PSI - Issue 42

A. Laureys et al. / Procedia Structural Integrity 42 (2022) 1458–1466 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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temperatures. Sanicro28 and Hastelloy G30 show the highest copper content, while 316Ti contains titanium, which was not the case for any other material. In the case of copper, the preferential dissolution of Fe, Cr, Ni, Mn and Mo leads to a residual stable Cu-enriched filmwhich inhibits steel dissolution (Itzhak and Peled (1986), Ogle et al. (2009)). As such, it is chemically capable to stifle incipient localized attack and, therefore, provides added resistance to reducing media such as phosphoric and sulfuric acids (Abdel-Kader et al. (2008)). Ogle et al. (2009) stated that an uneven copper distribution on the surface or a single monolayer of copper is sufficient to inhibit the anodic dissolution of stainless steels. Moreover, they suggest the possibility of an insoluble (oxidized) form of copper, which might also contribute to the inhibiting effect. Such thin layers cannot be identified by SEM/EDX. More accurate techniques such as XPS or Raman could give more information on the formed surface layers. 4. Conclusions The corrosion sensitivity of six industrial alloys in concentrated phosphoric acid at elevated temperatures was evaluated in the current work. For this purpose weight loss measurements, scanning electron microscopy (SEM) (imaging of the corroded surfaces) and energy dispersive X-ray spectroscopy (EDX) (chemical analysis of the surface) after corrosion testing were performed. The high concentrations of alloying elements in the selected metals allow them to form a protective passive surface film, which inhibits oxidation. Depending on the stability of the passive film, materials will be corrosion resistant up to higher temperatures. Hastelloy G35 and Sanicro35 showed the lowest corrosion rate for temperatures up to 140 °C. These alloys exhibited the highest amounts of Mo, which is considered to be mainly responsible for this higher corrosion resistance. These materials additionally showed the best resistance to localized corrosion. Hastelloy G30 and Sanicro28 showed the lowest corrosion rates at higher temperatures. This is most likely related to their relatively high Cu content. Cu is known to form a protective layer on the sample surface during corrosion. Even though a lower corrosion rate is calculated for Hastelloy G30, SEM analysis showed that deep pits formed on the sample surface at elevated temperatures. This failure mechanisms is considered more dangerous than uniform corrosion, as it can lead to early perforation of tubes and pipelines. Acknowledgements The research was supported by FWO (post-doc fellow project number 12ZO420N and 1248122N) and the special research fund (BOF) of Ghent University (grant BOF01P03516 and BOF15/BAS/062). References Craig, B.D., Anderson, D. B., 1995. “ Handbook for corrosion data ” . In: Materials Park, OH: ASM International. Guenbour, A., Faucheu, J., Ben Bachir, A., Dabosi, F., Bui, N., 1988. Electrochemical study of corrosion-abrasion of stainless steels in phosphoric acids. British Corrosion Journal, 23, 234-238. Neville, A., Hodgkiess, T., 1996. An assessment of the corrosion behaviour of high-grade alloys in seawater at elevated temperature and under a high velocity impinging flow. Corrosion Science, 38 , 927-956. Pardo, A., Otero, E., Merino, M.C., López, M.D., Utrilla, M.V., Moreno, F., 2000. Influence of pH and chloride concentration on the pitting and crevice corrosion behavior of high-alloy stainless steels. Corrosion, 56, 411-418. Escrivà-Cerdán, C., Blasco-Tamarit, E., García-García, D.M., 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. Schillmoller, C.M., 1988. Alloy selection in wet-process phosphoric acid plants. In: Toronto: NiDi Technical Series No. 10015, Nickel development Institute. Itzhak, D., Peled, P., 1986. The effect of Cu addition on the corrosion behaviour of sintered stainless steel in H2SO4 environment. Corrosion Science, 26, 49-54. Lizlovs, E. A., 1969. Corrosion Behavior of Types 304 and 316 Stainless Steel in Hot 85% Phosphoric Acid. Corrosion Nace, 25, 389-393.

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