<p>Pack-rust corrosion is a type of corrosion that affects steel built-up members especially old  bridges. It is a localized corrosion that happens in the crevice between two mating surfaces. Pack-rust corrosion does not only cause section loss like other types of corrosions, but also induces local distortion in the structural members that are not the intention of the original designs. This corrosion can change the behavior of the connection fixity and could also cause instability in the overall  built-up members. The size of distortion and section loss were observed to behave linearly between  the free edge and the first line of fasteners. As the distance is moving toward the free edge, the  distortion in the members and section loss in the base material were observed to be maximum. Another important observation was that pack-rust corrosion does not grow beyond the fastener at the fastener’s line. </p> <p>The literature revealed that there are no comprehensive experimental and analytical studies focused on the behavior and effect of pack-rust corrosion on the overall performance of built-up members and connections in compression. Therefore, this research studies the effects of pack-rust corrosion on the capacity of built-up compression members including but not limited to stiffness, yield strength, maximum capacity, and change in fastener force under applied load. This research was studied by performing large-scale experimental testing of flexural members with simulated pack rust. Pack-rust distortion was simulated by placing washers in the crevice between two plates and then the two plates were drawn together using high-strength fasteners. There were also members with real pack-rust corrosion damage from bridge components that used to be in service, and were tested in axial compression tests. </p> <p>The experimental results were compared with hand calculation using conventional design  equations. Finite element analysis was also studied to compare with the experimental results in  order to calibrate future models, but it is not presented in this report. The findings of the  experimental results of all the specimens show that pack-rust corrosion affects yield strength and  maximum capacity of the member and minimally affects the member’s stiffness. Maximum load  of the member affected by pack-rust corrosion can still be estimated conservatively using the  conventional design equations with some modifications. There was no indication of significant  increase in fastener force under applied load, so the likelihood of fastener failing in tension was  very small as observed from this study.   </p>

Les aciers inoxydables martensitiques sont utilisés dans l'industrie aéronautique où de hautes propriétés mécaniques sont requises. Cependant, dû à leur faible teneur en chrome, ils sont relativement sensibles à la corrosion localisée et particulièrement à la corrosion caverneuse qui se développe en milieu confiné. Tout d'abord, le comportement électrochimique de l'acier inoxydable martensitique X12CrNiMoV12-3 a été étudié dans une solution neutre et chlorurée (NaCl 0,1 M + Na2SO4 0,04 M) en plein bain. Des mesures électrochimiques (courbes de polarisation et mesures d'impédance) couplées à des analyses de surface par XPS ont permis de caractériser les films passifs formés pour différentes conditions. Les résultats obtenus ont permis de montrer le rôle important joué par l'oxygène dissous sur la formation et/ou la modification du film passif pendant l'immersion dans l'électrolyte. Les diagrammes d'impédance obtenus au potentiel de corrosion et en milieu aéré sont caractérisés par deux constantes de temps qui ont été attribuées au film passif (hautes fréquences) et au transfert de charges (basses fréquences). L'analyse de la partie hautes fréquences des diagrammes d'impédance électrochimique à l'aide du modèle en loi de puissance a permis de montrer de faibles variations de l'épaisseur des films pendant l'immersion. Des mesures électrochimiques ont ensuite été réalisées à l'aide du montage de la cellule à couche mince qui permet de travailler avec des épaisseurs d'électrolyte rigoureusement contrôlées. Les essais réalisés ont montré l'aptitude à la repassivation de l'acier inoxydable martensitique dès qu'il est en contact avec l'oxygène dissous en particulier pour des faibles épaisseurs d'électrolyte (inférieur à 100 µm). Lorsque le milieu est confiné entre deux parois en acier afin de reproduire une situation de corrosion caverneuse, il a été montré la corrosion est fortement accélérée lorsque l'épaisseur d'électrolyte est faible (inférieur à 500 µm). / Martensitic stainless steels are mainly used for applications where high mechanical performance is required. However, due to the low chromium content, they are relatively sensitive to localised corrosion, and particularly, to crevice corrosion encountered in confined environments. First, the electrochemical behavior of X12CrNiMoV12-3 martensitic stainless steel has been studied in a bulk neutral chloride solution (0.1 M NaCl + 0.04 M Na2SO4). Electrochemical measurements (polarisation curves and impedance measures) and XPS surface analysis were performed in order to characterise the passive films formed under different experimental conditions. The results showed the important role of dissolved oxygen to form and/or modify the passive film during immersion in electrolyte. The impedance diagrams are characterised by two time constants wich are attributed to passive film response (high frequency range) and to charge transfert resistance (low frequency range). The analyse of the high frequencies part of the diagrams by using the "power law model" showed low evolution of passive films thickness during immersion. Then, electrochemical measurements were perfomed in confined environments by using a thin layer cell where the electrolyte thickness were rigourosly adjusted. The measurements showed that the martensitic stainless steel is in passive state even for low electrolyte thickness (inferior in 100 µm). When the electrolyte is confined between two stainless electrodes in order to reproduce the same conditions find during crevice corrosion, the corrosion is sharply accelerated when the electrolyte thickness is above 500 µm

<p>As of 2013, the damage caused by corrosion on highway bridges has been estimated to cost approximately 14 billion dollars annually, and this cost has been increasing over the years. Corrosion is one of the natural phenomena that has been slowly deteriorating infrastructure systems across the United States. One of the most problematic types of corrosion is crevice corrosion, which is defined as the formation of rust between overlapping surfaces such as the case of a splice connection where flanges are attached by splice plates. A significant number of steel bridges in Indiana have developed crevice corrosion in splice connections. Therefore, this research focuses on the crevice corrosion, or “pack rust”, occurring in these structural elements. The application of coatings alone has not been enough to stop pack rust at these connections. In an attempt to look for approaches that can effectively mitigate this problem and maintain the designed service life of bridges, different strategies have been studied and tested. The first objective of this study is to determine the strength reduction as a function of the time of exposure to salt misting. To do this, specimens that simulate the bottom flange splice connection have been exposed to a corrosive environment for different periods of time and later tested under tension to assess the reduction in strength. The second objective is to evaluate the effectiveness of the mitigation strategies under different conditions. First, the mitigating products were initially applied before exposure to salt misting. Second, the mitigating products were applied as a repair, and in this case, the specimens corroded for a given period of time and were then repaired to evaluate any further deterioration. The assessment of the strategies’ effectiveness is based on the strength reduction and visual inspection of the specimens. The ultimate outcome of this study is a series of general guidelines to slow down crevice corrosion based on the results of the laboratory testing. </p>

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In dieser Arbeit wurde die Korrosion an Kanten und Flanschen unter unterschiedlichen Klimabedingungen und räumlichen Anordnungen untersucht und modelliert. Auf Basis von Versuchsdaten konnten Simulationsmodelle zur Vorhersage der Delaminationsweite an Kanten und der Korrosionstiefe in Flanschen entwickelt werden. Mittels Stromdichte-Spannungskurven und elektrochemischer Impedanzspektroskopie wurde die Korrosionskinetik sowie die Barrierewirkung der organischen Beschichtung in das Modell überführt. Das unterschiedliche Korrosionsverhalten von vertikal und horizontal orientierten Kanten wurde durch die von Elektrolyt benetzte Fläche berücksichtigt. Darüber hinaus wurde der Einfluss verschiedener Klimaparameter in zyklischen Wechselklimatests numerisch modelliert. Durch die Kombination empirischer Simulationsparameter konnte der Zyklus eines Wechselklimatests sowohl integral, als auch differentiell unter Berücksichtigung wechselnder Testparameter modelliert werden. Zur Modellierung der Flanschkorrosion wurde ein grundlegendes Potentialmodell vorgestellt.

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