic pressure, allowing water from said seabed to enter said upstream chamber via said launch device thereby bringing said upstream chamber to said hydrostatic pressure to drive said scraper through said subsea pipe toward said receiver trap device; allowing water to enter said downstream chamber via said receiver trap device in order to thereby equalize the pressure of said two chambers with respect to the hydrostatic pressure; and injecting a pressurized fluid into said downstream chamber via said receiver trap device to increase the pressure in said downstream chamber to a pressure higher than the hydrostatic pressure and sufficient to drive said scraper in an opposite direction, toward said launch device, whereby the respective roles of said launch device and of said receiver trap device are reversed.