In situ grazing incidence x-ray diffraction of sweet corrosion scaling across an X-65 weld

摘要

Within the oil and gas industry, CO_2-induced (sweet) corrosion of facilities fabricated from carbon steel is a constant threat to structural integrity. On this basis, significant effort continues to be applied to gain insight into this phenomenon. One specific area of activity is weld-joints, as such areas can be highly vulnerable to failure due to locally increased sweet corrosion rates. There, however, remains incomplete understanding of the mechanisms leading to this phenomenon, including detailed knowledge of potentially protective sweet corrosion scales formed on different regions of a weld-joint (base metal/heat affected zone/fusion zone). To gain further insight into these weld-joint scales, we have exploited grazing incidence x-ray diffraction (GIXRD) to identify the phases formed. Most notably, these measurements have been undertaken in situ, i.e. from a submerged sample, employing a custom built electrochemical cell (E-cell); the E-cell can be deaerated, and the solution temperature elevated up to ~ 80°C. Diffractograms were acquired using this E-cell at the XMaS beam line of the ESRF (France) from a X-65 pipeline steel weld-joint immersed in CO_2 saturated salt solution (pH ~ 4, T - 80°C). These data indicate how the scale composition (e.g. formation of siderite and chukanovite) varies across the width of the weld-joint as a function of immersion time.