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Carbon-based conductive coatings are complex composites, consisting of an organic or inorganic binder and conductive carbon components, for application as anodes in impressed current cathodic protection systems of reinforced concrete structures. The electrochemical properties of three coatings at different humidity and in saturated calcium hydroxide solution were studied by electrochemical methods, such as electrochemical impedance measurement, measuring of open circuit potential over time and galvanostatic polarization.
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.
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 “worstcase 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 reproduced 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.
Ferritic-martensitic high temperature alloys are used as building components for different power plant technologies. Depending on the type of fuel, the used power plant materials are exposed to different temperatures and reactive atmospheres containing e.g. CO2, O2, or SO2. Despite the sulfur chemistry is commonly present as an impurity in fossil or bio fuels; its role in high temperature corrosion is not entirely understood. During high temperature corrosion, high-alloyed steels often show sulfur precipitates with the ignoble alloy component(s) along grain boundaries within the base material. Sulfur precipitates are known to seriously influence the mechanical properties of the building component. In the case of VM12 and T92 steels, sulfur phases penetrate the base material along grain boundaries during the corrosion under oxyfuel atmosphere up to 20 µm within the first 960h (Fig. 1a). Figure 1a shows the oxide scale and (Cr, Mn, Fe)xSy grain boundary precipitates in the base material for a T92 steel aged for 960h under oxyfuel atmosphere. Figure 1b shows a thin oxide scale with nodules and also sulfur precipitates of (Fe, Cr)xSy along grain boundaries of the base material for a Fe13Cr model alloy aged for 24h under SO2 atmospheres. After 24h, sulfur precipitates already reached a depth of ca. 15 µm.
The present work shows the corrosion behavior of Fe-Cr model alloys with Cr-contents similar to technical steels up to 13 wt%, aged under oxyfuel (27H2O/60CO2/1SO2/10N2/2O2) and SO2 atmospheres in the temperature range of 550 °C < T < 700 °C and for different time scales between 24 h < t < 960 h. During aging, the reactive gases were added when the experimental temperature was reached. To focus on the reaction of the intended elements Fe, Cr, S, and O, model alloys of high purity are used. Transport depths of sulfur and the nucleation of the precipitates are discussed for both, model alloys and technical steels.
Corrosion of galvanized steel in carbonated concrete is different from the corrosion of reinforcement made of carbon steel. This is based on the corrosion mechanism of galvanized steel in dependence of the pH-value of carbonated concrete. To describe the influence of a lower pHvalue on the corrosion activity of galvanized reinforcement, different electrochemical measurements were made. The anodic and cathodic partial reaction were investigated by galvanostatic pulse measurements and potentiodynamic measurements. Especially the galvanostatic pulse measurements can describe the influence of the lower pH-value by the anodic polarization resistance with pt = 20 sec. (polarization time). Additionally, corrosion current measurements were performed, coupled with potential measurements, between galvanized steel in carbonated and non-carbonated concrete. Normally, the potential measurements are an indicator to localize the anodic and cathodic parts of a macro system. In this case the cathode was more negative than the anode before they were coupled. After the coupling of the two specimens the mixed potential was much more positive than the single potential of the galvanized steel in carbonated concrete. It increased up to the potential range of the non-carbonated specimens. This means that in case of carbonated outer areas, the embedded galvanized steel forms the cathodic part of a macro element.
In Kraftwerkstechnologien verwendete ferritische Fe-Cr-Stähle sind verschiedensten Temperaturen, Prozessdrücken und aggressiven, zum Teil schwefelhaltigen Verbrennungsgasen ausgesetzt, die zu Korrosion führen. Noch ungeklärt ist die Rolle der entstehenden Sulfide in der schützenden Oxidschicht und deren Auswirkung auf die Lebensdauer der Bauteile. Unsere Arbeit zeigt Korrosionsmechanismen ausgewählter Fe-Cr-Modelllegierungen unter Ar-SO2 Atmosphäre für verschiedene Zeitskalen. Der Focus dabei liegt auf Kurzzeitexperimenten (12h ≤ t ≤ 250h), um die initialen Stadien der Schwefelkorrosion zu untersuchen.
This talk demonstrates the results of the IGSTC-project entitled "NDT-Data Fusion".
Project approach:
Nondestructive testing (NDT) of concrete buildings allows to coordinate efficient repair measures. Multi-sensor platforms collect large data sets. Nevertheless, data analysis is typically performed manually. Data Fusion uses the full potential of a multi-sensory data set in order to:
improve information quality (reliability, robustness, accuracy, clarity, completeness) and enables automated algorithm based data analysis.
We present the project achievements, namely:
- Development of building scanner system for multisensory NDT
- Laboratory multi sensor investigations
- Development of data fusion concept for honeycombing and pitting corrosion
- Field testing
Half-cell potential mapping (HP) is the most popular nondestructive test (NDT)-method for the localization of corrosion damage in concrete. It is generally recognized, that HP is prone to the environmental factors that arise from salt induced deterioration, such as varying moisture and chloride gradients. Additional NDT-methods are capable to determine distinctive areas, but cannot yet be used to estimate more accurate testing results. We introduce a supervised machine learning (SML) based approach for data fusion to make use of the additional sensor information. SML are methods that explore relations between different (sensor) data from predefined data labels. We use a simple linear classifier named logistic regression to distinguish defect and intact areas. The test performance improves drastically compared to the best single method, HP. In order to generate representative, labeled data we conducted a comprehensive experiment that simulates the deterioration-cycle of a chloride-exposed building part in the lab. Our data set consist of 18 measurement campaigns, each containing HP-, ground-penetrating-radar-, microwave-moisture-, and Wenner-resistivity-data. We detail the challenges that arise with a data driven approach in NDT and how we addressed them.
The ageing of Fe-Cr model alloys in 0.5 % SO2 and 99.5 % Ar atmosphere was investigated to aim in a fundamental and systematic analysis of the combined oxidation and sulfidation mechanism. The crystallization and reaction paths for oxide and sulfide formation were followed in-situ by energy dispersive X-ray diffraction (EDXRD) in an early stage of corrosion (30 s – 24 h). For this technique, high energetic white synchrotron X-ray radiation (10-100 keV) was used as radiation source. Diffraction pattern were collected continuously in an early stage of corrosion up to 24 h during the complete ageing experiment.
The crystalline phases, growing on top of the coupons, were identified directly via their specific dhkl values. The evolution of the extracted integral intensities of specific reflections of the corrosion products as a function of time access direct information about the kinetics of the nucleation and growth. The results presented here show for iron with 2 wt% Cr wuestite formation first. Wuestite vanishes after 10 min of reaction only and magnetite and hematite appear. Magnetite formation proceeds simultaneously with sulfide formation. Sulfides growth proceeds after an incubation time, which differs for low alloyed (2 wt% Cr) and high alloyed (9 wt% Cr) material.