Chloridion Effects on Stress Corrosion Cracking of X70 Pipeline Steel in Simulated Deep-Sea Environments

Abstract

The effect of chloridion ion on the stress corrosion cracking (SCC) of pipeline steel was investigated in a pressure vessel with constant loading device to simulate deep-sea environment, using electrochemical, confocal scanning laser microscope analysis and SEM techniques. The results revealed that the threshold stress σSCC for SCC is 0.925σb, 0.875σb and 0.860σb in 0.2mol/L NaCl solution at 0.1MPa, 5MPa and 10MPa, respectively. The chloridion ion concentration increase to 0.6mol/L, σSCC decrease to 0.885σb, 0.775σb and 0.675σb, respectively. When the chloridion ion concentration increase further to 1.0mol/L, σSCC decrease further to 0.775σb, 0.725σb and 0.625σb, respectively. These results indicate that chloridion promotes SCC in simulate deep-sea environment. This study aims to be conductive to the fundamental understanding of the SCC of X70 steel in similar deep ocean environment.

Keywords: X70 pipeline steel, Hydrostatic pressure, Stress corrosion crack, chloridion ion