Effect of H2S on the Corrosion Behavior of Pipeline Steels in Supercritical and Liquid CO2 Environments

The objective of the present study is to evaluate the corrosion properties of pipeline steels in CO2/H2S/H2O mixtures with different amounts of water (undersaturated and saturated) related to a natural gas transportation pipeline. Corrosion behavior of carbon steel, 1Cr steel, and 3Cr steel was evaluated using an autoclave with different combinations of CO2 partial pressure and temperature (8 MPa/25 degrees C and 12 MPa/80 degrees C) with 200 ppm H2S. The corrosion rate of samples was determined by weight-loss measurements. The surface morphology and the composition of the corrosion product layers were analyzed using surface analytical techniques (scanning electron microscopy and energy dispersive x-ray spectroscopy). Results showed that the corrosion rate of materials in supercritical and liquid phase CO2 saturated with water was very low (<0.01 mm/y). However, adding 200 ppm of H2S to the supercritical and liquid CO2 system caused mild corrosion (<0.5 mm/y). Reducing water content to 100 ppm in the supercritical and liquid CO2 systems with 200 ppm of H2S reduced the corrosion rate to less than 0.01 mm/y.