HYDROGEN ENTRY MECHANISM FOR API X-65 STEEL EXPOSED IN NEAR NEUTRAL SOLUTIONS UNDER ADSORPTION-ACTIVATION CONDITIONS

摘要

Hydrogen-related attack is a specific mechanism that can contribute to SCC (Stress Corrosion Cracking), through its influence on internal stress and the microstructure due to atomic hydrogen concentration diffused and accumulated during operation conditions due to the formation of atomic hydrogen in presence and absence of polarization conditions (cathodic protection). In this work, an API X-65 grade steel pipeline is exposed to NS4 synthetic groundwater solution in hydrogen permeation cell type experiments in order to follow the hydrogen reaction in the cathodic compartment and to characterize the total current between anodic and cathodic compartments and the parameters obtained from polarization tests. A theoretical model based on adsorption coverage is used to characterize atomic hydrogen that forms and diffuses within the steel, as a competition of the hydrogen and bicarbonate ions for the available active sites at the interface. Electrochemical Impedance Spectroscopy is used to characterize the interfacial electrode-electrolyte interface reactions at different sodium bicarbonate concentrations at room temperature under static conditions in order to follow the influence of hydrogen ion for the surface active sites to form atomic hydrogen. For SCC conditions the AC impedance shows the behavior of the interface when molecular hydrogen is induced by polarization, qualitative analysis includes DC electrochemical testing associated with AC impedance measurements. Experimental analysis considers the quantification of atomic hydrogen by considering interfacial reactions and magnitudes obtained by AC impedance during potential bias experiments and associated with covering factors obtained from DC techniques. Steel pipelines samples were mechanical pretreated to influence the surface and increase the hydrogen sensitivity into the metallic structure SCC testing under different polarization conditions is presented as the consequence analysis for hydrogen entry mechanism under near neutral solution.