Quantitative analysis of localized corrosion in tensile armor wire of flexible riser submitted to sweet stress corrosion cracking testing with crevice

Abstract

Failure of flexible risers can occur, among several factors, due to their cold drawn carbon steel tensile armor wires collapse. These wires are susceptible to corrosion by seawater which increases propensity to a synergistic sweet stress corrosion mechanism, when they are associated with CO 2 -saturation, high tension, pressure, temperature, and crevices occurrence. In the present study, the influence of crevice in the annular region of flexible risers on the severity of pitting corrosion was quantified. Two different cold drawn carbon steel wires were compared. Corrosion tests by immersion were carried out on wires subjected to three-point bending in synthetic seawater environment at 0.1 MPa, 25 °C and 2 MPa, 60 °C. The crevice occurrence and the internal energy were significant intensifying factors for pitting corrosion, which was demonstrated by the higher frequency and depth of the pittings and by the arrangement of corrosion deposits in crevice assembly samples. The carbon content of the wire did not significantly influence corrosion.