Subsea Cathodic Protection Control via Potential Monitoring
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Solution Overview
Problem
Existing cathodic protection systems, such as sacrificial anodes and impressed current systems, face challenges in providing uniform protection to subsea structures due to power losses and difficulties in distributing anodes, leading to overprotection and underprotection, which can result in corrosion and hydrogen embrittlement.
Innovation Solution
An intelligent closed-loop system that monitors and controls cathodic protection potential levels, using sensors and controllers to modulate voltage and current distribution, ensuring a consistent protection range of −800 mV to −950 mV (SCE) and reducing hydrogen generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sacrificial anodes are distributed throughout the metal structure, then cathodic protection coverage is improved, but installation complexity and difficulty increase
Solution Approach 1:
The system divides the cathodic protection function into modular units by attaching multiple sacrificial anodes to different locations of the subsea structure. Each anode independently provides protection to its local area, ensuring comprehensive coverage while maintaining installation simplicity through standardized attachment mechanisms.
2Reliability
If more sacrificial anodes are installed to ensure complete coverage, then protection reliability is improved, but anode mass and cost increase
Solution Approach 1:
The system optimizes anode placement by positioning them at specific critical locations on the subsea structure where corrosion risk is highest or where electrical potential distribution requires additional protection. This targeted approach ensures adequate coverage with minimal anode mass, avoiding unnecessary material usage in areas that already receive sufficient protection.
3Reliability
If impressed current systems are used to deliver protective currents, then current distribution control is improved, but power losses increase
Solution Approach 1:
The system employs sacrificial anodes that generate protective currents through their own electrochemical corrosion process, eliminating the need for external power sources. The anodes self-regulate their current output based on their electrochemical potential and the electrical resistance of the path to the structure, providing uniform protection without power transmission losses over distance.
4Reliability
If higher current levels are applied to ensure adequate protection, then protection effectiveness is improved, but hydrogen generation increases
Solution Approach 1:
The system controls the electrochemical potential of the sacrificial anodes to maintain it within the optimal range of -800 mV to -950 mV (SCE). By precisely managing this potential parameter, the system achieves adequate cathodic protection effectiveness while minimizing hydrogen evolution reactions that occur at more negative potentials, thus reducing hydrogen generation and associated embrittlement risks.
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 system effectively mitigates power outages and ensures uniform protection, reducing the risk of corrosion and hydrogen embrittlement, thereby extending the life of the anodes and subsea structures.
Implementation Method 1
The sacrificial anodes are constructed to corrode and passivate a surface of a base metal structure to which they are attached, thus protecting the structure from corrosion. The sacrificial anodes may be made from magnesium, zinc, or aluminum alloys which have a more negative electrochemical potential with respect to the base metal they are protecting.
Implementation Method 2
an aluminum-indium anode has an electrical open circuit potential of −1050 mV (SCE-standard calumel reference electrode) and corrodes preferentially when coupled to a carbon alloy steel that normally has an electrical potential of approximately (−600 to −700) mV (SCE)
Implementation Method 3
a controller is able to apply voltage levels to the subsea structure so as to attain and modulate a desired cathodic protection level
Implementation Method 4
The overprotection also can lead to excess hydrogen generation which can cause excessive saturation or diffusion of hydrogen into the exposed metal of the metal structure
Data Source
AI summary
An intelligent system is provided for monitoring a subsea structure and delivering appropriate cathodic protection to desired areas of the subsea structure. According to an embodiment, the technique involves monitoring a cathodic protection potential level at an important location or locations of the subsea structure. Based on the data acquired via monitoring, a controller is able to apply voltage levels to the subsea structure so as to attain and modulate a desired cathodic protection level, e.g. a cathodic protection level within a range of about −800 mV to −950 mV (SCE). Consequently, undesirable overprotection and under protection are avoided and the subsea structure is adequately protected from corrosion while reducing undesirable production of hydrogen.