Application Of Cathodic Protection Research Articles

Failure analysis and preventive recommendations against corrosion of steel tubes of gas risers in natural gas urban distribution lines

In this case study, we have conducted the failure analysis of corroded steel tubes of natural gas risers subjected to a period of service in urban distribution network. Visual inspections and optical microscopy indicated that a severe corrosion was detected on the contact area covered with voids, cracks and corrosion products under a protective rubber cap inserted between the steel tubes and an outer freestanding supportive steel tube. The corrosion products were composed of rust (Fe2O3 and Fe3O4) as well as elemental chlorine, sulphur and phosphor. The water adsorption examination conducted on tape-coated tubes acquired from operating sites revealed remarkably more water adsorption compared to samples prepared in laboratory according to the standard. Based on potentiometric and potentiodynamic polarization studies, we find that water ingress and its adsorption on the tubes cause the failure. The contaminated water then accumulates under the rubber cap and corrosion under insulation (CUI) initializes the corrosion, which will then be associated with crevice corrosion owing to the presence of atmospheric corrosive species. Prevention of corrosion primarily include changing the design of risers by the elimination of rubber cap to avoid water penetration and accumulation, the implementation of standard tape wrapping in combination with additional anti-corrosion coatings, and application of cathodic protection.

Contact Corrosion of Metals under Low Amplitude Fretting

This article discusses fretting corrosion of different friction couples with the consideration of mechanical properties, chemical activity of contacted materials, effect of gaseous environment composition, and external electric current. It has been demonstrated that the fretting wear rate of materials of a friction couple depends on the difference of their electrode potentials. On the basis of the electron theory of adsorption and catalysis on semiconductors (oxides), the physical and chemical formation of a corrosive medium in the area of frictional contact, promoting development of electrochemical processes, have been analyzed. It is mentioned that the catalytic action of an oxide interlayer in fine dispersion is exposed in chemosorption acceleration of oxygen and moisture in a reactive radical in ion radical forms. It has been demonstrated that the existence of cathodic impurities in the alloy and an increase in cathodic depolarizer content (oxygen) in the friction area increases corrosion loss stipulated by electrochemical processes. Relative contribution of chemical and electrochemical corrosion of the friction contact is estimated during the progress of fretting. It is mentioned that the factors delaying the electrochemical processes are efficient for minimization of the fretting wear rate. Opportunities of application of cathodic and anodic electrochemical protection against fretting corrosion are considered.

Influence of Rust Removal Process on The Effectiveness of Sacrificial Anode Cathodic Protection in Repair Concrete

The accumulation of corrosion product on the steel surface may cause eventual failure to deliver of ionic current protection from sacrificial anode cathodic protection. The effect of cleaning of deteriorated steel bar before cathodic protection application is studied in this paper. Two specimens having a length of 580 mm and 150x100 mm of the cross-sectional area with deteriorated reinforcing bar and half-part of chloride contaminated concrete were fabricated to simulate the repair process. Two corroded reinforcing bar with the same surface condition (ø 13mm) were embedded in concrete parallel to each other with the intermediary distance of 40 mm and the cover depth of 30 mm in the bottom surface of the specimen. In the first specimen, rust on the steel bar surface in the repair section was removed. Discrete sacrificial zinc anode is connected to one steel bar in the repair section. During three-years observation, the specimens were exposed to several conditions: 20°C air curing, dry-wet cycle, dry laboratory air, and wet condition, respectively. Potential of both rebar and the sacrificial anode was monitored to understand the performance of the cathodic protection system. The result indicates that rust removal process of steel bar surface in repair concrete part is the most desirable initial condition when the sacrificial anode is applied on it to protect corroded steel bar in new and existing concrete.

Failures and a concept of corrosion protection system for spiral classifiers at KGHM Polska Miedź S.A. Ore Concentration Plant

The Ore Concentration Plant, where the process of flotation is carried out as well as the final production of copper concentrate, plays a key role in the entire production line of KGHM Polska Miedź S.A. Majority of operations related to the run-of-mine preparation to copper flotation enrichment are carried out in a water environment. The maintaining of production process continuity requires to pursue minimisation of many production limitations. The corrosive action of the technological medium, being a salted water suspension of ground copper ore, is one of them. The concept of spiral classifiers cathodic protection presented in this paper may become an alternative to the anti-corrosion protection methods of machinery and equipment used now at the KGHM.The obtained results of research indicate a possibility of significant reduction of classifiers corrosion rate at the application of cathodic protection and of a few times extension of the period of spiral classifiers operation, which replacement generates substantial operating costs.

Electrochemical and on-site tests for the application of cathodic protection on the inner surface of seawater pipes

Electrochemical and on-site tests for the application of cathodic protection on the inner surface of seawater pipes

A study of meshless methods for optimization of cathodic protection systems

Over the last decades, several computer codes have been developed aiming at the full 3D simulation of cathodic protection (CP) systems. CP is a technique applied to prevent corrosive processes and the main goal of the simulation has been to predict the degree of corrosion control achieved. Many pioneering works allowed for the successful application of the boundary element method (BEM) to CP systems. The aim of the present contribution is to introduce a brief overview of cathodic protection system modelling, including some numerical simulations. Mathematical formulations for the electrochemical potential problem are proposed, considering the following meshless methods: the method of fundamental solutions (MFS) and a meshless local Petrov-Galerkin (MLPG2) procedure. The meshless methods performances are evaluated comparing their results with a direct BEM solution procedure. The meshless applications are original first time attempts of such formulations to corrosion problems and cover a lot of practical situations found in actual cathodic protection applications.

Residual protection on a wharf structure following application of impressed current cathodic protection

Recent studies have suggested that residual protection is afforded to structures following the application of impressed current cathodic protection (ICCP), in some cases for significant periods of time, while others for periods of only a few days. This study reported the findings of the de-activation of a 20 year old ICCP system installed on a 50 year old structure. The ICCP was de-activated for 84 days and the steel potentials at locations on the front pile cap and front wall were monitored via the installed reference electrodes. An adjacent water anode system was also de-activated for 48 hours during the initial de-activation period to observe the impact on the steel potentials. The results showed that out of 42 reference electrodes, 17 achieved a 100 mv decay within 24 hours and 10 had more positive instant off potentials than -150 mV. Furthermore, all displayed a positive shift in potential following deactivation of the ICCP system for a period of time, indicative of residual protection, with 22 displaying this positive shift for the whole 94 days of the trial.

Development of mechanisms of hydrogen cracking of metal systems and methods to protect steel products from corrosion-mechanical destruction

The brittle destruction of high-strength metals and alloys used in the chemical and oil refining industry, caused by the influence of aggressive hydrogen-containing media, is a serious scientific issue, the relevance of which has increased dramatically in recent decades due to the discovery of the anomalous hydrogen effects on the complex properties of metals and alloys (abnormal plastic auto-deformation of iron, structural-phase transformations, synergistic effects of microplasticity, effect of reversible shape loss in amorphous metal alloys, and many others). A significant number of hydrogen sources (corrosion in aqueous solutions, hydrogen absorption in the production of welding operations and application of technological protective coatings or cathodic protection of underground pipelines) causes significant difficulties in describing the processes of hydrogen degradation of metal materials. Degradation is manifested in various ways, such as: hydrogen cracking of high-strength steels; hydrogen participation in the process of stress corrosion cracking of stainless steels; cracking of nuclear reactor tubes made of zirconium alloys and embrittlement of titanium alloys by hydride formation, GaAs degradation of monolithic microwave integrated circuits on satellites, etc. The harmful effect of hydrogen on mechanical properties was first noted by Johnson in 1875. Since then, scientists have made many advances in the development of metals with optimal parameters of strength and plasticity. Despite many years of research, the problem of interaction of metal-hydrogen systems remains open due to the variety of approaches and techniques to the assessment of embrittlement effects of hydrogen and hydrogen-containing media. So far it has not been possible to establish a single mechanism of interaction of hydrogen with metal materials, which would explain the whole set of phenomena, related to hydrogen destruction. Therefore, to analyze the mechanisms of hydrogen cracking of metal systems and to develop methods of steel products protection from corrosion-mechanical destruction are relevant areas of scientific and practical activities.

A fresh look at depolarisation criteria for cathodic protection of steel reinforcement in concrete

Criteria for the successful application of cathodic protection (CP) for steel reinforced concrete have been fixed for decades and form part of ISO EN12696. The most used criterion is the achievement of 100 mV depolarization over a period not exceeding 24 hours after discontinuation of the applied current. Although more empirical than theoretically based, the criterion has served the CP industry well. It does, however, exclude any systems that may not always achieve that level of depolarization but have been shown to offer adequate protection, and so there is a need to explore ways of assessing depolarisation data more effectively. On a fundamental level, non-linear polarisation, as described by the Butler Volmer equation, relates corrosion rate to polarisation for a given applied current density and shows that at low current densities, estimated corrosion rates can be shown to be still insignificant at less than 100 mV polarisations. This paper explores the use of non-linear polarisation as an additional supportive criterion based on the measured 24-hour depolarisation level for a known applied current density and tests its applicability in the laboratory and in the field. It speculates that a reducing apparent corrosion current density trend in combination with a depolarised potential moving in a more noble direction is likely to be a suitable alternative criterion, where 100 mV depolarisation is not achieved.

Electrochemical impedance spectroscopy evaluation on the protective properties of epoxy/DBSAdoped polyaniline-TiO2 nanocomposite coated mild steel under cathodic polarization

The dodecyle benzene sulphonic acid doped polyaniline (DBSA doped PANI) and dodecyle benzene sulphonic acid doped polyaniline-TiO2 (DBSA doped PANI-TiO2) nanocomposite were synthesized via in situ oxidative polymerization and characterized by Fourier transform infrared (FTIR) spectroscopy, ThermoGravimetric/differential ThermoGravimetric analysis (TGA/DTA), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The protective properties of epoxy/DBSA doped PANI and epoxy/DBSA doped PANI-TiO2 coated mild steel were evaluated by electrochemical impedance spectroscopy (EIS) in NaCl 3.5wt% at 65°C with and without cathodic protection (CP). Cathodic protection was applied at −500, −750, −1000, −1250 and −1500mV vs. Ag/AgCl. The application of cathodic protection at more negative potentials than −750mV affected the performance of the both coatings causing the decreasing of coating resistance (Rcoat). The coating resistance of epoxy/DBSA doped PANI and epoxy/DBSA doped PANI-TiO2 are in the order of 1×104Ωcm2 and 1×105Ωcm2, respectively. Accordingly, the coating capacitance and water uptake of epoxy/DBSA doped PANI is greater than epoxy/DBSA doped PANI-TiO2 at whole applied potentials. The protective performance of epoxy/DBSA doped PANI coating is improved in the presence of TiO2 nanoparticles under different cathodic potentials.

Experimental Assessment of The 100 mV Polarization Shift Criterion for Cathodic Protection Systems of the Prestressed Concrete Cylinder pipes

In this work, an experimental study was carried out to evaluate the 100 mV polarization shift criterion for confirming the effectiveness of applied cathodic protection viz via zinc sacrificial anodes to arrest progress of corrosion in uncorroded or partially corroded high tensile grade prestressing steel wires of the same grade as the one used to manufacture the prestressed concrete cylinder pipes (PCCP). Total number of 14 wire samples were placed under constant tension approximately 55% of their ultimate tensile strength by the use of specially designed and fabricated holding metal frames. All samples were individually immersed in glass vessels filled with alkaline solutions of pH around 12 and variable chloride ions concentration ranging from 500 to 3000 ppm. With the exception of one wire sample left unprotected; the remaining samples were cathodically protectedby systems of zinc sacrificial anodes such that an average measured polarization shift near 100 mV with variable chloride content in solution was maintained for 9 samples and near 75, 50, and 25 mV with constant chloride content of 3000 ppm. Evaluation of mechanical properties of wire samples suggested that 100 mV criterionand more than sufficient to confirm the adequacy and effectiveness of zinc sacrificial anodes cathodic protection system to arrest progress of corrosion of partially corroded and uncorroded prestressing steel wires in alkaline passivating environment contaminated with chloride ions up to 3000 ppm in solution and for shifts in polarization as low as 25 mV. It was also evident that corrosion progress in the prestressing steel wires can not be arrested in the 3000 ppm chloride environment without the application of cathodic protection.

Structures with chloride attack. Application of cathodic protection in the bridge to Illa de Arousa

The bridge of this project is a reinforced concrete structure of 1980m divided in 40 spans. The deck is a single-cell box girder and a total width of 13m including sidewalks and shoulders. After 25 years in marine environment, the structure showed reinforcement corrosion, especially in piles and deck bottom.It was repaired with four types of intervention: conventional reparation with patches, corrosion inhibitors, cathodic protection with sacrificial anodes and an hybrid cathodic protection system with an initial impressed current and galvanic current. In this research it is described the refurbishment and comparative results of the evolution of the repairs and therefore data of the corrosion progression and its effect in service life. The hybrid system, by the moment, is the system with the best results.

Protection of hot subsea risers by using thermally sprayed aluminium

PurposeIn spite of the high interest in thermally sprayed aluminium (TSA) to protect offshore structures, pipelines, risers, etc., data correlating the exposure of TSA-coated steel in hot seawater to its performance are lacking. No information is available on the performance of TSA in hot seawater, especially when damaged. This paper aims to address this knowledge gap and report the corrosion performance of damaged TSA on carbon steel exposed to boiling synthetic seawater for different periods (up to 5,000 h). It also attempts to understand the mechanism of formation of calcareous deposits in boiling synthetic seawater by using various characterisation tools.Design/methodology/approachTwin wire arc spray was used to coat carbon steel specimens with commercially pure aluminium. Holiday was drilled on the coated surface to expose the underlying steel, amounting to 4 per cent of the specimen surface area. These specimens were then exposed to boiling synthetic seawater for different periods: 2, 68, 188, 335 and 5,000 h. During exposure, the potential was monitored (vs standard calomel electrode [SCE]) and linear polarisation resistance (LPR) method was used to calculate the corrosion rate (CR). After exposure, these specimens were analysed by using characterisation tools such as X-ray diffraction (XRD) and scanning electron microscope (SEM)/energy-dispersive X-ray spectroscopy (EDX).FindingsThe TSA-coated steel samples with 4 per cent holiday showed a CR of approximately 0.008-0.015 mm y−1 and a stable potential (Ecorr) around −800 mV (SCE), when exposed to boiling synthetic seawater for approximately 5,000 h. Microstructural characterisation established that the deposits comprised brucite [Mg(OH)2] only (this is very different to what has been reported at ambient temperatures). The stable potentials obtained after 5,000 h suggest that the brucite layers provided effective corrosion mitigation. Thus, TSA seems to show the potential to protection hot carbon steel risers, even when damage exposing the external steel surface to the seawater is present.Originality/valueThe mechanism of calcareous deposit formation has been studied for many years, but most of the previously reported studies concentrate on low or ambient temperature behaviour. The reported studies mainly concentrate on the application of cathodic protection, rather than the effect of TSA. This is the first journal paper where the behaviour of damaged TSA in boiling synthetic seawater has been reported. The formation of brucite-only layer in the damaged area adjacent to the steel surface in boiling synthetic seawater is novel. And the mechanism of formation of this layer has been explained in the paper.

Investigation of processes occurring at cathodically protected underground installations: Mathematical modeling of reaction transport processes in soil

A dynamic mathematical modeling study of reaction‐transport processes taking place in the vicinity of a defect in coating of underground pipeline protected by cathodic protection is presented. The main chemical reactions providing buffering ability of the soil system (water autoprotolysis, carbon dioxide/bicarbonate/carbonate system, dissociation/precipitation of calcium carbonate) are considered. The model calculations provided qualitative and quantitative information on the dynamic variation of the soil solution pH after application of cathodic protection. A significant pH increase (>12), due solely to oxygen reduction, is proved. A moderate polarization (around Kuhn’s postulated protective potential) is, therefore, sufficient for effective protection of underground structures.

The influence of the internal microbiome on the materials used for construction of the transmission natural gas pipelines in the Lodz Province

This paper presents investigation results of the influence of gas microbes on the biocorrosion rate of the materials used for gas pipelines construction in the Lodz Province. Samples of two types of carbon steel and cast iron were stored in the laboratory pipeline model reflecting the real conditions of working natural gas pipelines were. In the next step the influence of cathodic protection with parameters recommended for protection of underground structures was tested. Analyses of biological corrosion products generated on the test surface were carried out using a scanning electron microscope with an X-ray analyzer. The level of ATP was measured to confirm presence of the adsorbed microorganisms on the observed structures. Corrosion rates were determined by gravimetric methods. In the course of the study it was revealed that the rate of biocorrosion of steel is lower than that for cast iron. Our results also proved that the weight corrosion rate depends on the number of adhered microorganisms. In addition, it has been found that application of the carbon steel cathodic protection decreases its weight corrosion rate. The information obtained will help to increase the knowledge on the rate of biological corrosion causing losses/pits inside gas pipline.

철근콘크리트의 방식기술 및 음극방식의 적용에 관한 고찰

철근콘크리트의 방식기술 및 음극방식의 적용에 관한 고찰

Influence of Sulfate-Reducing Bacteria on the Corrosion Behavior of High Strength Steel EQ70 under Cathodic Polarization.

Certain species of sulfate-reducing bacteria (SRB) use cathodes as electron donors for metabolism, and this electron transfer process may influence the proper protection potential choice for structures. The interaction between SRB and polarized electrodes had been the focus of numerous investigations. In this paper, the impact of cathodic protection (CP) on Desulfovibrio caledoniens metabolic activity and its influence on highs trength steel EQ70 were studied by bacterial analyses and electrochemical measurements. The results showed that EQ70 under -0.85 VSCE CP had a higher corrosion rate than that without CP, while EQ70 with -1.05 VSCE had a lower corrosion rate. The enhanced SRB metabolic activity at -0.85 VSCE was most probably caused by the direct electron transfer from the electrode polarized at -0.85 VSCE. This direct electron transfer pathway was unavailable in -1.05 VSCE. In addition, the application of cathodic protection led to the transformation of sulfide rusts into carbonates rusts. These observations have been employed to provide updated recommendations for the optimum CP potential for steel structures in the presence of SRB.

Micro-Biologically Induced Steel Corrosion and Corrosion Control in Simulated Marine Environment: Steel Electrochemical Response and Micro-Organisms Viability within Cathodic Protection Application

Micro-biologically induced corrosion (MIC corrosion) is a complex and challenging phenomena, associated with the metabolism of microorganisms. Corrosion resistance, surface properties and overall performance of steel structures in sea water, fresh waters or soil are affected by the inevitable existence of various types of microorganisms. Methods, techniques and practical applications are available, however, they are limited with respect to one or another fundamental mechanism, expected results, environmental conditions etc. The complexity of the related challenges results from the fact that there is no single mechanism involved on one hand. On the other hand, despite available knowledge, the fundamental processes related to MIC corrosion still need to be clarified for every environmental condition and/or practical application. The topic of this work is linked to a broad research project on studying in detail the predominant mechanisms within MIC-related corrosion and corrosion control for low-carbon steel in marine environment. One of the main objectives of this research is to justify the potentially superior performance of an alternative impressed current cathodic protection (ICCP), based on pulse technology, in view of controlled microorganisms viability, hence efficient MIC control. With this respect, except steel electrochemical response in relevant conditions, the behaviour of microorganisms with regard response to cathodic polarization, in the course of bio-film formation and/or restricted bio-film growth, are of significant importance and need to be studied and clarified. To this end, the paper will discuss results from preliminary and on-going investigation, as follows: The global electrochemical response of steel in biotic and abiotic environment (simulated sea water), compared to response after pulse ICCP. In addition to recorded evolution of open circuit and on-potentials (within ICCP) with time, the results are in terms of polarization resistance and corrosion current density, respectively, derived from electrochemical impedance spectroscopy (EIS), linear polarization resistance (LPR), potentio-dynamic polarization (PDP) and cyclic voltammetry (CVA). The local electrochemical response, derived from scanning vibrating electrode technique (SVET) and scanning electrochemical microscope (SECM), adds-up to the global electrochemical behaviour of the tested steel. The results provide information for the distribution of ionic currents during bio-film formation or re-distribution (following ICCP), as well as alterations in oxygen availability due to microorganisms metabolism. Additionally, SVET and SECM provide in-situ information on altered ionic current flow after ICCP and/or subsequent changes in microorganisms viability. Finally, fluorescent microscopy supports the electrochemical tests and justifies the effect of cathodic polarization on microbial metabolism and restriction thereof, hence “visualises” the effect of the alternative ICCP as a MIC-control approach. The results from this work serve as a base for further investigation on the application of a hybrid, bio-based coating for control of excessive hydrogen evolution within ICCP. This is especially relevant for the practical situation, when bacterial metabolism reduces ICCP efficiency i.e. when bio-film formation in conditions of conventional ICCP increases the demand for enhancing cathodic polarization. It is expected that the bio-based coating, together with the alternative ICCP, will result in optimum protection with minimum overprotection for steel in marine environment. The concept of this novel solution will be also discussed.

Design and Field Implementation of Auto Tuned Virtual Instrumentation Corrosion Controller

Corrosion in underground metallic pipeline leads to leakage which is hazardous when oil/natural gas is transported. Rate of corrosion in metal pipeline can be controlled by impressing dc current to the gas pipeline and thereby making metal pipeline to act as cathode of corrosion cell. Proportional integral controllers are used in impressed current cathodic protection application; tuning of proportional and integral constants of these controllers requires expertise. Step open, step close and relay tuning methods are compared; relay tuning provided better results for cathodic protection application. Ziegler–Nichols tuning formulas are used to select tuning parameters based on loop response. Virtual instrumentation is used for design, development, testing and field implementation of auto tuned PI controller. Proposed auto tuned proportional integral impressed current cathodic protection controller precisely controls corrosion in pipeline by selecting optimum proportional and integral constants. Controller effectiveness is cross verified using electrical resistance probe.

Performance evaluation of HVOF deposited cermet coatings under dry and slurry erosion

The present work reports on the examination of three High Velocity Oxy Fuel deposited coatings, Tungsten Carbide, Chromium Carbide and Aluminium Oxide, under slurry erosion and dry erosion conditions. The density and hardness of coatings produced in this manner are typically superior to other thermal spray processes, and are therefore suitable for use in corrosive and highly erosive environments. The primary aim of this investigation was to establish the total mass and volume loss from each coating under dry and slurry erosion testing conditions and compare the level of material loss following the respective testing regimes. The scope of the study incorporated the application of cathodic protection to prohibit the effects of corrosion in the case of slurry erosion testing. This approach ensured that any damage to the surface could be attributed to pure erosion, and as such, be assessed against the dry erosion test data. Subsequent examination of the resulting wear scars facilitated assessment of the level of damage caused by the impinging slurry. Results revealed variation in the level of degradation experienced by each coating type under the respective test conditions. Under both dry erosion and slurry erosion, Tungsten Carbide with a Cobalt binder proved an effective protective coating by exhibiting a reduction in material loss over other assessed coatings.