Unbonded Flexible Pipe Annulus Corrosion Control
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Solution Overview
Problem
Unbonded flexible pipes in subsea applications face corrosion issues due to gases like CO2 and H2S permeating through the inner sheath into the annulus, leading to localized corrosion that can cause damage and reduce the fatigue life of the riser, with existing methods either causing environmental harm or being ineffective in preventing localized damage.
Innovation Solution
Filling the annulus of the unbonded flexible pipe with a corrosion-promoting liquid, comprising at least 30% water and optional electrolytes, to evenly distribute corrosive gases and induce controlled corrosion, thereby preventing localized damage and extending the service life of the pipe.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the annulus is left empty or filled with conventional protective materials, then the pipe structure remains simple and installation is easy, but localized corrosion occurs causing damage and reduced fatigue life
Solution Approach 1:
The invention changes the chemical and physical parameters of the annulus by introducing a corrosion-promoting liquid with specific composition (pH 2-4, specific conductivity 0.5-5.0 S/m, density 1000-1200 kg/m³). This liquid creates controlled corrosion conditions that prevent localized damage while extending fatigue life, resolving the contradiction between reliability and structural simplicity.
2Reliability
If corrosion protection methods are applied to prevent localized damage, then the fatigue life is extended, but environmental harm may occur
Solution Approach 1:
The corrosion-promoting liquid is designed with controlled parameters (pH 2-4, specific conductivity 0.5-5.0 S/m) that enable effective corrosion protection while maintaining environmental compatibility. The liquid promotes uniform corrosion that is controllable and does not cause harmful environmental effects, thus extending fatigue life without environmental harm.
3Duration of action of stationary object
If the annulus is filled with corrosion-promoting liquid, then localized corrosion is prevented and fatigue life is extended, but the installation process becomes more complex
Solution Approach 1:
The corrosion-promoting liquid is introduced into the annulus during the installation process as a preliminary action. This allows the liquid to be in place before the pipe enters service, ensuring immediate protection against localized corrosion from the moment corrosive gases begin to permeate. The liquid can be introduced through injection ports or by filling the annulus during assembly, integrating the protection mechanism into the installation workflow.
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 method ensures even distribution of corrosion, reducing the risk of localized damage and maintaining the integrity of the armoring layers throughout the expected service life of the pipe, while being environmentally benign and cost-effective.
Implementation Method 1
gases like CO2 and H2S permeating through the inner sheath into the annulus
Implementation Method 2
gases like CO2 and H2S permeating through the inner sheath into the annulus
Implementation Method 3
induce controlled corrosion, thereby preventing localized damage and extending the service life of the pipe
Implementation Method 4
comprising at least 30% water and optional electrolytes
Data Source
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AI summary
The present invention relates to a method of installing an unbonded flexible pipe with a bore for transportation of fluid wherein the unbonded flexible pipe comprises an outer sheath, an inner sealing sheath inside the outer polymer sheath, an annulus between said outer sheath and said inner sealing sheath and at least one metallic armor layer comprising iron located in said annulus, wherein the method comprises filling at least a part of the annulus with a corrosion promoting liquid before or after installing the unbonded flexible pipe between a first installation and a second installation.