Flex-lock Metal Seal System for Wellhead Thermal Growth
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Solution Overview
Problem
Existing metal-to-metal seals in wellhead assemblies face leakage issues due to thermal growth and axial displacement, which reduces sealing forces and can cause leaks under thermal transients.
Innovation Solution
A metal seal ring with inner and outer conical surfaces separated by a conical slot, featuring an internal cavity in the energizing ring that allows deflection within the elastic range, maintaining radial preload forces and accommodating thermal displacements without loss of sealing engagement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a solid wedge-shaped energizing ring is used to deform the seal ring into sealing engagement, then the seal ring achieves initial sealing contact, but the sealing force is reduced during thermal transients due to axial displacement
Solution Approach 1:
The energizing ring is designed with a flexible structure featuring an internal cavity that allows it to deflect and flex during thermal transients. This flexibility enables the energizing ring to maintain radial inward and outward forces on the seal ring walls even when axial displacement occurs, ensuring continuous sealing contact without requiring rigid solid construction
Solution Approach 2:
The energizing ring's physical state changes during thermal transients - it deflects and flexes in response to temperature variations and axial displacement. This parameter change allows the ring to adapt its shape and maintain sealing force despite changes in operational conditions, transforming from a static solid wedge to a dynamically flexible component
2Reliability
If the seal ring is set by wedging action with axial displacement of energizing rings, then sealing engagement is achieved, but radial loading is lost due to thermal growth
Solution Approach 1:
The energizing ring transitions from a static pre-load mechanism to a dynamic flexible structure that actively responds to thermal conditions. The internal cavity allows the ring to flex and deflect in real-time during thermal transients, maintaining radial loading on the seal ring walls despite axial displacement and temperature changes, rather than relying on fixed initial positioning
3Reliability
If permanent deformation beyond yield strength is applied to the seal ring, then sealing engagement is achieved, but the seal cannot accommodate thermal movement
Solution Approach 1:
The energizing ring with its internal cavity acts as a flexible element that can deflect and flex elastically in response to thermal expansion and contraction. This flexibility allows the system to accommodate thermal movement of the seal ring and wellhead members while maintaining sealing contact, avoiding the need for permanent plastic deformation that would prevent such accommodation
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 seal ring maintains constant sealing forces and integrity under thermal conditions, ensuring a gas-tight seal even with reduced axial force, as the stored energy from the energizing ring's cavity compensates for thermal-induced movements.
Implementation Method 1
The energizing ring has an internal cavity located between the inner and outer conical surfaces to allow the inner and outer conical surfaces to deflect toward each other during installation. The deflection is within the elastic range of the energizing ring, thus creating radial inward and outward preload forces.
Implementation Method 2
Thermal growth between the casing or tubing and the wellhead may occur, particularly with wellheads located at the surface, rather than subsea. The temperature increase may cause the tubing hanger and/or casing hanger to move axially a slight amount relative to the outer wellhead member.
Data Source
AI summary
A wellhead seal assembly forms a metal-to-metal seal between the inner and outer wellhead members. A metal seal ring has inner and outer conical walls separated by a tapered slot. An energizing ring has inner and outer annular members that are separated by an annular cavity. When the energizing ring is moved further into the slot, the cavity width decreases but remains to provide a preloaded radial force to the seal ring.