A mechanistic model is developed to predict the corrosion rate caused by CO2The main features of this model include: prediction of uniform corrosion rate by CO2 INTRODUCTION Carbon steel is extensively used in oil and gas pipelines due to the merit of low cost. These pipelines are frequently exposed to the aqueous environments containing aggressive species, such as CO2(2), was developed exclusively based on public information. , H2S and organic acids which pose significant threat to the normal operation of pipelines. Intense research efforts have been made with the aim of understanding corrosion mechanisms caused by various corrosive species and factors that either promote or inhibit corrosion. As a result, a large number of publications have become available which deal with corrosion from different aspects. Although some issues remain unclear, most of the steps that are associated with CO2 and to a lesser degree H2S corrosion process are now understood. With available information, it is possible to establish a mechanistic model to predict corrosion rate and help further the understanding of corrosion process. In fact, a number of corrosion models for CO2 corrosion in wells and pipelines have been developed in recent years1. However, these models, most of which are proprietary and unavailable to public, often give a large scatter in the prediction due to different theories, assumptions and modeling strategies. This is aggravated by lack of transparency of the code behind the models. When more corrosive species are involved in the corrosion process, larger discrepancies are to be expected from various models. The project presented in this paper aimed at providing the corrosion community with a free mechanistic model for internal corrosion prediction of carbon steel pipelines. Strongly rooted in theories, this model can offer trustworthy predictions for a wide range of conditions that are typical for oil and gas pipelines, as will be shown in the following sections. This model, named FREECORP, H2S, organic acids and/or O2, simulation of iron carbonate film and iron sulfide film growth, identification of major corrosive species by quantifying respective contributions from various species, capability of distinguishing CO2/ H2S dominant corrosion processes, display and manipulation of polarization curves for CO2 dominant processes, or display of H2S concentration profile as a function of distance from steel surface for H2S dominant processes, capability of modifying the corrosion calculation process by adding user-defined reactions or excluding any undesired reactions., H2S, organic acids and/or O2. The aim of this model was to provide the corrosion community with a theoretically sound, simple and effective corrosion model for internal corrosion of mild steel lines. This model is available in the open literature and can be easily accessed on the internet. All the background information, including theories behind, data used for calibration, limitations, etc. is shared with users. In addition, the source code of the model, which has been written in object-oriented fashion, is open to the public to encourage utilization of any individual modules and development of add-on modules by third parties.

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