Characterizations of damage-induced magnetization for X80 pipeline steel by metal magnetic memory testing

Abstract

Metal magnetic memory (MMM) technique can be potentially applied to evaluate early damage of ferromagnetic materials nondestructively due to its high sensitivity to stress-strain state. An experimental investigation of the characterizations of mechanical damage-induced magnetization in X80 pipeline steel specimens has been undertaken. Different degrees of plastic deformation are introduced into specimens with different initial discontinuities. The surface strain distribution and metal magnetic memory signal in specimens are measured during and after tensile testing. The experimental results indicate that, at first the magnetization direction of material depends on the loading direction and the distribution pattern of magnetization reflects the existence of stress concentration. Second, the correlation between peak-valley amplitude of memory signal B_Z and maximum plastic deformation follows a similar formula proposed in this paper, which is independent of specimen type. The results of present work could potentially be used to quantitatively evaluate the degree of stress concentration of X80 pipeline steel components.