CO₂ corrosion behavior of X70 pipeline steel in wet gas environment

With a high-temperature and high-pressure condensation autoclave simulating the circumstance of CO₂ corrosion in wet gas pipelines,the variation in corrosion behavior and morphology of X70 pipeline steel was studied by changing the wet gas temperature and the temperature difference between the wet gas and the pipe wall.Scanning electron microscopy(SEM) and energy dispersive spectrometry(EDS) were employed to analyze the morphologies and characteristics of corrosion scales on the steel.The results were compared with those under solution-immersed conditions in a high-temperature and high-pressure autoclave.Using a corrosion prediction model,the influence of some important parameters on corrosion at the top of wet gas pipelines were preliminary studied,such as wet gas and pipe wall temperatures,temperature difference,condensed liquid film temperature and condensation rate.The results show that at the same temperature of the pipe wall(5℃),the corrosion rate increases with the wet gas temperature rising;while at the same temperature of wet gas(25℃ and 45℃),the corrosion rate decreases slightly with the pipe wall temperature rising.In the temperature range of 20 to 45℃,corrosion scales are easily peeled off from the substrate,and uniform corrosion is the predominant morphology.