PSI - Issue 22

L. Sena et al. / Procedia Structural Integrity 22 (2019) 171–180 173 Lígia T. Silva, Bruno Mendes, Carlos Oliveira, Cristina Reis, Paula Silva; José Silva / First International Symposium on Risk and Safety of Complex Structures and Components (2019), Porto, Portugal PADMALATHA, 2014). Studies using carbon steel in 1 Mol H3PO4 solution, at several concentrations of inhibitor and at different temperatures, investigated by the weight loss measurements, showed that for this also the corrosion rate in phosphoric acid solution approximately doubles, each 283.15 K of temperature (YARO, KHADOM, WAEL, 2013). In another experiment, with low alloy steel and martensitic stainless steel, which were placed in distilled water at 293.15 and 363.15 K, with a load of 1 Hz and outdoors, it was observed that aqueous environments at high temperatures cause the appearance of cracks, due to corrosion, by the destruction of the passive film and the anode region, which can lead to steam generation turbines to fail by fatigue (ELMAY, 2015). Similar results are found by analyzing the corrosion of cast iron. Tests carried out with iron being freely gasified in stagnant seawater confirmed that the material showed greater wear with increasing immersion time, from two to ten days, and measurements taken after 3,600 s and 86,400 s proved that increasing immersion times decreased the corrosion of cast iron as a result of the decrease of its cathodes, anodes, currents and corrosion rates (SHERIF, ABDO, ALMAJID, 2015). Then, as polarization increases, a thick film of iron oxides on the surface is observed, improving corrosion resistance and decreasing dissolution rate (SHERIF, ABDO, ALMAJID, 2015; OGUNDARE, 2012). Ductile cast iron exposed in air conditioning, brackish water and alkaline media, reinforces the fact that corrosion decreases with increasing exposure time (OLAWALE et al, 2013; UKOBA, OKE, IBEGBULAM, 2012). A high rate was observed in the first months, out of a total of six, in all environments, the highest being found in NaCl solution, followed by the outside environment (UKOBA, OKE, IBEGBULAM, 2012). The present work aimed to analyze the extent to which phosphoric acid can compromise the structure and properties of cast iron, verifying such factors from the variation of time, temperature and solution concentration. The specimens (CPs) were obtained from a gray cast iron plate (FC-250), with dimensions of 0.02 x 0.05 m and thickness of 0.0048 m, rectangular shape, according to ASTM standard. G31.16997 (NACE TM0169/G31). 36 CPs were used for the appropriate assays. The material composition may be seen in Table 1, through technical report provided by the foundry company. The preparation of the specimen was initially done by removing a small surface layer of material, removing impurities as well as the trimmed edges using a polisher and sandpaper 300mesh (NACE TM0169/G31). After preparation, immersion was done immediately to prevent oxidation. The solutions were obtained using phosphoric acid and distilled water at concentrations of 1, 2 and 3%, respectively, arranged in individual beakers for each CP. In the first phase the samples were immersed in corrosive medium, in 50 ml beakers, three samples for each percentage of the solution during 86,400 s and 424,800 s (24 and 118 hours, respectively), at a temperature of 298.15 K, considered as room temperature. 2. Materials and methods