ABTRACT

A comprehensive corrosion prediction model for multiphase oil and gas production and transmission systems was enhanced by incorporating a Top-of-Line corrosion capabilities. Key issues in development of the enhancements are discussed, including evaluation of an improved flow model implemented to facilitate accurate flow predictions. The model was evaluated with parameters commonly encountered in oil and gas production environments as well as transmission systems, and effects of various parameters on corrosion rates are described. Corrosion rates obtained from the enhanced model are compared with actual field and lab testing data as a basis to quantify accuracy and efficacy of the model.

INTRODUCTION

Although Top of the Line Corrosion (TLC) was observed as early as 1960, the potential damage to the oil and gas transportation lines was well recognized only in the past one or two decades1. Compared to typical aqueous corrosion, the phenomenon of TLC is understood to a much less extent, especially in H2S dominant environment. Research efforts undertaken in various research institutes and companies have shed some lights on the mechanisms and key factors governing TLC in CO2 environment. Several theories and methodologies have been proposed and developed to predict CO2 Top of the Line Corrosion1-10.

Top of the Line corrosion typically occurs in carbon steel pipelines/flowlines in which wet gas or stratified multiphase flow are transported. A significant temperature difference between the fluids inside the line and the ambient environment can lead to TLC initiation. Field experiences have suggested that continuous corrosion inhibitor application is usually ineffective in TLC scenario. This is because corrosion inhibitors tend to stay in the liquid phase and are unable to reach the top portion of the pipe in stratified flow. Moreover, for wet gas pipelines, it is usually very challenging to transport corrosion inhibitors in long distance and ensure complete coverage of internal pipe surfaces. As condensation occurs down the line, corrosion takes place and can exacerbate by the presence of acid gases, such as CO2 and acetic acid, which dissolves in the condensed water to generate exceptionally low pH.

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