Corrosion form transition of mooring chain in simulated deep-sea environments: Remarkable roles of dissolved oxygen and hydrostatic pressure

Abstract

The corrosion form and mechanical properties deterioration of mooring chain steel in simulated deep-sea environments were investigated. With the increase of ocean depth, not only the pressure increases, but also the dissolved oxygen content decreases. These two factors affect corrosion evolution of mooring chain steel in simulated deep-sea environments, which was studied for the first time. Compared with uniform corrosion of mooring chain steel in shallow sea with sufficient oxygen, low dissolved oxygen leads to the corrosion dominated by pitting with pit covers. Meanwhile, hydrostatic pressure distinctly accelerates pitting initiation and propagation. The higher the hydrostatic pressure is, the more serious the pitting is. For failure mechanism of unstressed mooring chain steel serving in simulated deep-sea environments, both absorbed hydrogen and corrosion morphology can degrade the ductility of mooring chain steel, in which the leading factor depends on the service time. The severe pitting is the main factor and causes remarkable ductility loss of the steel after long-term immersion. But hydrogen plays an important role on elongation loss in early stage.