Effects of Temperature on CO2 Top-of-Line Corrosion of Pipeline Steel

Much more attention on CO₂ Top of Line corrosion has been paid during offshore gas field exploration in China. In order to evaluate the failure risk and predict the corrosion rate of TOL in subsea wet gas pipeline design, effects of temperature, condensation rate, CO₂ partial pressure and flow rate on TOL have been investigated in this paper. HTHP autoclaves with a function of condensate forming on steel samples were used to simulate the corrosion conditions in wet gas pipeline. A comprehensive analysis of the effects of the characteristic of condensate water where the corrosion reactions really take place on the behavior of corrosion is performed, including the condensation rate and the film temperature. Research work has been focused on some parameters identified as having a significant influence on the state of the condensate film, such as partial pressure of CO₂, gas velocity and the differential temperature between the wet gas and the environment out of the pipe. When the temperature of wet gas or condensate film is relatively low, corrosion might be dominated by the electrochemical reaction with low corrosion rate. With the temperature increased, corrosion rate became higher due to increase of film temperature and condensation rate. However, when temperature of wet gas is higher or the liquid film is thicker, corrosion scale would deposit and protect the steel.