Effect of Temperature and H<sub>2</sub>S Concentration on Corrosion of X52 Pipeline Steel in Acidic Solutions

Abstract

The corrosion behavior of X52 pipeline steel in H2S solutions was investigated through immersion corrosion test which was carried out in a high temperature and high pressure autoclave at different temperatures and H2S concentrations. General corrosion rates were calculated based on the weight loss of samples. The morphology and the chemical composition of the corrosion products were obtained by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The crystal structure of corrosion products was analyzed by X-Ray diffraction patterns (XRD). The corrosion products consisted mainly of the sulfide compounds (mackinawite, cubic ferrous sulfide, troilite and pyrrhotite). The corrosion products included two layers: the inner iron-rich layer and the outer sulfur-rich layer. Under H2S concentrations of 27g/L, the corrosion rate increased with the increase of temperature up to 90°C and then decreased at 120°C, finaly increased again. The corrosion rate first increased with H2S concentrations then decreased at 120°C. The structure and stability of the corrosion products due to different corrosion mechanism had a major impact on the corrosion rate. The corrosion resistance of the corrosion products increased as follows: mackinawite < cubic ferrous sulfide < troilite < pyrrhotite.