Riser pipe for pivotally attached structure used to extract petroleum from beneath a body of water

In apparatus for extracting petroleum from beneath a body of water, which apparatus comprises a base at the bottom of said body of water, a base pipe carried by said base, an elongated structure pivotally attached at its lower end to said base by means of a universal joint and projecting above the surface of said body of water, a hollow guide shaft fixed to said structure and extending downward from above said surface toward said base, a plug closing the top of said guide shaft, a pipe within said guide shaft made from a plurality of successive pipe sections, one of which is lowermost, and at least one elastic centering device which centers said pipe in said guide shaft and comprises means providing communication between the spaces between said pipe and shaft above and below said centering means,

• the improvement which comprises:
• a remotely controlled releasable connector occupying a stationary position and comprising a first part fixed to said lowermost pipe section and a second part fixed to said base pipe,
• a slidable connector connecting said lowermost pipe section to the one above it, and
• a cylindrical sleeve in said guide shaft within which said slidable connector is slidable,
• said sleeve having an inner diameter slightly less than that of the remainder of said guide shaft, said slidable connector comprising means providing communication between the spaces below said pipe and guide shaft above and below said connector, and the part of said releasable connector fixed to the lowermost section of said pipe having an external diameter less than the internal diameter of said sleeve.