Axel Kranzmann

Corrosion Behavior of Ferritic and Martensitic Power Plant Steels Under Conditions of Dual Atmospheres

Abstract The most efficient construction materials for boiler water walls and superheaters in steam power plants are ferritic and martensitic steels. In practical operation, tubes are exposed simultaneously to combustion gas and air/steam on their opposite surfaces. The corrosion behavior of ferritic-martensitic steels under such dual atmospheres is nondistinctive and has been investigated in a specially designed test equipment between 500°C and 620°C. The power plant conditions were simulated with a flowing and pressurized (80 bar) combustion gas on the inner side of the tube, which contains water (H2O) and carbon dioxide (CO2). On the outer side, tube material was exposed to air. Oxides that formed on the air side under dual atmosphere conditions were significantly different from the oxide scales formed when the alloy was exposed to air only. It is assumed that the anomalous corrosion behavior during the dual atmosphere exposure is due to hydrogen and carbon diffusion through the bulk alloy from the com...

Influence Of CO2 On The Corrosion Behaviour Of13Cr Martensitic Stainless Steel AISI 420 AndLow-alloyed Steel AISI 4140 Exposed To SalineAquifer Water Environment

The CCS technique involves the compression of emission gasses in deep geological layers. To guarantee the safety of the site, CO2-corrosion of the injection pipe steels has to be given special attention when engineering CCSsites. To get to know the corrosion behaviour samples of the heat treated steel AISI 4140, 42CrMo4, used for casing, and the martensitic stainless injectionpipe steel AISI 420, X46Cr13 were kept at T=60°C and p=1-60 bar for 700 h8000 h in a CO2-saturated synthetic aquifer environment similar to the geological CCS-site at Ketzin, Germany. The isothermal corrosion behaviour obtained by mass gain of the steels in the gas phase, the liquid phase and the intermediate phase gives surface corrosion rates around 0.1 to 0.8 mm/year. Severe pit corrosion with pit heights around 4.5 mm are only located on the AISI 420 steel. Main phase of the continuous complicated multi-layered carbonate/oxide structure is siderite FeCO3 in both types of steel.

Microstructure, smoothening effect, and local defects of alumina sol-gel coatings on ground steel

Porous alumina films with thicknesses of a few microns were prepared via a dip-coating technique on steel P92. The coating is shown to protect the steel against massive corrosion, which is typical in the hot reactive environment of coal-fired power plants. To mimic real conditions ground steel plates were coated with a boehmite-sol. This leads to an overall smoothing of the formerly rough surface. In the following short annealing step the inner porous construction with worm-like particles consisting of nano-crystallites and amorphous alumina is formed. Due to the simultaneous diffusion of chromium and iron ions out of the bulk steel material into the porous alumina coating, a dense interface with satisfactory adhesion is formed. However, the film exhibits few local defects like cracks or dense alumina nodules caused by steep edges in the ground surface or agglomeration of boehmite-sol components, respectively. Cracks especially have to be avoided. This problem can be overcome so far by slight modifications in the sol preparation process and surface treatment of the substrates. Nevertheless, the results demonstrate the potential of sol-gel-based alumina coatings as a time-saving and cost-saving protection type for commercial steel P92.Graphical Abstract

Materials Testing under Mechanical Stress, Pressure and Turbulent Flow of Impure Supercritical CO2

Abstract The climate change necessitates measures to reduce carbon dioxide (CO2) emissions in the atmosphere, one of which is carbon dioxide capture and storage (CCS). Transmission of pressurized liquid or supercritical CO2 containing residual flue gas constituents in pipelines is an important component of CCS systems. Material testing under conditions as close as possible to real conditions is a prerequisite for reliable and safe implementation of CCS. A novel pipeline corrosion test facility was developed, accounting for major mechanical, physical and chemical influencing factors: elastic deformation, pressure, temperature, gas composition and flow velocity can be independently adjusted. Radial and tangential stress distributions on a round sample were experimentally investigated, indicating a good accordance with expected theoretical values. In this contribution the idea of the novel corrosion test facility and the assembled equipment as well as first results are presented and discussed.

Evaluation of Heat Treatment Performance of Potential Pipe Steels in CCS-Environment

To resist the corrosive geothermal environment during carbon capture and storage CCS -such as: heat, pressure, salinity of the aquifer, CO2-partial pressure, properties of pipe steels-require certain specification. For evaluation samples of differently heat treated high alloyed stainless injection-pipe steels AISI 420 X46Cr13, AISI 420J X20Cr13 as well as X5CrNiCuNb16–4 AISI 630 were kept at T=60 °C and ambient pressure as well as p=100 bar for 700 h up to 8000 h in a CO2-saturated synthetic aquifer environment similar to a possible geological situation in the northern German Basin. Corrosion rates and scale growth are lowest after long term exposure for steels hardened and tempered at 600 °C to 670 °C and pits -indicating local corrosion- decrease in diameter but increase in number as a function of carbon content of the steel. Martensitic microstructure is preferred with respect to these particular conditions.

The influence of chromium on early high temperature corrosion of ferritic alloys under SO2 atmosphere

Abstract Comprehensive insights into the early stages of corrosion mechanisms provide fundamental knowledge to further understand and model long time material behaviour. The present work studies the early stages of combined oxidation and sulphidation of ferritic model alloys for time scales up to 250 h at 650°C to observe the influence of chromium during the corrosion under SO2. Model alloys were used to focus on the reaction of the intended elements: Fe, Cr, S, and O. Pure iron simultaneously forms magnetite and iron-sulphide in an early stage of corrosion, covered by a pure oxide layer after 100 h. Iron with 13 wt-% Cr shows hematite and mixed Fe–Cr-oxides first, before sulphides nucleate in the inner corrosion zone. With increasing ageing time a magnetite layer is observed below the hematite layer. Quantitative phase fractions of all corrosion products observed were determined from cross section images. Characterisation of the Fe13Cr corrosion scale by FIB revealed a highly porous structure in the inner corrosion zone where Cr-rich (Fe, Cr)-sulphides are present, and caused the scale to spall easily.

The Role of Austenitizing Routines of Pipe Steels during CCS

Properties of pipe steels for CCS technology require resistance against the corrosive environment of a potential CCS-site (heat, pressure, salinity of the aquifer, CO2-partial pressure). The influence of austenitizing in heat treatment routines of two different injection pipe steels (1.4034, X46Cr13 and 1.4021, X20Cr13) was evaluated. Steel coupons were austenitized at different temperatures (900 – 1050 °C) for different lengths of time (30–90 min) before quenching and annealing prior to long term corrosion experiments (60°C, 100 bar, artificial brine close to a CCS-site in the Northern German Basin, Germany). In general, fewer pits are found on X46Cr13. Comparing steels with 13% chromium each the higher carbon content of X46Cr13 (0.46% C) results in a lower number of pits compared to X20Cr13 (0.20% C). It is found that neither the carbon content of the steels nor austenitizing temperature has much influence, but local corrosion behaviour is most susceptible towards austenitizing time.

Supercritical CO2-Corrosion in Heat Treated Steel Pipes during Carbon Capture and Storage CCS

Heat treatment of steels used for engineering a saline aquifer Carbon Capture and Storage (CCS) site may become an issue if handled trivially. Thus its influence on local corrosion (pitting) needs to be considered to guarantee reliability and safety during the injection of compressed emission gases (mainly containing CO2) into deep geological rock formations. 13% Chromium steel injection pipes heat treated differently (X46Cr13, 1.4034 with 0.46% Carbon and X20Cr13, 1.4021 with 0.20% Carbon) were tested in the laboratory under supercritical CO2 at 100 bar and 60 °C. Independent of the exposure time, the fewest pits were found on hardened steels with martensitic microstucture. For steels with similar Cr-content the higher C-content in 1.4034 resulted in fewer pits and lower maximum intrusion depth compared to 1.4021.

Predicting the life time of steels in CCS environment from long term local corrosion experiments

To predict the reliability and safety during the injection of compressed emission gases – mainly containing CO2 – into deep geological layers (CCS-technology, Carbon Capture and Storage), the influence of heat treatment on pit corrosion needs to be considered. Different heat treated steels used as an injection pipe with 13% chromium and 0.46% carbon (X46Cr13, 1.4034) and 0.2% carbon (X20Cr13, 1.4021) as well as 16% chromium steel X5CrNiCuNb16-4 (1.4542) were tested in laboratory experiments. The samples were exposed for up to 1 year to the distinct synthetic aquifer environment saturated with technical CO2 at a flow rate of 3 l/h. The corrosion rate generally does not exceed 0.03 mm/year. Pits with maximum pit heights around 300 µm were obtained for hardened X20Cr13 with martensitic microstructure. The least amount of pits is found on X46Cr13. The higher carbon content in, X46Cr13 (0.46% C), results in a lower amount of pits compared to X20Cr13 (0.20%).

Fusion multimodaler Daten am Beispiel eines Mikrolinsen-Arrays (Multimodal Data Fusion Exemplified on a Microlens Array)

Die Zusammenführung von Messinformationen aus verschiedenen Verfahren ermöglicht eine einheitliche und umfassende Charakterisierung von 3D-Geometrien und deren Kenngrößen. Es werden Methoden zur Verarbeitung, Vereinigung und Auswertung von multimodalen und multiskaligen Messdaten vorgestellt und anhand beispielhafter Messungen konkretisiert. Ein eingesetzter Probenkörper, basierend auf einem Mikrolinsenarray, wird mittels taktiler, konfokaler, interferometrischer Verfahren sowie Röntgentomographie und Streulicht untersucht. Anhand der resultierenden Messdatensätze werden Rauheitsspektren berechnet und diese wiederum zu einem gemeinsamen Rauheitsspektrum des Probenkörpers fusioniert. Nach der Registrierung der Datensätze mittels einer Pyramidenstruktur und Referenzmarken wird ein multimodaler Vergleich der verwendeten Messgeräte möglich. Merging information from different measurement procedures enables consistent and extensive characterization of 3D geometries and features. Methods of processing, merging, and analyzing multimodal measurement data are shown and used with exemplary measurements. The test specimen, based on a microlens array, is examined by means of atomic force and confocal microscopy, white-light interferometry, computed tomography, and angle-resolved scattering. The power spectral densities of selected data sets are evaluated and merged to a single power spectral density of the test specimen. The different data sets are registered using a reference structure with reference markers, thus enabling a multimodal comparison of the respective measurement instruments.