Filtern
Erscheinungsjahr
Dokumenttyp
- Zeitschriftenartikel (43)
- Beitrag zu einem Tagungsband (31)
- Vortrag (27)
- Beitrag zu einem Sammelband (8)
- Posterpräsentation (5)
- Dissertation (1)
- Forschungsbericht (1)
Sprache
- Englisch (69)
- Deutsch (40)
- Mehrsprachig (6)
- Französisch (1)
Schlagworte
- Corrosion (21)
- Schadensanalyse (15)
- CCS (13)
- Fraktographie (11)
- Impurities (8)
- CCUS (7)
- Carbon steel (7)
- CO2 (6)
- Additive manufacturing (5)
- Datenbank (5)
Organisationseinheit der BAM
- 5 Werkstofftechnik (41)
- 5.1 Mikrostruktur Design und Degradation (41)
- 7 Bauwerkssicherheit (19)
- 7.6 Korrosion und Korrosionsschutz (19)
- 9 Komponentensicherheit (10)
- 9.0 Abteilungsleitung und andere (5)
- 9.4 Integrität von Schweißverbindungen (4)
- 9.6 Additive Fertigung metallischer Komponenten (4)
- 8 Zerstörungsfreie Prüfung (2)
- 8.0 Abteilungsleitung und andere (2)
Eingeladener Vortrag
- nein (27)
An extended model of the tension-compression asymmetry of single crystal nickel-base superalloys
(1996)
An extended model of the tension-compression asymmetry of single crystal nickel-base superalloys
(1996)
End of November 2005 strong south-west wind and heavy snowfall were predominant in the region Münsterland, north-western part of Germany. This led to accretion of a considerable quantity of wet snow to overhead electrical lines in form of snow rolls on the conductors. Eighty-two transmission towers failed catastrophically, most of them by buckling, however some by brittle fracture. As a consequence nearly 250,000 people have been cut off from electrical power supply for several days with major media attention.
This paper describes the forensic analysis in order to investigate the failure cause. Therefore extensive materials investigations, mechanical testing of original components and specimens thereof, estimations for the real wind and snow loads and their combinations, structural analyses as well as detailed evaluations on the basis of previous investigations, literature and regulations were conducted. It was revealed that some of the examined components were manufactured from Thomas steel which was partially in embrittled condition. The investigated towers fulfilled the design codes valid at the time of erection. However the present line loads of the wet snow rolls on the conductors exceeded by far the ones given in the design codes valid at that time.
The load case leading to failure was reconstructed by the derived positions of loads mainly caused by unequal and asymmetric distribution of snow rolls on left and right electrical system. The loads and corresponding stresses acting on the structure before failure were estimated. By comparison with the fracture forces from mechanical testing of original members of the collapsed tower the component that primarily failed was localised. The primary fracture occurred on a diagonal member under tension made of Thomas steel which was weakened by embrittlement. The failure cause was a combination of heavy weather conditions (storm, approx. 0 °C and wet snowfall leading to heavy snow rolls on conductors), asymmetric loading conditions and the usage of Thomas steel which was partially embrittled. Finally, recommendations for avoiding future failures are given.
Basic research on the corrosive effect of flue gases has been performed at the BAM Federal Institute for Materials Research and Testing (Germany). Conditions at both high and low temperatures were simulated in specially designed experiments. Carburization occured in flue gases with high CO2 content and temperatures higher than 500 °C. In SO2 containing flue gases sulphur was detected in the oxide scale. At lower temperatures no corrosion was observed when gases with low humidity were investigated. Humidity higher than 1500 ppm was corrosive and all steels with Cr contents lower than 12% revealed corroded surfaces. At low temperatures below 10 °C a mixture of sulphuric and nitric acid condensed on metal surfaces. Acid condensation caused severe corrosion. Humidity, CO2, O2, and SO2 contents are the important factors determining corrosion. Below 300 °C acid condensation is the primary reason for corrosion. Low humidity and low temperatures are conditions which can be expected in the CO2 separation and treatment process. This work includes major conditions of the flue gas and CO2 stream in CCS plants and CCS technology.
Am 9. Juli 2008 entgleiste ein Hochgeschwindigkeits-Triebzug der Baureihe 403, ICE3, bei der Ausfahrt aus dem Kölner Hauptbahnhof. Ursache dafür war der Schwingbruch einer Radsatzwelle. Im Auftrag der Staatsanwaltschaft Köln untersuchte die BAM die Schadensteile, insbesondere die gebrochene Treibradsatz-Hohlwelle.
Zunächst wurden das Drehgestell, der Antriebsstrang, die Räder, die Bremsen und die gebrochene Radsatzwelle visuell untersucht und deren Zustand dokumentiert.
Anschließend erfolgte die zerstörungsfreie Prüfung der beiden Bruchstücke der Hohlwelle mit teilmechanisierter Ultraschall-Handprüfung.
Vor der Zerlegung der Radsatzwelle wurden ausgewählte Maße kontrolliert und die Oberfläche eingehend untersucht. Nach der Probenahme und Präparation wurden die relevanten spezifizierten Eigenschaften des Wellenwerkstoffs überprüft.
Mittels Bruchflächenanalyse konnte die Startstelle des Schwingrisses lokalisiert, aufgrund der starken Sekundärschäden auf der Bruchfläche und an den Bruchkanten jedoch nicht direkt ausgewertet werden. Durch die Kombination von Mikro-Computertomographie und Ultraschall-Tauchtechnik wurden u. a. nahe der Schwingriss-Startstelle Inhomogenitäten erkannt, die durch metallographische Zielpräparation als nichtmetallische Einschlüsse identifiziert wurden. Die Größe dieser Einschlüsse ist gemäß gefordertem Reinheitsgrad unzulässig. Vergleichbare Einschlüsse in diesem hochbeanspruchten Bereich der Radsatzwelle haben vermutlich den Schwingriss initiiert.
COORAL Teilprojekt MINIRISK
(2011)
A titanium (Ti-6242) matrix composite reinforced with continuous SiC fibers was studied. The mechanical behavior of the matrix and the composite was characterized by tensile, creep and isothermal fatigue tests at room temperature and up to 550°C. The thermo-mechanical fatigue behavior under in-phase and out-of-phase conditions was investigated for the composite between 100 and 550°C. Fracture surfaces were characterized by confocal light microscopy and by scanning electron microscopy to identify the damage mechanisms.
The process chain for Carbon Capture and Sequestration (CCS) includes tubing for injection of CO2 into saline aquifers. The compressed CO2 is likely to contain specific impurities; small concentrations of SO2 and NO2 in combination with oxygen and humidity are most harmful. In addition, CO2 saturated brine is supposed to rise in the well when the injection process is interrupted. The material selection has to ensure that neither CO2 nor brine or a combination of both will leak out of the inner tubing. In this comprehensive paper the investigated materials range from low-alloy steels and 13% Cr steels up to high-alloy materials. Electrochemical tests as well as long term exposure tests were performed in CO2, in brine and combination of both; pressure was up to 100 bar, temperature up to 60 °C. Whereas the CO2 stream itself can be handled using low alloy steels, combinations of CO2 and brine require more resistant materials to control the strong tendency to pitting corrosion. The corrosion behavior of heat-treated steels depends on factors such as microstructure and carbon content. For different sections of the injection tube, appropriate materials should be used to guarantee safety and consider cost effectiveness.
In July 2008 an ICE3 high speed train rated for 330 km/h service speed derailed during departure from Cologne, Central Station, Germany, due to fatigue failure of one of the driving axles. The train was emergency stopped immediately and, due to low travel speed at this point, no serious injuries occurred to passengers. Referring to public interest, the public attorneys office solicited the German Federal Institute for Materials Research and Testing (BAM) for the analysis of the root cause.
No deviations from specification were found in the geometries of the basic parts of the bogie or the wheelset assembly. Inspection of the axle fragments using standard acoustic non-destructive testing (NDT) techniques revealed no additional cracks and no indications of oversized discontinuities. Metallographic and chemical inspection of the axle material and its microstructure revealed all parameters to be acceptable except for an elevated impurity level.
The fracture surfaces of the axle fragments were heavily damaged due to some continued travel after final breakage on the high speed line before Cologne Central Station. Extensive visual inspection of the remaining beachmarks was carried out to find the origin of the fatigue crack. The region of the crack origin was located near the axle surface but could not be analysed in detail due to secondary damage. Fatigue was identified as the mechanism of crack growth until final fracture, but the reasons for crack initiation initially remained unclear.
Neither standard NDT techniques nor metallography according to the relevant axle specifications were able to identify inclusions in the material that could have served as crack initiation sites. However, discontinuities were detected near the crack origin in micro computer tomography and ultrasonic immersion testing. Subsequent metallographic sample preparation was targeted to specific areas based on the location coordinates of the flaws identified by these NDT techniques. These revealed non-metallic inclusions that were much larger than admissible for the relevant specifications. It is likely that the fatigue crack in the highly loaded axle volume initiated at those non-metallic inclusions.
Condensates from the gas stream in simulated CO2 transport pipelines have been identified during the experiments in the laboratory. Because of their acidic origin the corrosion resistance of pipeline steels used for CCS (carbon capture and storage) technology might be limited. Over the last years it has become clear that the amount of water and acid building constituents in the CO2 stream has to be controlled very well. In this work, condensates formed in experiments using gaseous CO2 containing high amounts of water, NO2 and SO2 were analyzed, replicated, and used for extensive electrochemical experiments. These highly acidic condensates were enriched with CO2 and then applied to characteristic steels planned to use in the CCS transport chain. Even high alloy steels are susceptible to localized corrosion under these conditions. The results implicate that condensation of aggressive acid droplets has to be avoided or the locations where condensation takes place have to be controlled extensively.
Number-average molecular weights and inherent viscosities were found for the soluble members of an alkoxy-substituted copolyester series. A liquid-crystalline (high-temperature) phase was distinguisehd by IR and wide-angle X-ray scattering on molten and quenched samples in form of a nematic sanidic phase. In this phase no relationship exists between the orientation of the aromatic polyester backbone and that of the laterally attracted alkoxy groups. Further, it was proven by IR that only the polyester backbone can be aligned by shear stress. If the applied shear stress is very strong, the orientation of the stiff backbone becomes sensitive to disturbance caused by mechanical forces.
When it comes to higher accuracies, new technologies and real applications in additive manufacturing, there is one topic which cannot be avoided: The material response on the chosen processing parameters and its agreement and correspondence with literature data of the wrought material grade counterpart. In industrial Additive Manufacturing (AM) standards in terms of printing parameters, protection gas atmospheres or powder handling instructions are not obligatory. Therefore, the question must be answered whether the AM process is reproducible and reliable over different printing companies. This was the motivation to realize a round robin test between 8 European printing companies and academic partners. The consortium had printed and tested fatigue and tensile testing bars under plant-specific conditions. A commonly used cast aluminum alloy, AlSi10Mg, was chosen as test material for the PBF-LB/M process. Differences of the results between the partners and the scatter itself were discussed in detail.
When it comes to higher accuracies, new technologies and real applications in additive manufacturing, there is one topic which cannot be avoided: The material response on the chosen processing parameters and its agreement and correspondence with literature data of the wrought material grade counterpart. In industrial Additive Manufacturing (AM) standards in terms of printing parameters, protection gas atmospheres or powder handling instructions are not obligatory. Therefore, the question must be answered whether the AM process is reproducible and reliable over different printing companies. This was the motivation to realize a round robin test between 8 European printing companies and academic partners. The consortium had printed and tested fatigue and tensile testing bars under plant-specific conditions. A commonly used cast aluminum alloy, AlSi10Mg, was chosen as test material for the PBF-LB/M process. Differences of the results between the partners and the scatter itself were discussed in detail.
Unexpected wind-induced vibrations of the hangers have caused an early fatigue crack on specific steel components and joints of a railway bridge over the Elbe River at Lutherstadt Wittenberg, Germany. During regular periodic inspection a fatigue crack of approximately 240 mm length was found near a butt weld of the longest hanger. The hanger was immediately secured by welded butt straps across the crack. Based on experimental investigations of hanger vibrations additional bracings were added between the hangers to avoid wind-induced vibrations. The weld heat influence zone which was affected by high cyclic stresses was replaced by new material.
Nevertheless it was impossible to determine sufficient remaining service life for those remaining bridge components that were exposed to extreme high real load cycles. The grinding of the affected steel surfaces was the key element of the remedial actions. Furthermore, additional fracture mechanic calculations were carried out in order to assess the remaining service life of the welded joints. In this respect, the calculation approach used by Deutsche Bahn AG was compared to further procedures from the mechanical engineering field. These investigations showed that the studied, repaired components have both, bearing and fatigue capacities within the validity of standards.
Investigations on the breakdown of a heat recovery steam generator during the initial operation run
(2014)
Several years ago, in 2003, an industrial heat recovery steam generator in charge of generating process steam in a petrochemical refinery was installed and prepared for initial operation. The steam generator enclosed an evaporator section and a superheater section consisting mainly of bundles of tubes with the longest up to several metres in length. During initial operation test runs severe leakages in the evaporator and superheater modules became noticeable. The test runs were stopped and after disassembly, through-wall cracks in several tube bends were found. BAM was commissioned to carry out the investigations in order to find out the reasons for the failure of the tubes. During on-site inspection a number of relevant damaged components and parts were selected and taken away to the laboratories for detailed inspection. Planned analyses were to comprise metallographic as well as fractographic investigations, mechanical fatigue testing and experimental as well as finite element vibration analyses on specimens and components. Soon, the fracture mechanism was found to be mechanical fatigue due to the fact that the examined fracture surfaces showed the very characteristic beachmarks and colouring patterns. To identify the particular loading and time at which crack initiation and crack propagation took place, experimental and numerical vibration analyses of specific tubes as well as mechanical fatigue tests on tube bends were carried out. Thus it was possible to identify the eigenfrequencies of individual tubes, to estimate the dynamic response as well as the nominal stresses and, hence, experimentally characterise the in-service fatigue strength of the components. Mechanical and thermal comparative tests on tube bends were performed simulating the conditions during the initial test run in order to get crack surfaces comparable to that of the originally damaged components. Thereby it became obvious that the fatigue cracks were initiated by vibrations the tube bundles were exposed to during rail transport from the manufacturers site to the place of installation. Based on these results, the damaged components could be repaired or exchanged without modification of the construction, but the rules relating packaging and securing for shipping had to be revised.
On October 24th 1950 the 'Freedom Bell' rung for the first time in the tower of the former West Berlin town hall. One year after the Berlin blockade and at a first climax of the 'Cold War', the 'American National Committee for a Free Europe' donated the bell to the city of West Berlin. The bronze bell has a weight of about 10 tons. Its clapper has a length of 2.40 m and a weight of nearly 1 ton. In 1966 the hanging of the clapper and in 1979 the clapper of the bell broke down. Both failures were found to be caused by fatigue fracture. In 1974, a crack in the bell body was detected. After years of periodic monitoring using non-destructive testing, the crack was closed in 2001.
The 100th anniversary of the death of Adolf Martens will be commemorated on July 24th, 2014. He is eponymously remembered today through the term martensite, which was first used by Floris Osmond as a name for the metastable phase that results from rapid quenching of carbon steels. Born in 1850 near to Hagenow in the region Mecklenburg, Germany, Martens was one of the pioneers of materials engineering in 19th century Europe.
Martens began his career working for the Prussian Eastern Railway before joining the Royal Industrial Academy in Berlin in 1880. In 1884, he was appointed director of the Royal Mechanical Experimental Station, a small institution associated to the academy. Failure analysis was continuously practiced at this institution, which became later the nucleus of the German Federal Institute for Materials Research and Testing (BAM), for the 110 years since. The history of Martens will be dealt with in an in-depth article in this special issue.
Since the 19th century, failure analysis techniques have been refined, and new methods of chemical analysis and non-destructive testing have been developed; however, the basic approach to failure analysis has not changed much since Martens' days. The basic tenets of failure analysis remain things like on-site inspection, extensive visual 'non-destructive' inspection, developing an understanding of the background story, performing materials testing, and 'connecting the dots.' Martens introduced and developed experimental techniques like macro photography, fractography, metallography, hardness measurements, and mechanical testing. Modern failure analysts continue adding even more techniques to this list, leading to a more interdisciplinary approach which many would say is the only way to find the root causes of complex failure events.
The present special issue of EFA presents an overview of more than 100 years of failure analysis at BAM and its predecessors, closing the circle from the beginnings of modern failure analysis done by Martens himself in the 1890s to its present-day application.
This special issue starts with an excursion back to Martens' work and innovations and presents a newly translated original manuscript of Martens from 1890. Whereas some papers of Martens and his co-workers are well documented, only little can be found about failure analysis in the period from 1914 to the 1950s. Most documents of this period have not survived until today. Beginning in the 1960s more and more significant works are preserved, which were using the interdisciplinary approach of Martens. Since the beginning of the digital age in the 1980s almost all text documents are accessible, whereas digital images were stored since the 1990s. Since then the problem is no longer accessibility but copyright issues that prevent many interesting case studies from being published. Maybe the next generation of failure scientists can reveal some of them later on.
Die Verwendung von höherfesten, vergüteten Stählen für Radsatzwellen wird zurzeit kontrovers diskutiert. Für die zuverlässige Auslegung mit diesen Werkstoffen werden verlässliche mechanische und bruchmechanische Kennwerte benötigt. Zudem müssen die aus Prüfungen an Kleinproben und Bauteilen gewonnenen Werte konsistent sein. Das war bisher nicht immer der Fall.
In einem von der Bundesanstalt für Materialforschung und -prüfung (BAM) Berlin im Auftrag des Verbandes der Bahnindustrie in Deutschland (VDB) durchgeführten Forschungsvor- haben wurden Proben aus dem Werkstoff A5T (42CrMo4+QT), entnommen aus Original-Radsatzwellen und aus 1:1-Proben eines anderen Forschungsvorhabens, untersucht. Alle Proben haben für den Werkstoff A5T und seinem Wärmebehandlungszustand den gültigen Normen entsprechende Kennwerte im Rahmen der geforderten Eigenschaften gezeigt. Gefügefehler konnten an den vorliegenden Prüfstücken nicht nachgewiesen werden. Die vorgenommenen Wärmebehandlungen beeinflussen das Gefüge und die mechanischen Eigenschaften in der erwarteten Weise.
The geological storage of carbon dioxide (Carbon Capture and Storage, CCS) in depleted gas reservoirs or in saline aquifers is a widely discussed issue. Carbon dioxide may induce corrosion on the piping steels during compression, transportation and injection. Therefore,
selection of appropriate piping steels is a key factor in order to increase the safety and reliability of the CCS technology, and to keep the processes cost-effective.
The here described subproject of the COORAL project (German acronym for “C02 purity for capture and storage”) deals with the levels of impurities in the C02 stream that will be acceptable when using specific steels. Material exposure to carbon dioxide (C02) containing
specific amounts of water vapor, oxygen (02) sulfur dioxide (S02), nitrogen dioxide (N02), carbon monoxide (CO) can be a challenge to steels. Within this subproject 13 different Steels are tested for suitability as materials used for compression, transportation and injection Units within the CCS chain.
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.
In the past few years, it has been discussed with increasing frequency, whether cube slip does occur in gamma' hardened nickel-base superalloys. Occurrence of cube slip has consequences for the modeling of orientation dependence of the CRSS. Until now, there are only few experimental investigations.
In principle, cube slip should be possible in primitive cubic lattices (e.g. L12 ordered gamma' phase) but not in face centered cubic ones (e.g. Ni solid solution). The most favourable specimen orientations are near [111], where the Schmid factors for this type of glide exceed those for octahedral systems.
There are two basic methods to detect cube slip: macroscopic slip trace analysis and Transmission electron microscopy (TEM) investigation of the dislocation structure. Few observations of cube slip by macroscopic slip traces are reported in the literature. But it is still uncertain under which test conditions cube slip occurs and what the dislocation mechanisms are. Cube slip was observed during tensile or compression tests of several first generation superalloys, but it seems not to occur during shear creep deformation (e.g. CMSX-4 at 980°C), and it is also lacking under conventional tensile or compression loading, if the gmma' particles are small. No observations were ever reported of dislocations gliding on {001} planes in matrix channels.
The technical systems to be investigated are disc brakes and steel–steel rolling contact. The friction processes in a disc brake are rather complex and not yet understood in detail. This is mainly due to the complexity of the brake pad material, which consists of a wide variety of components, and the complexity of the chemical reactions occurring at the wear interface between brake disc and brake pad. Whereas partner projects are studying on the chemistry and the crystallography, we are analyzing the topographic properties of the surfaces involved on the microscopic scale. For this purpose, several methods are known. But besides high lateral
resolution, relatively large object fields and height ranges are needed. Interference microscopy was therefore chosen as the main method. This paper deals with its advantages and disadvantages in wear experiments.
Disc brakes are widely used in cars, trains, and other vehicles. For understanding the basic processes occurring during the friction process, information on the surface topography of brake pads and discs is needed, in addition to information about chemistry and thermodynamics. In this paper, samples of pads and discs were analysed using white light interferometry. The topography of the surfaces was measured quantitatively. Using software tools described in a previous paper [Wear 248 (2001) 121], the distributions of area, height, and slope of the contact patches were computed. Characteristic properties of the contact patches were found to describe the influence of the test parameters such as friction power and testing time.
Aufbau einer Wissensbasis zu Bruchflächen und Gefüge in der fraktographischen online-Datenbank
(2016)
In einer fraktographischen online-Datenbank werden Informationen zum Bruchverhalten von technischen Werkstoffen zusammengetragen. Primäres Ziel ist die kontrollierte Erzeugung von Brüchen und deren anschließende Analyse, aber auch Beispiele aus Schadensfällen werden eingestellt. Die makroskopischen und mikroskopischen Merkmale von Bruchflächen, die Art der Beanspruchung und die dazugehörigen Werkstoffgefüge werden in Datensätzen zusammengefasst, die der interessierten Fachöffentlichkeit zu Verfügung stehen.
Oft sind von außen nicht sichtbare „Ungänzen“ im Innern die Ursache für das Versagen von Bauteilen. In manchen Fällen genügt eine herkömmliche metallographische Präparation, um der Schadensursache auf die Spur zu kommen. In anderen Fällen aber sind die Ungänzen zu klein oder ihre Lage zu ungewiss, um sie mit zufälligen Schnitten zu treffen. Zudem würde man durch Fehlversuche das Bauteil zu stark schädigen und so wertvolle Spuren verlieren sowie die weitere Untersuchbarkeit einschränken. In solchen Fällen ist es im wahrsten Sinn des Wortes zielführend, die Ungänzen mit Hilfe eines räumlich abbildenden ZfP-Verfahrens zu lokalisieren und dann mit den erhaltenen Koordinaten eine metallographische Zielpräparation präzise durchzuführen. Als Methoden kommen z.B. Mikro-Computer-Tomographie (µCT) und Tauch-Ultraschall in Frage. Bauteile können kleine elektronische Komponenten sein, aber auch große Bauteile wie Wellen aus Fahrzeugen oder Anlagen.
Modulare Hüftprothesen können individuell der Anatomie des Patienten angepasst werden und haben dadurch eine positive Auswirkung auf dessen Lebensqualität. Unter Betriebsbelastung sind in der zusätzlichen Konusverbindung zwischen Schaft und Kopfteil Relativbewegungen möglich. Selbst an Titan-Bauteilen bewirken diese durch Verletzung der Passivschicht Reibkorrosion und infolgedessen Spaltkorrosion. Verunreinigungen wie z.B. Knochenrückstände in der Konusverbindung bewirken eine erhöhte Relativbewegung und führen zusätzlich zu einer örtlichen Spannungsüberhöhung durch lokale Pressung. Die an der Mantelfläche des Schafts entstehenden Korrosionsdefekte reduzieren die Schwingfestigkeit des Schafts erheblich, so dass dort Schwingrisse initiiert werden können, welche dann durch die üblichen zyklischen Schwell-Biegebelastungen bis zum Restgewaltbruch wachsen.
Ziele dieser Arbeit waren die vergleichende Beschreibung des Verformungs-
und Bruchverhaltens der polykristallinen Legierung IN738LC und von
[001]-nah orientierten SC16-Einkristallen über einen großen Temperaturbereich sowie die Herstellung von Zusammenhängen zwischen
Versetzungs- und Bruchmechanismen. Besonderes Augenmerk galt dem
Tieftemperaturbereich bis 450 °C, dabei insbesondere der
Stapelfehlerbildung in der Gamma'-Phase, dem Fließspannungsminimum
im Zugversuch und der zusätzlichen zyklischen Verfestigung in diesem
Temperaturbereich. Spezifische Unterschiede zwischen beiden Werkstoffen
sollten herausgearbeitet werden. Dazu wurden hauptsächlich mikroskopische
Methoden, insbesondere die Transmissions-Elektronenmikroskopie eingesetzt.
Die Ausgangsgefüge wurden untersucht. Beide Werkstoffe hatten die übliche Standardwärmebehandlung erfahren und wiesen daher eine bimodale
gamma'-Verteilung auf. An SC16 wurden Auslagerungsversuche bei 950 °C vorgenommen und die Veränderung der gamma'-Morphologie beschrieben.
Die Temperaturabhängigkeiten der Verformungsmechanismen von SC16 und IN738LC sind vergleichbar mit den in der Literatur bezüglich einkristalliner
Superlegierungen mit höheren gamma'-Volumenanteilen beschriebenen. Beginnend
bei Raumtemperatur treten mit steigender Temperatur folgende Mechanismen auf:
Tieftemperatur-(LT-)Stapelfehler, Antiphasengrenzen-gekoppelte
Versetzungspaare, Hochtemperatur-(HT-)Stapelfehler und Orowan-Ringe um
die gaama'-Teilchen. Das Fließspannungsminimum des IN738LC bei 450 °C
kann einem Wechsel im Verformungsmechanismus zugeordnet werden. Die
Mechanismenwechsel finden bei SC16 bei höheren Temperaturen statt als bei IN738LC.
Von Raumtemperatur bis 750 °C wird bei IN738LC im LCF-Bereich bei
out-of-phase-Versuchen eine zusätzliche zyklische
Verfestigung beobachtet, die ihr Maximum bei 450 °C hat. Bei dieser Temperatur wird die plastische Verformung durch a/2<110>-Versetzungspaare erzeugt, die die gaama'-Phase parallel zu
{111} schneiden. Während der out-of-phase-Versuche werden
zusätzliche Gleitsysteme auf verschiedenen {111}-Ebenen aktiviert, was zu einer erhöhten Dichte von unbeweglichen Versetzungen führt. Bei höheren
Temperaturen können Versetzungen gaama'-Teilchen und andere Hindernisse durch
Quergleiten und Klettern umgehen.
Beim SC16 lassen sich LT- (bis 750 °C) und HT-Bruchverhalten (ab 750 °C) klar unterscheiden. Ersteres zeigt sich in großflächigem Abscheren und Bruchinitiierung an der Probenoberfläche. Der HT-Bruch wird an Poren im Innern initiiert und führt zu einem "Teller-Tasse"-Bruch mit einer ringförmigen Scherlippe im äußeren Bereich.
Beim IN738LC hingegen treten die beim SC16 gefundenen Elemente in den
Bruchflächen nur in untergeordneter Weise hervor. Der Rissverlauf ist fast
immer interdendritisch und nur zum Teil transkristallin. Primärkarbide werden
im LT-Bereich gespalten, im HT-Bereich abgelöst.
Minima der Temperaturabhängigkeit der Bruchdehnung des IN738LC gehen jeweils mit lokalisierter Gleitung in einzelnen Gleitbändern einher. Immer wenn bei einer bestimmten Temperatur ein neuer Verformungsmechanismus einzusetzen beginnt, werden inhomogene Gleitverteilungen beobachtet, die zu einer
geringen Verformbarkeit führen.
CO2 streams captured from power stations or industrial plants may contain impurities that impact the consecutive steps of the CO2 capture and storage (CCS) chain. As the basis for an optimization of CO2 purity over the whole CCS chain, impacts of different impurities were investigated at key steps including studies on (i) corrosion of metallic materials in CO2 streams and brine, (ii) fluid and interfacial properties as a function of pressure, temperature and CO2 stream composition and their implications for CO2 transport, injection and geological storage, (iii) costs of different pipeline design options, (iv) geochemical alterations at typical reservoir conditions and their implications for geomechanical rock properties. Major findings are synthesized for two exemplary single source-single sink CCS chain scenarios involving CO2 stream compositions typical for pre-combustion capture and oxyfuel combustion. Recommendations for material selection for compression, transport and injection were derived for various CO2 stream compositions. To reliably control corrosion, a limitation of water contents to 50 ppmv is recommended for pipeline transportation of all CO2 streams. At geological storage conditions, the presence of either O2, NOx or SO2 only weakly affected fluid-mineral/rock interactions that still impacted geomechanical rock properties.
Kohlendioxid (C02), das z.B. aus dem Abgas von fossilgefeuerten Kraftwerken, Stahlwerken oder Zementwerken abgetrennt wird, enthält Verunreinigungen. Dies sind beispielsweise Wasserdampf, 02, S0X, NOx und H2S. Derartige Gasmischungen sind instabil und ihre Komponenten können zu weiteren Produkten reagieren. Wenn Wassermoleküle zur Verfügung stehen, können saure Lösungen kondensieren. Die Korrosion von Werkstoffen und Bauteilen in Kontakt mit den transportierten Gasmischungen wird an der BAM in Laborversuchen untersucht, Das wichtigste Ziel ist, sichere und bezahlbare Kombinationen von zugelassenen Konstruktionswerkstoffen und Grenzwerten für Verunreinigungen im C02-Strom vorzuschlagen. In den bisherigen Arbeiten hat sich herausgestellt, dass für eine verlässliche Aussage die Experimente möglichst realitätsnah durchgeführt werden sollten. Hierfür müssen die Parameter: hoher Druck (um 100 bar), Temperatur (um 60 °C), Strömungsverhältnisse (laminar oder turbulent) sowie mechanische Spannung kombiniert werden. Für diese Anforderungen wurden Prüfstände entwickelt und Experimente durchgeführt.
Application of 4Q-BSE detector and dedicated software enables 3D surface measurements of fracture samples in SEM. 3D surface measurement is independent from magnification and material invariant. Quantitative height measurements require careful detector adjustment and system calibration. Live 3D view allows a fast assessment of topographical features. In addition to SE and BSE imaging, 3D surface data help to analyse and interpret fracture samples.
Aufbau einer Wissensbasis zu Bruchflächen und Gefüge in der fraktographischen online-Datenbank
(2016)
Fraktographisches Wissen in Form von Vergleichsbildern von Bruchflächen werden in einer fraktographischen online-Datenbank zusammengetragen und der interessierten Fachöffentlichkeit zur Verfügung gestellt. Zu diesem Zweck werden Vergleichsversuche durchgeführt, insbesondere Schwingversuche. Die erzeigten Bruchflächen werden makroskopisch und mikroskopisch analysiert und dokumentiert. Das dazu gehörige Werkstoffgefüge wird ebenfalls dargestellt. Das Augenmerk der aktuellen Arbeiten liegt daher auch auf Zusammenhängen zwischen Bruchmechanismen und Gefügestrukturen. Zur Einleitung wird eine Schadensanalyse von Adolf Martens aus dem Jahre 1884 vorgestellt.“
Fraktographischen Daten aus Schadensanalysen, Vergleichsversuchen und Vorhaben könnten der Fachöffentlichkeit im Bereich Fraktographie zur Verfügung gestellt werden, sofern das Urheber-recht es zulässt und außerdem ein geeignetes Medium existiert. Ein solches Medium könnte eine offene fraktographische online-Datenbank sein. Eine solche wird im Rahmen der AG Fraktographie im DVM-DGM Gemeinschaftsausschuss "Rasterelektronenmikroskopie in der Materialprüfung" zurzeit erarbeitet.
Fraktographischen Daten aus Schadensanalysen, Vergleichsversuchen und Vorhaben könnten der Fachöffentlichkeit im Bereich Fraktographie zur Verfügung gestellt werden, sofern das Urheberrecht es zulässt und außerdem ein geeignetes Medium existiert. Ein solches Medium könnte eine offene fraktographische online-Datenbank sein. Eine solche wird im Rahmen der AG Fraktographie im DVM-DGM Gemeinschaftsausschuss "Rasterelektronenmikroskopie in der Materialprüfung" zurzeit erarbeitet.
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.
Die Grundlagen der Metallographie wurden in der zweiten Hälfte des 19. Jahrhunderts von Henry Clifton Sorby in England und Adolf Martens in Deutschland gelegt. Den verfügbaren Quellen nach erfolgten diese Arbeiten unabhängig voneinander. In diesem Beitrag werden die Beiträge von Adolf Martens und Emil Heyn zur Etablierung der Metallographie als ein eigenständiges Fach im Rahmen der Metallkunde dargestellt. Dabei werden Aspekte der Werkstoffprüfung, der Fraktographie und der Schadensanalyse einbezogen. Abschließend wird die führende Rolle dieser Pioniere der Metallkunde bei der Gründung der Deutschen Gesellschaft für Materialkunde (DGM) sowie des Deutschen Verbands für Materialforschung und -prüfung (DVM) gewürdigt.
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). 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.
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.
The round robin test investigated the reliability users can expect for AlSi10Mg additive manufactured specimens by laser powder bed fusion through examining powder quality, process parameter, microstructure defects, strength and fatigue. Besides for one outlier, expected static material properties could be found. Optical microstructure inspection was beneficial to determine true porosity and porosity types to explain the occurring scatter in properties. Fractographic analyses reveal that the fatigue crack propagation starts at the rough as-built surface for all specimens. Statistical analysis of the scatter in fatigue using statistical derived safety factors concludes that at a stress of 36.87 MPa the fatigue limit of 107 cycles could be reached for all specimen with a survival probability of 99.999 %.
Undetected and undesired microstructural variations in components produced by laser powder bed fusion are a major challenge, especially for safety-critical components. In this study, an in-depth analysis of the microstructural features of 316L specimens produced by laser powder bed fusion at different levels of volumetric energy density and different levels of inter layer time is reported. The study has been conducted on specimens with an application relevant build height
(>100 mm). Furthermore, the evolution of the intrinsic preheating temperature during the build-up of specimens was monitored using a thermographic in-situ monitoring set-up. By applying recently determined emissivity values of 316L powder layers, real temperatures could be quantified. Heat accumulation led to preheating temperatures of up to about 600 °C. Significant differences in the preheating temperatures were discussed with respect to the individual process parameter combinations, including the build height. A strong effect of the inter layer time on the heat accumulation was observed. A shorter inter layer time resulted in an increase of the preheating temperature by more than a factor of 2 in the upper part of the specimens compared to longer inter layer times. This, in turn, resulted in heterogeneity of the microstructure and differences in material properties within individual specimens. The resulting differences in the microstructure were analyzed using electron back scatter diffraction and scanning electron microscopy. Results from chemical analysis as well as electron back scatter diffraction measurements indicated stable conditions in terms of chemical alloy composition and austenite phase content for the used set of parameter combinations. However, an increase of the average grain size by more than a factor of 2.5 could be revealed within individual specimens. Additionally, differences in feature size of the solidification cellular substructure were examined and a trend of increasing cell sizes was observed. This trend was attributed to differences in solidification rate and thermal gradients induced by differences in scanning velocity and preheating temperature. A change of the thermal history due to intrinsic preheating could be identified as the main cause of this heterogeneity. It was induced by critical combinations of the energy input and differences in heat transfer conditions by variations of the inter layer time. The microstructural variations were directly correlated to differences in hardness.
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.
In the current study, the 3D nature of the melt pool boundaries (MPBs) in a 316 L austenitic steel additively manufactured by laser-based powder bed fusion (L-PBF) is investigated. The change of the cell growth direction and its relationship to the MPBs is investigated by transmission electron microscopy. A hitherto unreported modulated substructure with a periodicity of 21 nm is further discovered within the cell cores of the cellular substructure, which results from a partial transformation of the austenite, which is induced by a Ga+ focused ion beam. While the cell cores show the modulated substructure, cell boundaries do not. The diffraction pattern of the modulated substructure is exploited to show a thickness ≥200 nm for the MPB. At MPBs, the cell walls are suppressed, leading to continuously connecting cell cores across the MPB. This continuous MPB is described either as overlapping regions of cells of different growing directions when a new melt pool solidifies or as a narrow planar growth preceding the new melt pool.
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.
A global transition towards more sustainable, affordable and reliable energy systems is being stimulated by the Paris Agreement and the United Nation's 2030 Agenda for Sustainable Development. This poses a challenge for the corrosion industry, as building climate‐resilient energy systems and infrastructures brings with it a long‐term direction, so as a result the long‐term behaviour of structural materials (mainly metals and alloys) becomes a major prospect. With this in mind “Corrosion Challenges Towards a Sustainable Society” presents a series of cases showing the importance of corrosion protection of metals and alloys in the development of energy production to further understand the science of corrosion, and bring the need for research and the consequences of corrosion into public and political focus. This includes emphasis on the limitation of greenhouse gas emissions, on the lifetime of infrastructures, implants, cultural heritage artefacts, and a variety of other topics.
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.
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.
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.
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.
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.
Die klassische Metallographie basiert auf Abbildungen einzelner Schliffebenen und kann auf räumliche Formen und Anordnungen des Gefüges nur bedingt schließen. Die Idee, aus metallographischen Serienschliffen dreidimensionale Gefügestrukturen zu rekonstruieren, ist daher naheliegend und nicht neu. Allerdings ist der Aufwand, in Handarbeit viele Einzel-Schliffe zu präparieren und zu Bildstapeln zusammenzusetzen, sehr hoch und steht einer häufigen Anwendung entgegen.
Deshalb wird an der BAM ein Roboter-gestütztes 3D-Metallographie-System entwickelt, das an einer Schliffprobe die Schritte Präparation und Bildeinzug vollautomatisch mit vielen Wiederholungen ausführt. Die Präparation umfasst Schleifen, Polieren und optional Ätzen der Schlifffläche, der Bildeinzug autofokussierte lichtmikroskopische Aufnahmen bei mehreren Vergrößerungsstufen. Der erhaltene Bildstapel wird anschließend vorverarbeitet, segmentiert und in ein 3D-Modell umgesetzt, das einer mikrotomographischen Aufnahme ähnelt, allerdings mit besserer lateraler Auflösung bei großem Volumen. Im Gegensatz zu tomographischen Verfahren besteht die Möglichkeit der Kontrastierung durch klassische chemische Ätzung. Die Integration eines REMs ist geplant. Bislang durchgeführte Arbeiten verdeutlichen die Möglichkeiten der Darstellung von Heißgas-Korrosionsschichten, Grauguss-Werkstoffen und Keramik-basierten mikroelektronischen Strukturen (Vias).
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.
Fatigue failure of a component can occur at service loads considerably lower than the yield strength of the material. Under fatigue loading condition, the material in the vicinity of the tip of a propagating crack repeatedly deforms plastically, leaving microscopic marks on the crack surface, commonly known as fatigue striations. Counting and measuring fatigue striations is a method in estimating the number of loading cycles a component went through until fracture. Some studies suggest a one-to-one relation between the number of fatigue striations and the number of load cycles, but this relation is still debatable, given that there are many factors influencing the formation of those striations. The main purpose of this work is to analyze the influence of microstructure and mechanical strength on the formation of fatigue striations in structural steels, in order to understand how these material properties are related to the fatigue crack behavior. For such, standard Charpy-V samples were subjected to hardness, fatigue and impact testing. Metallography was performed to characterize the microstructure, and a fractographic analysis by using optical and scanning electron microscopy was carried out to investigate the fracture surface. This study shows that steels with higher ductility have a closer one-to-one relation than those with a higher tensile strength. Above a certain level of tensile strength, fatigue striations do form rarely or completely disappear.
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.
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.
This third part of the review on defects as root cause of fatigue failure addresses cavities (pores, micro-shrinkages, unmelted regions), defective microstructures and microcracks as material defects and defects due to local damage during manufacturing, service and maintenance such as dents, scratches and localized corrosion. In addition, damage due to contact fatigue and the effect of surface roughness are discussed in the context of fatigue failure. Also addressed is the competition between different kinds of defects in controlling the initiation and early growth of fatigue cracks.
According to the definition of the ASM handbook [1,3], a defect is "an imperfection. that can be shown to cause failure by a quantitative analysis and that would not have occurred in the absence of the imperfection". The topic of the present three-part review is a discussion of defects which can cause failure in cyclically loaded structures. The features discussed comprise material defects such as non-metallic inclusions, pores or micro-shrinkages, etc. and geometric defects such as surface roughness and secondary notches which have their origin in manufacturing, and defects such as surface damage due to scratches, impact events or contact fatigue as well as corrosion pits which arise in service. In this first part, the discussion is prefaced by an introduction to basic aspects which are essential for a deeper understanding of the characteristics and mechanisms how the defects influence fatigue crack initiation and propagation. These include the life cycle of a fatigue crack from initiation up to fracture, crack arrest, multiple crack initiation and coalescence, and the material and geometrical properties affecting these.
Defects as a root cause of fatigue failure of metallic components. II: Non-metallic inclusions
(2019)
This second part of the review on defects as root cause of fatigue failure comprises the origin, the nature and the effects of non-metallic inclusions. Topics addressed are the different kinds of inclusions formed during the manufacturing process, various types of mis-match causing local stresses and, as a consequence, fatigue crack initiation, and effects of characteristics such as size, morphology, localization, spatial distribution and orientation of the defects on the fatigue behavior. Methods for inclusion counting and sizing are discussed along with statistical aspects necessary to be considered when evaluating structural components.
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.
Une transition mondiale vers des systèmes énergétiques plus durables, abordables et fiables a été initiée par l’accord de Paris et l’Agenda 2030 des Nations unies pour un développement durable. Il s’agit là d’un défi industriel majeur car les systèmes et infrastructures énergétiques résilients au changement climatique exigent de se positionner pour le long terme. Se pencher sur le comportement dans la durée des matériaux structurels - principalement des métaux et des alliages - s’impose alors comme une nécessité. Dans cette optique, « La corrosion : un défi pour une société durable »présente une série de cas montrant l’importance de la tenue à la corrosion et de la protection anticorrosion des métaux et des alliages pour le développement de systèmes durables, économiques et fiables de production d’énergie.