PSI - Issue 54

Ana Dantas et al. / Procedia Structural Integrity 54 (2024) 593–600 AnaDantas / Structural Integrity Procedia 00 (2023) 000–000

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reaction, electrons are freed and, than, used up at the cathodic site. This translates into the existence of corrosion current between the anodic and cathodic sites, which consists in the flow of electrons within the metal and ionic transfer within the electrolyte (Quadri et al., 2022). When considering the specific case of steel, the anodic reaction of iron (Fe), which is its major constituent, is defined as (Milella, 2013; Revie and Uhlig, 2008):

Fe → Fe n +

+ ne −

(1)

The degree of corrosion occurrence can be measured as a function of mass loss ( ∆ m ) and the corrosion rate is related to two main factors: the properties of the material and the characteristics of the environment surrounding it (Quadri et al., 2022). The marine environment can be divided into di ff erent zones - atmospheric, splash / spray, tidal, submerged and mud zone - as the corrosion mechanisms vary between them. It is generally accepted that the splash zone is the most critical one, as there is continuous wetting and drying with tidal variations, in addiction to being a excessively windy seawater environment, where thin barrier films, even if formed, are washed away. In this study the simulated environment is the submerged zone where the contact with seawater is constant (Baboian, 2005; Chandrasekaran and Jain, 2017). There is a wide spectrum of di ff erent tests involving corrosion degradation and mechanical testing. These tests encompass scenarios where both mechanical testing and corrosion occur simultaneously ( in situ testing), cases where specimens are pre-corroded, and situations in which specimens are pre-corroded and then subjected to mechanical testing within a corrosive environment (Baboian, 2005). Regarding pre-corrosion of the material, it can undergo natural corrosion in the real environment over time or can be artificially corroded. One of the simplest and widely adopted methods for artificially inducing corrosion is conducting a salt spray test, or one of its variants (modified salt spray), depending on which environment is intended to be simulated. For instances, Dang et al. (2022) pre-corroded tensile and fatigue specimens using three types of salt spray variants: a simple salt spray at 25 ◦ C, a dry / wet cycle at 25 ◦ Cand a dry / wet cycle at 50 ◦ C (ASTM Internatinal, 2011; ASTM International, 2009; Dang et al., 2022). In alternative Zhao et al. (2023), pre-corroded quasi-static tensile specimens in a solution of 3.5% NaCl solution, by applying a current of 0.06 A for three di ff erent durations - 40 min, 80 min and 120 minutes - and compared the stress–strain curves obtained to stress–strain curves of the same material at an not corroded state (Zhao et al., 2023). In the context of in situ experiments, there are two distinct scenarios to consider. In some cases, specimens are tested within the actual environment, where corrosion occurs naturally (without being artificially accelerated). In other cases, corrosion acceleration takes place simultaneously with mechanical testing. Guo et al. (2020) performed fatigue crack growth tests using specimens from high-strength steel bar HRB400 in four distinct environments: in air; in distilled water; in a 3.5% NaCl solution and in an artificially accelerated corrosive environment. In this last environment, the specimens were tested while being immersed in a 3.5%NaCl solution and being imposed a current of 0.5 A (Guo et al., 2020). In addition, there are cases were the specimens are pre-corroded and also tested in a corrosive environment. As an example, Liu et al. (2021), pre-corroded steel wires, using salt spray, to simulate the existing corrosion damage of in-service bridge wires. After pre-corroding the wires, these were used as the working electrode in a three-electrode cell in tensile and fatigue tests while immersed in a 3.5% NaCl solution (which acted as the electrolyte) (Liu et al., 2021). Structural steels with a higher mechanical strength, such as S690 steel, are of progressing interest in o ff shore structures applications due to weight reduction advantages. As a result, analyzing S690 steel’s mechanical properties in both corroded and non-corroded conditions is essential. Thus, this work aims to characterize a S690 steel under simulated marine environment conditions using a three electrode setup, with the objective of accelerating the specimen’s surface corrosion. As such, a methodology for inducing accelerated pre-corrosion is developed and applied to quasi static tensile specimens. Its e ff ect on the me chanical properties, with emphasis on the tensile behaviour of the material, is evaluated through testing in accordance with ASTM E8 standard (ASTM International, 2022).