Lockdown Member for Wellhead Seal Energizing Ring
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Solution Overview
Problem
High pressure cycles and temperature cycles can cause the energizing ring in subsea wellhead seals to move upward, leading to a loss in seal pressure rating, and existing solutions fail to effectively prevent this upward loosening movement.
Innovation Solution
A lockdown member is designed to secure the energizing ring in a set position by exerting a downward preload force, with a lower end that bears against both the energizing ring and the casing hanger, and includes a split ring that engages with annular retaining grooves in the wellhead housing to prevent axial movement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the energizing ring is allowed to move freely under cyclic stresses, then the seal can accommodate pressure and temperature changes, but the energizing ring moves upward causing loss in seal pressure rating
Solution Approach 1:
The lockdown member is pre-installed in the wellhead housing with its lower end positioned to bear against the upper end of the energizing ring. This preliminary positioning ensures that when the energizing ring is set in its downward position, the lockdown member is already in place to prevent upward movement, thus maintaining seal pressure rating while allowing the seal to accommodate cyclic stresses
Solution Approach 2:
The lockdown member acts as an intermediary element between the energizing ring and the wellhead housing. It transfers the constraint force from the wellhead housing to the energizing ring, preventing upward movement without interfering with the seal's ability to accommodate pressure and temperature cycles. The lockdown member mediates between the need for seal adaptability and the need for pressure rating maintenance
2Reliability
If a lockdown member is added to prevent upward movement of the energizing ring, then the seal pressure rating is maintained, but the device complexity increases
Solution Approach 1:
The lockdown member is segmented into distinct functional portions: an upper portion that bears against the energizing ring and a lower portion that bears against the casing hanger. This segmentation allows each portion to perform its specific function independently, simplifying the overall design while maintaining reliability. The split ring configuration also segments the locking mechanism into manageable parts that can be installed and maintained separately
Solution Approach 2:
The lockdown member serves multiple functions simultaneously: it prevents upward movement of the energizing ring, maintains seal pressure rating, and provides a mechanical constraint without requiring additional complex mechanisms. The same structure that prevents movement also provides the bearing surfaces for force transmission, eliminating the need for separate components for each function
3Force
If the lockdown member bears against both the energizing ring and casing hanger, then the preload force is effectively applied, but the manufacturing precision requirements increase
Solution Approach 1:
The lockdown member is designed with bearing surfaces that create equipotential contact zones with the energizing ring and casing hanger. The upper portion's bearing surface against the energizing ring and the lower portion's bearing surface against the casing hanger are positioned to ensure uniform force distribution. This equipotential design allows the preload force to be applied effectively without requiring extremely tight alignment tolerances, as the force is distributed across optimized contact areas
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 lockdown member effectively maintains the seal pressure rating by preventing upward movement of the energizing ring, ensuring reliable containment of internal well pressure despite cyclic stresses.
Implementation Method 1
the lockdown member exerts a downward preload force on the energizing ring while the energizing ring is in the set position
Implementation Method 2
A split ring, when actuated, mates with annular retaining grooves formed in the wellhead housing bore
Implementation Method 3
the energizing ring pushed into the slot in the seal to deform the inner and outer walls apart into sealing engagement
Implementation Method 4
The setting tool forces the seal surfaces of the seal assembly against the wickers, causing the crests to embed into the seal surface
Data Source
AI summary
A wellhead housing has a bore with a landing shoulder aid an annular retaining groove spaced above the landing shoulder. A casing hanger connects to a string of easing and lands on the landing shoulder. A seal assembly between the hanger and an interior side wall of the wellhead housing below the retaining groove has an energizing ring that moves axially downward relative to the seal member to a set position that causes the seal member to sealingly engage the hanger and the interior side wall. A lockdown member has an outer lower end portion that bears against an upper end of the energizing ring and an inner lower end portion that hears against an upper end of the hanger. A lockdown ring mounted to the lockdown member engages the retaining groove to prevent upward movement of the lockdown member.