Zajec (2020): Stress corrosion crack initiation testing with tapered specimens in high-temperature waterresults of a collaborative research project, Corrosion Engineering, Science and Technology,
This paper studies the stress corrosion cracking (SCC) behaviour of Incoloy 800 in pure 10%NaOH and, respectively, 10%NaOH+0.33g/l NaCl solutions. Notched and un-notched C-ring specimens were tested in a static autoclave at 2600C and 50 bars. To evaluate the electrochemical behaviour of different metal/environment systems, the most important electrochemical parameters were calculated from polarization curves recorded between (�800)mVvsSCE and (+1200)mVvsSCE (scan rate 1mV/s), at 850C. It was emphasised that the presence of Cl- in caustic environment conducts to the decreasing of corrosion rate and corrosion current. Optical microscopy (OM) and scanning electron microscopy (SEM) revealed that the initiation mechanism and penetration depth of SCC cracks depend on the composition of the testing solution: in pure caustic solution, the SCC initiation is transgranular the SCC cracks propagated up to 120m, while in the presence of the Cl-, the SCC cracks started from the pits formed on the samples surface and the SCC depth is shorter than in the pure caustic solution (only up to 20m). X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS) analyses were used to identify the composition of the oxide layer build-up on the surface of the specimens exposed in autoclaves. The results indicate that, in the presence of the Cl- anions, the spinel oxide NiCr2O4 is formed in a bigger amount. Due to this compound formation, a greater SCC resistance of Incoloy 800 was observed.
Geological disposal is identified by nearly all experts in the field of waste management as the only safe and sustainable option presently available, but the progress towards its implementation is slow. The nuclear waste must be safely storaged for hundreds of thousand years. Titanium alloys are some of the most promising candidates as container materials for the long-term disposal of high level nuclear waste (HLW) in rock salt formations. In the case of titanium waste containers, between the containers walls and the surrounding buffer material used to pack the disposal borehole some crevices can appear in the welded zone container/ shielding lid, under a biofilm etc. For this purpose we studied the effect of chloride concentration on crevice corrosion of some welded titanium alloys (Grade 2 and Grade 12, respectively) in chloride solutions at 90oC by electrochemical methods (Ecorr vs time, potentiodynamic tests).
The main cause of failure of CANDU-type fuel bundles during their operation is the
Stress Corrosion Cracking (SCC). This mechanism appears in presence of the simultaneous action
of a corrosive agent and of mechanical stress. The presence of precipitated zirconium hydride
platelets can affect the propagation of the SCC cracks. For this reason, we studied the influence of
content of hydrogen on the initiation and the propagation of SCC crack. To do this study, some Crings
samples with different content of hydrogen (100-500ppm) were exposed in a corrosive
environment containing iodine (10-4g/cm2) at 320°C. The stress state, the concentration of the
corrosive environment and the temperature were maintained constant. For comparison, in the same
conditions some as-received samples were exposed. To relieve the morphology of the precipitates
of the zirconium hydride the samples were been investigated using metallographic method, before
and after thermal treatments. While before the experiment a circumferential orientation of the
hydrides precipitates was observed, after the thermal treatments a reorientation of hydrides in a
radial direction was been remarked. Investigation by SEM method revealed the propagation modes
of cracks in the case of the as-received samples and it was put in evidence the existence of the
microcracks on the inner surface of tested samples.
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