Riser connector

A system for connecting and disconnecting a lower end of a marine riser (25) to and from a blow out preventer stack on a subsea wellhead, comprising:

• a riser connector (19) comprising:
• gripping members (26) movable between a clamping position in which they clamp the riser end (25) and a release position in which the riser end (25) is released,
• a lock element (27) movable between a lock position in which the lock element (27) lock the gripping members (26) in the clamping position and an unlock position in which the gripping members (26) are free to move to their release position,
• primary hydraulic actuators (28, 29) able to move the lock element (27) between the lock position and the unlock position,
• secondary hydraulic actuators (30) merely able to move the lock element (27) to the unlock position, and
• hydraulic circuitry comprising:
• a hydraulic lock circuit (1, 2, 3, 41, 42) for actuating the primary actuators (28, 29) to move the lock element (27) to the lock position and move the secondary actuators (30) to a position from which they can move the lock element (27) to the unlock position,
• a hydraulic primary unlock circuit (5, 20, 39, 43, 44) for actuating the primary actuators (28, 29) to move the lock element (27) to the unlock position,
• a hydraulic secondary unlock circuit (21, 40, 45, 46) for actuating the secondary actuators (30) to move the lock element (27) to the unlock position, characterized in that
• the primary unlock circuit (5, 20, 39, 43, 44) comprises a first primary unlock circuit (5, 39, 43, 44) for actuating first primary actuators (28) and a second primary unlock circuit (20, 39, 43, 44) for actuating second primary actuators (29), and the system further comprises:
• a hydraulic backup unlock circuit (9, 11 16) for actuating the primary and secondary actuators (28, 29, 30) to move the lock element (27) to the unlock position, the backup unlock circuit comprises a source (16) for pressurised hydraulic fluid and a triple flow divider (8) for dividing fluid flow from the source (16) into one flow for actuating the first primary actuators (28), one flow for actuating the second primary actuators (29) and one flow for actuating the secondary actuators (30).