ABSTRACT: Carbon steel pipelines are being used across the world as a cost effective option for wet gas transportation. When these pipelines operate in a stratified flow regime, top-of-line (TOL) corrosion can occur as a result of water condensation at the top of the pipeline in the presence of corrosive species such as acid gases (CO2, H2S) and volatile organic acids. The ability to predict and control TOL corrosion is necessary to ensure long term integrity of these pipelines. This paper will discuss a TOL corrosion model that can be used to assess the risk of TOL corrosion and optimize the use of carbon steel pipelines. The foundation of this TOL corrosion model is the development of a mechanistic understanding of TOL corrosion based on laboratory testing. The model accounts for the relevant chemistry and physics of the TOL corrosion process, including the effects of condensation rate, temperature, partial pressure of acid gases, detailed water chemistry, and flow characteristics. Case studies are presented that demonstrate how the TOL corrosion modeling in conjunction with laboratory testing can be used to evaluate the use of carbon steel pipe, while ensuring the operational integrity of equipment and facilities.
INTRODUCTION Top-of-line (TOL) corrosion can occur in wet gas pipelines operating in stratified flow. Although these first reported cases of TOL corrosion were in sour fields 1,2, sour TOL corrosion has historically been treated as a sweet corrosion phenomenon. Recent publications 3, 4 have described the mechanism of sour TOL corrosion and determined its dependence on variables such as temperature, condensation rates, gas velocity, and TOL water chemistry. In this work, it was determined that sour TOL corrosion was mainly dependent on iron sulfide scale characteristics which are a function of temperature and condensation rate was identified as a secondary parameter.