Abstract
A series of autoclave experiments were conducted in order to improve the understanding of how gas temperature and water condensation rate affects sour top of the line corrosion (TLC) of X65 steel. The experimental work was conducted in a 20L autoclave, especially designed for top of the line corrosion investigations, at a total pressure of 2.5 MPa with 0.2 MPa and 1.0 MPa partial pressures of H2S and CO2, respectively. The gas temperatures for the experiments, each of 21 days duration, were 25°C, 40°C, 60°C and 80°C. These experiments facilitated water condensation at steel temperatures ranging from 15°C to 75°C, resulting in TLC. Experimental work included weight loss calculations and characterization of the corrosion product layers formed under these conditions. As a general trend, the top of the line corrosion rate decreased with increasing steel temperature. Higher gas and steel temperature led to the formation of more coherent FeS layers that conferred a greater degree of protectiveness. The water condensation rate had a minimal effect on the corrosion rate. Mackinawite and cubic FeS were always identified at the top of the line for most of the tested conditions, while troilite was observed at a steel temperature of 75°C.
