Pitting Corrosion of Bare Stainless Steel 304 under Chloride Solution Droplets

Pitting corrosion behavior of stainless steel 304 (SS304) under droplets of chloride solution was investigated using a Kelvin probe (KP). Droplets of different volumes of MgCl_2 solution were placed on the steel surface and exposed to a constant low relative humidity (RH). As the concentration increased during the exposure of the drop to low RH, the open-circuit potential (OCP) and the shape change of the drop were monitored by the KP. Pit initiation was detected by a sudden decrease in the OCP. Pits initiated earlier under small droplets than under large drops. The chloride concentration at initiation was between 3.0 and 8.4 M for droplets with a starting concentration of 0.88 M Cl^−. The initiation concentration increased when the initial concentration of the droplet was higher. The anodic current demand of pits growing at the OCP decreased with time as did the available cathodic current. When the current demand exceeded the available cathodic current, the active pit area decreased. A mechanism for pit formation and growth under droplets of MgCl_2 solution was proposed

Crossover of interface growth dynamics during corrosion and passivation

We study a model of corrosion and passivation of a metalic surface in contact with a solution using scaling arguments and simulation. The passive layer is porous so that the metal surface is in contact with the solution. The volume excess of the products may suppress the access of the solution to the metal surface, but it is then restored by a diffusion mechanism. A metalic site in contact with the solution or with the porous layer can be passivated with rate p and volume excess diffuses with rate D. At small times, the corrosion front linearly grows in time, but the growth velocity shows a t^{-1/2} decrease after a crossover time of order t_c ~ D/p^2, where the average front height is of order h_c ~ D/p. A universal scaling relation between h/h_c and t/t_c is proposed and confirmed by simulation for 0.00005 <= p <= 0.5 in square lattices. The roughness of the corrosion front shows a crossover from Kardar-Parisi-Zhang scaling to Laplacian growth (diffusion-limited erosion - DLE) at t_c. The amplitudes of roughness scaling are obtained by the same kind of arguments as previously applied to other competitive growth models. The simulation results confirm their validity. Since the proposed model captures the essential ingredients of different corrosion processes, we also expect these universal features to appear in real systems.Comment: 17 pages, including 7 figures; submitted articl

Pitting Corrosion in Austenitic Stainless Steel Water Tanks of Hotel Trains

The water storage tanks of hotel trains suffered pitting corrosion. To identify the cause, the tanks were subjected to a detailed metallographic study and the chemical composition of the austenitic stainless steels used in their construction was determined. Both the tank water and the corrosion products were further examined by physicochemical and microbiological testing. Corrosion was shown to be related to an incompatibility between the chloride content of the water and the base and filler metals of the tanks. These findings formed the basis of recommendations aimed at the prevention and control of corrosion in such tanks. Se han detectado problemas de corrosión por picaduras en los depósitos de agua de trenes hotel. Para identificar las causas se llevó a cabo un detallado estudio metalográfico así como de la composición química de los aceros inoxidables austeníticos utilizados en su construcción. También se realizaron estudios fisicoquímicos y microbiológicos de los productos de corrosión. Se ha encontrado que los problemas de corrosión están relacionados con la incompatibilidad entre el contenido en cloruros del agua y los metales base y de aporte de la soldadura de los tanques. En base a estos hallazgos se proponen una serie de recomendaciones encaminadas a la prevención y control de la corrosión de dichos depósitos

The contribution of hydrogen to the corrosion of 2024 aluminium alloy exposed to thermal and environmental cycling in chloride media

This work is focused on the role of hydrogen in corrosion damage induced by the cyclic exposure of 2024 aluminium alloy to chloride media with air emersion periods at room and/or negative temperatures. Various analysis and microscopic observation techniques were applied at intergranular corrosion defects. A mechanism involving the contribution of hydrogen to the degradation of the alloy mechanical properties is presented. Several consecutive stress states appear during cycling, resulting from volume expansion of the electrolyte trapped in the intergranular defects during emersion phases at -20°C. These stress states lead to hydrogen diffusion, transport and trapping

In situ monitoring of the electrochemical reactivity of aluminium alloy AA6060 using the scanning vibrating electrode technique

Localized electrochemical activation of aluminium alloy AA6060 surfaces during immersion in chloride-containing aqueous solution has been characterised using the scanning vibrating electrode technique (SVET). Ionic current flows in the electrolyte phase adjacent to corroding microcells are imaged in situ, allowing their evolution with time to be monitored with spatial resolution. A heterogeneous response due to the presence of intermetallic inclusions in the material is found on AA6060 surfaces. The highly localized anodic activity was thus detected, which has been interpreted as a result of the galvanic coupling between the matrix and the intermetallic particles. Metallic inclusions behave cathodically whereas the aluminium matrix undergoes metal dissolution due to the activation of anodic sites in the proximity of those inclusions. Hydrolysis of aluminium ions leads to local acidification of the electrolyte adjacent to the anodic sites, and it is accompanied by hydrogen evolutio

The effect of Sc and Yb microalloying additions and aged-hardening heat treatment on corrosion behavior of Al-Mg alloys

Sc-containing Al alloys are potentially applied in saline environment. However, the corrosion behavior and its mechanisms of Sc-containing Al alloys have not been paid much attention. In this research, the corrosion behavior of Al-4Mg, Al-4Mg-0.3Sc, and Al-4Mg-0.24Sc-0.06Yb alloys was investigated in 3.5wt% NaCl solution by immersion and potentiodynamic polarization analysis. Scanning electron microscope (SEM), transmission electron microscopy (TEM) and high-resolution TEM were used to characterize intermetallic phases and localized corrosion. The results showed that the Fe-containing intermetallic particles are cathodic with respect to the matrix and can lead to localized corrosion, whereas the high content of Mg makes the Fe-containing intermetallic particle less noble to the matrix. Yb-containing intermetallic particles did not show any dissolution of the matrix at the periphery of these particles. The results indicated that active dissolution and localized corrosion were the dominant corrosion mechanisms for Al-4Mg alloy. However the polarization curves of Al-4Mg-0.3Sc and Al-4Mg-0.24Sc-0.06Yb alloys showed spontaneous passivation followed by pitting corrosion. Results suggested that age-hardening heat treatment improved the stability of the passive film on Al-4Mg-0.3Sc and Al-4Mg-0.24Sc-0.06Yb alloys.This research was supported by The Project Bridging The Gap, funded by the Erasmus Mundus External Cooperation Window Program. Acknowledgements also to the University of Minho, for the provision of research facilities.info:eu-repo/semantics/publishedVersio

Dynamic Sensing of Localized Corrosion at the Metal/Solution Interface

A Mach-Zehnder interferometer is employed to detect localized corrosion at the metal/solution interface in the potentiodynamic sweep of the iron electrode in solutions. During the electrochemical reactions, local variations of the electrolyte's refractive index, which correlate with the concentration of dissolved species, change the optical path length (OPL) of the object beam when the beam passes through the electrolyte. The distribution of the OPL difference was obtained to present the concentration change of the metal ions visually, which enable direct evidence of corrosion processes. The OPL difference distribution shows localized and general corrosion during the anodic dissolution of the iron electrode in solutions with and without chloride ions, respectively. This method provides an approach for dynamic detection of localized corrosion at the metal/solution interface

Corrosion behavior of friction stir welded lap joints of AA6061-T6 aluminum alloy

In this work, the corrosion behaviors of friction-stir lap welding of 6061-T6 Al-alloy are studied. The friction-stir lap welding was performed under different welding conditions (rotation speed and welding speed). The corrosion behavior of the parent alloy, the weld nugget zone (WNZ), and the heat affected zone (HAZ) of each welded sample working as an electrode, were investigated by the Tafel polarization test in 3.5 wt. (%) NaCl at ambient temperature. The morphology of the corroded surface of each region was analyzed by scanning electron microscopy together with energy dispersive spectroscopy (SEM-EDS). The results showed that the corrosion resistance of the parent alloy was better than the WNZ and the HAZ in both welding conditions. Localized pit dissolution and intergranular corrosion were the dominant corrosion types observed in the parent alloy, WNZ, and HAZ. The parent alloy, WNZ, and HAZ exhibited similar corrosion potentials (Ecorr) after T6 heat treatment. This treatment had a better effect on the corrosion resistance of the welded regions than the parent alloy

Passivation behaviour of Alloy 31 (UNS N08031) in polluted phosphoric acid at different temperatures

The influence of temperature (20–80 °C) and chloride concentration (0.06–0.42 wt.% KCl) on the electrochemical behaviour of the UNS N08031 was studied in 40 wt.% polluted phosphoric acid solution. Passivation behaviour was investigated by using potentiostatic tests at different potentials. From the linear regions of the log i vs. log t transients, the parameter n was obtained. The results showed that the applied potential hardly affects on the passivation rate n. However, n values decreased when temperature increased. The values of n demonstrated that the passive film formed on Alloy 31 was compact and highly protective.The authors express their gratitude to the MAEC of Spain (PCI Mediterraneo C/8196/07, C/018046/08, D/023608/09 and D/030177/10), to Programa de Apoyo a la Investigacion y Desarrollo de la UPV (PAID-06-09) and to the Generalitat Valenciana (GV/2011/093) for the financial support and to Dr. Asuncion Jaime for her translation assistance.Escrivá Cerdán, C.; Blasco Tamarit, ME.; García García, DM.; García Antón, J.; Guenbour, A. (2012). Passivation behaviour of Alloy 31 (UNS N08031) in polluted phosphoric acid at different temperatures. Corrosion Science. 56:114-122. https://doi.org/10.1016/j.corsci.2011.11.014S1141225