Detection of Microdefects on the Surfaces of Corroded Steel Pipes
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DETECTION OF MICRODEFECTS ON THE SURFACES OF CORRODED STEEL PIPES P. O. Maruschak,1, 2 Ya. V. Lytvynenko,1 V. O. Dzyura,1 R. T. Bishchak,3 and M. S. Polutrenko2
UDC 670.191.33
The micromechanisms of biocorrosion damage to specimens of 17G1S-U pipe steel are studied on the basis of a combination of the profilometry approaches with fracture mechanics. We develop new methods for the numerical analysis of stress concentration factors regarded as parameters of localization of the microscopic concentrators of corrosion stresses. The improved approach is applied to the analysis of profilograms of corroded pipe steel. The possibility of appearance of safe (admissible) corrosion defects is substantiated with regard for the stress concentration in the vicinities of microscopic notches corresponding to depressions in the profilograms. Keywords: biocorrosion, analysis of profilograms, diagnostics, stress concentration.
Introduction The vital activity of sulfate-reducing bacteria (SRB) is one of the causes of local corrosion damage and the appearance of pits on walls of gas mains. Thus, these bacteria are responsible for the anaerobic cathodic depolarization with iron as an anode. This phenomenon significantly increases the rate of fracture processes in the pipe [1, 2]. Moreover, SRB also support the activity of iron sulfide as a cathode. In numerous works, the variations of microtopography were regarded as an indication of the presence of defects on the surfaces of structures and some models of self-organization of the components of these structures were developed. It was shown that the averaged characteristics of state of the surface are not always sensitive to variations of the geometric parameters of the surface topography. Hence, as one of the main tasks, we can mention the search for informative parameters that can be used for the evaluation of the surface geometry and the development of automated algorithms of the determination of these parameters [3–5]. In analyzing the mechanical characteristics of the bodies with microscopic inhomogeneities of the surface topography, it is necessary to take into account their shapes, sizes, number, and mutual arrangement. In numerous cases, the force loads applied to structural elements vary as functions of time. Therefore, the investigation of the concentration of stresses in the vicinities of microdefects seems to be a quite urgent problem [6]. In a series of works, it is indicated that the informativity of standard parametric criteria used for the evaluation of microscopic surface topography is restricted and insufficient for the solution of diagnostic and optimization problems [7–11]. Actually, by analyzing the biocorrosion of the surfaces of 17G1S-U pipe steel, it is possible to find their most damaged sections, establish their physicomechanical characteristics according to changes in their geometry and the formation of microscopic depressions (notches) whose vertices have certain 1 2 3
Pulyui Ternopil National Technical University, Ternopil, Ukraine. Corresponding author; e-ma
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