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A centralizer for centering a marine riser in an opening in a working deck. The assembly comprises a plurality of cam arm units pivotally coupled to a portion of the working deck for pivotal movement about pivot axes parallel to the top planar surface of the deck and a plurality of hydraulic power d

A centralizer for centering a marine riser in an opening in a working deck. The assembly comprises a plurality of cam arm units pivotally coupled to a portion of the working deck for pivotal movement about pivot axes parallel to the top planar surface of the deck and a plurality of hydraulic power devices for pivoting the cam arm units from a retracted position spaced away from the riser to an active position engaging the riser. Each cam arm unit includes a camming surface which increases in radius from the pivot axis thereof from a first end towards a second end, this second end engaging the riser when each unit is in the active position. Each camming surface is defined by surfaces of a plurality of rollers, two of which are located at the largest radii second end and have the same radii from the pivot axis.

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A centralizer assembly for centering a pipe in an opening in a support, the combination comprising: a plurality of support blocks equally spaced around the opening and rigidly coupled to the top, substantially planar surface of the support; a plurality of cam units, each pivotally coupled to one of

A centralizer assembly for centering a pipe in an opening in a support, the combination comprising: a plurality of support blocks equally spaced around the opening and rigidly coupled to the top, substantially planar surface of the support; a plurality of cam units, each pivotally coupled to one of said support blocks for pivotal movement about a pivot axis parallel to the plane containing the top surface of the support, each of said cam units including a camming surface facing radially inwardly towards the longitudinal axis of the opening for engaging the pipe, said camming surface increasing in radius from said pivot axis from a first end towards a second end; and power means, coupled to each of said support blocks and cam units, for pivoting each of said cam units from a retracted position spaced away from the pipe located in the opening to an active position wherein said larger radii second end of said camming surface engages the pipe, said camming surfaces included in each of said cam units each comprising the surfaces of a plurality of rollers rotationally coupled to each of said cam units about axes parallel to the pivot axes of the cam units associated therewith.