Most stress corrosion cracking (SCC) mechanisms initiate from localised corrosion (pitting, intergranular attack, de-alloying), which provides local stress concentration. Alloys are generally more susceptible to SCC than pure metals because selective dissolution or oxidation is possible. De-alloying involves the selective dissolution of the less noble (LN) component from an alloy. The more noble (MN) component enriches on the surface forming a brittle, metallic, nanoporous layer. In noble metal alloys and brass, SCC shows correlation with the threshold LN content below which de-alloying stops (the parting limit). In Fe-Ni-Cr engineering alloys de-alloying may be responsible for Cl-SCC, although this has not been proven explicitly. Initial indications show that de-alloying causes SCC in hot, caustic environments. In some cases, Ni enrichment and porosity are associated with cracks in stainless steel after long-term service in nuclear high temperature water environments, but it is unclear if this plays a causal role in cracking. Here the de-alloying mechanism (primarily the effect of Ni (MN) content) and its relationship to SCC in Fe-Ni-Cr materials (Fe10Ni, 310SS and Alloy 800) is examined using a hot caustic environment, and compared to classical de-alloying systems. De-alloyed layers formed on all materials, although Alloy 800 required a higher temperature. Increasing Ni content improved de-alloying resistance according to classical theory. Unlike classical systems, de-alloying occurred with concurrent MN dissolution and, at open circuit potential (OCP), the layers retained significant Fe and Cr (LN) instead of being ‘almost pure’ MN. Layers formed with applied anodic potential were friable and highly LN depleted. This behaviour was successfully modelled in Kinetic Monte Carlo simulations. Recently, it has been shown that SCC in noble element alloys depends on the mechanical integrity (quality) of the de-alloyed layer; a finding that was reflected here. At 140 °C at OCP the layer on 310SS was too thin to promote SCC and Alloy 800 did not de-alloy significantly. Layers formed with anodic potential did not result in SCC. In 50% NaOH at 280 °C, severely stressed 310SS cracked where thick de-alloyed layers formed. However, the thin layer formed on Alloy 800 was associated with SCC, even with low residual stress.

Graduation date: 1991

Most stress corrosion cracking (SCC) mechanisms initiate from localised corrosion (pitting, intergranular attack, de-alloying), which provides local stress concentration. Alloys are generally more susceptible to SCC than pure metals because selective dissolution or oxidation is possible. De-alloying involves the selective dissolution of the less noble (LN) component from an alloy. The more noble (MN) component enriches on the surface forming a brittle, metallic, nanoporous layer. In noble metal alloys and brass, SCC shows correlation with the threshold LN content below which de-alloying stops (the parting limit). In Fe-Ni-Cr engineering alloys de-alloying may be responsible for Cl-SCC, although this has not been proven explicitly. Initial indications show that de-alloying causes SCC in hot, caustic environments. In some cases, Ni enrichment and porosity are associated with cracks in stainless steel after long-term service in nuclear high temperature water environments, but it is unclear if this plays a causal role in cracking. Here the de-alloying mechanism (primarily the effect of Ni (MN) content) and its relationship to SCC in Fe-Ni-Cr materials (Fe10Ni, 310SS and Alloy 800) is examined using a hot caustic environment, and compared to classical de-alloying systems. De-alloyed layers formed on all materials, although Alloy 800 required a higher temperature. Increasing Ni content improved de-alloying resistance according to classical theory. Unlike classical systems, de-alloying occurred with concurrent MN dissolution and, at open circuit potential (OCP), the layers retained significant Fe and Cr (LN) instead of being ‘almost pure’ MN. Layers formed with applied anodic potential were friable and highly LN depleted. This behaviour was successfully modelled in Kinetic Monte Carlo simulations. Recently, it has been shown that SCC in noble element alloys depends on the mechanical integrity (quality) of the de-alloyed layer; a finding that was reflected here. At 140 °C at OCP the layer on 310SS was too thin to promote SCC and Alloy 800 did not de-alloy significantly. Layers formed with anodic potential did not result in SCC. In 50% NaOH at 280 °C, severely stressed 310SS cracked where thick de-alloyed layers formed. However, the thin layer formed on Alloy 800 was associated with SCC, even with low residual stress.

In the present study, the corrosion behaviour of several magnesia-chrome (MC) and magnesia-alumina spinel (MA) bricks against fayalite type slags was investigated and the role of the spinel phases was highlighted. The experimental results revealed that the corrosion resistance of the MC bricks was superior to the MA bricks against KIVCET slags in static and dynamic conditions. As a result of the interaction between MgO from MC bricks and the slag, a modified forsterite phase (Mg, Fe, Zn, Ca) ���SiO��� was formed, which destroyed the precipitated complex spinel bonds at the grain boundaries of periclase and magnesia-chromia spinel. Furthermore, both MgO and MgO-MgAl���O��� spinel in the MA brick dissolved into the slag, which resulted in modified forsterite phases of (Mg, Fe, Zn, Ca)���SiO��� and (Mg, Fe, Zn)(Fe, Al)���0��� complex spinels, respectively. In addition, the accretion formation in the KIVCET furnace was investigated through solubility experiments of Cr���0��� in the KIVCET slag with various amounts of lead, which revealed that the net contribution of Cr���03 to the spinel formation is the highest in the barren (no Pb) slag, followed by high-lead (11% Pb) and it is the lowest for the low-lead (6% Pb) slag. The amount of spinel solid solution increased consistently with increasing Cr���0��� dissolved and the PbO existent in the slag. From examinations of several used bricks from the tuyere area of a Peirce Smith nickel converter, it was found that the corrosion is due to the interaction of the partially oxidized matte penetrating deep into the brick and the magnesia grains forming (Mg, Fe, Ni, Co) XOy spinels. Analyses of brick samples used in the KIVCET Electric Furnace roof identified deep reaching sulphation, which weakened the bonding phase between coarse magnesia grains. In the Bottom Blown Oxygen Converter, a highly aggressive lead and bismuth oxide rich slag penetrated deep into the brick, which destroyed the grain boundaries, causing the refractory to be easily eroded at the refractory-slag interface. Our studies concluded that the spinel phases, either as magnesium chromate, magnesium aluminate or complex spinel [(Mg, Fe)(Cr, Al, Fe) ���O���], enhanced the corrosion resistance of a basic refractory to fayalite type slags from the non-ferrous smelting and converting furnaces.

The corrosion behaviour of pure copper, zinc and aluminum in selected commercial beverages was studied. Experiments were also conducted in the presence of citric and phosphoric acid to investigate their role in the corrosion process in these beverages. Two experimental approaches were used to investigate the corrosion behavior: a chemical method in which the dissolved metal concentration was measured after immersion of a sample in a beverage and an electrochemical method using the Tafel extrapolation technique. The metal surfaces were also examined by SEM/EDX after the immersion tests and electrochemical polarization. Among the important conclusions from this research are that the order in which the various beverages affect the corrosion rate as evaluated by Tafel extrapolation of the polarization curves did not agree with the order based on measurement of the dissolved metal concentration as determined by the immersion tests except when a 1- day immersion test was used for Al. The dissolved Al, Zn and Cu concentrations obtained from short-term immersion tests differed from those measured in long-term tests, although the same ranking of the corrosiveness of the seven soft drinks was obtained after 1- and 3- day immersion tests. These discrepancies likely stem from the complicated dynamics of the corrosion of these metals and the various physical, chemical and electrochemical processes that take place in these beverages. No simple correlation was found between the beverage properties and composition and the dissolved copper, zinc and aluminum concentrations after immersion, whether based on short-term or long-term tests. However, the corrosion rate of copper in the 7 soft drinks as determined by the Tafel extrapolation method was found to depend on the pH. Uniform corrosion was observed in all iv cases except for Al immersed in Gatorade. Pitting cavities were observed on the surface of Al after both the 5-day immersion test and Tafel polarization measurements. Of the beverages considered in this study, Gatorade was consistently found to be the most corrosive for the three test metals.

The research thesis is based on the study of Kaohsiung MRT Orange Line. On condition that bilateral power is supplied during the target year, make two-minute interval as the background simulation, and use MATLAB & Simulink software for analysis tools. Through the establishment of the equivalent in the stray current model, discuss the original ground construction of Kaohsiung MRT Orange Line, and change the resistance of the track structure, in order to analyze whether that affects stray currents. Besides, simulate the maximum stray current density and its length in each station. To study cathode corrosion of underground metal pipeline due to stray current, the equivalent circuit model is applied for computer simulation. By changing the distance between the underground metal pipelines and MRT rail tracks the voltage potential of the pipe lines introduced by the stray current of MRT system is derived. The mitigation strategy of cathode corrosion due to stray current is also proposed in the thesis.

The effect of silica nanoparticles on corrosion of steel by molten carbonate eutectic (42.7 percent Li2CO3, K2CO3) was investigated. The experimental design was based on static coupon immersion methodology where a coupon (material under study, in this case a rectangular stainless steel specimen of SS304 with dimensions approximately 5X20X.6mm and weight .5gm) is exposed to a static corroding environment for predetermined periods of time. The testing times were 2, 4 and 6 weeks. The temperature during testing was maintained at a constant 520C. The instantaneous corrosion rates were determined by normalizing the mass loss with respect to time and area. The mass loss was determined by descaling the corroded steel coupons using concentrated hydrochloric acid. The instantaneous corrosion rates obtained from all three times showed a reduction in corrosion of steel by molten carbonate eutectics when doped with silica 1 percent by weight in comparison to the molten base carbonate eutectics. The results showed that doping the carbonate eutectic with silica nanoparticles (1 percent by weight) reduced the corrosion of steel by half in comparison to the corrosion without doping.

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Concepts for the development of a model to predict natural gas transmission pipeline lifetime in a corrosive environment are constructed. Primarily, the effects of environmentally assisted cracking (EAC) are explored. Tensile test specimens from a sample of API 5L X-52 pipeline were tested in a simulated groundwater solution and subsequently analyzed. The results suggested that the simulated environment ultimately reduced the ductility of the test specimens; however, no evidence of ??classical?? stress corrosion crack morphology was discovered. However, corrosion pits up to 0.75 mm (0.03 in) were revealed during metallographic analysis. A Marin factor analogy and an energy method concept are suggested and explored. Ultimately, the test data set was too small for the results to be of any directly applicable significance.

Thèse de doctorat : Électrochimie : Paris 12 : 2006. / Version électronique uniquement consultable au sein de l'Université Paris 12 (Intranet). Titre provenant de l'écran-titre. Bibliogr. : 110 réf.