Subsea Line Handling With Controlled Overrun to Prevent Grip Overload
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Solution Overview
Problem
The existing methods for laying and recovering flexible lines in water bodies face challenges with uneven stress distribution on gripping members, leading to potential line drops due to exceeding the nominal holding capacity, especially with long suspended lines, necessitating significant safety margins that reduce laying capacity.
Innovation Solution
Implementing a method that includes limited downward overrun, a time delay, and subsequent raising of the line from a change of direction position to a stop position, controlled by the system's motors and control unit, to manage stress and prevent line drops without reducing laying capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If significant safety margins are applied to gripping members, then reliability of line retention is improved, but laying capacity is reduced
Solution Approach 1:
The control unit performs preliminary actions by detecting the line stop position and automatically executing the overrun-raising sequence before the line can cause harmful effects. This preliminary detection and response ensures reliable line retention while maintaining full laying capacity, as the system prepares and corrects positioning issues before they compromise safety margins.
2Reliability
If gripping members are oversized to handle long suspended lines, then reliability is improved, but device complexity and cost increase
Solution Approach 1:
The invention replaces the need for oversized mechanical gripping members with an automated control system that uses standard-sized gripping members combined with motor control and position detection. The control unit monitors line position and executes overrun-raising sequences to prevent line drops, substituting mechanical oversizing with electronic control and automation, thereby reducing device complexity and cost while maintaining reliability.
3Speed
If mechanical brake systems are used to stop the line, then stopping capability is improved, but stress distribution on gripping members becomes uneven
Solution Approach 1:
The control unit implements feedback by continuously detecting the line stop position and using this information to control the motors that drive the gripping members. This feedback mechanism ensures that the gripping members maintain proper tension and position during stopping, preventing uneven stress distribution that would occur with passive mechanical brake systems. The system adjusts motor torque and gripping member position based on real-time line position feedback.
Data Source
AI summary
A line laying and/or recovering method in a body of water that includes providing a laying device including two facing upstream grippers and two facing downstream grippers, defining a passage for the circulation of the line; lowering the line to at least one stop position; stopping the line in the at least one stop position; and, prior to the at least one stopping of the line in the stop position, limited downward overrun past the stop position to a change of direction position; time delay in the change of direction position; limited raising of the line from the change of direction position to the stop position.