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Integrated Coating System for Corrosion Protection of Carbon Steel in Artificial Geothermal Brine
(2022)
Corrosive geothermal brines are a major challenge to geothermal power-plants. For cost reasons, plant designers prefer to use carbon and low alloyed steels, which are susceptible to uniform and localized corrosion when exposed to geothermal brines having acidic and saline properties. To solve such problem, coatings or inhibitors would be a protective solution as an alternative to the use of high alloyed materials.
This study investigated a coating system consisting of polyaniline/silicon dioxide based on resources locally available in Indonesia. Protection against corrosion of carbon steel was shown by long-term (28 day) exposure and electrochemical tests of coated carbon steels, performed in an artificial acidic and saline geothermal brine, comparable to the conditions encountered at a site in Indonesia.
Therefore, an integrated coating system is proposed for corrosion protection, combining the electrochemical functionality of polyaniline and the physical advantages of silica.
Carbon Capture, Utilization and Storage (CCUS) has been proposed as a promising technology for the mitigation of CO2 emissions into the atmosphere from fossil-fuel-operated power generation plants. As the reliability and cost effectiveness of the pipeline transport network is crucial to the overall operability and resilience of the CCUS system, it is vital to realize the possible corrosion risks of the employed pipeline steels corresponding to the impurity level of the gas source.
Recent studies have shown that even the high alloyed materials might be susceptible to general and/or localized corrosion by the condensates forming from the impurities such as SOx, NOx, CO, O2 and water [1]. Up to now, however, there is no regulation procedure which defines the maximum acceptable level of impurities and the combination of them for each employed pipeline steels. Herein, systematic experiment series were conducted by mixing pure CO2 gas with varying concentration of each impurity and with the varying combination of them. Each time, the mixture was then fed (1 L/min) into the reactor containing 12 specimens for 120-600 h at 5°C (to simulate the sub-level pipeline transport). The resulted condensate was collected and analyzed by ionic chromatography and atomic absorption spectroscopy to determine the chemical composition. In this study, the “worst-case scenario” gas mixture, containing 2.5 % H2O, 1.8 % O2, 1000 ppm NO2, and 220 ppm SO2 as impurities, resulted in the condensate containing H2SO4 0.114 M and HNO3 0.0184 M (pH 2.13). This “original” condensate was then re-produced to carry out exposure tests and electrochemical characterization including corrosion potentials and impedance spectroscopy in CO2 saturated condition for 7-14 days at the same temperature. The corrosion rate was also measured by mass loss method.
We can conclude that, at the initial stage, HNO3 plays the dominant role in Fe dissolution process, while H2SO4 is responsible for the pit initiation followed by pitting corrosion. Future studies will be focused on the combination effect from the impurities and the exposure test under the regularly changing condensate to mimic the real CO2 pipeline system.
Dieses Buch ist definitiv eine Empfehlung an alle, die mit RFA arbeiten müssen. Außerdem bietet es nützliche und praktische Informationen für Forscher, die an einem bestimmten Thema arbeiten, das im Antragsteil erwähnt wird. Dies wird ihnen während ihrer Forschung helfen, Proben vorzubereiten sowie Fehler in der RFA-Analyse zu erkennen und somit zu vermeiden.
Die Stärken des Buches liegen im verständlichen Text und darin, dass alle notwendigen Schritte der Analysenverfahren Punkt für Punkt aufgeführt sind. Obwohl die Autoren eine unglaubliche Arbeit geleistet haben, um den Leser auf den neuesten Stand zu bringen, sind einige Teile ziemlich kurz gehalten. Die Auflistung von weiterführender Literatur, einschließlich wichtiger Normen und Gesetze, verringert dieses Manko etwas und verweist die interessierten Leser auf ergänzende Quellen.
Environmental and sustainable economical concerns are generating a growing interest in biofuels predominantly produced from biomass. It would be ideal if an energy conversion device could directly extract energy from a sustainable energy resource such as biomass. Unfortunately, up to now, such a direct conversion device produces insufficient power to meet the demand of practical applications. To realize the future of biofuel-fed fuel cells as a green energy conversion device, efforts have been devoted to the development of carbon-based nanomaterials with tunable electronic and surface characteristics to act as efficient metal-free electrocatalysts and/or as supporting matrix for metal-based electrocatalysts. We present here a mini review on the recent advances in carbon-based catalysts for each type of biofuel-fed/biofuel cells that directly/indirectly extract energy from biomass resources, and discuss the challenges and perspectives in this developing field
CCUS-Technologie (CO2-Abtrennung; Nutzung und Speicherung, engl. Carbon Dioxide Capture, Utilization and Storage) gilt als eine vielversprechende Methode zur Abschwächung des Beitrags von fossilen Emissionen zur globalen Erwärmung. Dabei wird das in den Verbrennungsprozessen entstandene Treibhausgas aufgefangen, zu verschiedenen Lagerstätten transportiert und langzeitig gespeichert bzw. einer chemischen Nutzung zugeführt.
In bisher veröffentlichten Untersuchungen wurde gezeigt, dass die CO2-Transport-Pipelines in hohem Maße gefährdet sind, wenn sie korrosiven Begleitstoffen des CO2-Stroms, wie SOx, NOx bei einem hohen Wasserdampfanteil ausgesetzt sind. Screening-Tests zeigten, dass bei einer Konzentration von 1000 ppmv H2O die Reaktionen und Kondensation von SO2 und NO2 mit O2 und H2O zu Säuretropfen (pH ~ 0,5) auf der Oberfläche von Metall-Prüfkörper und Gefäß führen. Die Werkstoffe 1.0582, 1.8977, 1.4313 und 1.4562 wurden in CO2-gesättigtem Kondensat mit unterschiedlichem Verhältnis der säurebildenden Komponenten untersucht. Diese Studien zeigten grundsätzlich den Mechanismus sowie die Rolle jedes CO2-Strom-Begleitstoffes auf den Korrosionsprozess. Allerdings spiegeln die bei Auslagerung und elektrochemischen Messungen in der künstlichen CO2-gesättigten Kondensat-Lösung auftretenden Bedingungen nicht im Detail die Realität in der Praxis, wo sich nur Tröpfchen bilden, wider.
Diese Arbeit konzentriert sich auf den Korrosionsprozess von Kondensat in Form von Tröpfchen, auf der Oberfläche von Rohrleitungswerkstoffen unter CO2-Atmosphäre bei 5 °C (Simulation des Transportzustandes). Die Experimente wurden nicht nur für Auslagerungsversuche, sondern auch für elektrochemische Tests mit nur einem Tröpfchen (weniger als 20 µL) konzipiert. Die Auslagerungs-versuche wurden sowohl unter Normaldruck als auch bei hohem Druck (> 70 bar) durchgeführt, wobei das CO2 als dichte – den Tropfen umgebende - Phase vorliegt. Die korrodierten Prüfkörper wurden rasterelektronenmikroskopisch (REM) und mittels Energiedispersiver Röntgenspektroskopie (EDX) analysiert, um nicht nur Korrosionsform, sondern auch die Elementverteilung der Korrosionsprodukte zu zeigen.
Carbon Capture Utilization and Storage (CCUS) is a promising technology for the reduction of CO2 emissions from fossil-fuel operated power plants, steel and cement mills or refineries. Crucial points for a sustainable and future-proof CCUS procedure are reliability and cost efficiency of the pipeline transport network especially concerning corrosion risks under impurities and moisture in the CO2 stream. Recent studies have shown that even high alloyed steels might be susceptible to general and/or localized corrosion caused by condensates. It was concluded from our study on carbon steels in normal and high pressure conditions, that the combination of these gas impurities, resulted in the acidic condensate, is not only a simple sum of each corrosive effect, but highly accelerates the corrosion rate of the pipeline steel, indicating the need of dynamic tests before installing the network pipeline system.
CCUS-Technologie (CO2-Abtrennung; Nutzung und Speicherung, engl. Carbon Dioxide Capture, Utilization and Storage) gilt als eine vielversprechende Methode zur Abschwächung des Beitrags von fossilen Emissionen zur globalen Erwärmung. Dabei wird das in den Verbrennungsprozessen entstandene Treibhausgas aufgefangen, zu verschiedenen Lagerstätten transportiert und langzeitig gespeichert bzw. einer chemischen Nutzung zugeführt.
In bisher veröffentlichten Untersuchungen wurde gezeigt, dass die CO2-Transport-Pipelines in hohem Maße gefährdet sind, wenn sie korrosiven Begleitstoffen des CO2-Stroms, wie SOx, NOx bei einem hohen Wasserdampfanteil ausgesetzt sind. Screening-Tests zeigten, dass bei einer Konzentration von 1000 ppmv H2O die Reaktionen und Kondensation von SO2 und NO2 mit O2 und H2O zu Säuretropfen (pH ~ 0,5) auf der Oberfläche von Metall-Prüfkörper und Gefäß führen. Die Werkstoffe 1.0582, 1.8977, 1.4313 und 1.4562 wurden in CO2-gesättigtem Kondensat mit unterschiedlichem Verhältnis der säurebildenden Komponenten untersucht. Diese Studien zeigten grundsätzlich den Mechanismus sowie die Rolle jedes CO2-Strom-Begleitstoffes auf den Korrosionsprozess. Allerdings spiegeln die bei Auslagerung und elektrochemischen Messungen in der künstlichen CO2-gesättigten Kondensat-Lösung auftretenden Bedingungen nicht im Detail die Realität in der Praxis, wo sich nur Tröpfchen bilden, wider.
Diese Arbeit konzentriert sich auf den Korrosionsprozess von Kondensat in Form von Tröpfchen, auf der Oberfläche von Rohrleitungswerkstoffen unter CO2-Atmosphäre bei 5 °C (Simulation des Transportzustandes). Die Experimente wurden nicht nur für Auslagerungsversuche, sondern auch für elektrochemische Tests mit nur einem Tröpfchen (weniger als 20 µL) konzipiert. Die Auslagerungs-versuche wurden sowohl unter Normaldruck als auch bei hohem Druck (> 70 bar) durchgeführt, wobei das CO2 als dichte – den Tropfen umgebende - Phase vorliegt. Die korrodierten Prüfkörper wurden rasterelektronenmikroskopisch (REM) und mittels Energiedispersiver Röntgenspektroskopie (EDX) analysiert, um nicht nur Korrosionsform, sondern auch die Elementverteilung der Korrosionsprodukte zu zeigen.
Synergistic effects of impurities in the condensate on the corrosion of CO2 transport pipeline
(2017)
For the reliability of transport pipelines the corrosion resistance of the materials used needs to be determined in conditions, which are possible during the transport process. In some situations condensation of components out of the CO2 stream can occur.
To study the effect of condensate on transport pipeline steel, a “worst-case scenario” gas mixture, containing 2.5 % H2O, 1.8 % O2, 1000 ppmv NO2, and 220 ppmv SO2, was proposed, fed (1.5 L/min) into a glass reactor containing coupon-shaped specimens for 120 600 h at 278 K (to simulate the underground pipeline transport), and resulted in the condensate containing 0.114 M H2SO4 and 0.0184 M HNO3 (pH 2.13). Basing on this “original” condensate, exposure tests and electrochemical characterization together with pH and conductivity in CO2 saturated condition at the same temperature were carried out. The role of each gas impurity and the combination of them, when the condensate is formed, was studied by investigating the role of individual and varying combination of acidic components in the condensate on the corrosion behaviors of the commercial pipeline-steel (L360NB). The stability and protectability of the corrosion film were further studied by periodically changing the condensate during the exposure tests.
It can be concluded that although the condensation of NOx in form of HNO3 causes faster corrosion rate, it is the condensation of SOx or the combination of SOx and NOx that may cause much more severe problems in form of localized and pitting corrosions. Different to the corrosion products formed in CO2 atmosphere without impurities (mainly iron carbonate) the corrosion products resulted from these acidic condensation have no protectability, indicating the need of controlling gas quality during the transportation within the pipeline network.
Synergistic effects of impurities in the condensate on the corrosion of CO2 transport pipeline
(2017)
For the reliability of transport pipelines the corrosion resistance of the materials used needs to be determined in conditions, which are possible during the transport process. In some situations condensation of components out of the CO2 stream can occur. To study the effect of condensate on transport pipeline steel, a “worst-case scenario” gas mixture, containing 2.5 % H2O, 1.8 % O2, 1000 ppmv NO2, and 220 ppmv SO2, was proposed, fed (1.5 L/min) into a glass reactor containing coupon-shaped specimens for 120 600 h at 278 K (to simulate the underground pipeline transport), and resulted in the condensate containing 0.114 M H2SO4 and 0.0184 M HNO3 (pH 2.13). Basing on this “original” condensate, exposure tests and electrochemical characterization together with pH and conductivity in CO2 saturated condition at the same temperature were carried out. The role of each gas impurity and the combination of them, when the condensate is formed, was studied by investigating the role of individual and varying combination of acidic components in the condensate on the corrosion behaviors of the commercial pipeline-steel (L360NB). It can be concluded that although the condensation of NOx in form of HNO3 causes faster corrosion rate, it is the condensation of SOx or the combination of SOx and NOx that may cause much more severe problems in form of localized and pitting corrosions. Different to the corrosion products formed in CO2 atmosphere without impurities (mainly iron carbonate) the corrosion products resulted from these acidic condensation have no protectability, indicating the need of controlling gas quality during the transportation within the pipeline network.
Korrosion von Stählen in flüssigen und überkritischen CO2–Strömen unter realitätsnahen Bedingungen
(2017)
CCUS-Technologie gilt als eine vielversprechende Methode zur Abschwächung des Beitrags von fossilen Emissionen zur globalen Erwärmung. Dabei wird das in den Verbrennungsprozessen entstandene Treibhausgas aufgefangen, zu verschiedenen Lagerstätten transportiert und langzeitig gespeichert bzw. einer chemischen Nutzung zugeführt.
CO2-Transport-Pipelines sind potentiell gefährdet, wenn sie korrosiven Begleitstoffen des CO2-Stroms, wie SOx, NOx bei einem hohen Wasserdampfanteil ausgesetzt sind. Screening-Tests zeigten, dass bei einer Konzentration von 1000 ppmv H2O die Reaktionen und Kondensation von SO2 und NO2 mit O2 und H2O zu Säuretropfen (pH ~ 0,5) auf der Oberfläche von Metall-Prüfkörpern und Gefäßen führen. Die Werkstoffe 1.4313 1.8977 und 1.4562 wurden in CO2-Atmosphäre mit unterschiedlichen Verhältnissen der säurebildenden Komponenten SO2, NO2, H2S mit H2O untersucht. Diese Studien zeigten grundsätzlich den Mechanismus sowie die Rolle jedes CO2-Strom-Begleitstoffes auf den Korrosionsprozess.
Carbon Capture Utilization and Storage (CCUS) is a promising technology for the reduction of CO2 emissions, e.g. from fossil-fuel operated power plants or cement mills. Crucial points for a sustainable and future-proof CCUS procedure are reliability and cost efficiency of the pipeline transport network. Due to the absence of certified benchmarks for upper limits, systematic experiments with impurities in the CO2 stream were carried out. For oxidation processes SO2 and NO2 acted as corrosive components, and for reductive atmosphere H2S. Carbon steel L485MB (pipeline), martensitic steel 1.4313 (compression) and austenitic steel 1.4562 (injection) were selected as specimens. Experiments were performed at 0 bar or 100 bar and within a temperature range 278 K ≤ T ≤ 313 K. High-alloyed Cr-Ni steels revealed no corrosion (1.4562, 1.4313), while for carbon steel considerable corrosion was observed. The type and intensity of corrosion was strongly coupled with the applied corrosive species and the level of humidity in the CO2 stream, leading to different compositions of acidic condensates. Applying a reducing atmosphere results in very little corrosion rates, but provokes pitting corrosion. In contrast, oxidizing or mixed settings lead to a clearly increased growth of the corrosion layer, but exhibit shallow uniform corrosion. Exceptional nitric acid results in intergranular corrosion. Investigations on the specimens were carried out by optical microscopy, XRD, SEM/EDX, and AAS/IC.
This study evaluates on the possibility of using gold nanoparticles functionalizedwith the luminol derivative N-(aminobutyl)-N-(ethylisoluminol)(ABEI) and hybridizedwith graphene oxidenanoribbons on acarbon based screen-printedelectrode (ABEI-AuNP-GONR/SPE) as an enzymaticelectrochemiluminescence (ECL) urea sensor.The electrocatalytic activity and ECL intensity of ABEI-AuNP-GONR/SPE were found to increase proportionally with the concentrationofurea in the analyte sample,owing to the rise in pH value.These phenomena are attributed to increased formation of luminol monoanion precursors for further electrochemical oxidation,which in turn produce eitherluminol radicals or excited3-amino-phthalate molecules.The luminescence is most likely caused by the interaction of luminol radicals with superoxide radicals formed from dissolved oxygen. Thesensitivity of our sensor was determinedtobe 170.58 mM@1 and 16.23 mM@1 for urea concentrations from 2to5.82 mM and from 5.82 to 30 mM, respectively, coveringthe normal urea level in human blood.
CCS technology - Carbon Dioxide Capture and Storage, has been recognized as an excellent technology to reach the target of CO2 reduction. However, the safety issue and cost effectiveness currently hinder the future of CCS. Recent studies have shown that even at a very low concentration of impurities (less than 100 ppmV of SO2, NO2, O2 and H2O) the droplet formation and condensation of sulfuric and nitric acids in dense phase CO2 are possible and observable [1-3].To reveal the mechanism of droplet corrosion in dense CO2 at high pressure and low temperature, further studies on factors that affect wettability and resulting corrosion behaviors of transport pipeline steels are needed.
In this work, carbon steel 1.8977 (L485MB), CrMo-alloyed steel 1.7225 (42CrMo4), martensitic steel 1.4313, and superaustenite steel 1.4562 (alloy 31) were investigated. The wettability was determined by contact angle measurement of sessile drop in CO2 atmosphere, at different pressure and temperature. The corrosion behavior of steels was investigated with standard exposure tests, followed by mass loss determination, surface characterization by scanning electron microscope (SEM) and chemical analysis by Energy Dispersive X-Ray Analysis (EDX). Exposure tests with and without the synthetic CO2 saturated water droplets were performed at both low temperature (278 K) and higher temperatures (288 K and 313 K) at high pressure where CO2 is supercritical or in dense phase. The investigated flue gases were SO2 (70-220 ppmV) and O2 (6700 ppmV) and water (50-200 ppmV). To reveal the effects of surface morphology, carbon steel coupons with different surface roughness were prepared to expose to CO2 stream containing oxidizing/reducing impurities to observe the condensation and the corrosion process that followed.
According to the results of the experiments carried out, the following points can be concluded:
1. Exposure tests showed that specimens with the addition of SiO2 particles and polyaniline particles exhibit better corrosion resistance than specimens with the addition of only polyaniline particles or binder only.
2. Open circuit potential measurements showed that in the beginning of the experiments, both coatings had an open circuit potential 100 mV higher than carbon steel. Within one day of immersion, the potential of carbon steel increased significantly, indicating the formation of oxide layer. After extended exposure the carbon steel potential sat between PS1 (which had higher potential) and PS2 (which had a lower potential) and all three were in the range –600 mV to –500 mV vs Ag/AgCl.
3. Both coatings PS-1 and PS-2 were degraded with increasing exposure time, shown by the decrease of absolute impedance value at low frequency range after 2, 4, and 6 days exposure.
4. Potentiodynamic test was performed after 3 hours and 6 days exposure, and it was shown that the coating in the initial stage exhibited more passive behavior than the specimens exposed for 6 days.
Recent studies have shown that even at a very low concentration of impurities (less than 100 ppmv of SO2, NO2, O2 and H2O) the droplet formation and condensation of sulfuric and nitric acids in dense phase CO2 are possible and observable. To reveal the mechanism of droplet corrosion in dense phase CO2 at high pressure and low temperature, further studies on factors that affect wettability and resulting corrosion behaviors of transport pipeline steels are needed. In this study, effects of surface morphology were investigated by varying surface roughness of carbon steel coupons exposed to CO2 stream containing impurities to measure the wettability by contact angle and to observe the condensation as well as possible droplet corrosion that followed. Other considered factors were: pH of the droplet, temperature, droplet volume, and exposure time.
To set up recommendations on how to define “reasonable minimum composition thresholds” for CO2 streams to access CO2 pipeline networks, we investigated potential impacts of CO2 streams with different and temporally variable compositions and mass flow rates along the CCS chain. All investigations were based on a generic “CCS cluster scenario” in which CO2 streams captured from a spatial cluster of eleven emitters (seven fossil-fired power plants, two cement plants, one refinery and one steel mill) are collected in a regional pipeline network. The resulting CO2 stream (19.78 Mio t impure CO2 per year) is transported in a trunk line (onshore and offshore) and injected into five generic replicate storage structures (Buntsandstein saline aquifers) offshore. Experimental investigations and modeling of selected impacts revealed beneficial as well as adverse impacts of different impurities and their combinations. Overall, no fundamental technical obstacles for transporting, injecting and storing CO2 streams of the considered variable compositions and mass flow rates were observed. We recommend to define minimum composition thresholds for each specific CCS project through limiting
i) the overall CO2 content,
ii) maximum contents of relevant impurities or elements,
iii) acceptable variability of concentrations of critical impurities, and defining impurity combinations to be avoided.
Al2O3 has been widely used as a coating in industrial applications due to its excellent chemical and thermal resistance. Considering high temperatures and aggressive mediums exist in geothermal systems, Al2O3 can be a potential coating candidate to protect steels in geothermal applications. In this study, γ-Al2O3 was used as a coating on martensitic steels by applying AlOOH sol followed by a heat treatment at 600 °C. To evaluate the coating application process, one-, two-, and three-layer coatings were tested in the artificial North German Basin (NGB), containing 166 g/L Cl−, at 150 °C and 1 MPa for 168 h. To reveal the stability of the Al2O3 coating in NGB solution, three-layer coatings were used in exposure tests for 24, 168, 672, and 1296 h, followed by surface and cross-section characterization. SEM images show that the Al2O3 coating was stable up to 1296 h of exposure, where the outer layer mostly transformed into boehmite AlOOH with needle-like crystals dominating the surface. Closer analysis of cross-sections showed that the interface between each layer was affected in long-term exposure tests, which caused local delamination after 168 h of exposure. In separate experiments, electrochemical impedance spectroscopy (EIS) was performed at 150 °C to evaluate the changes of coatings within the first 24 h. Results showed that the most significant decrease in the impedance is within 6 h, which can be associated with the electrolyte penetration through the coating, followed by the formation of AlOOH. Here, results of both short-term EIS measurements (up to 24 h) and long-term exposure tests (up to 1296 h) are discussed.
Early Stage of Corrosion Formation on Pipeline Steel X70 Under Oxyfuel Atmosphere at Low Temperature
(2020)
The early stage of corrosion formation on X70 pipeline steel under oxyfuel atmosphere was investigated by applying a simulated gas mixture (CO2 containing 6700 ppmv O2, 100 ppmv NO2, 70 ppmv SO2 and 50 ppmv H2O) for 15 h at 278 K and ambient pressure. Short-term tests (6 h) revealed that the corrosion starts as local spots related to grinding marks progressing by time and moisture until a closed layer was formed. Acid droplets (pH 1.5), generated in the gas atmosphere, containing a mixture of H2SO4 and HNO3, were identified as corrosion starters. After 15 h of exposure, corrosion products were mainly X-ray amorphous and only partially crystalline. In-situ energy-dispersive X-ray diffraction (EDXRD) results showed that the crystalline fractions consist primarily of water-bearing iron sulfates. Applying Raman spectroscopy, water-bearing iron nitrates were detected as subordinated phases. Supplementary long-term tests exhibited a significant increase in the crystalline fraction and formation of additional water-bearing iron sulfates. All phases of the corrosion layer were intergrown in a nanocrystalline network. In addition, numerous globular structures have been detected above the corrosion layer, which were identified as hydrated iron sulphate and hematite. As a type of corrosion, shallow pit formation was identified, and the corrosion rate was about 0.1 mma−1. In addition to in-situ EDXRD, SEM/EDS, TEM, Raman spectroscopy and interferometry were used to chemically and microstructurally analyze the corrosion products.
In this work, the focus was set on the corrosion process of condensate as drops on the surface of carbon steels (X52, X70), martensitic steel UNS S41500, and superaustenite UNS N08031 in CO2 atmosphere with impurities at 278 K (to simulate the transportation condition in a buried pipeline). Exposure tests were performed at both normal pressure and high pressure where CO2 is supercritical or in dense phase. The drop, 1 ‑ 10 μL in volume, was prepared by dropping CO2 saturated ultra-pure water onto the surface of steel coupons in a one-liter-autoclave. The CO2 gas stream, simulating the oxyfuel flue gas with varying concentration of impurities (SO2 and O2 ), was then pumped into the autoclave to observe the condensation and corrosion impacts of impurities. Comparable exposure tests were carried out with the same gas mixture and the same volume of water as vapor to observe the drop formation and the corrosion process that follows. The wettability and stability of drops on the surface of steel coupons in CO2 supercritical/dense phase environment was evaluated additionally by contact angle measurement.
Geothermal energy is one of the most promising energy resources to replace fossil fuel. To extract this energy, hot fluids of various salts and gases are pumped up from a geothermal well having a certain depth and location. Geothermal wells in volcanic regions often contain highly corrosive CO2 and H2S gases that can be corrosive to the geothermal power-plants, which are commonly constructed of different steels, such as carbon steel. This research focuses on the corrosion behaviour of carbon steel exposed to an artificial geothermal fluid containing CO2 gas, using an artificial acidic-saline geothermal brine as found in Sibayak, Indonesia. This medium has a pH of 4 and a chloride content of 1,500 mg/L. Exposure tests were conducted for seven days at 70 °C and 150 °C to simulate the operating temperatures for low and medium enthalpy geothermal sources. Surface morphology and cross-section of the specimens from the above experiments were analysed using scanning electron microscope (SEM) and energy dispersive X-ray (EDX). Electrochemical tests via open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) were performed to understand the corrosion processes of carbon steel in CO2-containing solution both at 70 °C and 150 °C. Localized corrosion was observed to a greater extent at 70 °C due to the less protectiveness of corrosion product layer compared to that at 150 °C, where FeCO3 has a high corrosion resistance. However, a longer exposure test for 28 days revealed the occurrence of localized corrosion with deeper pits compared to the seven-day exposed carbon steel. In addition, corrosion product transformation was observed after 28 days, indicating that more Ca2+ cations incorporate into the FeCO3 structure.
Carbon Capture and Storage (CCS) is identified as an excellent technology to reach the target of CO2 reduction. However, the safety issue and cost-effectiveness hinder the future of CCS. For the reliability and safety issues of injection wells, the corrosion resistance of the materials used needs to be determined.
In this study, representative low-cost materials including carbon steel 1.8977 and low alloyed steel 1.7225 were investigated in simulated pore water at 333 K and under CO2 saturation condition to represent the worst-case scenario: CO2 diffusion and aquifer fluid penetration. These simulated pore waters were made from relevant cement powder to mimic the realistic casing-cement interface. Electrochemical studies were carried out using the pore water made of cement powder dissolved in water in comparison with those dissolved in synthetic aquifer fluid, to reveal the effect of cement as well as formation water on the steel performance. Two commercially available types of cement were investigated: Dyckerhoff Variodur® and Wollastonite. Variodur® is a cement containing high performance binder with ultra-fine blast furnace slag which can be used to produce high acid resistance concrete. On the other hand, Wollastonite is an emerging natural material mainly made of CaSiO3 which can be hardened by converting to CaCO3 during CO2 injection.
The results showed the pH-reducing effect of CO2 on the simulated pore water/aquifer (from more than 10 to less than 5) leading to the active corrosion process that happened on both 1.8977 and 1.7225. Electrochemical characterization showed negative free corrosion potential and polarisation curves without passive behaviors. The tested coupons suffered from pitting corrosion, which was confirmed by surface analysis. Interestingly, basing on the pit depth measurements from the tested coupons and the hardness of cement powder, it is suggested that Variodur® performed better than Wollastonite in both aspects. The electrochemical data was compared to that resulted from exposure tests to give a recommendation on material selection for bore-hole construction.
Electrochemical deposition of polyaniline on carbon steel for corrosion study in geothermal solution
(2019)
Polyaniline has been widely developed for many applications, e.g. sensor, supercapacitor components, electrochromic devices, and anticorrosion pigments. Although the addition of polyaniline pigment in organic coatings has been an alternative for corrosion protection in industrial applications, the protection mechanism is still not fully understood. Herein in this study, as a part of the development of polyaniline/silicon dioxide coating for geothermal application, polyaniline has been deposited electrochemically on carbon steel surface in oxalic acid medium and tested in geothermal solution to understand the contribution of polyaniline to the corrosion protection of a polyaniline-based composite in the geothermal system. To observe the surface/interface reaction between the electrolyte and electrode surface during the electrochemical polymerization, electrochemical impedance spectroscopy (EIS) was applied after each cycle. For corrosion study in the geothermal application, an artificial geothermal solution was used with the composition of 1,500 mg/l Cl⁻, 20 mg/l SO₄²⁻, 15 mg/l HCO₃⁻, 200 mg/l Ca²⁺, 250 mg/l K⁺, and 600 mg/l Na⁺, and pH 4 to simulate a geothermal brine found in Sibayak, Indonesia. An electrochemical measurement was performed by monitoring the open circuit potential over seven days, with the interruption by EIS every 22 hours. The experiments were performed at room temperature and 150 °C (1 MPa) in an oxygen-free environment. Impedance spectra showed a reduction of the total impedance value of approximately 10 times for specimens measured at 150 °C compared to the specimens measured at room temperature, suggesting a less stable layer at high temperature.
This contribution provides current findings regarding materials susceptibility for carbon capture, utilization and storage (CCUS) applications. Basing on results gathered in 2 German long-term projects (COORAL and CLUSTER) suitable materials are introduced as well as dominating impurities of the CO2-stream and corrosion mechanisms. Investigations cover the whole CCUS process chain and provide material recommendations for certain parts.
This study focuses on the corrosion mechanism of carbon steel exposed to an artificial geothermal brine influenced by carbon dioxide (CO2) gas. The tested brine simulates a geothermal source in Sibayak, Indonesia, containing 1500 mg/L of Cl-, 20 mg/L of SO4 2-, and 15 mg/L of HCO3-with pH 4. To reveal the temperature effect on the corrosion behavior of carbon steel, exposure and electrochemical tests were carried out at 70 °C and 150 °C. Surface analysis of corroded specimens showed localized corrosion at both temperatures, despite the formation of corrosion products on the surface. After 7 days at 150 °C, SEM images showed the formation of an adherent, dense, and crystalline FeCO3 layer. Whereas at 70 °C, the corrosion products consisted of chukanovite (Fe2(OH)2CO3) and siderite (FeCO3), which are less dense and less protective than that at 150 °C.
Control experiments under Ar-environment were used to investigate the corrosive effect of CO2. Free corrosion potential (Ecorr) and electrochemical impedance spectroscopy (EIS) confirm that at both temperatures, the corrosive effect of CO2 was more significant compared to that measured in the Ar-containing solution. In terms of temperature effect, carbon steel remained active at 70 °C, while at 150 °C, it became passive due to the FeCO3 formation. These results suggest that carbon steel is more susceptible to corrosion at the near ground surface of a geothermal well, whereas at a deeper well with a higher temperature, there is a possible risk of scaling (FeCO3 layer). A longer exposure test at 150 °C with a stagnant solution for 28 days, however, showed the unstable FeCO3 layer and therefore a deeper localized corrosion compared to that of seven-day exposed specimens.
Specific amounts of oxidizing and reductive impurities as well as some moisture were added to dense phase CO2 to replicate CO2 streams from sources in a CCS pipeline network. Due to the moisture content being only 50 ppmV no visible acid condensation took place. To simulate stress conditions at the inside pipeline surface due to fluid pressure (10 MPa) specimens were preloaded using a load frame. Experiments conducted at 278 K and at 313 K revealed the highest corrosion rate at lower temperature. Corrosive effect of impurities was strongest applying mixed atmosphere, containing oxidizing and reductive components, closely followed by CO2 streams with pure oxidizing character. By far, the lowest corrosion rate (10x lower) resulted from reductive atmosphere. In general, at constant temperature and pressure the CO2 stream composition strongly influences the morphology, thickness and composition of the corrosion products. Applying oxidizing or mixed impurities, iron hydroxides or oxides (e.g. goethite, hematite) occur as dominating corrosion products, capable to incorporate different amounts of sulfur. In contrast, using reductive atmosphere very thin corrosion layers with low crystallinity were developed, and phase identification by XRD was unfeasible. SEM/EDX analysis revealed the formation of Fe-O compounds, most likely attributed to the oxygen partial pressure in the system induced by CO2 (≥0.985 volume fraction) and volatile H2O. In addition to the surface covering corrosion layer, secondary phases had grown locally distributed on top of the layer. These compounds are characteristic for the applied atmosphere and vary in number, shape and chemical composition.
Al2O3 coatings are often used as protective layers on steels against electrochemical and high-temperature corrosion because they are chemically inert and stable at elevated temperatures. This study presents preliminary work on the possibilities of using Al2O3 sol-gel coatings for corrosion protection of martensitic stainless steels in geothermal environments. Al2O3 sol-gel coatings were applied on UNS S42000, which is known to be susceptible to uniform and localized corrosion. The coated steel specimens were then tested in two types of artificial geothermal water, which simulate the geothermal fluids found in Sibayak (SBY), Indonesia, and North German Basin (NGB), Germany, respectively. SBY has pH 4 and 1.5 g/L of chloride ions, whereas NGB has a pH of 6 and 166 g/L of chloride ions. All experiments were carried out in autoclaves at 150 °C and 1 MPa under the deaerated condition. Evaluations were performed by investigating the surface profiles of both uncoated and coated steels before and after the corrosion test using a Laser Scanning Microscope (LSM) and Scanning Electron Microscope (SEM). Finally, Electrochemical Impedance Spectroscopy (EIS) was performed to compare the corrosion resistance of Al2O3 coated steels in SBY and NGB solutions. It was observed from the corrosion test that Al2O3 coatings are more suitable for use in the geothermal water with a higher pH.
Nachdem im Verbundprojekt COORAL das Hauptaugenmerk auf überkritisches CO2 gelegt wurde, d. h. Transport über kurze Strecken bei erhöhter Temperatur, wurde in CLUSTER ein größeres lokales Transport-Netzwerk betrachtet, bei dem CO2 bei geringeren Temperaturen, also vorwiegend im flüssigen Zustand transportiert wird. Wurden in COORAL die CO2-Ströme von Kohlekraftwerken untersucht, ging es in CLUSTER zusätzlich um die Emissionen von relevanten Industrien, deren CO2-Emissionen nicht ohne Weiteres vermieden werden können.
Aufgrund der Erfahrungen in COORAL konnte eine Auswahl von kommerziellen Werkstoffen getroffen werden, die für einen konkreten Einsatz für CCS zur Verfügung stünden. Die gemischten und fluktuierenden CO2-Zusammensetzungen sind bei geeigneten Begrenzungen der Begleit¬stoffe im CO2 bezüglich Korrosionsvorgänge beherrschbar. Die Machbarkeit eines lokalen CCS-Clusters erscheint daher gegeben, soweit dies die Anlagen für Kompression, Transport und Injektion betrifft.
For reliability and safety issues of injection wells, corrosion resistance of materials used needs to be determined. Herein, representative low-cost materials, including carbon steel X70/1.8977 and low alloyed steel 1.7225, were embedded in mortar to mimic the realistic casing-mortar interface. Two types of cement were investigated: (1) Dyckerhoff Variodur commercial Portland cement, representing a highly acidic resistant cement and (2) Wollastonite, which can react with CO2 and become stable under a CO2 stream due to the carbonation process. Exposure tests were performed under 10 MPa and at 333 K in artificial aquifer fluid for up to 20 weeks, revealing crevice corrosion and uniform corrosion instead of expected pitting corrosion. To clarify the role of cement, simulated pore water was made by dispersing cement powder in aquifer fluid and used as a solution to expose steels. Surface analysis, accompanied by element mapping on exposed specimens and their crosssections, was carried out to trace the chloride intrusion and corrosion process that followed.
Carbon Capture and Storage (CCS) is identified as an excellent technology to reach the target of CO2 reduction. However, the safety issue and cost effectiveness hinder the future of CCS. For the reliability and safety issues of injection wells the corrosion resistance of the materials used needs to be determined.
In this study, representative low cost materials including carbon steel 1.8977 and low alloyed steel 1.7225 were embedded in cement to mimic the realistic casing-cement interface. Electrochemical studies were carried out using these metal-cement specimens in comparison with those made of metal only in CO2 saturated synthetic aquifer fluid, at 333 K, to reveal the effect of cement on the steel performance. The results showed the protective effect of cement on the performance of pipeline metals during polarisation process. However, the corrosion current density was high in all cases, with and without cement, indicating that the corrosion resistance of these materials is low. This conclusion was supported by the surface analysis of the polarized specimens, which revealed both homogenous and pitting corrosions.
To study the effects of condensed acid liquid, hereafter referred to as condensate, on the CO2 transport pipeline steels, gas mixtures containing a varying concentration of H2O, O2, NO2, and SO2, were proposed and resulted in the condensate containing H2SO4 and HNO3 with the pH ranging from 0.5 to 2.5. By exposing the pipeline steel to the synthetic condensate with different concentration of acidic components, the corrosion kinetic is significantly changed. Reaction kinetic was studied using electrochemical methods coupled with water analysis and compared with surface analysis (scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffractometry (XRD)) of corroded coupons. The results showed that, although the condensation of NO2 in the form of HNO3 causes faster general corrosion rate, it is the condensation of SO2 in the form of H2SO4 or the combination of SO2 and NO2 that may cause much more severe problems in the form of localized and pitting corrosions. The resulting corrosion forms were depended on the chemical nature of acids and their concentration at the same investigated pH. The effects of changing CO2 flow rate and renewing condensate on pitting corrosion were further studied.
The collaborative project “Impacts of impurities in CO2 streams captured from different emitters in a regional cluster on transport, injection and storage (CLUSTER)” aimed to set up recommendations on how to define “reasonable minimum composition thresholds” that CO2 streams should meet when accessing CO2 transport pipeline networks. Within CLUSTER, we investigated potential impacts of CO2 streams with different and temporally variable compositions and mass flow rates along the whole CCS chain. Investigations included, amongst others, impacts on:
• corrosion of pipeline steel,
• pipeline network design and related transport costs,
• alteration of well bore cements,
• pressure development and rock integrity,
• geochemical reactions, and
• petrophysical and geomechanical rock properties.
All investigations are based on a generic CCS chain scenario. In this scenario, CO2 streams are captured from a spatial cluster of eleven emitters and collected in a regional pipeline network. Emitters comprise seven fossil fuel-fired power plants equipped with different capture technologies, two cement plants, one refinery and one integrated iron and steel plant. In total, 19.78 Mio t CO2 (including impurities) are captured in the emitter cluster annually. The combined CO2 stream is transported in a trunk line with a length of 400 km (100 km of these offshore) and is injected into five generic storage structures. The storage reservoirs are saline aquifers of the Buntsandstein.
The investigations revealed beneficial and deteriorating impacts of different impurities and combinations thereof. Overall, no fundamental technical obstacles for transporting, injecting and storing CO2 streams of the modelled variable compositions and mass flow rates were observed. Based on the results, the CLUSTER project team recommends not to define “minimum composition thresholds” for CO2 streams as strict threshold values for each individual impurity in the stream. Instead, CO2 stream compositions and variabilities for specific CCS projects should be constrained with regard to a set of parameters including i) the overall CO2 content, ii) maximum contents of relevant impurities or elements, iii) acceptable variability of CO2 stream composition, and iv) impurity combinations to be avoided.
Study of Polyaniline/Silicon Dioxide based Coating on Carbon Steel in Artificial Geothermal Brine
(2021)
Geothermal brines are corrosive in nature because of their salt contents and high temperatures. Therefore, they pose a major challenge to geothermal power-plants, which are mostly built of low alloyed steels, e.g., carbon steel. Carbon steel is susceptible to uniform and localized corrosion when exposed to geothermal brines having acidic-saline properties. To overcome this limitation, geothermal power plants should be built by either high alloyed materials or by integrating protection systems on carbon steel, such as coatings and inhibitors. We studied a coating system containing polyaniline/silicon dioxide basing on locally available resources that provides protection against corrosion of carbon steel and enhance the thermal resistance in geothermal environments. Here, exposure and electrochemical tests of coated carbon steels were performed in an artificial geothermal brine. The solution had a pH of 4, with the composition of 1,500 mg/L of chlorides, which is based on the chemical analysis of geothermal brine found in Sibayak, Indonesia. All exposure tests were conducted using autoclaves at 150 °C with a total pressure of 1 MPa, which was performed for up to six months to evaluate the durability of the coating system. Post-experimental analyses were performed by assessing the surface of specimens using optical and electron microscopes. On the other hand, electrochemical tests were performed for seven days at 25 °C and 150 °C to investigate the kinetics of electrochemical reactions by measuring open circuit potential and electrochemical impedance spectra. Experimental results showed the corrosion resistance of PANI/SiO2 composite coatings, where polyaniline and SiO2 play their roles as stabilizers.
To reveal the corrosion resistance of casing steel/mortar interface in CO2 injection condition, sandwich samples were prepared and exposed up to 20 weeks in aquifer fluid under 10 MPa and 60 °C. Cross section analysis revealed the crevice corrosion as main mechanism instead of pitting corrosion, which would be expected to happen in the extremely high Chloride concentration. Detailed analysis using EDS line scan shown the slow diffusion of Chloride, suggesting why pitting did not happen after 20 weeks. To mimic the passivated steel surface, the steel coupon was passivated in simulated pore solution having pH 13.5 for 42 days. The passivated coupon was further exposed to NGB solution for 28 days. Electrochemical characterization was performed along the exposure processes to reveal the change in impedance, indicating the corrosion resistance of steel casing/mortar interface.
Die Analyse von Bruchflächen wird in der Schadensanalyse meist auf der Basis von Erfahrungswissen vorgenommen, welches aus vorliegenden Untersuchungen, eigenen Vergleichsversuchen und aus der Literatur stammt. Durch Vergleiche mit bereits vorliegenden Bildern werden qualitativ Bruchmechanismen ermittelt. Grundlage sind zumeist zweidimensionale Bilder aus licht- und elekt-ronenoptischen Verfahren. Quantitative Aussagen beziehen sich bislang beispielsweise auf makroskopische Anteile von Bruchmechanismen oder die Ausmessung von Schwingstreifen. In jüngerer Zeit gibt es vermehrt Ansätze, Computer-Algorithmen einzusetzen, die in der Lage sind, unterschiedlich strukturierte Bruchmerkmale zu finden und zu klassifizieren. Im hier vorgestellten IGF-Vorhaben „iFrakto“, IGF Vorhaben Nr.: 21477 N, werden licht- und elektronenoptisch Topographie-Bilder erzeugt und die gewonnenen 3D-Informationen zusammen mit den klassischen 2D-Bildern ausgewertet.
Carbon Capture Utilization and Storage (CCUS) is a promising technology to reach the target for reduction of CO2 emissions, e.g. from fossil-fuel operated power plants or cement mills. Crucial points for a sustainable and future-proof CCUS procedure are reliability and cost efficiency of the whole process chain, including separation of CO2 from the source, compression of CO2, its subsequent transportation to the injection site and injection into geological formations, e.g. aquifers.
Most components that are in contact with CO2-stream consist of steel. Depending on the operating conditions (e.g. temperature, pressure, and CO2-stream composition) specific suitable steels should be used. The compressed CO2-stream is likely to contain process specific impurities; small amounts of SO2 and NO2 in combination with oxygen and water are most harmful.
One approach, as currently preferred by pipeline operators, is to clean the CO2-stream to such levels, acceptable for carbon steel, commonly used as pipeline material. Another consideration would be, to use more corrosion resistant alloys for CO2-streams with higher amounts of impurities.
Due to the absence of certified benchmarks for upper limits, systematic experiments with impurities in the CO2-stream were carried out reflecting mainly transport and injection conditions.
Within the COORAL project (German acronym for “CO2 purity for capture and storage”) levels of impurities in the CO2-stream, being acceptable when using specific steels, were evaluated. Material exposure to dense or multiphase carbon dioxide (CO2) containing specific amounts of water vapor, oxygen (O2) sulfur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO) can be a challenge to steels. In some situations, condensation of impurities and reaction products from the CO2 stream can occur.
CO2 saturated brine is supposed to rise in the well when the injection process is interrupted. The material selection shall ensure that neither CO2 nor brine or a combination of both will leak out of the inner tubing.
This COORAL-work was extended by a follow-up project, called CLUSTER. Here the additional influence of impurities was investigated when merging CO2 streams from different sources, combined within a “so-called” cluster.
Results are summarized within the following table regarding suitability for different parts of the process chain.
Interfacial properties related to wettability and corrosion in CO2 transport pipelines are experimentally determined by the sessile and the pendant drop methods. The contact angle of a water drop in a compressed CO2 atmosphere is analyzed on an X70 pipeline carbon steel and compared to that on a martensitic steel S41500 to elucidate the effect of corrosion process on active wetting behaviour. The measurements are performed with liquid CO2 at 278 K and pressures ranging from 5 to 20 MPa. The results show that the contact angle (CA) increases with pressure from 132 ° to 143 ° for S41500 and from 117 ° to 137 ° for X70 and decreases with drop age by 20 ° to 24 ° regardless of the pressure and of the fact that corrosion only occurs on X70, which is confirmed by scanning electron microscopy, element mapping and energy dispersive x-ray spectrometry (EDS) analysis. At higher pressure, the contact angles on both materials converge. Further, related properties like density and interfacial tension were determined. CO2 - saturated water has a higher density than pure water: At 5 MPa saturated water reaches a density of 1017 kg⋅m^(-3) and at 20 MPa 1026 kg⋅m^(-3) compared to pure water with a density of 1002 kg⋅m^(-3) and 1009 kg⋅m^(-3), respectively. In this pressure range the IFT drops from 33 mN⋅m^(-1)at 5 MPa to 23 mN⋅m^(-1) at 20 MPa.
The research focus of this study was set on the corrosion process of condensate as droplets on the surface of carbon steels (X52, X70) martensitic steel UNS S41500, and super austenite UNS N08031 in CO2 atmosphere with impurities at 278 K (to simulate the offshore transportation condition in a buried pipeline). The possibility of dew/droplet formation on the steel surface and wetting behavior of corresponding materials were evaluated by contact angle measurement in dense CO2 at 278 K. To observe the effect of impurities (SO2 and O2) on droplet corrosion process, exposure tests were carried out in the mixed atmosphere with a drop, 1 ‑ 10 µL in volume, of CO2 saturated ultra-pure water on steel surface. Comparable exposure tests were carried out with the same gas mixture and the same volume of water, as vapor, to observe the droplet formation and the corrosion process that follows. Effects of surface roughness on the droplet formation and its corrosion process were further studied and showed no significant role upon long time exposure. The results from droplet experiments were compared to those from the bulk electrolyte for the further recommendation on the quality control of gas stream along with the use of carbon steels as transport pipelines in CCS - Carbon Capture and Storage system.
Bei der Untersuchung von Bruchflächen werden zunächst Beobachtungen gemacht, d.h. makroskopische und mikroskopische Merkmale analysiert und in Bildern dokumentiert. Im zweiten Schritt werden anhand der gefundenen Merkmale Rissverlauf und Bruchmechanismen ermittelt. Abschließend sollen diese Ergebnisse in einem Bericht oder Gutachten zusammengefasst werden. Hierbei ist eine skizzenhafte Darstellung der fraktographischen Befunde hilfreich für das Verständnis des Lesers. Ein vorgefertigter fraktographischer Symbolsatz würde dies erheblich vereinfachen.
Skizzen von fraktographischen Befunden sind in der Literatur recht häufig zu finden, z.B. in der VDI 3822 oder dem ASM Handbook Fractography, allerdings gibt es hierzu keine umfassende Systematik, wie sie z.B. aus der Meteorologie (Wetterkarten), Geographie (Landkarten, Seekarten) oder Geologie (Bodenkarten) seit langer Zeit bekannt sind. Deshalb wird hier der Versuch unternommen, einen Symbolsatz zu entwickeln und zur Verfügung zu stellen, mit dessen Hilfe fraktographische Befunde in eindeutiger und übersichtlicher Weise veranschaulicht werden können. Der fraktographische Symbolsatz ("Fracto Graphics") befindet sich in Entwicklung, ist offen zur Diskussion sowie für Verbesserungen.
Die „auffälligen großen Streifen“ sind von echten Schwingstreifen nur sehr schwer zu trennen, weil sie parallel zu den Schwingstreifen verlaufen und meistens ebenfalls nicht sehr groß sind. Die im Labor getesteten Proben zeigten, dass diese großen Streifen zusammen mit Verreibungen auftraten und „tire tracks“ („Reifenspuren“) verursachten. Dies wurde durch eine hochauflösende REM-Untersuchung bestätigt, die „tire tracks“ auf den „großen Streifen“ zeigte. Ein weiterer Hinweis ist die Änderung des R-Werts von -1 auf 0,1, was zu einer Bruchfläche ohne große Streifen und „tire tracks“ führt.
Impact of acid condensation on wetting and corrosion behavior of CO2 transport-pipeline steel
(2018)
Es ist allgemein akzeptiert, das Korrosion in CO2-Transport-Pipelines vernach¬lässigbar ist, solange der Wassergehalt des CO2-Stroms deutlich unter der maximal löslichen Menge liegt. Bisher gibt es keinen allgemeinen Konsens darüber, welcher maximale Wassergehalt in zu transportierendem CO2 zugelassen werden sollte. Bei einem Druck von 100 bar und im Temperaturbereich von 277 K bis 298 K beträgt die Löslichkeit von Wasser in CO2 ca. 1.900 bis 3.200 ppmv, aber die Korrosionsrate von Stählen steigt schon ab einem Wassergehalt von 500 ppmv deutlich an. Bei Anwesenheit von Begleitstoffen wie SO2, NO2 und O2, können sich HNO3, H2SO3 und H2SO4 bilden. Menge und Zusammensetzung von kondensierter Säure sind von der Gaszusammensetzung abhängig, und der Korrosionsmechanismus und die Korrosionsform sind vom Kondensationsverhalten abhängig.
Carbon Capture and Storage (CCS) is identified as an excellent technology to reach the target of CO2 reduction. However, the safety issue and cost effectiveness hinder the future of CCS. For the reliability and safety issues of injection wells the corrosion resistance of the materials used needs to be determined.
In this study, representative low cost materials including carbon steel 1.8977 and low alloyed steel 1.7225 were embedded in cement to mimic the realistic casing-cement interface. Electrochemical studies were carried out using these metal-cement specimens in comparison with those made of metal only in CO2 saturated synthetic aquifer fluid, at 333 K, to reveal the effect of cement on the steel performance. The results showed the protective effect of cement on the performance of pipeline metals during polarisation process. However, the corrosion current density was high in all cases, with and without cement, indicating that the corrosion resistance of these materials is low. This conclusion was supported by the surface analysis of the polarized specimens, which revealed both homogenous and pitting corrosions. Furthermore, to reveal the possible protective performance of FeCO3, the pipeline steels were pre-carbonated and then tested in the same condition as freshly polished specimens.
In this work, the focus was set on the corrosion process of condensate as drops on the surface of carbon steels (X52, X70), martensitic steel UNS S41500, and superaustenite UNS 08031 in CO2 atmosphere with impurities at 278 K (to simulate the transportation condition in a buried pipeline). Exposure tests were performed at both normal pressure and high pressure where CO2 is supercritical or in dense phase. The drop, 1 ‑ 10 µL in volume, was prepared by dropping CO2 saturated ultra-pure water onto the surface of steel coupons in a one-liter-autoclave. The CO2 gas stream, simulating the oxyfuel flue gas with varying concentration of impurities (SO2 and O2), was then pumped into the autoclave to observe the condensation and corrosion impacts of impurities. Comparable exposure tests were carried out with the same gas mixture and the same volume of water as vapor to observe the drop formation and the corrosion process that follows. The wettability and stability of drops on the surface of steel coupons in CO2 supercritical/dense phase environment was evaluated additionally by contact angle measurement.
This work examined the droplet corrosion of CO2 pipeline steels caused by impurities in CO2 supercritical/dense phase at 278 K, simulating the underground transport condition. The wetting properties of carbon steels (X52 and X70) as well as martensitic steel UNS S41500, and superaustenite UNS N08031 were studied by contact angle measurement, revealing reactive wetting behavior of carbon steels. Exposure tests with CO2 saturated water droplet on steel surface showed that the impurities (220 ppmv SO2 and 6700 ppmv O2) diffused into the droplet and then reacted with metal coupons in supercritical/dense phase condition, forming the corrosion product instantly during pumping process. Due to the active wetting behavior, the carbon steels suffered from heavily attack, while negligible corrosion product was observed in cases of martensitic steel UNS S41500 and superaustenite UNS 08031 coupons. Condensation experiments that were carried out on fresh polished coupons in CO2 with 1200 ppmv H2O showed that the formation and aggregation of droplet is dependent on the presence of impurities. Without SO2 and O2, the same concentration of H2O did not cause observable corrosion process after a week of exposure. With 220 ppmv SO2 and 6700 ppmv O2 even low water concentration (5-30 ppmv) still resulted in heterogeneous nucleation and subsequent growth of droplets, leading to corrosive process on carbon steel surface albeit to a lesser extent.
In this work, the focus was set on the corrosion process of condensate as drops on the surface of carbon steels (X52, X70), martensitic steel UNS S41500, and superaustenite UNS 08031 in CO2 atmosphere with impurities at 278 K (to simulate the transportation condition in a buried pipeline). Exposure tests were performed at both normal pressure and high pressure where CO2 is supercritical or in dense phase. The drop, 1 ‑ 10 µL in volume, was prepared by dropping CO2 saturated ultra-pure water onto the surface of steel coupons in a one-liter-autoclave. The CO2 gas stream, simulating the oxyfuel flue gas with varying concentration of impurities (SO2 and O2), was then pumped into the autoclave to observe the condensation and corrosion impacts of impurities. Comparable exposure tests were carried out with the same gas mixture and the same volume of water as vapor to observe the drop formation and the corrosion process that follows. The wettability and stability of drops on the surface of steel coupons in CO2 supercritical/dense phase environment was evaluated additionally by contact angle measurement.
Carbon Capture and Storage (CCS) is identified as an excellent technology to reach the target of CO2 reduction. However, the safety issue and cost-effectiveness hinder the future of CCS. For the reliability and safety issues of injection wells, the corrosion resistance of the materials used needs to be determined.
In this study, representative low-cost materials including carbon steel 1.8977 and low alloyed steel 1.7225 were investigated in simulated pore water at 333 K and under CO2 saturation condition to represent the worst-case scenario: CO2 diffusion and aquifer fluid penetration. These simulated pore waters were made from relevant cement powder to mimic the realistic casing-cement interface. Electrochemical studies were carried out using the pore water made of cement powder dissolved in water in comparison with those dissolved in synthetic aquifer fluid, to reveal the effect of cement as well as formation water on the steel performance. Two commercially available types of cement were investigated: Dyckerhoff Variodur® and Wollastonite. Variodur® is a cement containing high performance binder with ultra-fine blast furnace slag which can be used to produce high acid resistance concrete. On the other hand, Wollastonite is an emerging natural material mainly made of CaSiO3 which can be hardened by converting to CaCO3 during CO2 injection.
The results showed the pH-reducing effect of CO2 on the simulated pore water/aquifer (from more than 10 to less than 5) leading to the active corrosion process that happened on both 1.8977 and 1.7225. Electrochemical characterization showed negative free corrosion potential and polarisation curves without passive behaviors. The tested coupons suffered from pitting corrosion, which was confirmed by surface analysis. Interestingly, basing on the pit depth measurements from the tested coupons and the hardness of cement powder, it is suggested that Variodur® performed better than Wollastonite in both aspects. The electrochemical data was compared to that resulted from exposure tests to give a recommendation on material selection for bore-hole construction.
Carbon Capture Utilization and Storage (CCUS) is a promising technology to reach the target for reduction of CO2 emissions. Crucial points for a sustainable and future-proof CCUS system are reliability and cost efficiency of the whole process chain, including separation of CO2 from the source, compression of CO2, its subsequent transportation to the injection site and injection into geological formations, e.g. aquifers. Recent studies have shown that even at a very low concentration of impurities, condensation of sulfuric and nitric acids in dense phase CO2 are possible and observable. Thus, impact of impure CO2 stream toward corrosion susceptibility of materials to be used in CCUS system need to be considered. In this talk, basing on results achieved from two German long-term projects (COORAL and CLUSTER), the dominating impurities of the CO2 stream and corrosion mechanisms are addressed. Investigations cover the whole CCUS process chain and provide a material recommendation for certain parts.