Subsea Tree Cap with Buoyancy and Self-Aligning Lock
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Solution Overview
Problem
Existing subsea tree caps require specific radial alignment for installation, which can damage seals and is difficult to manage with a remote-operated vehicle (ROV), and they often trap fluid that causes corrosion and hinder proper landing on the tree spool.
Innovation Solution
A retrievable tree cap with integral buoyancy and a hot stab injector that allows hydraulic locking and sealing, enabling installation at any radial orientation, fluid pressure to set seals, and a mechanism to remove trapped water and inject corrosion inhibitors, while being lightweight and orientable for easy ROV handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a tree cap requires specific radial alignment for installation, then the sealing can be ensured, but the installation difficulty increases and seal damage risk increases when using ROV
Solution Approach 1:
The locking mechanism profile is designed with asymmetric features that can only engage in one orientation, automatically guiding the tree cap to the correct radial alignment during installation. This eliminates the need for precise manual alignment while ensuring proper seal engagement.
Solution Approach 2:
The tree cap incorporates self-aligning features where the locking profile and seal carrier automatically orient the cap to the correct radial position during insertion. The mechanism self-corrects orientation without requiring external alignment tools or complex ROV manipulation.
2Strength
If the tree cap is made heavier for structural integrity, then the locking mechanism can be more robust, but the ROV handling difficulty increases
Solution Approach 1:
Buoyant material is integrated into the tree cap structure to counterbalance the weight of the metal components. This reduces the effective submerged weight, making the cap easier for the ROV to manipulate and install while maintaining the structural strength needed for robust locking mechanisms.
Solution Approach 2:
The tree cap uses composite construction combining metal components for strength with buoyant materials for weight reduction. This composite approach maintains structural integrity for robust locking while improving ROV handling characteristics through reduced effective weight.
3Ease of operation
If fluid is trapped within the tree cap cavity during installation, then the landing on tree spool is hindered, but adding drainage mechanisms increases device complexity
Solution Approach 1:
Drainage ports and corrosion inhibitor injection ports are pre-configured in the tree cap structure to automatically drain trapped fluid during the installation process. This preliminary drainage action ensures proper landing on the tree spool without requiring complex active drainage systems.
Solution Approach 2:
The drainage ports serve multiple functions: they drain trapped installation fluid, allow corrosion inhibitor injection, and provide pressure equalization. This multi-functionality reduces device complexity by combining several needed features into simple integrated ports.
4Reliability
If corrosion inhibitor injection capability is added, then corrosion prevention is improved, but the device complexity increases
Solution Approach 1:
The same drainage ports in the tree cap structure are designed to serve dual purposes: draining trapped fluid during installation and injecting corrosion inhibitors during operation. This multi-functional design provides corrosion protection without adding separate injection mechanisms, thereby avoiding increased device complexity.
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
Facilitates secure and damage-free installation of the tree cap on subsea trees, reduces submerged weight, prevents corrosion, and allows for efficient sealing and pressure testing, enhancing operational safety and efficiency.
Implementation Method 1
The tree cap may include buoyant material, such as syntactic foam, to decrease the submerged weight of the tree cap. The buoyant material may be configured to orient the tree cap in a vertical position when submerged.
Implementation Method 2
A hot stab injector may be used to apply fluid pressure to the tree cap to first engage a first locking mechanism to selectively lock the tree cap to the subsea tree and to then the pressure may be used to set or energize a plurality of seals within the bore of the subsea tree.
Data Source
AI summary
A retrievable tree cap for use on a subsea tree having a concentric bore. The tree cap may be installed and retrieved using a remotely operated vehicle. Hydraulic pressure may be used to lock the tree cap onto the subsea tree and to set the tree cap seals. The tree cap is locked onto the subsea tree before setting the seals within the concentric bore. The tree cap includes a locking means that may engage a profile within the subsea tree regardless of the radial orientation of the tree cap. The tree cap may be used to hydraulically isolate an annulus bore from the production bore of the subsea tree. The tree cap may provide for the injection of a corrosion inhibitor within a cavity of the tree cap and may also provide for the removal of water trapped between the tree cap and the subsea tree.