Offshore Platform Deck-to-Column Locking Mechanism
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Solution Overview
Problem
Existing systems for connecting and disconnecting extendable columns with a deck on offshore platforms face challenges such as reliance on actuators for locking, potential bending of locking pins under load, and the need for welding or careful ballasting for disconnection, which can lead to instability and complexity in operations.
Innovation Solution
A deck-to-column connection assembly using a pawl and shim that allows for secure locking and unlocking of the column with the deck through sequential de-ballasting and ballasting, eliminating the need for continuous actuator support and avoiding the need for welding or precise ballast balancing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a pawl and chain system is used to connect columns to the deck, then the connection can be made and broken, but the pawl only prevents upward movement and the system depends on chains to hold the deck and legs together, requiring continuous actuator support
Solution Approach 1:
A shear key is introduced as an intermediary element between the column and deck. The shear key engages with a groove in the column and a recess in the deck, providing a positive mechanical lock that prevents both upward and downward movement. This intermediary component transfers loads directly through mechanical engagement rather than relying on chains and actuators, thereby improving reliability while maintaining ease of operation.
Solution Approach 2:
The connection system is designed to be self-locking through the shear key mechanism. Once the column is lowered and the shear key engages with the groove and recess, the connection automatically locks without requiring continuous actuator support. The shear key's geometry ensures that it remains engaged under load, providing self-service locking that eliminates the need for active maintenance of actuator support.
2Strength
If locking pins are used to secure the column to the deck, then the connection can be strong, but the pins may bend under the load of ballasting or de-ballasting the column
Solution Approach 1:
Instead of using a pin that protrudes from the column and engages the deck, the design inverts the engagement geometry. The shear key forms a groove that receives a protruding element from the deck, reversing the traditional pin-and-hole configuration. This inversion allows the shear key to resist bending moments more effectively by distributing loads across its entire length and geometry, preventing the bending failures that occur with traditional locking pins.
Solution Approach 2:
The shear key is designed as a composite structural element that combines multiple geometric features (groove, flanges, web) to resist different types of loads. The geometry is optimized to resist both shear forces and bending moments simultaneously, creating a composite-like structure that distributes stresses more effectively than a simple pin, thereby preventing bending under ballasting loads.
3Strength
If welding is used to permanently connect the deck to the legs, then the connection is strong, but the weldments need to be cut off to retract the legs at a later time
Solution Approach 1:
The connection system is segmented into separable components: the shear key, the groove in the column, and the recess in the deck. This segmentation allows the connection to be strong when engaged while remaining easily disassemblable. The shear key can be withdrawn from the groove and recess without damaging the column or deck, enabling leg retraction without cutting or permanent modification, thus resolving the contradiction between strength and retractability.
4Productivity
If a tapered load is applied to the actuation means, then the column can be lowered, but the tapered load may compromise the ability to maintain the tapered shear key in position, causing unintended upward movement
Solution Approach 1:
The shear key geometry is designed with built-in load distribution features that cushion against concentrated tapered loads. The groove and recess are shaped to distribute the ballasting load evenly along the shear key's length, preventing stress concentration that could cause the shear key to shift or fail. This beforehand cushioning through geometric design maintains position stability even during the dynamic loading of column lowering operations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution provides a stable and secure connection that withstands sea forces without requiring continuous actuation, allowing for easy disconnection and retraction of the columns, enhancing operational reliability and simplifying the deployment process.
Implementation Method 1
The columns are initially installed in a raised position, and then lowered to a submerged position when the EDP has been moved to a deeper water site. Each column is divided by longitudinal internal bulkheads and horizontal flats (decks) into a plurality of compartments, the compartments including generally known system for introducing water into them for ballasting purposes when the columns are lowered to their submerged positions.
Implementation Method 2
Further, a heave plate pontoon assembly is generally attached to the bottom of the columns that helps to stabilize the EDP against the heave action of waves and swells.
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The disclosure provides a system and method for locking and unlocking an extendable column (3) to a deck (2). A deck-to-column connection assembly includes a pawl and shim used in a sequential de-ballasting and ballasting of the column to the deck that can easily lock and unlock the column with the deck. Generally, the locking method includes ballasting the column to insert a pawl (11) between the column and the deck, de-ballasting the column to raise the column relative to the deck and create a vertical gap between the column and the deck, inserting a shim (15) to fill the gap and secure the pawl in a deployed position, and further de-ballasting the column to raise the deck connected to the column. Generally, the unlocking method lowering the deck to float on water, de-ballasting the column to remove compressive stress on the shim, removing the shim, ballasting the column, and retracting the pawl.