US 4,395,160 A · Tensioning system for marine risers and guidelines

Abstract

A double rack and pinion device (17) is used to maintain substantially constant upward tension on a marine riser (16) that extends from stationary equipment (11) on the ocean floor to a floating structure (10) on the ocean surface. A preferred embodiment of the double rack and pinion device (17) comprises a sleeve (21) fitted over an upper segment of the riser (16), with a generally cylindrical weighted structure (40) surrounding the sleeve (21). Racks (33, 34, 35) are secured to or formed integrally on the exterior surface of the sleeve (21), and corresponding racks (53, 54, 55) are secured to the interior surface of the weighted structure (40). Pinions (63, 64, 65) are supported by the floating structure (10), and extend into the spacing between corresponding pairs of racks on the sleeve (21) and on the weighted structure (40). Thus, teeth on the pinion (63) engage teeth on the racks (33 and 53), teeth on the pinion ( 64) engage teeth on the racks (34 and 54), and teeth on the pinion (65) engage teeth on the racks (35 and 65). The gravitational force downward on the weighted structure (40) causes a torque to be applied by the racks (53, 54, 55) to the pinions (63, 64, 65), thereby tending to rotate the pinions (63, 64, 65). Concomitantly, the pinions (63, 64, 65) exert an upward force on the racks (33, 34, 35) tending to urge the sleeve (21) upward. Upward movement of the sleeve (21) is restrained, however, by a collar (22) affixed to or formed integrally on the upper segment of the riser (16). As the floating structure (10) changes position on the ocean surface due to environmental forces, vertical motion is imparted to the pinions (63, 64, 65). The pinions (63, 64, 65) travel up and down along the racks (33, 34, 35), producing concomitant vertical motion of the weighted structure (40) relative to the riser (16). In this way, a substantially constant upward tensioning force is exerted on the riser (16) regardless of the position of the floating structure (10) relative to the stationary equipment (11).

Claims46

Dependent claims

A method of maintaining substantially constant tension on an elongate structure, said elongate structure being secured to a stationary underwater object and extending upward to a buoyant object, said method comprising the steps of:

(a) positioning a weighted structure in proximity to said elongate structure;
(b) positioning first rack means to interact with said elongate structure so that said elongate structure restrains upward motion of said first rack means;
(c) securing second rack means to said weighted structure, said second rack means facing said first rack means;
(d) securing pinion means to said buoyant object, said pinion means extending between said first and second rack means and having teeth that mesh with corresponding teeth on said first and second rack means, gravity acting downward on said weighted structure thereby causing said second rack means to exert a torque on said pinion means that causes said pinion means to impart an upward force to said first rack means, said pinion means undergoing rotational motion as said buoyant object changes position relative to said underwater object, said rotational motion of said pinion means causing said pinion means to travel vertically along said first rack means and to produce concomitant vertical motion of said weighted structure relative to said elongate structure, said upward force imparted to said first rack means remaining substantially constant as said pinion means travels along said first rack means, thereby causing a substantially constant upward tension to be transmitted to said elongate structure.

1 more element

An apparatus for maintaining substantially constant tension on an elongate structure, said elongate structure being secured to a stationary underwater object and extending upward to a buoyant object, said apparatus comprising:

(a) a weighted structure positioned in proximity to said elongate structure;
(b) first rack means positioned to interact with said elongate structure so that said elongate structure restrains upward motion of said first rack means;
(c) second rack means secured to said weighted structure, said second rack means facing said first rack means;
and
(d) pinion means secured to said buoyant object, said pinion means extending between said first and second rack means and having teeth that mesh with corresponding teeth on said first and second rack means, gravity acting downward on said weighted structure thereby causing said second rach means to exert a torque on said pinion means that causes said pinion means to impart an upward force to said first rack means, said pinion means undergoing rotational motion as said buoyant object changes position relative to said underwater object, said rotational motion of said pinion means causing said pinion means to travel vertically along said first rack means and to produce concomitant vertical motion of said weighted structure relative to said elongate structure, said upward force imparted to said first rack means remaining substantially constant as said pinion means travels along said first rack means, thereby causing a substantially constant upward tension to be transmitted by said first rack means to said elongate structure.

2 more elements

(a) a lateral member having an aperture through which said elongate structure passes;
(b) means for maintaining substantially constant upward tension on said lateral member, said tensioning means including a plurality of tensioning devices connecting said lateral member to said buoyant object, each of said tensioning devices being a double rack and pinion device having:
(i) a bar on which first rack means is formed;
(ii) a generally cylindrical weighted structure surrounding said bar, second rack means being secured to said weighted structure, said second rack means facing said first rack means;
and
(iii) pinion means secured to said buoyant object, said pinion means extending between said first and second rack means and having teeth that mesh with corresponding teeth on said first and second rack means, gravity acting downward on said weighted structure thereby causing said second rack means to exert a torque on said pinion means that causes said pinion means to permit an upward force to said first rack means, said pinion means undergoing rotational motion as said buoyant object changes position relative to said underwater object, said rotational motion of said pinion means causing said pinion means to travel vertically along said first rack means and to produce concomitant vertical motion of said weighted structure relative to said bar, said upward force imparted to said first rack means remaining substantially constant as said pinion means travels along said first rack means, thereby causing a substantially constant upward tension to be transmitted by said first rack means to said bar;
and
(c) means for transmitting upward tension from said lateral member to said elongate structure.

5 more elements

A system for recovering energy resources from a deposit located beneath the floor of a body of water, said system comprising:

(a) a floating structure to be positioned on the surface of the body of water generally over the deposit;
(b) stationary equipment to be positioned on the floor of the body of water generally over the deposit;
(c) an elongate riser extending between said floating structure and said stationary equipment;
and
(d) double rack and pinion means for maintaining substantially constant upward tension on said riser, said double rack and pinion means including:
(i) a weighted structure surrounding said riser;
(ii) first rack means positioned to interact with said riser so that said riser restrains upward motion of said first rack means;
(iii) second rack means secured to said weighted structure, said second rack means facing said first rack means;
and
(iv) pinion means secured to said floating structure, said pinion means extending between said first and second rack means and having teeth that mesh with corresponding teeth on said first and second rack means, gravity acting downward on said weighted structure causing said second rack means to exert a torque on said pinion means that causes said pinion means to impart an upward force to said first rack means, said pinion means undergoing rotational motion as said floating structure changes position relative to said stationary equipment, said rotational motion of said pinion means causing said pinion means to travel vertically along said first rack means and to produce concomitant vertical motion of said weighted structure relative to said riser, said upward force imparted to said first rack means remaining substantially constant as said pinion means travels along said first rack means, thereby causing a substantially constant upward tension to be transmitted to said riser.

7 more elements

Dependencies are inferred from the claim text.

Tensioning system for marine risers and guidelines

Life of this patent

Tensioning system for marine risers and guidelines

Life of this patent

Abstract

Claims46