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Previous issue date: 2016-03-23 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / Funda??o de Amparo ? Pesquisa do Estado do Rio Grande do Sul - FAPERGS / This study investigates the influence of pressure on the formation of corrosion product scales on API 5L X65 steel used in the oil and gas industry. Experiments were performed in humid CO2 and water saturated with CO2 environments at 50?C for periods of 168 and 360 hours in 2 MPa and 5 MPa subcritical conditions and 10 MPa, 15 MPa and 20 MPa supercritical conditions. The thermodynamic model of Duan was used to obtain information about CO2 solubility in water, the water concentration present in the humid CO2 and the pH for the experimental conditions used in this work. Corrosion rates were determined by weight loss tests, and the scales were characterized by scanning electron microscopy, electrochemical measurements and X-ray diffraction. The results showed that for the 168 hours exposure time, the size of iron carbonate crystals formed in CO2 saturated water was bigger in relation to the ones formed in humid CO2 environments, with the exception of the experiment performed at 20 MPa. The scales formed in 168 hours and 360 hours exposure time, in both environments and pressures, showed typical morphology of iron carbonate. It was also observed that the films tend to be more compact with increased immersion time, but not necessarily more protective. Corrosion rates were classified as severe according to NACERP- 07-75 for both subcritical to supercritical pressures in CO2 saturated water environment and for both exposure times. In the case of 168 hours of exposure and CO2 saturated water environment, the highest corrosion rate occurred at 15 MPa. Already for 360 hours exposure times, performed at supercritical pressures, the corrosion rates increased with increasing pressure and the higher corrosion rate values were observed in water saturated with CO2. Electrochemical impedance tests showed no significant differences in resistance to polarization in subcritical pressures to 168 hours for both environments. As for supercritical pressures, higher polarization resistance was 15 MPa for also both environments. As for supercritical pressures, higher polarization resistance was 15 MPa in CO2 environment. Potentiodynamic polarization tests indicated that at 168 hours of immersion, there was a reduction in the rate of dissolution of the films formed at 10 MPa and 20 MPa in both environments. For the 360 hours of immersion, the corrosion potential was most active at 5 MPa for water saturated with CO2, with no significant differences of humid CO2 environment. / Neste estudo avaliou-se a influ?ncia da press?o na forma??o dos filmes de produto de corros?o no a?o API5L X65 utilizado na ind?stria de petr?leo e g?s. A corros?o foi promovida em ambientes de CO2 ?mido e ?gua saturada com CO2 a 50?C, durante 168 horas e 360 horas, em press?es subcr?ticas de 2 MPa e 5 MPa e supercr?ticas de 10 MPa, 15 MPa e 20 MPa. Utilizou-se o modelo termodin?mico de Duan a fim de obter informa??es sobre solubilidade do CO2 em ?gua, a concentra??o de ?gua presente no CO2 ?mido e o pH para as condi??es experimentais utilizadas neste trabalho. As taxas de corros?o foram determinadas por ensaios de perda de massa, os filmes de produtos de corros?o foram caracterizados por microscopia eletr?nica de varredura, por medidas eletroqu?micas de imped?ncia e de polariza??o potenciodin?mica e difra??o de raios X. Os resultados indicaram que, para 168 horas, os cristais de carbonato de ferro foram maiores para o meio de ?gua saturada com CO2 que em meio de CO2 ?mido, com exce??o em 20 MPa. Os filmes de produtos de corros?o formados durante 168 horas e 360 horas, em ambos os meios e press?es, apresentaram morfologia t?pica de carbonato de ferro. Os filmes tendem a ser mais densos com o aumento do tempo de imers?o, por?m n?o necessariamente mais protetores. As taxas de corros?o foram classificadas como severas, segundo a NACE-RP-07-75 tanto para as press?es subcr?ticas quanto para supercr?ticas no meio de ?gua saturada com CO2, em ambos os tempos de exposi??o. Em 168 horas a maior taxa de corros?o ocorreu em 15 MPa em ?gua saturada com CO2. Para 360 horas, em press?es supercr?ticas, a taxa de corros?o aumentou com o aumento da press?o e as taxas de corros?o mais altas foram observadas para o meio de ?gua saturada com CO2. Os ensaios eletroqu?micos de imped?ncia n?o apresentaram diferen?as significativas ? resist?ncia ? polariza??o em press?es subcr?ticas, para 168 horas, para ambos os meios. Em 360 horas, em press?es subcr?ticas, a maior resist?ncia ? polariza??o foi em 5 MPa tamb?m para os dois meios. J? para press?es supercr?ticas, a maior resist?ncia ? polariza??o foi em 15 MPa no meio de CO2. Os ensaios de polariza??o potenciodin?mica indicaram que em 168 horas houve redu??o na velocidade de dissolu??o dos filmes formados em 10 MPa e 20 MPa em ambos os meios. Para 360 horas, o potencial de corros?o foi mais ativo em 5 MPa para ?gua saturada com CO2, n?o havendo diferen?as significativas para o meio de CO2 ?mido.
| Identifer | oai:union.ndltd.org:IBICT/oai:tede2.pucrs.br:tede/7060 |
| Date | 23 March 2016 |
| Creators | Rodrigues, Tania Regina Schmitz de Azevedo |
| Contributors | Costa, Eleani Maria da |
| Publisher | Pontif?cia Universidade Cat?lica do Rio Grande do Sul, Programa de P?s-Gradua??o em Engenharia e Tecnologia de Materiais, PUCRS, Brasil, Faculdade de Engenharia |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/doctoralThesis |
| Format | application/pdf |
| Source | reponame:Biblioteca Digital de Teses e Dissertações da PUC_RS, instname:Pontifícia Universidade Católica do Rio Grande do Sul, instacron:PUC_RS |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | -7432719344215120122, 600, 600, 600, 600, 600, -655770572761439785, 4518971056484826825, 2075167498588264571, -3614735573891122254 |
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