METHODICAL APPROACH TO THE STUDY OF STRESS CORROSION CRACKING MECHANISM OF PIPELINE STEEL AT CATHODIC PROTECTION BY LINEAR SWEEP VOLTAMETRY

Abstract

A methodological approach to the rapid assessment by linear sweep voltammetry method stress corrosion cracking (SCC) mechanism of pipeline steels of various grades under cathodic protection has been developed. The proposed approach serves as the basis for the electrochemical study of the mechanism of stress corrosion cracking of pipeline steel at various protective potentials for laboratory conditions. The ratio of polarization currents at fast () and slow () scanning potential rate was determined, its analysis was carried out depending on the polarization potential for steels of various grades. It was established that polarization potentials at which the difference between corrosion rate of the crack’s tip and the other surface is the maximum (maximum value of ) and the rapid development of stress corrosion cracks begin, which is differ for steels of various grades and equal near -0.75 V for X70 steel, -0.85 V for 09G2S steel and -0.8 V for 17G1S steel. The boundaries of the polarization potentials are established, beyond which the SCC mechanism of the investigated steels in the model soil environment NS4 changes, namely: from -0.75 V to -1.05 V for X70; -0.85 V to -1.0 V for 09G2S; from -0.8 V to -0.98 V for 17G1S. This indicates the possibility of SCC development with different rates and patterns, all other things being equal. The results of the work can be useful both for a theoretical understanding of the SCC mechanism and for an express assessment of the SCC mechanism in a soil environment and, in particular, in underfilm electrolyte under a disbanded coating.