Study on the Growth of Corrosion Scales on X65 Steel in CO₂ Top-of-Line Corrosion Environment

Carbon dioxide (CO2) corrosion is one of the most serious problems in the oil and gas industry, and CO₂ Top-of-Line Corrosion (TLC) has caused many failures in wet gas pipelines. Corrosion behavior of X65 pipeline steel was studied in a high temperature and high pressure condensation autoclave, simulating the CO₂ TLC environment, under both static and flowing condition. A series of experiments were carried out at the test duration of 3 d, 7 d, 15 d and 29d. Under different test duration, the thickness, compactness and crystalline state of corrosion scales were compared and the growth mechanism of corrosion scales in wet gas environment was analyzed. The corrosion rate was measured by weight loss method. Scanning Electron Microscope (SEM) was employed to analyze the surface and cross-section morphology of corrosion scales. The results indicated that the corrosion scales was thickened gradually with the increase of test duration, and the corrosion scales exhibited layered structure. The severity level of localized corrosion changed under different test duration. It was deduced that the localized corrosion occurred under TLC environment was related to the characteristic of corrosion scales.