Subsea Protective Cap Locking System for Mandrel Sealing
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Solution Overview
Problem
Subsea wellhead assemblies face challenges during temporary abandonment, as they are susceptible to damage from external objects and corrosion in seawater, leading to issues with sealing and connection integrity due to corrosion and deposit formation, and existing protective cap assemblies are heavy, costly to install, and may not securely remain coupled to the mandrel.
Innovation Solution
A lightweight protective cap assembly with an active locking system that uses a locking pin with a vent channel and an actuator to securely engage the mandrel or hub, allowing for ROV installation and maintaining a sealing relationship while injecting corrosion inhibitor fluid to prevent corrosion and deposit formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective cap assembly is installed to prevent corrosion and damage to subsea equipment, then reliability is improved, but weight increases making installation costly
Solution Approach 1:
The protective cap assembly is divided into a cap body and a separate locking system with multiple locking assemblies. Each locking assembly includes a locking pin, actuator, and sealing elements that can be independently positioned and secured, allowing the system to protect subsea equipment while maintaining manageable weight through modular construction
Solution Approach 2:
The locking pin is designed with a groove that allows it to be driven through the cap body and engage with the mandrel or hub. The locking assemblies use composite construction with sealing elements and actuating mechanisms that reduce overall weight while maintaining structural integrity and protective function
2Reliability
If a locking system is used to secure the protective cap assembly, then reliability of coupling is improved, but device complexity increases
Solution Approach 1:
The locking system is designed to be self-securing through the interaction of locking pins, actuators, and sealing elements. Once the cap assembly is positioned on the mandrel or hub, the locking pins automatically engage with the grooves and shoulders, providing self-locking functionality that ensures reliable coupling without requiring complex external locking mechanisms
Solution Approach 2:
The actuators enable dynamic engagement and disengagement of the locking pins. The locking system transitions from an unlocked state during installation to a locked state during operation, providing adaptive security that simplifies the overall device structure while ensuring reliable coupling when needed
3Reliability
If corrosion inhibitor fluid is injected into the protective cap assembly, then protection effectiveness is improved, but risk of lifting and seal compromise increases
Solution Approach 1:
The locking system is designed to preemptively counteract the lifting force generated by corrosion inhibitor fluid injection. The locking pins engage with the grooves and shoulders of the mandrel or hub before injection begins, creating a pre-established mechanical connection that resists the upward force. The sealing elements are positioned to maintain the sealing relationship even under the stress of fluid injection pressure
Data Source
AI summary
An apparatus for installation to a subsea equipment mandrel or hub, including a body having a cylindrical sidewall defining one or more receptacles and a locking system to couple the body to the mandrel or hub. The locking system may include one or more locking assemblies received within a respective receptacle and coupled to the cylindrical sidewall. Each locking assembly may include a locking body, a locking collar, an annular seal, an actuator, and a locking pin. The annular seal may be seated within an annular groove and configured to engage the shoulder of a receptacle in a sealing relationship, and the locking collar may couple the locking body to the cylindrical sidewall. The actuator may be adjustably coupled to the locking body and configured to move radially. A locking pin may be configured to selectively engage the angled shoulder surface of the mandrel or hub.