Flexible Pipe Annulus Circulation for Corrosion Control
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Solution Overview
Problem
Flexible pipelines in offshore petroleum production are prone to corrosion due to corrosive gases like CO2 and H2S, which current technologies fail to adequately address, especially when the annulus loses integrity, leading to stress corrosion and pitting corrosion, and existing solutions do not provide effective forced circulation methods to mitigate these issues.
Innovation Solution
A system and method for forced circulation of fluids through the annulus of flexible pipes, comprising injector and return pipes for each segment, allowing independent circulation, leak testing, and injection of inert fluids to remove corrosive agents, with optional valves for controlling fluid communication between segments, enabling efficient removal of corrosive fluids and maintenance of the armour.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional flexible pipe construction without integrated forced circulation system is used, then the pipe structure is simpler, but corrosive gases accumulate in the annulus causing stress corrosion and pitting corrosion
Solution Approach 1:
The flexible pipe is divided into multiple segments with independent forced circulation systems in each segment. Each segment has its own injector and return pipes, allowing localized corrosion protection without requiring a complete system redesign of the entire pipe. This segmentation enables targeted circulation control and simplifies the overall system architecture.
Solution Approach 2:
The forced circulation system serves multiple functions: it removes corrosive gases from the annulus, provides leak detection capabilities through pressure monitoring, enables sampling of annulus contents, and maintains armour integrity. This multi-functionality reduces the need for separate systems and justifies the added complexity by delivering comprehensive protection.
2Productivity
If annular space is restricted with conventional layers, then the pipe structure is more compact, but circulation of corrosive gases and fluids becomes difficult
Solution Approach 1:
The system uses hydraulic principles by injecting fluid at one end of the annulus and relying on pressure differential to force circulation through the restricted space. The injector creates a pressure gradient that drives the circulation of corrosive gases and fluids through the narrow annular gap, overcoming the geometric restrictions imposed by compact pipe design.
Solution Approach 2:
The circulation system is designed to be dynamically adjustable, with controllable injectors that can modify flow rates and pressure levels based on operational conditions. This dynamic capability allows the system to maintain effective circulation even in restricted annular spaces by adapting flow parameters to the specific geometric constraints of each pipe configuration.
3Reliability
If segments are interconnected for gas reduction, then corrosive gas concentration decreases, but water condensation and sea water ingress cannot be prevented
Solution Approach 1:
The forced circulation system operates continuously to maintain protective conditions in the annulus. By constantly circulating fluid through the annular space, the system prevents water condensation by maintaining temperature and flow, and prevents sea water ingress by maintaining positive pressure. This continuous action provides ongoing protection against multiple harmful factors simultaneously.
Solution Approach 2:
The circulated fluid acts as an intermediary medium that protects the armouring from direct contact with corrosive substances. The fluid circulation creates a protective barrier between the corrosive environment (corrosive gases, condensed water, sea water) and the armouring, preventing corrosion mechanisms while allowing the pipe structure to remain compact.
4Difficulty of detecting and measuring
If independent circulation systems are provided for each segment, then leak detection and maintenance become easier, but the system complexity increases
Solution Approach 1:
The flexible pipe is divided into multiple segments with independent forced circulation systems in each segment. Each segment has its own injector and return pipes, allowing localized corrosion protection without requiring a complete system redesign of the entire pipe. This segmentation enables targeted circulation control and simplifies the overall system architecture.
Solution Approach 2:
The system incorporates monitoring capabilities that provide feedback on the condition of each segment. By measuring parameters such as pressure, flow rate, and temperature in each segment's circulation system, the system can detect leaks or anomalies and trigger appropriate responses. This feedback mechanism simplifies leak detection by providing real-time data from each segment independently.
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 solution effectively reduces corrosive fluid concentrations, prevents corrosion, allows individualized leak detection and maintenance, and facilitates sampling for quality analysis, thereby enhancing the integrity and longevity of flexible pipelines.
Implementation Method 1
a system configured to force circulation of fluids through an annulus between an inner barrier and an outer cover of a pipe
Implementation Method 2
an injector pipe configured to inject circulating fluid substantially at a first end of the annulus
Implementation Method 3
a return pipe configured to remove circulating fluid from the annulus of the segment, the return pipe being positioned at a second end of the annulus
Data Source
AI summary
Pipelines with a control system and forced circulation of fluids through the annulus between an inner barrier and an outer cover of a pipe use a system configured to force circulation of fluids through the annulus. The pipe includes segments (T1, T2, T3, TN) joined together by means of connectors, wherein each segment of the pipe has an injector pipe (I1, I2, I3, IN) for injecting fluid into the annulus at a first end of the segment, and a return pipe (R1, R2, R3, RN) for removing fluid from the annulus at a second end of the segment.