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The impact of Cl on alkali-induced high-temperature corrosion of stainless steels/FeCrAl alloys after breakaway oxidation was investigated in a simulated biomass- and waste-fired boiler environment at 600 °C. For this investigation, three alloys were exposed to low Cl load environment (H2O+KCl) and to high Cl load (H2O+KCl+HCl). Post-exposure analysis showed that the stainless steel SVM12 experiences fast oxidation and forms thick double-layered Fe-rich oxide scales. The corrosion attack is further accelerated with addition of HCl for this material with the effect being more pronounced in the inward-growing scale. The FeCrAl and FeCrNi alloys exhibit slower oxidation kinetics after the breakaway corrosion compared to SVM12 in the H2O+KCl exposure. Furthermore, in contrast with SVM12, the addition of HCl did not accelerate the corrosion attack on these alloys. It is argued that the properties of the secondary oxide layer formed after breakaway corrosion are important in the continued corrosion resistance against chlorine-induced corrosion attack. Especially, the Cr content in the inner scales is suggested to be important in corrosion mitigation. [ABSTRACT FROM AUTHOR]

This paper presents finite-element simulations to reinterpret a series of full-model and particle image velocimetry (PIV) (half model) centrifuge tests to study the uplift of skirted foundations. The focus is on the influence of uplift rate on the uplift capacity and the mechanism of breakaway (i.e., the phenomenon of sudden loss of uplift resistance). A backbone curve, quantifying the uplift rate-capacity relationship, is established for uplift based on the numerical and experimental results. The dimensionless velocities V=6 and 130 are found to be the boundaries for drained, partially drained, and undrained conditions. The breakaway is found related to ambient water infiltration. In the numerical modeling, the remaining length of the skirt inside soil is used as an indicator for breakaway, i.e., breakaway happens when this length is smaller than a critical value. This hypothesis is demonstrated to be effective by comparing the numerical modeling with the experimental results. [ABSTRACT FROM AUTHOR]

This paper presents the detailed formulation of a coupled hydro‐mechanical structure‐soil interface and demonstrates its application in simulating uplifting problems. This interface features real‐time prediction of the pore pressure generation and structure‐soil separation, and thus rate dependency and 'breakaway' can be modeled without user intervention. Constitutive relations of this interface were derived by considering the coupling between soil skeleton and fluid along the interface. A complete finite element formulation and numerical implementation of the interface is provided based on an eight‐node element. The performance of this interface is demonstrated by simulating lifting a surface footing at varying rates (spanning across undrained, partially drained and drained conditions), compared with existing theoretical solutions, numerical results and experimental data. The good agreement achieved indicates that this interface is capable of modelling uplift at varying rates, which is an extremely challenging topic in offshore engineering. Sensitivity studies were conducted to investigate the parameters affecting uplifting behaviour. A unified backbone curve was established correspondingly, which is shown to be different from existing studies in compression, due to the difference in the mechanism between the two cases. [ABSTRACT FROM AUTHOR]

Zircaloy-4 isothermal oxidation tests were conducted at 1000 °C under an oxygen atmosphere with flow rates varying from 20 to 200 mL/min. In this research, a breakaway time delay phenomenon was discovered. The temperature of the atmosphere near the cladding was measured in order to estimate the oxidation rate and identify the condition of the phenomenon. A sharp escalation in the cladding temperature was observed in the early stage of oxidation as the flow rate increased. In addition, macroscopic and microscopic observations were performed to identify the effects of initial temperature escalation. The results showed that the thickness of the dense columnar oxide increased in the oxide scale when the initial peak temperature exceeded 1050 °C. Based on these observations, it can be assumed that temperature escalation in the early stage can influence the thickness of dense oxides, and this in turn affects the oxidation behaviors, especially the breakaway time. [ABSTRACT FROM AUTHOR]

Zircaloy-4 isothermal oxidation tests were conducted at 1000 °C under an oxygen atmosphere with flow rates varying from 20 to 200 mL/min. In this research, a breakaway time delay phenomenon was discovered. The temperature of the atmosphere near the cladding was measured in order to estimate the oxidation rate and identify the condition of the phenomenon. A sharp escalation in the cladding temperature was observed in the early stage of oxidation as the flow rate increased. In addition, macroscopic and microscopic observations were performed to identify the effects of initial temperature escalation. The results showed that the thickness of the dense columnar oxide increased in the oxide scale when the initial peak temperature exceeded 1050 °C. Based on these observations, it can be assumed that temperature escalation in the early stage can influence the thickness of dense oxides, and this in turn affects the oxidation behaviors, especially the breakaway time.

• TG steam oxidation (600–1200 °C) done on Zr-2.5Nb and microstructure characterized. • Different microstructural features observed for tests in 600–900 °C and 900–1200 °C. • Breakaway oxidation and high hydrogen pick up observed at 1000 °C. • Discontinuity in the slope of parabolic rate constants with temperature seen at 900 °C. • Activation energy higher for tetragonal rich oxide than monoclinic rich oxide. Zr-2.5Nb pressure tube material was subjected to isothermal steam exposures in the range 600–1200 °C for different durations to predict its oxidation behavior during hypothetical accident scenarios. The oxidation exponent obtained from power law fitting of the thermogravimetry (TG) curves deviated from parabolic regime. Nevertheless, oxidation kinetics was described by determining the parabolic rate constants (K p) in two temperature ranges: K p = 0.029 exp(-111075/RT) (kg/m2)2/ sec for 600–900 °C whereas K p = 77652.6 exp(-254824/RT) (kg/m2)2/ sec for 900–1200 °C. In the tested durations, only the 1000 °C sample has shown breakaway transition, after approximately 105 min and has absorbed the highest amount of hydrogen amongst all samples. The trend in hydrogen pickup fraction (HPUF) was verified by two complementary hydrogen determination methods. Clear differences were identified in the α-Zr(O) layer formed on the samples below and above 900 °C. In the α + β range of 600–900 °C, α-Zr(O) consisted of tiny β precipitates. At and above 900 °C in the fully β range, columnar α-Zr(O) grains were observed. [ABSTRACT FROM AUTHOR]

The addition of small concentrations of alloying elements to pure zirconium can prevent nuclear fuel cladding material from undergoing unstable oxide growth in aqueous environments at light water reactor operating temperatures. The role of alloying elements in stabilizing the oxide growth is examined in this paper, to better understand the oxide growth stabilization mechanism. To this end, a set of initial, short-duration corrosion experiments were performed, followed by oxide layer characterization. Specifically, ten model Zr alloys were selected to test the effect of small alloying additions on the alloy corrosion rate and corrosion breakaway. These alloys were corrosion tested in pure water in an autoclave at 360 °C for up to 70 days. The alloys included crystal bar Zr, sponge Zr, and model alloys with small concentrations of Sn, Fe, and Cr. After testing, the alloys were characterized using scanning electron microscopy (SEM) and synchrotron µ-X-ray fluorescence (µXRF) to study how the structure of the oxide and alloying element distribution related to unstable oxide growth. Initial results in the 360 °C water environment showed breakaway oxidation may be caused by unstable oxide growth due to heterogeneous distribution of the alloying elements. Heterogeneous distribution of alloying elements was correlated to the occurrence of unstable oxide growth (either nodule-like, grain boundary penetration, or differential grain-to-grain growth). It is possible that this heterogeneity, made possible by low alloying element content, can cause breakaway corrosion, but further study is warranted. [ABSTRACT FROM AUTHOR]