An integrated study of corrosion and scale interactions in the absence and presence of combined chemicals

The most common form of treatment for calcium carbonate scale and CO2 corrosion in the oil and gas industry is the application of corrosion and/or scale inhibitors. Surface scaling of pipework rarely occurs in environments where no corrosion exists, yet techniques used to develop and assess the performance of scale inhibitors tend to focus on assessing and reducing solely bulk/surface scaling, without affording consideration towards corrosion, whilst corrosion inhibitors are frequently evaluated in non-scaling environments. Furthermore, both chemicals tend to be evaluated independently meaning that any potential antagonistic effects between the chemicals can go unrecognised.
This project presents a setup and methodology to enable the occurrence of scale and CO2-corrosion to be monitored simultaneously (in the presence and absence of combined scale/ corrosion inhibitors). The test cell focuses on evaluating four parameters: (i) bulk scale precipitation, (ii) surface scaling, (iii) general corrosion and (iv) localised corrosion.
The results demonstrate that the methodology implemented is effective at assessing the efficiency of combined inhibitors regarding scale and corrosion. At low inhibitor concentration, results showed interactions and competitive effects in reducing both phenomena. Higher concentration highlights the difference between bulk and surface scaling with different induction times detected on the sample surface and in the bulk phase.
A second part of the thesis focuses on formation of iron carbonate as a corrosion product. Tests were conducted to assess the influence of iron on scale and corrosion processes and on the performances of a combined inhibitor. Iron has been found to reduce scale and corrosion processes but not necessarily impaired the inhibitor performance. Moreover, a protocol using an in-situ atomic force microscope has been developed and its ability for monitoring the first steps of iron carbonate formation was shown.