Flexible Pipe Armour Cathodic Protection With Distributed Anodes
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Solution Overview
Problem
Conventional cathodic protection systems for flexible pipes in deep and ultra-deep water environments face limitations due to attenuation effects, requiring frequent end fittings and increasing complexity and cost, while providing effective protection along the entire length of the pipe remains a challenge.
Innovation Solution
The implementation of a flexible pipe design featuring helically wound monofilament armour wires with non-circular cross sections and interposed elongate anode elements, made from more reactive materials like magnesium, aluminium, or zinc, which extend along the pipe length and provide effective cathodic protection by reducing attenuation effects and allowing for local anode sites.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional cathodic protection systems are used with traditional anode placement, then corrosion protection is provided at discrete locations, but attenuation effects require frequent end fittings increasing complexity and cost
Solution Approach 1:
The cathodic protection system is segmented into multiple independent anode elements distributed along the pipe length, each providing localized protection. This segmentation allows the system to maintain effectiveness without requiring frequent end fittings, as each anode element operates independently to protect its local zone.
Solution Approach 2:
Conductive tape is introduced as an intermediary element to electrically connect the anode elements to the armour wires. This mediator enables the cathodic protection current to reach the armour wires effectively over longer distances, reducing the need for frequent end fittings while maintaining protection reliability.
2Reliability
If anode elements are placed at frequent intervals to overcome attenuation, then cathodic protection coverage is improved, but system cost and installation complexity increase
Solution Approach 1:
The anode elements are combined with the armour wire structure itself, with anode elements positioned between armour wire windings. This merging eliminates the need for separate anode installation processes and reduces overall system complexity, providing continuous protection without increasing manufacturing or installation costs.
Solution Approach 2:
The armour wires serve dual functions: providing mechanical strength and serving as the cathode for cathodic protection. The same structural components (armour wires and anode elements) provide both structural integrity and corrosion protection, eliminating the need for additional dedicated protection structures.
3Reliability
If traditional cathodic protection systems are used in deep water environments, then protection is provided at discrete points, but attenuation effects limit effective protection along the entire pipe length
Solution Approach 1:
Conductive tape is pre-installed along the pipe length before anode elements are positioned. This preliminary action creates an extended electrical pathway that allows cathodic protection current to reach armour wires over longer distances, effectively extending the protection length without increasing anode frequency.
Solution Approach 2:
The system transitions from one-dimensional point protection (discrete anodes at specific locations) to a two-dimensional distributed protection network, where conductive tape creates continuous electrical pathways along the pipe length, enabling protection to extend over much longer distances.
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
This solution enables continuous cathodic protection along the flexible pipe, reducing the need for frequent end fittings and lowering costs by minimizing attenuation effects, thus enhancing the durability and reliability of the pipe in extreme environments.
Implementation Method 1
Cathodic protection is a mechanism for providing corrosion protection and such cathodic protection is well known to those skilled in the art. For example recommended practice DNV-RP-B401 or recommended practice DNV-RP-F103 provide guidelines for providing cathodic protection (CP) systems for submarine pipelines and flexible pipe risers.
Implementation Method 2
the armour wires and anode elements are formed from different materials... the implementation of a flexible pipe design featuring helically wound monofilament armour wires with non-circular cross sections and interposed elongate anode elements, made from more reactive materials like magnesium, aluminium, or zinc
Data Source
AI summary
A flexible pipe for subsea transportation of production fluids, a method of manufacturing flexible pipe body and a method of providing corrosion protection to armour wires of at least one tensile armour layer of a flexible pipe having a breached pipe annulus are disclosed. The flexible pipe comprises a fluid retaining layer, an outer sheath and at least one tensile armour layer comprising a plurality of helically wound monofilament armour wires of a first material, each having a non-circular cross section with an aspect ratio of greater than 1:2 disposed between the fluid retaining layer and the outer sheath. The tensile armour layer further comprises at least one helically wound elongate anode element substantially having a cross-section aspect ratio of 1:1 and comprising a further material, interposed between armour wires, the anode element cross section having an area that is 50% or less of a corresponding area of said non-circular cross section.