Couple effect of hydrostatic pressure and dissolved oxygen on corrosion behaviour of low-alloy high strength steel in 3.5 wt-% NaCl solution

Hydrostatic pressure (HP) and dissolved oxygen (DO) both change with the increase of ocean depth. In order to unmask the corrosion phenomena of metals in deep sea environment, studying their combined effect on corrosion is necessary. In this report, couple effect of HP and DO (HP + DO) on corrosion behaviour of low-alloy high strength steel in 3.5 wt-% NaCl solution was investigated by Electrochemical measurements, SEM observations, XPS characterisations and 3-D size measurements. The results show that the corrosion rate of low-alloy high strength steel increases with increasing HP + DO under each immersion period, appearing an exponential decay growth. As HP + DO increases to a critical value, 30 ATO, its acceleration to corrosion process becomes limited. Moreover, HP + DO remarkably increases the growth of corrosion film on steel surface and leads to more loose structure in corrosion film. Finally, HP + DO stimulates the propagation of corrosion pits in 3D direction.