Subsea Riser Breakaway Connection Shear Pin Design
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Solution Overview
Problem
Conventional subsea drilling risers are prone to failure due to excessive tensile, bending, and torsional loads, leading to potential damage of subsea equipment and obstruction of subsequent operations when the upper portion breaks, as the unsupported lower portion falls to the sea floor.
Innovation Solution
A breakaway connection system for subsea risers, comprising a tubular stabbing member and a female member with shear pins and an annular locking ring, designed to disconnect at a predetermined tensile load, preventing the entire length of the riser from falling and causing damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the riser is designed to be continuous and strong to withstand extreme loads, then the strength and reliability are improved, but the weight and complexity of the system increase, and the risk of catastrophic failure with long debris fall increases
Solution Approach 1:
The riser system is divided into upper and lower sections connected by a breakaway connection that includes a male section, female section, and locking overshot. This segmentation allows the connection to be designed with controlled weak points (shear pins) that can fail at predetermined loads, preventing catastrophic failure of the entire riser system while maintaining the strength of individual sections.
Solution Approach 2:
The locking overshot acts as an intermediary device between the male and female sections, providing a mechanical locking mechanism with shear pins that serve as controlled weak points. This intermediary connection allows the system to withstand normal operational loads while providing a predetermined failure mode under extreme conditions, resolving the contradiction between strength and controlled failure.
2Reliability
If the riser connection is made robust and permanent to prevent accidental disconnection, then the reliability is improved, but the ability to perform controlled disconnection for remedial operations is reduced
Solution Approach 1:
The connection system transitions from a static permanent connection to a dynamic system with controlled failure modes. The shear pins are designed to fail at specific load thresholds, allowing the connection to adapt its strength based on operational conditions. This dynamic characteristic enables both reliable operation under normal conditions and controlled disconnection when needed for remedial operations.
Solution Approach 2:
The connection strength parameter is made variable through the shear pin design, which can be selected with different yield strengths to match specific operational requirements. By changing the shear pin material or dimensions, the controlled disconnection load can be adjusted, providing both high reliability during operation and the capability for controlled disconnection when required.
3Force
If the upper riser section breaks and the lower portion falls to the sea floor, then the immediate tensile load on the drilling vessel is reduced, but damage to subsea equipment and obstruction of subsequent operations occurs
Solution Approach 1:
The breakaway connection with shear pins is installed in advance as a preventive measure against catastrophic failure. When extreme loads are anticipated, the shear pins fail at predetermined load levels, causing a controlled disconnection that prevents the lower riser section from falling and damaging subsea equipment. This preliminary protective action addresses the harmful effects before they can occur.
Solution Approach 2:
The potential harm of riser failure under extreme DP system failure conditions is converted into a beneficial controlled disconnection event. Instead of the entire riser breaking and creating dangerous debris, the pre-designed weak points in the breakaway connection fail first, sacrificing the connection components to protect the valuable drilling vessel, riser sections, and subsea equipment from more severe damage.
4Reliability
If shear pins are used as the failure mechanism in the breakaway connection, then the controlled disconnection at predetermined load is achieved, but the complexity of the connection system increases
Solution Approach 1:
The failure function is extracted from the main riser structure and placed into separate, dedicated shear pin components. This extraction allows the primary riser sections to be designed for strength and continuity, while the shear pins provide the controlled failure capability. The complexity of the failure mechanism is isolated to replaceable pins rather than the entire connection system, simplifying maintenance and replacement.
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
The breakaway connection system effectively manages excessive loads by disconnecting the riser at a controlled load, preventing damage to subsea equipment and maintaining operational integrity by keeping the riser suspended, thus reducing the risk of obstruction and facilitating remedial operations.
Implementation Method 1
a plurality of shear pins, wherein each shear pin is threadably disposed in one threaded hole, and wherein each shear pin has a radially inner end seated in the annular recess
Data Source
AI summary
A breakaway connection for a subsea riser, the connection including a tubular stabbing member having a central axis, an upper end, a radially outer cylindrical surface, a radially inner surface, and an annular recess in the outer cylindrical surface. The breakaway connection also includes a tubular female member having a central axis, a lower end, a radially outer surface, a radially inner surface defining a receptacle extending axially from the lower end, and a plurality of circumferentially-spaced threaded holes extending radially from the radially outer surface to the receptacle, wherein the stabbing member is disposed in the receptacle and coaxially aligned with the female member. The breakaway connection further includes a plurality of shear pins, wherein each shear pin is threadably disposed in one threaded hole, and wherein each shear pin has a radially inner end seated in the annular recess.