Electrochemical Study of External Corrosion of Three API Steels Exposed to Seawater and Sediment from Seabed of the Gulf of México

Abstract

An electrochemical study of three API steels: X52, X65, and X80, exposed to seawater and sediment from seabed is presented. Two seabed samples were collected at 60 meters depth near a platform (seabed A) and at a distance of 500 m (seabed B) from the same platform of the Sonda of Campeche, Mexico. In both samples, the seawater and sediment were separated in order to characterize their corrosiveness in an electrochemical cell of 100 mL. The physicochemical and electrochemical responses were determined in the water and sediment. Electrochemical impedance spectra and polarization curves for both water and sediment from the two seabed samples were carried out. A cathodic protection analysis for the three steel surfaces exposed to sediment was proposed based on cathodic polarization curves. Corrosion rates for the three studied low carbon steels could be attributed to their physicochemical properties and low temperatures from a specific seabed area. Thus, high susceptibility to corrosion was identified when three API steels were in contact with seabed B. A corrosive gas fixation and discharges of produced water into the seabed that are able to conduct the corrosion process were suggested. In order to study the activation energies of corrosion for the API steels exposed to sediment, a low temperature dependence was taken into account using the Arrhenius equation and Rct values from impedance data. Activation energy values were Ea = 23.06, 31.7, and 43.2 J mol–1 in X52, X80, and X65 steels, respectively.