Adjustable Riser Suspension Locking Mechanism
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Solution Overview
Problem
Existing solutions for shortening risers under tension in offshore oil and gas production are either wasteful by removing material or costly due to the difficulty of threading under extreme axial loads.
Innovation Solution
An adjustable riser suspension system that uses a riser hanger, mating sleeve, and ratchet-latch mechanism to lock the riser in place, allowing for tensioning without material removal or excessive threading, utilizing a running tool with hydraulic expansion to achieve and maintain desired tension.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the inner riser is shortened by clamping and cutting while lifting under tension, then the desired tension is achieved, but material is removed from each successive riser making the solution wasteful
Solution Approach 1:
The riser shortening process is divided into two independent stages: (1) tensioning the riser to the desired level while it remains fully extended, and (2) subsequently shortening the riser by threading the suspension system. This segmentation allows the riser to be tensioned first without material removal, then shortened afterward using a threaded mechanism that does not require extreme axial loads.
Solution Approach 2:
The riser is tensioned to the desired level before any shortening operation occurs. The suspension system is threaded onto the riser while the riser is in its tensioned state, allowing the threading process to occur at a more favorable load condition rather than attempting to thread under extreme axial tension.
2Reliability
If the inner riser is shortened by tightening a threaded portion while lifting under tension, then the desired tension is achieved, but the threads must be very robust and have very tight tolerances making the solution costly
Solution Approach 1:
The riser is tensioned to the desired level before the threaded suspension system is engaged. This preliminary tensioning allows the threading operation to occur when the axial load on the riser is already managed, rather than attempting to thread the suspension system while the riser is under extreme axial tension.
Solution Approach 2:
The system transitions from a static threaded connection (which would require extreme axial loads to tighten) to a dynamic process where the riser is first tensioned independently, then the threaded suspension system is engaged at a more favorable load state. This dynamic approach allows standard threading tolerances and robustness to suffice.
3Force
If the riser is lifted to achieve desired tension, then the weight on the subsea wellhead is reduced, but the riser must be shortened to compensate for length increase from tension making the process complex
Solution Approach 1:
The riser suspension system integrates multiple functions into a single threaded component: (1) it provides the tensioning mechanism by being threaded onto the riser, (2) it serves as the shortening mechanism through the threading action itself, and (3) it provides the anchoring function to maintain the desired tension. This merging eliminates the need for separate clamping, cutting, and anchoring operations.
Solution Approach 2:
The threaded suspension system performs multiple functions simultaneously: it tensions the riser, shortens the riser to the correct length, and anchors the riser to maintain tension. This universal component replaces what would otherwise require multiple separate devices and operations including clamps, cutting tools, and anchoring mechanisms.
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
Enables efficient and cost-effective tensioning and locking of risers, reducing material waste and operational costs while maintaining desired tension without the need for extreme threading.
Implementation Method 1
a ratchet-latch sleeve located inside the mating sleeve with an external profile configured to engage an internal profile of the mating sleeve and an internal profile configured to engage an externally threaded face of the riser. The riser hanger and mating sleeve are configured to move downward relative to the riser such that the mating sleeve fits over at least a portion of the riser, causing the ratchet-latch device to ratchet over the external threads of the riser.
Implementation Method 2
urging the riser hanger downward relative to the riser, causing a mating sleeve to move over at least a portion of the riser
Data Source
AI summary
An adjustable riser suspension system for suspending a riser under tension including a riser hanger, a mating sleeve rotationally coupled to the riser hanger, a ratchet-latch sleeve located inside the mating sleeve with an external profile configured to engage an internal profile of the mating sleeve and an internal profile configured to engage an externally threaded face of the riser. The riser hanger and mating sleeve are configured to move downward relative to the riser such that the mating sleeve fits over at least a portion of the riser, causing the ratchet-latch device to ratchet over the external threads of the riser. The mating sleeve is configured to rotate relative to the riser, causing the internal and external profiles of ratchet-latch device to lock the riser and the mating sleeve to prevent movement of the riser relative to the mating sleeve.