Unbonded Flexible Pipe Secondary Maintaining Passage Corrosion Control
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Solution Overview
Problem
Flexible pipes used for offshore fluid transportation, particularly for hydrocarbons and gases, face corrosion issues due to gas migration through the inner sealing sheath into the annulus, leading to reduced durability and potential damage from accumulated pressure.
Innovation Solution
The implementation of an unbonded flexible pipe design with a secondary maintaining passage system that allows for continuous or intermittent flushing of the annulus with a maintaining fluid, reducing corrosion of armouring elements and extending the pipe's lifespan without significant complexity or cost increase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If gas migration through the inner sealing sheath is allowed to occur, then pressure buildup in the annulus can be relieved, but corrosion of armouring elements occurs reducing pipe durability
Solution Approach 1:
The patent extracts the harmful gas (CO2, H2S, H2O) that migrates through the inner sealing sheath by providing a dedicated drainage system. The drainage conduit removes these gases from the annulus, preventing them from causing corrosion to the armouring elements while maintaining the ability to relieve pressure buildup.
Solution Approach 2:
The patent introduces an intermediary substance (maintaining fluid) that is circulated through the drainage conduit to actively remove harmful gases from the annulus. This maintaining fluid acts as a mediator between the harmful gases and the armouring elements, preventing direct contact and corrosion while allowing pressure management.
2Object-affected harmful factors
If a drainage system is added to remove permeate gases, then corrosion is reduced, but device complexity increases
Solution Approach 1:
The drainage conduit serves multiple functions: it drains harmful gases from the annulus, provides a pathway for maintaining fluid circulation, and can accommodate sensors for monitoring annulus conditions. By combining these functions into a single structural element, the patent reduces overall system complexity compared to having separate systems for each function.
Solution Approach 2:
The drainage conduit can be implemented as a flexible structure that integrates with the existing pipe layers. The conduit may be positioned within or between existing armouring layers, utilizing the flexible nature of the pipe construction to incorporate the drainage system without significantly increasing overall complexity or rigidity.
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 secondary maintaining passage system effectively minimizes corrosion of armouring elements in the annulus, thereby increasing the pipe's durability and operational life while maintaining the flexibility and ease of production of existing flexible pipes.
Implementation Method 1
The secondary maintaining passage is arranged such that a maintaining fluid can be flushed in the pathway provided by the primary and secondary maintaining passages
Data Source
Figure 1~2
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Figure 5~6a
AI summary
The invention relates to an unbonded flexible pipe for sub sea transportation of fluids. The pipe has a length and comprises a tubular inner sealing sheath (2) defining a bore and an axis (8) of the pipe. In a pipe length section it comprises a second sealing sheath (9) surrounding the inner sealing sheath (2) and forming an annulus between the inner sealing sheath and the second sealing sheath. The annulus provides a primary maintaining passage along the length of the pipe length section with a first and a second end. The pipe comprises at least one secondary maintaining passage (5) along the length of the pipe with a first and a second end. The secondary maintaining passage is arranged with an axial distance which is larger than the axial distance of the inner sealing sheath (2). The first end of one of the primary and the secondary maintaining passages is arranged as an input end for a maintaining fluid and the first end of the other of the primary and the secondary maintaining passages is arranged as an outflow end for the maintaining fluid, and the primary and the secondary maintaining passages are in fluidic connection with each other at their second ends to provide a pathway for the maintaining fluid. The pathway for a maintaining fluid makes it possible in a simple and effective manner to keep the corrosion of elements - such as armouring elements in the annulus - relativly low, and accordingly the duration of the unbonded flexible pipe can thereby be increased.