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Prediction of the flexible pipe annulus pH at high CO2 content and high temperature

Abstract : Previous works have shown that the typical ratio between the volume of electrolyte and the exposed steel surface observed in the annulus of flexible pipelines leads to a specific corrosive environment whose pH deviate from the classical thermodynamic models. In this case, due to the supersaturation in iron ions in the annulus, the commercial models even with their most recent updates cannot precisely predict the measured pH. Due to these specificities, tests are necessary to overcome these limitations and to improve with a better accuracy the pH considered in the design of the flexible pipes. Nowadays, with the development of the Brazilian oil and gas pre-salt basins, a high CO2 partial pressure associated with high temperature are observed in the flexible pipe annulus. Due to the lack of experimental data concerning the pH evolution under these conditions, tests were carried out with a continuous pH monitoring at CO2 partial pressure and temperature up to, respectively, 70 bara and 84 °C. The test results presented in this article show an amplitude between the experimental data and the predicted pH values of at least +0.4 pH units which confirms the conservatism of the thermodynamic models at saturation. In all the tests, the pH reached a maximum value after the first days of immersion followed by a decrease and fast stabilization after this event. An impact of the temperature was verified on the pH behavior in these tests. Keywords Flexible pipes; annulus pH; high pressure; high temperature 2
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Leandro Santos, Dayanne Menezes, Li Ke, Carol Taravel-Condat, Jean Kittel. Prediction of the flexible pipe annulus pH at high CO2 content and high temperature. Eurocorr 2017, Sep 2017, Praha, Czech Republic. ⟨hal-02462622⟩

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