Erosion-corrosion of carbon steel pipework on an offshore oil and gas facility

Erosion-corrosion is a destructive process which can be encountered in the oil and gas industry when carbon steel pipelines transport sand particles in CO2-containing salt water and hydrocarbons. The high degradation rates attributed to this mechanism can create increased challenges to project economy and operation where material integrity, accurate corrosion rate prediction and long term performance are key concerns. This thesis presents a project with a firm foundation in practical engineering problems, supported by strong generic engineering science which holds wider applications. The research focuses on understanding and inhibiting the degradation processes occurring on a North Sea offshore facility which had experienced a number of unexpected failures and reportedly high degradation rates between 2005 and 2010. An empirical erosion-corrosion model is developed for the facility to provide accurate assessment of degradation rate. The prediction tool is subsequently compared to commercially available CO2 corrosion models and validated using inspection data. An assessment of the corrosion inhibition strategy on the facility and the screening of numerous corrosion inhibitors are conducted through gravimetric analysis and insitu AC/DC electrochemical techniques in static and dynamic conditions. The research discovers a more efficient chemical for controlling degradation processes on the facility whilst highlighting the ability of electrochemical techniques to help understand inhibition mechanisms and behaviour. The methods presented for interpreting the results using generic science demonstrate wider applications in both inhibited and non-inhibited environments. A review of inhibition in more extreme erosion-corrosion environments is performed to elucidate the effect of increased levels of erosion on the degradation process. The application of in-situ electrochemistry in dynamic conditions allowed the individual contribution of erosion and corrosion components of mass loss to be quantified, producing information on the different mechanisms by which inhibitors mitigate degradation effects. Finally, the optimum inhibitor in this study is broken down into is constituent components for individual analysis. A test matrix is implemented to determine the effect of synergy between the individual components. The adsorption process of the most influential component onto carbon steel is studied and determined through the implementation of electrochemistry and Fourier Transform Infrared Spectroscopy (FT-IR) before a colorimetric technique is tailored for residual analysis purposes.