Actual field corrosion rate of offshore structures in the Baltic Sea along depth profile from water surface to sea bed

Abstract

The paper presents the results of field electrochemical investigations on the corrosion rate of carbon steel in seawater of the Baltic Sea at the location of the Baltic Beta production rig. The measurements were conducted throughout the year in seawater at different depths from the sea surface to the sea bed (about 75 m). The results revealed corrosion aggressiveness of the seawater along the entire depth profile. There was no multiple decrease in the corrosion rate of carbon steel at deeper levels (below 15 m), which had been observed in the literature reporting the investigations in the seas and oceans of higher salinity (3.5%) than southern Baltic Sea (about 0.8%). A model for monitoring water physico-chemical parameters along a depth profile showed the presence of a substantial amount of oxygen far below the sea surface, which translated into high corrosion aggressiveness of the Baltic seawater. Throughout the year corrosion rate is higher than 0.8 mm/year at the sea surface and even 0.4 mm/year at the sea bed. Presented results can constitute a guideline for the design of the anticorrosion protection systems for offshore wind farms or oil and gas production platforms in the Baltic Sea region.