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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2. Accelerated Corrosion: Methodology

The main objective was to induce surface pre-corrosion to five quasi static specimens (of the geometry depicted in Figure 4) equivalent to half a year of exposure to a corrosive environment in a significantly shorter time frame. To accomplish the set goal, a three-electrode setup (represented in Figure 1) was developed, the mass loss equivalent to six months in the environment was determined and a similar mass loss was induced in two hours and twenty six minutes by applying a current of 0.25 A to the system. 2.1. Setup and Specimen Preparation For this study, the three-electrode cell setup (1) encompasses: the working electrode, which is a specimen of the S690 QL steel; the platinum wire counter electrode and the silver chloride electrode (Ag / AgCl electrode) reference electrode. All elements were immersed in a water-based solution of 3.5% sodium chloride (3.5%NaCl) acting as the electrolyte (contained by the glass reservoir) and connected to a potentiostat as schematized in 1 (c). This solution acts as a controlled substitute for the seawater, which its two major chemical constitutes are, in fact, Na + and Cl − . The potentiostat used is the Gamry Interface 1000E (Gamry, USA) (Baboian, 2005; Chandrasekaran and Jain, 2017).

Fig. 1: Three-electrode setup, (a) upper view, (b) side view and (c) schematic representation: 1 - Working electrode (specimen), 2 - Ag / AgCl Reference electrode, 3 - Counter electrode (platinum wire), 4 - Gamry Interface 1000E, 5 - 3.5% NaCl electrolyte

The gripping system, schematically represented in Figure 2, is composed of a main component, permanently fixed to the lid, and an interchangeable element, which acts as an adaptor for di ff erent specimens’ geometries. The remaining components are a nail and a spring. Additionally, five barriers were put in place inside the reservoir to reduce the necessary volume of solution. The barriers were modelled having in mind the need to not obstruct the viability to the inside of the reservoir. All the components were designed in a 3D modeling software and then produced by additive manufacturing using fused filament fabrication. The material used was a commercially available PET-G filament by Prusa. The purpose of the nail was to act as an extension of the specimen (anode), connecting it to the rest of the three electrode system, as PET-G is non-conductive. The potentiostat is connected to the specimen through the head of the nail and the spring was fixed on the nail, promoting a constant contact between the nail and the specimen. Regarding the specimens preparation, in order to achieve a similar initial surface state throughout all specimens, by degreasing the surface of the specimens and removing naturally formed oxides, the specimens were polished with grit papers of #400, #800, #1000 and #2000 in succession and in this order and cleaned in an ultrasonic bath using ethanol. Another concern in the specimen preparation was to protect the grips from corrosion. Therefore, a coating of spray paint was applied on both sides and a layer of black electrical tape followed by a coating of silicone were applied on the side that would be immersed in the solution (being the side in constant contact with it). 2.1.1. Parameters Definition First, a polarization curve correspondent to the material (S690QL) and environment (3.5%NaCl), under analysis, was built by performing a potential sweep and can be consulted in Figure 3. The limits of the potential sweep were