Corrosion Simulation Newsletter
BEASY attended the NACE Corrosion Conference in Vancouver this March where we were active at the exhibition as well as presenting and participating in the technical sessions and exchange groups.
It was great to meet many friends at the conference and discuss how modelling can be used to improve and optimize CP systems and mitigate interference.
At this year's conference there were a number of papers presented by BEASY staff and customers and BEASY CEO Tim Froome also gave a presentation on modelling of well casings at the Technical Exchange Group meeting. Some of the papers presented are described below.
Case Study of an ICCP Design and Installation for Well Casings Using Boundary Elements Software, Evaluating Different Deep Anode Architectures and Interference to Nearby Casings
Norberto Aldo Pesce & Norberto Antonio Pesce, Omnitronic S.A. Héctor C. Albaya Sistemas de Protección Catódica S.A. Guy Bishop & Andrés Peratta CM BEASY Ltd.
Impressed current cathodic protection (ICCP) systems can be used very effectively to achieve appropriate mitigation of well casing corrosion, but it may be difficult and expensive to define the most convenient anode distribution in order to adequately protect the desired casings and not interfere with nearby
Figure 1 Predicted current density on the well casing structures.
Once the system is installed, the cost of redesign may be high if experimental measurements indicate that the required protection is not achieved or that destructive interference is taking place. It is therefore both desirable and cost-effective to establish performance of the ICCP system before it is installed. Such assessment can be achieved through the use of mathematical modelling performed using numerical techniques. Of the available methodologies it is the boundary element method that is applied in this work.
To perform such simulation a model of the well casings is constructed (reflecting the directionally drilled profile) and the multiple anode ground-beds, including the return-path resistances along the cables and well casings. In order to effectively capture the electrical behavior of the currents, the resistivity of the ground through which current passes must be identified. Running alternative scenarios of the models to readily quantify the effects of alternative assumptions, provides valuable understanding to the CP system designer of probable behavior, and contributes to design robustness.
How Interference Can Impact The Life Of CP Systems. An FPSO Case Study
Robert Adey, Cristina Peratta, John Baynham, CM BEASY Ltd
The design rules used to design CP systems in the main do not take into account the interference between the anodes provided to protect a structure or interactions between the structures themselves. CP systems will always interact with each other to some extent when they are in the same electrolyte even when there is no metallic electrical connection and this can radically affect the protection provided to the structure and the life of the CP system.
A case study is presented involving the design of the CP system of an FPSO (Floating production storage and offloading vessel). The aim of the study was to verify the performance of the CP system to ensure that the structure was protected for the design life and the anodes had sufficient capacity. Computer modelling was used to simulate the performance of the CP system which comprised of an ICCP system and sacrificial anodes. The study identified some interesting and unexpected interactions which required the design of the CP system to be modified.
Figure 2 Comparison of the protection potentials on the Moon Pool-Turret-Chain Connectors-Chains
for two different connection resistances at End Of Life
Interference Between Sacrificial CP Systems In The Marine Environment
John Baynham, Tim Froome CM BEASY Ltd
It is generally accepted that destructive interference can occur between impressed and sacrificial cathodic protection systems, which can result in difficulty with control of the ICCP system, and which can also cause problems with performance of the sacrificial CP system
Less well known is the possibility of interference between multiple sacrificial CP systems. Such interference can occur under a number of different circumstances, and may for example arise when different design approaches are used for sub-structures which are then to be integrated together. Each CP system may be competently designed for stand-alone operation, but when combined together, protection potentials and life of the systems may be affected by interference. Consequences may include early consumption of anodes and more positive potentials towards end of life.
Figure 3 Projected anode life (in years) calculated in year 0 for the 330 anodes
Such effects can readily occur when different types of anode material are used, but may also occur when anodes in both CP systems are made from the same anode material.
This paper shows how mathematical modelling has been used to simulate performance of both stand-alone and integrated sacrificial systems. It goes on to identify interference effects between such systems, and investigates a number of different situations in which destructive interference can occur. Conclusions are reached of practices that can be adopted to avoid such destructive interference.
Using Predicted Corrosion Damage To Determine Stress Concentration, Fracture And Crack Growth
Sharon Mellings, Andres Peratta, John Baynham, Tim Froome CM BEASY Ltd
Structure surfaces damaged by corrosion may develop stress concentrations which lead to initiation of cracks and possible crack growth.
Simulation of the galvanic effects leading to corrosion takes account of the properties of the electrolyte as well as the structural materials, to determine electric fields within the electrolyte, attenuation in the return path, and the surface current densities and potentials. If dissimilar materials are present or a CP system is not adequately designed, areas may exist where anodic current occurs on a structural surface, causing mass loss from the surface. The magnitude of the anodic current density, determined from simulation, can be used to determine surface shape change.
Such shape change generally results in indentations, which act as stress-raisers. Simulation to determine magnitude of the stress concentration can identify likely sites for crack initiation. The possibility of crack growth, and the time taken for the growth, can be determined using fracture and crack growth simulation.
This paper explores the combined use of galvanic simulation and fracture/crack growth simulation.
Figure 4 Predicted geometry changes in the specimen due to corrosion damage
Dr Andres Peratta presented some recent conceptual work on the application of simulation modelling to predict the corrosion related potentials and electric and magnetic fields on and surrounding naval vessels at the International Conference On Marine Electromagnetics (MARELEC) in Philadelphia, USA. Modelling is used to predict the corrosion related potentials on the vessel itself, and the electric and magnetic fields surrounding the vessel. For naval vessels, modelling can be exploited to not only assess the performance of cathodic protection systems on the vessel (ICCP and sacrificial) but also the corrosion related magnetic fields as they make a significant contribution to the vessel signature.
The paper evaluated the magnetic field caused by return-path current flowing in the hull of a vessel, and compared the electromagnetic fields calculated using different assumptions regarding how the cathodic protection currents flow. The cases assessed included flow along an equivalent horizontal wire, and flow through the vessel skin to selected collection points at which cables return current to the power supply. The effects of different layouts of collection points were investigated to determine the sensitivity of the magnetic field to the layout.
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BEASY attended the NACE Corrosion Conference in Dallas this March where we were active at the exhibition as well as presenting and participating in the technical sessions and exchange groups.
It was great to meet many friends at the conference and discuss how modelling can be used to improve and optimize CP systems as well as providing further confidence in their performance as part of "due diligence" activities.
In addition to the activities by BEASY staff there were papers presented at NACE incorporating BEASY modelling, including Application Of Linear Anodes To Protect Isolated And Unisolated Piping In A Petrochemical Plant by Mobeen Hassan, Sharjah, United Arab Emirates & Stephen Wroe Corrosion Technology Services LLC Sharjah, United Arab Emirates.
The paper describes an application of cathodic protection using linear anodes in a congested petrochemical plant in the Middle East. The initial design of the cathodic protection is discussed along with the problems found due to faulty isolating flanges and loss of current to other structures. Computer modelling of a typical electrically continuous cathode including steel in concrete and earth rods is included to demonstrate the need to consider all components of complex structures. Lessons learnt from this case study are applicable for the application of cathodic protection in plant using distributed anodes.
The results shown below illustrate the effect of adding continuous reinforced concrete paving into the circuit. The dramatic effect is that the pipe potentials are hardly shifted from the natural potential even with the anode operating at 100mA/m.
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An interesting article was published in a recent issue of the NACE Materials Performance magazine.
Researchers used modelling tools to design effective cathodic protection systems that address challenging seawater conditions and coating damage from ice abrasion.
According to researchers Min-Jeong Lee, senior engineer, and Chae-Seon Lim, principal research engineer, both in the Material & Coating Research Department at Samsung Heavy Industries, Co., Ltd, South Korea, the performance of a CP system for a ship's external hull is dependent on several factors, including the geometry of the ship's hull, the resistivity of the surrounding seawater, the chemicals in the seawater, and the degree of coating damage. The ICCP design for many commercial vessels is often based on current density (CD) calculations and the designers' experience rather than an analytical method. For an icebreaker travelling in Arctic conditions, the researchers note, this traditional approach to CP design may not result in an adequate amount of corrosion protection for the hull in this environment.
To determine the optimum ICCP design for the external hull of an icebreaker, the researchers explored a modelling approach using computational analysis based on the boundary element method (BEM). Lee comments that modelling tools are often used to design ICCP for stationary offshore structures such as oil and gas production platforms; floating production, storage, and offloading (FPSO) units; and semi-submersibles.
Using computational analysis and modelling was successful in determining that an ICCP system design is effective for a vessel exposed to Arctic seawater conditions. Going forward, Lee expects more use of CP modelling when designing ICCP systems for ship hulls, particularly those headed for the Arctic.
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BEASY will once again be attending the annual NACE Corrosion Conference, which this year is being held in Dallas, Texas, between 16th and 19th March.
We will be active in both the conference program and exhibit hall showing our corrosion modelling services and software.
Please come and visit us at booth 21096, or if you would like to set up a meeting to discuss any aspect of BEASY's modelling and software services, please contact us
An article in December 2014's MP magazine looked at the effect of grounding on the cathodic protection (CP) potential distribution at an oil station, which had been studied using BEASY's corrosion and cathodic protection simulation software.
Influences from four factors were analysed: grounding system material, relative position between the grounding conductor and the pipeline, and length and buried depth of the grounding conductors. CP designs with and without grounding were compared.