Flexible Pipe Riser Annulus Corrosion Protection via Buffer Fluid Circulation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Corrosion of armor wires and other steel elements within the annulus of flexible pipe risers in offshore hydrocarbon production facilities due to hydrogen sulfide, carbon dioxide, and water vapor diffusion, leading to corrosion fatigue and potential failure.
Innovation Solution
Circulating a corrosion-inhibiting fluid or buffer fluid through a closed loop within the annulus of the flexible pipe riser, which includes the annulus and an umbilical tube, to protect the armor wires and steel elements from corrosion by flushing out harmful gases and vapors, and optionally using image-sensitive materials for imaging purposes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the annulus is left open or vented to atmosphere, then corrosion products and harmful gases can escape, but corrosion of armor wires continues due to exposure to hydrogen sulfide, carbon dioxide, and water vapor
Solution Approach 1:
The patent introduces a buffer fluid (inert atmosphere) into the annulus to displace corrosive gases (hydrogen sulfide, carbon dioxide, water vapor) and create a protective environment around the armor wires. The buffer fluid acts as an inert barrier that prevents direct contact between corrosive substances and the steel armor wires, thereby reducing corrosion while maintaining system integrity.
2Reliability
If the annulus is sealed closed, then corrosion products accumulate and increase internal pressure, but corrosion of armor wires is reduced by preventing external corrosive substance ingress
Solution Approach 1:
The patent extracts harmful corrosive substances from the annulus environment by circulating a buffer fluid that absorbs and removes hydrogen sulfide, carbon dioxide, and water vapor. The circulation system continuously extracts these harmful components and replaces them with fresh buffer fluid, preventing accumulation while maintaining a protective atmosphere.
Solution Approach 2:
The patent implements a feedback mechanism through the buffer fluid circulation system that continuously monitors and adjusts the annulus environment. The circulation pump, controlled by a controller, maintains optimal buffer fluid levels and composition in the annulus, dynamically responding to changes in corrosive substance accumulation and ensuring continuous protection of the armor wires.
3Reliability
If buffer fluid is circulated through the annulus, then corrosion protection is enhanced by flushing out harmful gases, but system complexity increases due to additional circulation equipment
Solution Approach 1:
The patent makes the buffer fluid circulation system multi-functional by integrating it with existing umbilical infrastructure. The same umbilical that provides electrical power and control signals to the subsea template is also used to circulate the buffer fluid through the annulus. This eliminates the need for separate dedicated circulation lines and reduces overall system complexity.
Solution Approach 2:
The circulation system is designed to be self-regulating, where the buffer fluid naturally circulates through the annulus due to density differences created by temperature and composition variations. The system requires minimal external control and can maintain its own circulation without complex control mechanisms, reducing device complexity while ensuring continuous corrosion protection.
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
Reduces corrosion incidence and associated corrosion fatigue of armor wires, thereby extending the lifespan and reliability of the flexible pipe risers by creating a protective environment within the annulus.
Implementation Method 1
pumping the buffer fluid into a closed loop at sufficient pressure to cause buffer fluid to circulate through the loop
Implementation Method 2
These components, hydrogen sulfide in particular, as well as water vapor, can accumulate within the annulus
Data Source
AI summary
Disclosed is a process and system for circulating fluid within the annulus of a flexible pipe used in a riser in an offshore hydrocarbon production facility. Fluid, such as corrosion inhibitors, can be circulated in a closed loop which includes the annulus of the riser terminating at a platform or floating vessel, a fluid storage tank located on the platform or vessel and an umbilical tube terminating at the platform or vessel and at a subsea location. Use of the system to flow the fluid through the annulus can prevent or reduce corrosion of the steel members within the annulus and increase the fatigue life of the riser.