Friction stir welding is an excellent alternative process used in pipelines circumferential welds due to fusion welding low corrosion resistance. This study describes the corrosion resistance as a function of the microstructural features resulting from an API X70 FSW weld joint. The microstructural features were examined by optical microscopy, scanning electron microscopy, and X-ray diffraction. The corrosion analysis was conducted employing potentiodynamic polarization tests using an electrochemical microcell, which allowed to test small circular areas delimited by a 2mm in diameter O-ring gasket. The base metal and heataffected zone were the most susceptible region to corrosion due to the banded microstructures, and the re-stirred-zone and stir zone was the most resistant region to corrosion because of grain refinement.
The hydrogen embrittlement (HE) leads to severe steel degradation of mechanical properties. The hydrogen atoms diffuse into the steel and get positioned into reversible and irreversible trap sites. The pipe to transport oil and gas needs to be welded to construct long‐distance pipeline projects; thus, friction‐stir welding (FSW) has proven an excellent alternative to joining these pipelines. Therefore, this work assessed and analyzed the influence of hydrogen on the microstructure and fracture toughness of API 5L X70 steel welded by friction‐stir welding. The in‐service conditions were simulated by charging the specimen electrolytically in a 3.5% NaCl water solution with an intensity current of 2 mA·cm−2. According to fracture toughness tests, the base metal (BM) was more affected by hydrogen embrittlement than the friction‐stir zone (SZ), with a fracture toughness reduction of 20% after hydrogen charging. The SZ fracture toughness did not statistically show changes in hydrogen charging by the used times; however, the fracture mechanism changed from ductile to brittle‐like after 4 days of charging. The SZ depicted a better fracture toughness than BM due to the bainitic microstructure, a significant amount of irreversible hydrogen trapping.
A novel method to classify the aggressiveness of soil considering its physicochemical content and the development of new synthetic solutions for lab uses is proposed. The results showed that the main criteria existing in the literature for soil corrosivity classification might cause misunderstandings about the real aggressiveness. The synthetic solutions proposed aim to cover a wide range of soil found worldwide in order to refine the assessment of their characteristics hence their corrosivity. For the lab experiments, an API 5L X65 pipeline carbon steel was used. The solutions presented great reliability, and they seemed to be adequate to simulate soils with the presence of sulfate-reducing bacteria (SRB), chloride, and high pH.
RESUMOAs estruturas enterradas (tanques, bases de linhas de transmissão e dutos) estão expostas a diferentes tipos de solos e níveis de corrosividade. Neste caso, se torna necessário o estudo de corrosão do aço carbono nestes diferentes tipos de solos. Para estudos em laboratório, utiliza-se a solução NS4 para simular solos sintéticos. No entanto, devido aos diversos tipos de solos, é necessário o desenvolvimento de soluções sintéticas para simular estes solos com diferentes níveis de corrosividade. Assim, o objetivo deste trabalho foi desenvolver soluções sintéticas para uso em laboratório que abranjam uma variedade de tipos de solos com diferentes propriedades físico-químicas. Os ensaios eletroquímicos realizados foram curvas de polarização potenciodinâmicas, impedância eletroquímica e perda de massa. As soluções foram desenvolvidas alterando as concentrações da solução padrão NS4 nas seguintes condições: desaerada, na qual foi adicionado tiossulfato de só-dio para simular o ambiente anaeróbico das bactérias redutoras de sulfato; em condições aeradas para simular solos contaminados com sulfeto de hidrogênio; adicionando cloreto de sódio para simular solos em região costeira e adição de cimento para simular solos anticorrosivos. Os resultados mostraram que o aço carbono apresenta maior taxa de corrosão quando exposto a soluções de cloreto de sódio e tiossulfato. A adição de 5% (m/v) de cimento foi o suficiente para simular solos anticorrosivos, nos quais ocorreu o processo de passivação. Para garantir o processo passivo no metal nas soluções sintéticas com a presença de tiossulfato de sódio foi necessária adição 5% (m/v) de cimento. O processo de passivação estável não foi alcançado nas soluções sintéticas com cloreto de sódio ao se adicionar 5%, 10% e 15% (m/v) de cimento. Palavras-chave:Corrosividade dos solos, soluções sintéticas de solo, cimento, tiossulfato de sódio e cloreto de sódio. ABSTRACTThe buried structures (tanks, bases of line transmissions, pipelines) are commonly exposed to different kind of soils and corrosivity levels. Due to this condition, it is necessary to study the corrosion on the carbon steel on these different environments. In laboratory, the NS4 solution is used to simulate synthetic soils. However, due to different kind of soils, it is necessary to develop synthetic solutions that evaluate these soils and their corrosivity. Therefore, the objective of this work was to develop synthetic solutions for laboratory use that include a large variety of kinds of soil with different physicochemical properties. The performed electrochemical tests were polarization curves, electrochemical impedance and mass loss. The solutions were obtained by altering the concentration of a standard solution of NS4 in these following conditions: in deaerated condition, in which was added sodium thiosulphate to simulate anaerobic environment of sulphate-reducing Autor Responsável: Joseane Moreira Giarola Data de envio:
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.