Flexible Pipe End-Fitting Insulation for Leak Current Suppression
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Solution Overview
Problem
Unbonded flexible pipes used for offshore hydrocarbon transport face issues with leak currents due to high flexibility and the need for electric heating, leading to local heating, sparks, and eventual system failure.
Innovation Solution
An end-fitting design with mechanically anchored armour layers and electrical insulation between them, incorporating a local volume for a functional fluid to prevent unintended current paths, using materials like carbon steel and insulating fluids such as transformer oil or SF6 to suppress leak currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If electric heating is applied to the unbonded flexible pipe, then the transport of viscous hydrocarbons is improved, but leak currents occur causing local heating and sparks
Solution Approach 1:
An electrically insulating layer is introduced as an intermediary between the first and second armour layers to prevent unintended current paths. This insulating layer acts as a mediator that blocks leak currents while allowing the electric heating system to function effectively for transporting viscous hydrocarbons.
Solution Approach 2:
The harmful leak current paths are extracted and eliminated by removing the electrical conductivity between armour layers through the insulating layer. This separates the heating function from the structural armour layers, preventing sparks and local heating while maintaining heating effectiveness.
2Device complexity
If metallic armour layers are used as electrical conductors for heating, then the heating system is simplified, but unintended current paths occur through the armour layers
Solution Approach 1:
An electrically insulating layer is placed between the first and second armour layers to prevent unintended current paths. This insulating layer acts as a mediator that blocks leak currents while allowing the electric heating system to function effectively.
Solution Approach 2:
The insulating properties are applied locally at the interface between armour layers where leak currents occur, rather than making the entire armour structure insulating. This maintains the simplicity of using metallic armour as conductors while preventing harmful current paths at critical locations.
3Ease of operation
If the unbonded flexible pipe is made highly flexible for offshore installation, then the ease of installation is improved, but the electrical insulation between armour layers deteriorates
Solution Approach 1:
A dedicated electrically insulating layer is introduced as an intermediary between armour layers to provide reliable electrical insulation that maintains its insulating properties even when the pipe is flexed during offshore installation and operation.
Solution Approach 2:
The pipe structure uses composite construction with metallic armour layers for flexibility and strength, combined with an electrically insulating layer for electrical isolation. This composite structure maintains both the flexibility needed for offshore installation and the electrical insulation reliability.
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 leak currents, preventing local heating and spark formation, thereby extending the lifespan of the electrical insulation and reducing the risk of galvanic corrosion in the end-fitting.
Implementation Method 1
the first and the second armour layers being electrically insulated from each other by at least one electrically insulating layer in the end-fitting, wherein a local volume in the end-fitting adjacent to the electrically insulating layer is adapted for injection of a functional fluid
Implementation Method 2
The functional fluid may be a moisture absorbing fluid
Implementation Method 3
a current of several hundred Amperes is needed. As the unbonded flexible pipes may have a length of several hundred meters or more, the voltage needed to drive the required current through the pipes is typically in the order of several thousand volts
Data Source
AI summary
The present invention relates to an assembly including an end-fitting for terminating an unbonded flexible pipe and an unbonded flexible pipe. The unbonded flexible pipe includes a first and a second armour layer co-axially arranged, and an electric heating system. The end-fitting includes means for mechanically anchoring the first armour layer to the end-fitting and includes electrical connections for connecting the first armour layer to a power-source. The end-fitting also includes means for mechanically anchoring the second armour layer to the end-fitting. The first and the second armour layers are electrically insulated from each other by at least one electrically insulating layer in the end-fitting and the end-fitting includes a local volume in the end-fitting adjacent to the electrically insulating layer adapted for injection of a functional fluid.