Study of the strained state of steel plates of small thickness using coercimetry

Abstract

The results of studying the strain state and depth of dents in K08Yu low-carbon steel plates of small thickness (3-5 mm) using the method of coercimetry are presented. It is known that mechanical stresses and strains that occur in steel rods and base metal of oil and gas pipes have a significant impact on the magnitude of the coercive force (CF) near the sample surface. The effect of plate deformation and geometric dimensions of the dents on the CF magnitude is analyzed using a KM-445.1 coercimeter and tools for stepwise determination of the depth of dents (calipers with a depth gauge, tape measures, metal strip, marker). The calculated differential dependences linking the curvature of the plate with the dent depth are obtained. The intensity of linear strains occurring in the plate is determined. The relations between the coercive force and strain characteristics of plates with different types of collapsing are determined, namely, it is shown that in a plate with a single dent, the value of the coercive force increases monotonically with the depth and intensity of deformations, whereas in a plate with a double dent, there is a complex wave-like dependence of the coercive force magnitude on the depth and intensity of deformations with a characteristic inflection point and the character of the dependence provides a possibility for determination of the size and type of the dent. The proposed analysis of the stress state using the method of coercimetry makes it possible to detect geometric imperfections on the surface of the plates and carry out their non-destructive diagnostics.