Microdefects of Biocorroded Pipe Steel Surfaces and Safety Assessment of Localized Stress Concentrators

Abstract

The effect of sulfate-reducing bacteria (SRB) on the corrosion of steel 20 was investigated. Results demonstrated that the chemical composition of corrosion products, the corrosion rate, and corrosion type were altered due to the adherence of SRB and the subsequent formation of biofilm on the steel 20 surface. The micromechanisms of biocorrosion damage of specimens from pipe steel 20 were quantified on the basis of the microgeometry of the degraded surface and the localization parameters of corrosive stress microconcentrators. Stress concentrators in the vicinity of the micro-cuts, which are the depths of the profilograms, make it possible to evaluate safe (allowable) microcorrosion damage. The proposed approach complements the well-known methods for monitoring biodeterioration of pipe steels. With its help, it was found that a decrease in the corrosion rate of specimens with the addition of an inhibitor does not always clearly indicate its effectiveness. The case where the introduction of an inhibitor led to the destruction of the SRB biofilm on the surface of specimens from steel 20, but caused the activation of local corrosion processes and the formation of a more developed microrelief, is considered. The hollows of such microrelief are potential places of origin of defects, which require additional control.

Keywords

• pipeline steel
• microbiologically influenced corrosion
• inhomogeneous biofilm
• stress concentrators