Decoupled Central Ring Swivel for Offshore Sealing
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Solution Overview
Problem
Current swivel designs for offshore hydrocarbon production face challenges in manufacturing accuracy due to complex non-linear parameters affecting seal annulus gap variations, requiring advanced Finite Element Analysis and high machining accuracies, leading to potential seal failures from 3D effects and non-uniform deformations.
Innovation Solution
The swivel design features upper and lower bearing structures with independently displaceable central ring members relative to the upper and lower ring members, decoupling them axially to minimize internal loads and enhance stiffness near the bearings, using L-shaped ring members and static sealing elements to maintain seal integrity under thermal, pressure, and mechanical loading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If advanced Finite Element Analysis and high machining accuracies are used to govern seal annulus gap variation, then sealing reliability is improved, but manufacturing complexity and cost increase significantly
Solution Approach 1:
The inner ring is segmented into multiple independent rings (first inner ring, second inner ring, third inner ring) that can move independently relative to each other. This segmentation allows each ring to accommodate deformations locally without requiring complex overall design analysis, simplifying manufacturing while maintaining sealing reliability.
Solution Approach 2:
The invention changes the design parameter from fixed rigid rings to rings with controlled mobility and compliance. The inner rings are designed to move axially and radially within defined ranges, allowing the system to adapt to pressure-induced deformations without requiring precise pre-calculation of all deformation parameters through FEA.
2Reliability
If the number of stacked machined rings is increased to achieve the desired seal annulus gap, then sealing performance is improved, but cumulated fabrication tolerances increase leading to unsuitable seal extrusion gaps
Solution Approach 1:
Rather than using many thin rings that accumulate tolerance errors, the invention uses a few substantial inner rings (first, second, and third inner rings) with defined mobility. This reduces the number of machining interfaces and minimizes cumulated fabrication tolerances while maintaining consistent seal annulus gaps.
Solution Approach 2:
The inner rings are designed with controlled mobility allowing them to move dynamically in response to pressure changes. This dynamic capability compensates for manufacturing variations, ensuring consistent seal annulus gaps without requiring extremely tight machining tolerances on each individual ring.
3Reliability
If face seals are mounted in complementary stepped annular regions, then sealing capability is improved, but the axial sealing space decreases due to Poisson's effect under pressurisation
Solution Approach 1:
The sealing system is segmented into multiple independent sealing zones with multiple inner rings. Each ring-carrier assembly can deform independently, distributing the Poisson's effect across multiple zones rather than concentrating it in a single axial region, thereby preserving axial sealing space.
Solution Approach 2:
The invention introduces axial mobility of inner rings as an additional degree of freedom. Instead of relying solely on radial face seal contact, the inner rings can move axially to accommodate pressure-induced deformations, effectively adding a dimensional compliance mechanism that preserves sealing capability while maintaining axial space.
4Length of moving object
If the outer seal ring deflects outwardly due to pressurisation, then axial sealing space increases, but radial deformations become non-uniform affecting seal performance
Solution Approach 1:
The outer seal ring is segmented into multiple independent inner rings that can deform independently. This segmentation allows non-uniform radial deformations to occur locally in each ring without affecting the entire sealing system, maintaining overall seal performance while accommodating necessary axial space variations.
Solution Approach 2:
Each inner ring is designed with specific local properties allowing it to deflect radially by different amounts based on local pressure conditions. This local quality approach allows non-uniform radial deformations to occur naturally in each ring while the overall sealing system maintains performance through the collective action of all rings.
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 design improves manufacturing accuracy, reduces seal annulus gap variations, and enhances sealing area stiffness, minimizing deformations and seal failures by decoupling ring members and using static sealing elements, ensuring reliable fluid containment.
Implementation Method 1
the inner and outer rings being rotatably interconnected via a bearing structure
Implementation Method 2
upper and lower sealing members being situated in the seal annulus gap
Data Source
AI summary
A swivel includes an inner and an outer ring. The rings are coaxial and rotatable relative to one another around a central axis, and define a toroidal chamber and an axial seal annulus gap between the rings. The inner and outer rings are rotatably interconnected via a bearing structure. The swivel includes an upper bearing structure and a lower bearing structure on each side of the toroidal chamber. Each bearing structure interconnects the inner and outer rings. An upper and a lower sealing member is situated in the seal annulus gap near a respective upper and lower bearing structure. At least one of the inner and outer rings includes an upper member, a lower member and a central member. The upper and lower members are fixedly attached to the respective upper and lower bearing structures and the central member is independently displaceable relative to the upper and lower ring members.