Corrosion Simulation Newsletter
In early 2017 at the NACE Corrosion Conference in New Orleans BEASY staff presented some recent developments and applications 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.
Assessment of Effects of Cavities and Narrow Channels on CP Design in the Marine Environment
Underwater termination assembly, mud mat, split casing, armour
termination and bend limiters being readied for deployment.
At this year NACE John Baynham and Tim Froome presented an interesting paper on the difficulties presented by the geometry of certain structures in obtaining adequate CP protection.
CP system design work in the marine environment makes use of structure surface area, required current density, and anode resistance formulae to select the number and mass of anodes required to protect a structure. These formulas do not take account of restrictions to current flow caused by close proximity of structural surfaces to each other, and consequently CP systems which have been designed in the recommended way may sometimes not protect parts of a structure.
This paper investigates the protection provided to the structure when cavities and narrow channels/annuli are present, and identifies patterns of behaviour. A series of computer-based parameter studies was performed in which, for example, separation between two structural surfaces is varied, and the extent of the protected area is determined. The paper also investigates effects of geometry on current flowing through a hole in a plate. This situation frequently occurs in design of mud-mats - when the interest is to determine current drain to buried surfaces, and sometime occurs when free flooding cavities need to be protected. Again computer-based studies are used, and for example the size of the hole is varied.
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There were a number of papers published this year which featured BEASY modelling.
Optimization of the quantity, locations and output currents of anodes to improve cathodic protection effect of semi-submersible crane vessel
S.H.Xing, Y.Li, China University of Petroleum, Qingdao. H.Q.Song, Y.G.Yan, M.X.Sun. Luoyang Ship Material Research Institute, Qingdao
Potential profiles on SSCV after optimization for the different cases considered which represent the loading of the crane and the coating condition
In this paper published in the Journal Ocean Engineering a 3-D boundary element model of a semi-submersible crane vessel (SSCV) is combined with movement of anodes and adjustment of currents to optimize the anode quantity and location. The protection in four different states of the crane vessel representing the loading and coating condition were predicted and the simulation results indicate that the SSCV is well protected for the whole service life when the protective coating on the hull is repainted every seven years.
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Optimization of the Cathodic Protection Design in Consideration of the Temperature Variation for Offshore Structures
M. S. Hong, J.-H. Hwang and J.H. Kim. Hyundai Heavy Industries Co., Ltd.,
Optimized simulation results of FPSO: (a) ﬁnal stage at 5°C and (b) ﬁnal stage at 28°C.
In this study published in Corrosion, electrochemical tests were performed to obtain the carbon steel (EH36; UNS K12821(1)) cathodic polarization curves which contained environmental information under tropical (28°C) and arctic (5°C) environment model conditions, and the surface morphology was analyzed after the potentiostatic polarization test using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS).
Based on the polarization data, a computational analysis was conducted to verify and optimize the CP design of the floating production storage and offloading (FPSO).
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BEASY is working on a project supported by the United States Navy Sea Based Aviation Program and the Air Force to validate and develop computational corrosion modelling tools which can be used to predict the location and severity of corrosion within aircraft structures. The increased use by engineers of corrosion simulation tools during design and maintenance has the aim of improving the durability of an aircraft through better material selection, improved corrosion resistant design, and better predictive maintenance schemes. Improved aircraft durability will ultimately reduce fleet maintenance and life-cycle corrosion costs.
Experimental test configuration with an Aluminum plate connected to an Stainless Steel Plate.
The plates are segmented so that the distribution of current can be measured
The work is building upon the BEASY Corrosion Manager software and is extending this technology to predict the long term galvanic corrosion risk to structures. We envision that this modelling technology will support a radical change in design philosophy for aircraft and other vehicle structures by providing engineers with corrosion simulation tools needed for current and future corrosion challenges.
In conjunction with Luna Innovations Inc and the University of Virginia experimental tests have been performed to validate the galvanic corrosion models under "bulk" electrolytes and thin film conditions. For example good agreement has been obtained across a range of electrolyte film thicknesses comparing measured and model predictions of the corrosion current density distribution across a segmented electrode test specimen as shown in the figures. Details of this study will be published NACE Corrosion 2018.
BEASY once again attended the annual NACE Corrosion Conference, which this year was held between March 26-30, 2017 in New Orleans, Louisiana.
We were active in both the conference programme and exhibit hall showing our modelling services and software to support engineers with responsibility for corrosion aspects related to offshore and onshore structures, and also in the wider manufactured sector (aircraft, vehicles, etc).
Predicting The Impact Of Interference On the Corrosion Control Of Offshore Oil & Gas Assets
Designing and operating cathodic protection (CP) systems to protect oil and gas structures from corrosion in offshore marine environments is a complex task as interference can degrade the protection provided and accelerate anode depletion. Modern developments frequently consist of connected assets like well casings, seabed flow lines, pipelines, well-head structures, risers, and surface vessels such as floating production, storage, and offloading (FPSO) units.
Although these structures are often separated by large distances, the relatively low resistance of seawater means they pose the potential to interfere with each other and significantly affect the overall performance of a CP system. Computer modelling technologies provide improved predictions of CP system performance and identify the risks of interference.
Mitigating Pipeline Interference From DC Railways
Mitigating Pipeline Interference From DC Railways Predictive modelling can play a significant role in the design, planning and operation of cathodic protection systems used to protect pipelines. It can also be used to verify the protection provided, inform selection of an optimum design and assess and facilitate assessment and mitigation of interference from third parties such as railways etc.
The problem of stray current interference from railway, metro and tram sources is a growing concern as it may cause pipeline corrosion resulting in environmental pollution, unsafe operations, and reduction of the pipeline service life.
These are just some of the applications we will be discussing and presenting at NACE 2017. Please come and visit us at booth 2027, or if you would like to set up a meeting to discuss any aspect of BEASY's modelling and software services, please contact us.
BEASY were again at EUROCORR this year which was held in Montpellier, France, and we presented a number of papers on subjects including Internal Cathodic Protection of Offshore Sea Water Pump Caissons, Modelling Cathodic Protection/Prevention of Reinforcement in Concrete, and Using Predicted Corrosion Damage to Determine Stress Concentration, Fracture and Crack Growth. Tim Froome was on hand to discuss both the papers and applications of BEASY modelling.
Seminar Programme China
BEASY in conjunction with Beijing Safetech Pipeline Co., Ltd recently presented a popular series of seminars in China on Cathodic Protection and Interference Modelling
Bob Adey introducing BEASY and a series of
CP Modelling & Interference Case Studies at the seminar in Chengdu
If you are interested in this subject or need help and advice about interference, then please contact us for more information.
New Case Studies
BEASY have recently published two new Case Study data sheets.
Case Study: Interference Between A Pipeline & A DC Railway Metro System
Interference Between A Pipeline & A DC Railway Metro System A planned metro line with a car parking yard and ten traction zones is to be constructed. The line will cross an existing oil pipeline within 9m of a traction zone. It will run parallel with the metro car parking yard at a separation of about 40m for several hundred metres. A stray current interference assessment is required to evaluate the interference level and how to mitigate it if an unacceptable interference is found to occur.
A model is used to predict the protection provided by the CP system and the interference between the pipeline and the metro system under different operating conditions
Case Study: HVDC Interference On Pipelines HVDC Interference On Pipelines
A new HVDC transmission line is being planned with a voltage of ±500kV and a distance of 577 km. The distance of one planned electrode from a nearby constructed pipeline is about 9 km. The pipeline is likely susceptible to interference from the HVDC systems. There is a need to assess the interference level and its risk, and the feasibility of mitigation.
A simulation model was used to predict and quantify the interference caused by the system operating under bipolar conditions where the HVDC ground electrodes may pick-up current from the ground or discharge current into the ground. Mitigation measures were also investigated.
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