Abstract
The aim of this research was to investigate the influence of metallurgy on the corrosion behaviour of separate weld zone (WZ) and parent plate (PP) regions of X65 pipeline steel in a solution of deionised water saturated with CO2, at two different temperatures (55 °C and 80 °C) and at initial pH~4.0. In addition, a non-electrochemical immersion experiment was also performed at 80 °C in CO2, on a sample portion of X65 pipeline containing part of a weld section, together with adjacent heat affected zones (HAZ) and parent material. Electrochemical impedance spectroscopy (EIS) was used to evaluate the corrosion behaviour of the separate weld and parent plate samples. This study seeks to understand the significance of the different microstructures within the different zones of the welded X65 pipe in CO2 environments on corrosion performance; with particular attention given to the formation of surface scales; and their composition/significance. The results obtained from grazing incidence X-ray diffraction (GIXRD) measurements suggest that, post immersion, the parent plate substrate is scale free, with only features arising from ferrite (α-Fe) and cementite (Fe3C) apparent. In contrast, at 80 °C, GIXRD from the weld zone substrate, and weld zone/heat affected zone of the non-electrochemical sample indicates the presence of siderite (FeCO3) and chukanovite (Fe2CO3(OH)2) phases. Scanning Electron Microscopy (SEM) on this surface confirmed the presence of characteristic discrete cube-shaped crystallites of siderite together with plate-like clusters of chukanovite.
Highlights
Dissolved carbon dioxide (CO2) in oilfield brines, which accompany extracted oil and gas, causes the internal “sweet” corrosion of steel pipelines
In considering CO2 corrosion in weld regions, studies have shown that there is a strong correlation between susceptibility to corrosion and weld composition
We report here on the results of electrochemical measurements made on individual parent plate and weld regions of X65 pipeline steel at temperatures of 55 °C and 80 °C
Summary
Dissolved carbon dioxide (CO2) in oilfield brines, which accompany extracted oil and gas, causes the internal “sweet” corrosion of steel pipelines. In addition to inducing uniform corrosion, there have been numerous cases of serious localised CO2 attack— evident in scale or deposit regions [1]. Understanding the formation, chemistry and role of CO2-induced corrosion scales and surface films in oilfield environments remains of considerable interest. Concerning CO2 oilfield corrosion, one specific topic of interest in recent years has been the preferential weld corrosion of carbon steels [5,6,7,8]. Olsen and co-workers suggest that weld failures are a combination of the corrosion susceptibility of the weld and the film forming properties of the CO2 saturated environment [9]. CO2 corrosion scales are suspected to form in the initiation stages of weld corrosion [11,12]. Crolet and co-workers highlighted that the nature of the initial phases can determine whether or not the subsequent layer would be protective [13]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
