Validation plan for boundary element method modeling of impressed current cathodic protection system design and control response

ABSTRACTCathodic protection is commonly used for corrosion protection of the underwater hull structures of naval platforms. Cathodic protection works by establishing an electrostatic field that provides the desired potential and current distributions in the seawater surrounding the structures to be protected. Interference to a ship’s cathodic protection system may occur when the ship is alongside a jetty or another naval ship due to the influence of the electrostatic field associated with the cathodic protection system employed on the jetty or another naval ship. The interference may alter the electrostatic field surrounding the ship and, therefore, the level of corrosion protection to the ship hull. In the current study, a physical scale modelling technique is used to evaluate how, and to what extent, the level of cathodic protection on a ship hull could be affected by an external current source. A 1/100 scale ship model with two-zone four-anode impressed current cathodic protection (ICCP) system is used in the study. The modelling results indicate that the presence of stray current may affect the potential distribution along the ship hull. The extent of stray current effect depends on a number of factors including the relative position and layout of stray current source, the magnitude and direction of the stray current flow and the operating mode of the shipboard ICCP system.

Development of optimum system configurations for ships using scale models (physical scale modelling) The purpose of this fundamental study was to establish optimum cathodic corrosion protection system configurations for ship hulls. Comprehensive surveys were conducted in order to develop a better understanding of the electrochemical processes occurring on a ship hull in a seawater electrolyte. The results obtained show that the performance of a system can only be evaluated when it is installed on a real object. However, once installed the location of the impressed current anodes and the reference electrodes cannot be changed if the potential distribution over the underwater hull is not optimal. Hence, a procedure had to be established that permits the development and optimisation of system configurations for future objects. A validated, experimental laboratory technique using scale ship models was established to determine the fundamentals of cathodic corrosion protection and to develop a theoretical understanding of the underlying mechanisms. The findings obtained in practice could be applied to the models. The model studies were conducted in a systematic manner and under defined conditions in German standard (DIN) artificial seawater and in a natural electrolyte. The experiments clearly showed the functional correlation between the geometric configuration of the reference electrodes on the hull and the locations of the anodes. The results reflect the interrelationships between the electrochemically more positive bronze propeller and the steel. The configuration developed in the course of the experiments provided an optimum distribution of the protection current over the entire hull model. The data from the model study were applied to the design features of the Class 123 Frigate. Subsequently, the efficiency of this procedure was evaluated on a real object in a real electrolyte. The results obtained clearly demonstrate that physical scale modelling is a rational, scientific method for the evaluation and design of impressed current cathodic protection systems.

This paper introduces an innovative improvement to impressed current cathodic protection (ICCP) systems by integrating a pulse-feeding technique designed to address metal protection degradation during off-potential periods, a common issue in conventional systems. The proposed system enhances the overall effectiveness and reliability of ICCP, providing consistent corrosion protection for critical metal structures. A notable advantage of this method is its simplicity, utilizing a cost-effective microcontroller for pulse feeding. This approach simplifies integration processes and enhances cost-effectiveness, making it an attractive solution for improving cathodic protection system performance without substantial additional costs. The method addresses conventional ICCP weaknesses by applying a high-frequency pulse current during off-potential periods. This reduces excessive negative charge buildup on metal surfaces during interruptions, boosting the system’s effectiveness and stability. Research laboratory experiments were conducted using pulse width modulation (PWM) on an ATmega328P microcontroller to demonstrate the method’s effectiveness. Additionally, an IoT-monitored ICCP system was developed using an ESP32 microcontroller and the Blynk application. Results highlight the superiority of a 50 kHz pulse feeding frequency in preventing corrosion compared to lower frequencies. Overall, this advancement significantly enhances ICCP systems, providing improved corrosion protection and durability in harsh environments.

The ground is full of all kinds of pipelines of different sizes, materials, pressures and cathodic protection (CP) systems. Most metallic or concrete pipes installed these days utilize a cathodic protection system of some kind. How do you ensure that the cathodic protection system of your new pipeline will not be compromised by existing cathodic protection systems nearby? Freese and Nichols, Incorporated (FNI) recently designed 27,200 feet of 48-inch and 47,400 feet of 42-inch treated water pipeline for the North Texas Municipal Water District in rural North Texas. Paralleling existing utility corridors was favored during pipeline alignment selection to avoid severing properties and reduce overall land acquisition costs, but this also posed challenges during design. The route selected for this pipeline included paralleling an existing natural gas transmission line continuously for approximately 22,000 feet. The existing gas line, configured with an impressed current cathodic protection system, could have significant impacts on corrosion protection systems and life-span of parallel pipelines. Reducing the chance of interference between the two pipelines' cathodic protection systems and ensuring measures were taken to monitor any potential interference in order to extend the life of this asset was a driving factor for the cathodic protection design of this pipeline. This paper discusses the pipe materials considered including bar-wrapped pipe and polyurethane coated steel pipe, as well as the cathodic protection systems considered including impressed current, magnesium ribbon and magnesium groundbeds. Other cathodic protection considerations for a rural pipeline including test station details, rectifier details and placement and pipeline crossing details are discussed in this paper.

This article describes in detail the process of corrosion control by cathodic and anodic protection. The discussion covers the basic concept of cathodic and anodic protection systems, their types and equipment used, and the advantages, limitations, and applications of these protection systems. The types of cathodic protection systems include sacrificial cathodic protection and impressed-current cathodic protection systems. Some of the technical problems associated with cathodic protection include the effects of stray currents on the corrosion of adjacent metal structures, the effects of the chemical reactions occurring at the surface of the protected structure, and the effects of cathodic protection on coatings.

Above ground storage tank (AST) bottom plate soil-side corrosion is a major cause for AST bottom deterioration with subsequent environmental impact of leaks in petrochemical facilities. AST construction, prior to 1987's, were often on a Continuous Asphalt/sand mix pad (API 651clause 5.3.6) with a thought that asphalt helps in the compacted back filling leveling and would minimize the external corrosion of bottom plates soil side as it is a physical barrier. Unfortunately, the asphalt retained the contaminated rainwater that was introduced from the walls of the tank and underneath through the damaged ring wall seals which together with oxygen entry encouraged by tank bottom flexing caused a corrosive environment. After 11 years of services and conducting bottom plate magnetic flux leak (MFL) scan which revealed many locations with sever metal loss (more than 70 % of nominal thickness at about sixty locations for each tank which already repaired by patch plates), Impressed current cathodic protection (ICCP) systems with distributed High Silicon Iron (HSCI) anodes outside the concrete walls was installed to control this corrosion. Although the ICCP operated at the design current and the measured tank to soil potential appeared to meet the protection criteria, it was apparent that the ICCP system was not operating as intended. An inaccurate predesign drain current test misleads the assessment as the asphalt/sand mix layer shields the Cathodic Protection current from reaching the external bottom plate surfaces of the tank and the measured metal to soil potential were revealing the underground piping potential which shorted with the tank shell. The upcoming MFL scans after 10 years of cathodic protection installation showed other spots of sever metal loss which led to tank bottom plate replacement for eight tanks, One tank, asphalt layer removed during bottom plate replacement and the existing CP system provided full protection for bottom plate as the electrical insulation material (asphalt) got removed, other tanks bottom plate replaced with new dry sand back filling, leak detection system with HDPE barrier and new CP system with MMO grid anodes. The effectiveness of cathodic protection (CP) was further evaluated by using Clamp- on meter to measure the direct current (DC) in the connected pipes and cables to find the amount of CP current lost to other underground structures. The results revealed that most of the CP current was impressed on to the underground plant network and little to the AST. Thus, contrary to the total current and potentials at the circumference of the tank indicating effective CP, the AST soil side bottom plate did not receive sufficient CP current. As the measured tank- to-soil potential during the CP survey only reflect the potentials of the underground plant piping which electrically shorted with tank shell and not underneath the tank bottom plate, A CP survey should include current measurements in all connecting metallic paths such as piping and earthing cables (electrical grounds). These tanks which considered without cathodic protection system and volatile corrosion inhibitor (VCI) along with corrosion probes were installed to mitigate and monitor the tank bottom plate soil side corrosion till the bottom plate replacements with new cathodic protection system with grid MMO anodes and chloride free sand backfilling.

The cost of repairing damage to marine structures and ships attributed to corrosion have lead to the development of technologies which try to limit the corrosion process. Use of cathodic protection systems take advantage of the electrochemical nature of the corrosion processes and attempt to limit the degree of corrosion which occurs. External sources of electrical current are used in impressed current cathodic protection (ICCP) systems. Current is supplied through source anodes and voltage levels are monitored through reference cells. ICCP systems are currently in use on a wide variety of structures.

Physical scale modeling (PSM) is an experimental technology that has been used to evaluate and design shipboard impressed current cathodic protection (ICCP) systems by various researchers and designers. PSM is also a preferred tool for validating ICCP numerical modeling results, owing to the well-controlled conditions in PSM experiments. However, one issue in using PSM for the validation of numerical modeling results is the lack of information on the actual polarization behavior of the cathodes on a model hull during PSM experiments. Consequently, the polarization curve data used as boundary conditions in numerical modeling trials is usually different from the polarization behavior of the cathodes in PSM experiments. This difference can result in a discrepancy between the numerical modeling and the PSM results, which is difficult to separate from other numerical errors. A discrete area current control (DACC) technique was developed in a previous ICCP PSM study to simulate the polarization behavior of a propeller material under various conditions. The present study extended the DACC technique to simulate the polarization curve behavior of four discrete cathodes representing one nickel aluminum bronze (NAB) propeller and three discrete steel patches. This study also demonstrated that use of the DACC technique can ensure that both PSM and numerical modeling studies use identical polarization curve relationships as boundary conditions. The technique facilitates the use of the PSM results for comparison with numerical modeling results. The comparison study showed good agreement between the PSM results and numerical modeling results, in both simulated static and dynamic flow conditions.

Adaptive gridding methods are of fundamental importance both for industry and academia. As one of the computing methods, the Boundary Element Method (BEM) is used to simulate problems whose fundamental solutions are available. The method is usually characterised as constant elements BEM or linear elements BEM depending on the type of interpolation used at the elements. Its popularity is steadily growing because of its advantages over other numerical methods most important of which being that it only involves obtaining data at the boundary and computation of the solution in the domain is merely a case of post processing through the use of an identity. This results in the reduction of the problem dimension by unity. Although there is a reduction in dimension when we use BEM, the method usually results in full matrices which can be expensive to solve. This makes the method costly for problems that require very fine grids like those with hot spots as in the example of impressed current cathodic protection systems (ICCP). The BEM is a global method in nature in that the solution in one node depends on the solutions in all the other nodes of the grid. Hence an error in one node can pollute the solution in all the other nodes. In this thesis, we first focus our attention on defining and studying both the local and global errors for the BEM. This is not a completely new study as the literature suggests, however, our approach is different. We use the basic foundations of the the method to define the errors. Since the method is a global method, first we use the interpolation error on each element to define what we have called a sublocal error. Then using the sublocal error we have defined the local error. Understanding the local errors enabled us study the global error. Theoretical and numerical results show that these errors are second order in grid size for both the constant and linear element cases. Then, having explored errors, we study a method for adaptive grid refinement for the BEM. Rather than using a truly nonuniform grid, we present a method called local defect correction (LDC) that is based on local uniform grid refinement. This method is already developed and documented for other numerical methods such as finite difference and finite volume methods but not for BEM. In the LDC method, the discretization on a composite grid is based on a combination of standard discretizations on several uniform grids with different grid sizes that cover different parts of the domain. At least one grid, the uniform global coarse grid, should cover the entire boundary. The size of the global coarse grid is chosen in agreement with the relatively smooth behaviour of the solution outside the hot spots. Then several uniform local fine grids each of which covers only a (small) part of the boundary are used in the hot spots. The grid sizes of the local grids are chosen in agreement with the behaviour of the continuous solution in that part of the boundary. The LDC method is an iterative process whereby a basic global discretisation is improved by local discretisations defined in subdomains. The update of the coarse grid solution is achieved by adding a defect correction term to the right hand side of the coarse grid problem. At each iteration step, the process yields a discrete approximation of the continuous solution on the corresponding composite grid. We have shown how this discretisation can be achieved for the BEM. We apply the discretisation to an academic example to demonstrate its implementation and later show how to use it for an application as the ICCP system. The results show that it is a cheaper method than solving on a truly composite grid and converges in a single step.

With the advent and application of Impressed Current Cathodic Protection (ICCP) systems to confined spaces, the ability of an externally controlled ICCP system to effect sufficient cathodic protection to internal components is questionable. This paper seeks to evaluate the ability of ICCP systems to provide adequate corrosion control for confined and sensitive surfaces. Both a boundary element and a physical model were utilized to understand the effects of current distribution within a confined space, through a 1.27 mm gap. Initially, tests were performed to quantify polarization levels in a simplified parallel plate configuration. Then more complicated geometries and materials were modeled to effectively evaluate real world scenarios. Previous tests have determined that adequate cathodic polarization is achieved for simple and complex geometries at the increased driving voltages experienced with sacrificial anode systems. The results of this work provide evidence that adequate cathodic protection may be provided at controlling potentials more electropositive to conventional galvanic cathodic protection system.

An oil drilling and producing jacket was installed in the North Sea in 1980, 100 miles off the coast of Scotland in 160 m depth seawater. The jacket has 8 legs and was installed with traditional standoff galvanic anodes. Surveys from 2010 to 2013 indicated a reduction in corrosion protection from the cathodic protection system, and plans were implemented to upgrade the cathodic protection (CP) system., A remote anode sled impressed current cathodic protection (ICCP) system was selected, installed and commissioned in early 2016. This paper discusses the design process and challenges in choosing what was at the time, the largest ever cathodic protection retrofit in terms of delivered current capacity offshore, and the actual current the structure required to maintain protection.

Computational modeling techniques have long been applied to corrosion problems. Boundary element techniques are well suited for cathodic protection systems intended to minimize electrochemical corrosion on the exterior of ship hulls. The performance of these systems is governed by LaPlace's equation and these systems exist in unbounded domains (i.e. the open sea). This article reviews the work performed in the past decade (1987present) on boundary element modeling of ship impressed current cathodic protection systems.

An investigation was performed by using carbon fiber-reinforced polymer (CFRP) as the anode material in the impressed current cathodic protection (ICCP) system of steel reinforced concrete structures. The service life and performance of CFRP were investigated in simulated ICCP systems with various configurations. Constant current densities were maintained during the tests. No significant degradation in electrical and mechanical properties was found for CFRP subjected to anodic polarization with the selected applied current densities. The service life of the CFRP-based ICCP system was discussed based on the practical reinforced concrete structure layout.

Purpose Under normal conditions, there are different protection objects inside and outside the gas station, so two sets of independent cathodic protection systems are adopted. At the same time, an insulating flange is applied at the position where trunk pipelines access to the gas station, which realizes electrical isolation of the structures inside and outside the station. However, as a result of short distance between the two cathodic protection systems, there will be stray current interference between them. The purpose of this paper was to study on the interference between cathodic protection systems of gas station and long distance trunk pipeline. Design/methodology/approach Based on the above, in this paper, first, the mathematical model of interference between cathodic protection systems was established and the control equations solved using the boundary element method. Second, the influence of cathodic protection system of gas station on long distance trunk pipeline and the influence of cathodic protection system of long distance trunk pipeline on gas station were studied separately using BEASY software. Finally, a new thought of cathodic protection design for local station was put forward. Findings It was concluded that there were serious interference problems between the cathodic protection systems of gas station and long distance trunk pipeline. By moving the potential control point to area outside the influence scope of anode ground bed could avoid the influence of cathodic protection system of gas station on long distance trunk pipeline. By moving the auxiliary anodes away from gas station could avoid the influence of cathodic protection system of long distance trunk pipeline on pipelines in gas station. The new thought of cathodic protection design could avoid the interference between the cathodic protection systems effectively. Originality/value It is considered that the results can guide cathodic design for gas station and long distance trunk pipeline. The results can also avoid the interference corrosion between the structures in gas station and trunk pipeline.

This paper summarizes an assessment of the feasibility of implementing cathodic protection (CP) as an internal corrosion prevention strategy for nuclear waste storage tanks. The study investigates the principles of cathodic protection and its applicability to the unique environment of nuclear waste storage. By reviewing the relevant literature, this research explores the various threats and challenges associated with implementing CP in this specific context. A boundary element analysis (BEA) model of a steel tank with a simplified impressed current cathodic protection (ICCP) system was developed using polarization curves that were experimentally measured from coupons in simulated waste. This model was developed to evaluate the interaction of electrochemical potentials of the various waste layers within the tank. The modeling results indicate that the simulated ICCP system is capable of shifting the polarized potentials of the internal tank surfaces to levels required to mitigate stress corrosion cracking (SCC) and corrosion.