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Eingeladener Vortrag
- nein (21)
Sulfur and water have a fundamental impact on the corrosion rate and potential failure of materials. It is therefore necessary to understand the mechanisms, rates, and potential means of transport, as well as the reactions of these elements with an alloy. This work investigates the effect of water vapor in the initial stages of SO2 corrosion of an ferritic model alloy containing 9 wt% Cr and 0.5 wt% Mn.
The exposure experiments were studied at 650°C in situ under laboratory conditions using energy-dispersive x-ray diffraction analysis. Two separate experiments were run, one with a 99.5% Ar + 0.5% SO2 atmosphere and one with a 69.5% Ar + 0.5% SO2 + 30% H2O atmosphere. With a wet atmosphere, the alloy formed a scale with decreasing oxygen content towards the scale–alloy interface. Sulfides were identified above and below a (Fe, Cr)3O4 layer in the inner corrosion zone. In contrast to this, the overall scale growth was slower in a dry SO2 atmosphere.
Chromia forming high alloyed ferritic-austenitic steels are being used as boiler tube materials in biomass and coal-biomass co-fired power plants. Despite thermodynamic and kinetic boundary conditions, microstructural features such as grain orientation, grain sizes or surface deformation contribute to the oxidation resistance and formation of protective chromium-rich oxide layers. This study elucidates the impact of microstructure such as the grain size and number of carbide precipitates on high temperature oxidation at 650°C in 0.5% SO2 atmosphere. Cold-rolled Fe-16Cr-0.2C material was heat-treated to obtain two additional microstructures. After exposure to hot and reactive gases for 10 h < t < 1000 h layer thicknesses and microstructure of oxide scales are observed by scanning electron microscopy and Energy-dispersive X-ray spectroscopy. The two heat treated alloys showed reasonable oxidation resistance after 1000 h of exposure. The oxidation rate was substantially higher for the alloy with a duplex matrix after heat treatment compared to the fine-grained material.
In Europe biodiesel gained from rapeseeds are considered as an alternative to common fossil fuels due to its environmental performance and its independence from import of raw materials. Biodiesel is also suitable to serve as blending component to heating oil. In that case, it must be considered that changes of fuel composition might cause material degradation.
The objective of this research was to investigate the resistance of metallic materials exposed to heating oil, heating oil blend B20 with 20 % biodiesel and pure biodiesel. Furthermore, the resistance of metals to eight-year aged B10 and six-year aged pure biodiesel was evaluated. Ageing of biodiesel forms acids and water which might propagate metal corrosion. The investigated metals (aluminium, unalloyed steel, austenitic CrNi-steel, copper, die cast zinc and brass) are commonly used for components in middle distillate facilities.
According to DIN 50905-4 the immersed metals were exposed in a climate chamber at 50°C for 4 weeks. The metallic materials were evaluated as resistant if the annual corrosion rate due to uniform corrosion remained under 0.1 mm/year and no localized corrosion in the form of pitting occurred.
The corrosion rates of the exposed materials stayed far below the limit of 0.1 mm/year for all tested fuels. An exception was die cast zinc ZP0410 in eight-year aged B10; a corrosion rate up to 0.3 mm/year due to uniform corrosion was measured. In no case localized corrosion occurred. Copper and brass caused discolouration of biodiesel from yellow to green.
In conclusion, the tested metallic materials were resistant in heating oil, heating oil blend B20 and pure biodiesel at 50 °C. Even the metals exposed to six-year aged biodiesel and eight-year aged B10 showed no uniform or localized corrosion; except for zinc, which was not resistant in eight-year aged B10.
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.
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.
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.
The composites combining aluminum and silica nanoparticles with the addition of tetramethylammonium hydroxide (Al-SiO2(T)) and butanol (Al-SiO2(B)) as mixing media have been successfully fabricated. Corrosion behavior of Al-SiO2 composites before and after exposure in 1M NaCl solution was examined using potentiodynamic polarization (Tafel curve analysis). The study was also equipped with scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and X-ray diffraction (XRD) investigations. Before exposure, Al-SiO2(T) exhibited the best corrosion resistance. Performance improvement was indicated by Al-SiO2(B) up to 10 times better than Al-SiO2(T) after exposure. The increased SiO2 content did not significantly enhance the corrosion resistance of the composites. The Al-SiO2 composites with 5% SiO2 content showed very high corrosion resistance (as the optimum composition). Furthermore, pitting corrosion was observed in the Al-SiO2 composites, indicated by the formation of corrosion products at grain boundaries. The product was affected by the presence of SiO2 in the Al matrix and the NaCl environment at 90 °C (approach to synthetic geothermal media: Na+, Cl, H+, OH-). Our study revealed the presence of γ-Al2O3, γ-Al(OH)3, and Al(OH)2Cl as the dominant corrosion products.
Microbiologically influenced corrosion (MIC) of iron is usually attributed to sulfate-reducing microorganisms (SRM) in oil and gas facilities. SRM act upon the metal by the re-activeness of hydrogen sulfide (HS-), and by withdrawal of the available electrons in electrical contact with the metal (EMIC). Methanogenic archaea (MA) can also cause MIC (Mi-MIC). Several MAs were identified to be corrosive by using elemental iron as the sole electron donor for methanogenesis, including Methanobacterium-affliated IM1 and Methanococcus maripaludis Mic1c10. Currently, low corrosion rates were reported for MA, possibly due to the formation of siderite (4Fe + 5HCO3- + 5H+ ® 4FeCO3 + CH4 + 3H2O). Since MA do not produce HS-, withdrawal of electrons may be their main corrosive mechanism; however, mechanistic details and kinetics of the overall process are poorly understood.
To investigate the corrosion potential of MA, we studied the EMIC methanogenic strains (IM1 and Mic1c10) individually or part of a syntrophic co-culture with SRM. Corrosion studies were conducted using an in-house developed flow-through system to simulate fluctuating environmental conditions. Results indicate that the rates of iron corrosion by MA (up to 0.4 mm/yr) are higher to that caused by the marine SRM Desulfovibrio alaskensis (0.15 mm/yr) and the co-culture (0.1 mm/yr). Scanning electron microscopy (SEM) images of the metal incubated with MA showed severe pitting corrosion. Genomic analysis of the EMIC MA was conducted to provide an insight on the possible cellular mechanisms that could be involved. Furthermore, low concentrations of MA-targeting biocides will be applied to EMIC MA in static and flow conditions to gain insights for possible mitigation strategies. Such knowledge and deeper understanding also from an electrokinetic point of view may not only provide further models in microbial electrophysiology, but also contribute to mitigation strategies in MIC.
The church of Koszewko (Poland) is a brick building edified in the 15th century built on cobblestone foundations. There are five windows in the sanctuary. Three of them enclose heraldic panels from the Küssow’s family from the 15th century which are surrounded with Goethe glass from the 18th century to complete the windows. The colored heraldic panels are strongly damaged and corroded with massive paint layer losses, glass- and leadbreakages. Those medieval glass fragments have been shortly discovered and are of particular interest for Poland since only few medieval glazing have been conserved.
The damages as well as the glass compositions have been investigated with ESEM/EDX. Two categories of medieval glass compositions have been identified. The blue glass is particularly sensible to corrosion because of his high content in K2O. The colorless and the red glass samples belong to a stable glass type. Due to the thickness of the gel layer, it is easy to see that the degradation is strongly proceeded. The protection of those medieval stained-glass panels is absolute necessary.
The medieval panels have been restored and surrounded from a copper frame. Then they have been fixed on the wood frame in the church. The exterior glazing has been closed with a panel of Goethe glass. The gap between the Goethe- and the medieval glass is about 3 cm. The Goethe glass panel has been stabilized with a film based on polyester to protect the medieval glasses against any damages. In this way, a low cost protective glazing has been installed for a long-term conservation of each medieval stained-glass panels. The climate measurements over the period of one year on the restored windows are in process. The temperature and the relative humidity are recorded in the church interior, in the gap between the original and the Goethe glass and outdoors.
Microbially influenced corrosion (MIC) of iron is usually attributed to sulfate-reducing microorganisms (SRM) which act upon the metal by the reactiveness of hydrogen sulfide, and by withdrawal of the available electrons in electrical contact with the metal. Methanogenic archaea can also cause MIC by directly withdrawing electrons from the iron surface for methanogenesis. However, the mechanistic details and kinetics of the overall process are poorly understood. Precipitation of siderite, a by-product of methanogenesis, (4Fe + 5HCO3 + 5H+ 4FeCO3 + CH4 + 3H2O) can lead to an insulating layer on the metal surface and lower the corrosion rate. Still, the extent of FeCO3 precipitation may be significantly influenced by environmental conditions such as pH and advective processes.
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.
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.
By exposure and electrochemical tests in the laboratory the Cu-effect on corrosion behavior of carbon steel, high-alloyed steels and Ti-alloy can be assessed.
Critical materials specific properties were determined by static exposure and electrochemical tests in an artificial geothermal water with high salinity and low pH, containing Cu. Conclusions were drawn using characteristic potential values.
It could be shown that significant Cu-deposition and -precipitation only occurred in combination with carbon steel. High-alloyed materials (S31603, S31653, S31700, S31703, S31803 and N08904) prevent the disturbing Cu-agglomeration. Therefore, they are suitable to be chosen for future design of the piping system, either in massive or in cladded form, if formation of crevices with non-metallic materials can be excluded.
From the interactions and pitting corrosion point of view, R50400 seems to be most favorable.
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.
Microbiologically influenced corrosion (MIC) of iron is usually attributed to sulfate-reducing microorganisms (SRM) in offshore industries, such as the oil and gas pipelines, due to the high concentrations of sulfate in the seawater. SRM act upon the metal by the reactiveness of hydrogen sulfide (HS-), and by withdrawal of the available electrons (Fe --> Fe2+ + 2e-; E° = -0.47 V) in electrical contact with the metal (EMIC). However, methanogenic archaea can also cause MIC. Because they do not produce HS-, withdrawal of electrons may be their main corrosive mechanism; however, mechanistic details and kinetics of the overall process are poorly understood.
To investigate the corrosion potential of methanogens, we studied the EMIC methanogenic strains isolated from marine sediments (Methanobacterium-affiliated strain IM1) and crude oil tanks (Methanococcus maripaludis Mic1c10), in an in-house developed flow-through cell to simulate a fluctuating environment. A co-culture of M. maripaludis and D. alaskensis was also established to study the effect of syntrophic growth on metal corrosion that may occur in industrial pipelines. Results indicate that the rates of iron corrosion due to coupled methanogenesis (up to 0.4 mm/yr) are higher to that caused by the marine SRM Desulfovibrio alaskensis (0.15 mm/yr). Surface analyses of the metal showed severe pitting with high methane production. Genomic analysis of the EMIC methanogen M. maripaludis Mic1c10 will provide an insight on the mechanisms of MIC. Such knowledge and deeper understanding also from an electrokinetic point of view may not only provide further models in microbial electrophysiology, but also contribute to mitigation strategies in MIC.zeige weniger
Microbiologically influenced corrosion (MIC) of iron is usually attributed to sulfate-reducing microorganisms (SRM) in offshore industries, such as the oil and gas pipelines, due to the high concentrations of sulfate in the seawater. SRM act upon the metal by the reactiveness of hydrogen sulfide (HS-), and by withdrawal of the available electrons (Fe --> Fe2+ + 2e-; E° = -0.47 V) in electrical contact with the metal (EMIC). However, methanogenic archaea can also cause MIC. Because they do not produce HS-, withdrawal of electrons may be their main corrosive mechanism; however, mechanistic details and kinetics of the overall process are poorly understood.
To investigate the corrosion potential of methanogens, we studied the EMIC methanogenic strains isolated from marine sediments (Methanobacterium-affiliated strain IM1) and crude oil tanks (Methanococcus maripaludis Mic1c10), in an in-house developed flow-through cell to simulate a fluctuating environment. A co-culture of M. maripaludis and D. alaskensis was also established to study the effect of syntrophic growth on metal corrosion that may occur in industrial pipelines. Results indicate that the rates of iron corrosion due to coupled methanogenesis (up to 0.4 mm/yr) are higher to that caused by the marine SRM Desulfovibrio alaskensis (0.15 mm/yr). Surface analyses of the metal showed severe pitting with high methane production. Genomic analysis of the EMIC methanogen M. maripaludis Mic1c10 will provide an insight on the mechanisms of MIC. Such knowledge and deeper understanding also from an electrokinetic point of view may not only provide further models in microbial electrophysiology, but also contribute to mitigation strategies in MIC.