Swivel Stack Annular Seal Layout for High-Pressure Seal Change-Out
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Solution Overview
Problem
Existing swivel stacks face challenges in maintaining seal integrity and ease of seal replacement due to high pressure differences and mechanical wear, particularly in offshore oil and gas applications, where the large size of swivel parts complicates in-situ seal change-outs and makes it difficult to meet seal design criteria for varying diameters, temperatures, and pressures.
Innovation Solution
A swivel stack design featuring a rotary interface composed of annular elements with a radial gap and toroidal chamber, allowing for easier assembly and disassembly, and the use of face seal type seal rings in annular cavities, along with a coupling ring system for joined rotation, which minimizes hydraulic area and reduces the vertical force on seals, enabling simpler seal replacement and improved seal performance under high pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of repair
If traditional swivel stack design is used, then seal integrity can be maintained under high pressure, but seal replacement becomes extremely difficult due to large size and complex assembly
Solution Approach 1:
The rotary interface is divided into multiple separable components including a first rotary element, a second rotary element, and a coupling element that connects them. This segmentation allows the seal components to be accessed and replaced independently without disassembling the entire swivel stack, significantly easing maintenance while maintaining structural integrity under high pressure.
Solution Approach 2:
The coupling element is designed to connect the first and second rotary elements in a nested configuration, where the coupling element fits between the two rotary elements. This nested structure allows for compact assembly while enabling straightforward disassembly for seal replacement, reducing both device complexity and maintenance difficulty.
2Reliability
If seal diameter and operating pressure are increased to meet design criteria, then seal performance improves, but mechanical wear and replacement difficulty increase
Solution Approach 1:
By segmenting the rotary interface into separable elements with accessible seal components, the design enables replacement of large-diameter seals without increasing overall replacement difficulty. The segmented structure provides access points for seal maintenance even as seal size and pressure ratings increase.
Solution Approach 2:
The coupling element acts as an intermediary component that facilitates seal access and replacement. It provides a mechanical interface that allows maintenance personnel to work on seals without handling the entire heavy swivel assembly, making large seal replacement feasible even under high-pressure design criteria.
3Duration of action of stationary object
If vertical force on seals is reduced to minimize hydraulic area, then seal life extends, but structural strength may be compromised
Solution Approach 1:
The segmentation of the rotary interface allows the vertical load to be distributed across multiple components (first rotary element, second rotary element, and coupling element) rather than concentrated on the seals alone. This load distribution extends seal life by reducing vertical force while maintaining overall structural strength through the composite structure.
Solution Approach 2:
The coupling element is positioned and designed to counterbalance some of the vertical hydraulic forces acting on the seals. By providing a mechanical counterweight effect, it reduces the net vertical force on the seals, extending their service life while the distributed structural components maintain the required strength.
Data Source
AI summary
A swivel stack for transfer of fluid across a rotary interface around a rotation axis between incoming and outgoing flow-lines, includes: a group of lower, upper and central annular elements; the lower, upper and central element each being centered around the axis; the central element positioned between the lower and upper elements; an outer annular element centered around the axis between the lower and upper elements; a toroidal chamber between the central and outer elements; downward and upward facing surfaces of the outer element being adjacent to the upward surface of the lower element and the downward surface of the upper element; the lower element's upward surface and the upper element's downward surface having a first stepped surface and the outer element's upward and downward surfaces have a second stepped surface, such that at least two annular cavities centered around the rotation axis are provided.