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

Characterization of pitting corrosion of stainless steel using artificial neural networks

In this work, different classification models were proposed to predict the pitting corrosion status of AISI 316L stainless steel according to the environmental conditions and the breakdown potential values. In order to study the pitting corrosion status of this material, polarization tests were undertaken in different environmental conditions: varying chloride ion concentration, pH and temperature. Two different techniques were presented: k nearest neighbor (KNN) and Artificial Neural Networks (ANNs). The parameters for the classifiers were set based on a compromise between recall and precision using bootstrap as validation technique. The ROC space was presented to compare the classification performance of the different models. In this frame, Bayesian regularized neural network model proved to be the most promising technique to determine the pitting corrosion status of 316L stainless steel without resorting to optical metallographic studies

Manual Ecomar de corrosión y protección

La mayor parte de los metales utilizables industrialmente sufren fenómenos de corrosión, es decir se deterioran o destruyen por la acción de medios agresivos de diferentes características. En la Armada existe una larga experieneia en la lucha contra la corrosión, por la agresividad del ambiente marino sobre los componentes estructurales de las unidades. Para cuantificar la importancia de es te problema sería necesaria una referencia económica concreta y ésta es difícil de establecer, por cuanto ademas de las pérdidas directas, que se refieren al valor de los materiales destruidos, hay una inmensa variedad de pérdidas indirectas, de difícil análisis. Entre estas últimas pueden citarse las siguientes: vidas humanas por accidentes catastróficos de los materiales estructurales, paralización del uso de sistemas por reparación, pérdida o contaminación de productos íntermedios o final es, aumento de consumo de energía, disminución de rendimiento como consecuencia de la modificación de las características hidrodinámicas de un buque por acumulación de productos de corrosión e incrustaciones. Es por estos motivos que la Armada Argentina, a través del Servicio Naval de Investigación y Desarrollo, decidió oportunamente apoyar las tareas de investigación que realizaban científicos de diferentes organismos (CNEA, CITEFA, INIFTA, CIDEPINT), brindando su aporte en forma de subsidios para que se efectivizara el PROGRAMA ECOMAR, interinstitucional y muítidisciplinario. Se orientaron así aquellos esfuerzos al estudio de la cor ros ion marina y su control. Hace más de un lustro que se está trabajando en el tema y son numerosas las publicaciones científicas y asesoramientos ya real izados. Muchos de los trabajos efectuados han sido presentados en reuniones científicas nacionales e internacionales. Además, en el año 1973, se publicó un tomo sobre CORROS ION MARINA, donde estos problemas fueron analizados exhaustivamente. Complementando esta tarea de transferencia de conocimientos, el SENID ha encarado la edición de este MANUAL ECOMAR DE CORROSIÓN Y PROTECCIÓN, donde se consideran casos de interés práctico y se procura, mediante un lenguaje sencillo, llegar al mayor número posible de interesados en el tema.Material digitalizado en SEDICI-CIC Digital gracias a la Biblioteca del Centro de Investigación y Desarrollo en Tecnología de Pinturas (CIDEPINT)

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

Effect of temperature on passive film formation of UNS N08031 Cr-Ni alloy in phosphoric acid contaminated with different aggressive anions

tThe influence of temperature and the effect of aggressive anions on the electrochemical behaviour of UNSN08031 stainless steel in a contaminated phosphoric acid solution were evaluated. Stabilisation of thepassive film was studied by potentiodynamic polarisation curves, potentiostatic tests, electrochemicalimpedance spectroscopy (EIS) measurements, Mott Schottky analysis and X-ray photoelectron spec-troscopy (XPS). The stability of the passive film was found to decrease as temperature increases. The filmformed on the stainless steel surface was a n-type semiconductor and the XPS spectrum revealed thepresence of fluoride ions.Authors express their gratitude to the Ministry of Education of Spain (MHE2011-00202) for its financial support during the stay at University of Manchester, to MAEC of Spain (PCI Mediterraneo C/8196/07, C/018046/08, D/023608/09 and D/030177/10) and to the Generalitat Valenciana (GV/2011/093) for the financial support. The authors would also like to acknowledge the support of the School of Materials at the University of Manchester for providing analytical and technical support for the study.Escrivá Cerdán, C.; Blasco Tamarit, ME.; García García, DM.; García Antón, J.; Akid, R.; Walton, J. (2013). Effect of temperature on passive film formation of UNS N08031 Cr-Ni alloy in phosphoric acid contaminated with different aggressive anions. Electrochimica Acta. 111:552-561. https://doi.org/10.1016/j.electacta.2013.08.040S55256111

Stress corrosion cracking: Characteristics, Mechanisms and Experimental study

Stress corrosion cracking (SCC) is a phenomenon in which the cracking of a metal alloy usually results from the combined action of a corrodent and tensile stress. Stresses that cause cracking can be residual or may be applied during service. A degree of mechanistic understanding of SCC will enable most metallic engineering materials to operate safely though stress corrosion cracking failures still continue to occur unexpectedly in industry. In this paper, the characteristics, mechanisms and methods of SCC prevention are reviewed. The results of experimental studies on alpha brass are also reported of which the failure mode conformed with the film-rupture and anodic dissolution mechanism