Cathodic Protection of Highly Complex and Shielded Components

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.

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.

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.

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.

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.

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.

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.

Anodic corrosion is a direct contributor to external well casing leaks. For some of the exploration and production (E&P) companies, it has been effectively addressed by investing in and installing cathodic protection systems using surface DC rectifier systems that supply Impressed Current Cathodic Protection (ICCP) in wells across all oil and gas fields. Yet, casing leaks due to external corrosion remain a recurrent conundrum, and casing completions still require continual monitoring and repairs despite significant capital investment and energy expenditure. Recommended design of efficient ICCP systems via modeling is one of the solutions for achieving optimum casing protection. The method for determining whether all anodic zones are eliminated and to ensure that too much energy is not consumed and wasted is to physically measure current flow across the entire casing length, establish flow direction, as well as authenticate the depth of maximum ICCP effectiveness through an effective monitoring program. This paper describes multiple wells utilizing ICCP, measuring downhole current flow within casings while utilizing existing or historic surface impressed amperage. Once the direct current (DC) profile is acquired across the casings and an effective ICCP depth is established, then surface amperage is either adjusted higher to increase maximum casing protection depth or it is tuned lower to reduce amperage for the purpose of economizing power consumption. Using proper cathodic protection systems not only optimizes the amount of the cathodic current requirement but also enhances the life of the solar modules for solar photovoltaic systems or life of anodes for the ICCP. In addition to ICCP profiling and fine tuning the cathodic current, the corrosion logs for these wells are also compared with detailed analysis.

Chapter 16 - Impressed current cathodic protection

In the past 20 years, the US Navy has used the physical scale modeling (PSM) technique to design effective cathodic protection (CP) systems for the ships underwater hull, nickel-aluminum-bronze props and other hull components.In more recent years, a number of computational techniques have been devised in an attempt to fulfill this purpose.Physical models have proven highly adept at ICCP design, since modeled information provides a direct relationship to the actual hull and can be scaled up directly because of confidence in the physically measured data.Boundary element (BE) models have been correspondingly devised that mimic actual hull design and even the PSM layout, but because the BE method is a computational methodology, the calculated data requires systematic validation with a physical analog to insure confidence in the control response.BE literature has discussed design issues regarding mesh layout, intrinsic geometric complexities, accuracy of material response input, the predictive engineering design capability for zonal response, and assessment of electric field response.It does not significantly discuss the accuracy of the BE model calculated work predictive design capability, without the need for "tweaking," and ultimately a rigorous validation of both the mesh and resultant system design technique.This paper presents validation requirements, for any BE model, that is inherently robust enough to be used for CP design and control, and a proposed four-point methodology that will allow for the comprehensive validation of the BE model to predict the ICCP control responses and system performance behavior.

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 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.

Applications of protective coatings and cathodic protection are recognized corrosion-control methods for marine steel structures. With the growing use of tall offshore structures for deep waters, corrosion control has become critical and difficult to provide throughout the life of the structures. Typically, coatings have not been used in the submerged areas of offshore steel structures because of a lack of confidence in their ability to perform in conjunction with cathodic protection. With short life expectancy, they appeared too costly. Attempts to cathodically protect bare steel structures have not been completely successful because of excessive current requirements, shielding problems, limitations of anode throwing power, and weight. Since 1975, an experimental program has been conducted by Ameron to evaluate the performance of coatings both with and without cathodic protection in simulated marine exposure. Numerous marine coating systems have been tested over a 5-year period using protection levels of -850, -1100 and -1200 mv to Cu/CuS04 electrode. The tests are described and results are presented and discussed. The results indicate that certain coatings are compatible with cathodic protection, with 2 specific systems offering relative insensitivity to long-term overvoltages of -1200 mv (Cu/CuSO4 electrode). Lower protective current densities required for coated steel coupled with more uniform protection offer potential benefits. The design of a cathodic protection system can be simplified and the systems efficiency improved by using the long-term compatibility data developed in this program. Problems associated with cathodic protection of offshore steel structures can be reduced by use of coatings for the submerged portion. INTRODUCTION During the past decade there has been a dramatic increase in the size and complexity of both oceangoing deep draft vessels and offshore structures. Nowhere have these developments been more evident than in the production and exploration platforms recently designed and installed throughout the world. It is expected that the design of the structures will continue to provide engineering challenges as the search for petroleum expands into the deeper and more hostile ocean environment. The corrosion protection of offshore structures has continued to increase in sophistication with certain basic systems partially standardized in Europe and North America. 1, 2 Above the tidal zone, high performance, well-recognized protective coating systems have been specified and successfully used for several decades. These typically comprise inorganic zinc-rich primers, epoxy or vinyl mid coats and, occasionally, chlorinated rubber, acrylic or urethane topcoats. 1,3 In the tidal zone area there has been increasing use of monolithic epoxy cladding materials which offer both erosion and corrosion protection. For the submerged areas the use of cathodic protection has been generally accepted. Either impressed-current or sacrificial-anode systems are used to protect the. bare steel that is totally immersed. 2,4 Impressed current cathodic-protection systems have not been as popular as sacrificial-anode systems because of the former's need for very careful design, and electrical power coupled with constant monitoring when in service in order to assure continued optimum performance. 3,5 Cathodic-protection systems will probably remain the preferred method of corrosion control for the submerged portions of these offshore structures.

Prevention of soil-side corrosion of the bottom plates of Aboveground Storage Tanks (ASTs) is a major challenge for the oil and gas storage industry. AST bottom plates are generally 0.25 inch (6.35 mm) thick A36 carbon steel. Literature suggests that the corrosion rate of the soil–side bottoms can be up to 200 mpy (5 mm/year). The soil-side surfaces of the bottom plates are usually protected by an impressed current cathodic protection (CP) system. However, when the bottom plate flexes the tank fill levels are varied, creating air gaps between the bottom plate and the tank bed leading to reduced CP effectiveness and potential corrosive conditions for the tank bottoms. Furthermore, in many situations, CP could become ineffective due to the poor ionic conductivity within tank beds and failure of anodes. Limited research and fieldwork have shown that vapor corrosion inhibitors (VCIs) by themselves or in combination with CP can be used to protect the bottoms of ASTs from external corrosion. VCIs could reduce corrosion incidents by 70–90 percent and decrease the incidence of pitting corrosion. This paper discusses methodologies to evaluate the compatibility between VCI and CP for the tank bottom application. Experimental work is reported to evaluate the CP criteria applicability in presence of VCIs, the work also provides a guideline for selecting an effective corrosion mitigation strategy for combined VCI and CP systems. In summary, VCI and CP, used in combination, are found to have a synergistic interaction to mitigate tank–bottom corrosion to acceptable levels.

A simple electro-chemical test and an optimization system for impressed current cathodic protection (ICCP) for the A36 hot-rolled steel bar is presented in this article. A simple two-electrode based test system using an electro-chemical cell to test the corrosion rate of the target metal is proposed. The Tafel plot to determine the corrosion rate of the target metal is prepared using our simple test systemand the corrosion current(i corr ) is extrapolated from the Tafel plot. A novel technique by impressing the corrosion current to protect the target metal using ICCP is implemented and tested. The proposed protection system further simplifies the corrosion protection system compared to the current methods. To determine effectiveness of the proposed protection system, weight loss of a freely corroding target metal and a protected sampleof the target metal are compared. For0.6 M NaCl solution as a test environment, both the metal samples are tested for two weeks. The protected metal sample is protected using our novel closed-loop protection system using 2.4 – 4.25 mW power with protection feedback every 24 hours. The weight reduction of the freely corroding metal sample is 0.017533 weight percentage per day and for the protected metal sample is 0.003357 weight percentage per day. Hence, the weight lost of the freely corroded metal is 5.22 times faster than the protected metal sample.