Deformation Effects on Metal Magnetic Memory in API 5L X70 Steel

Metal magnetic memory technology is a passive magnetic method of non-destructive testing based on the residual magnetic field of a ferromagnetic component. The MMM measurements were performed on a series of X70 pipeline steel samples for various values of uniaxial elastic and plastic deformation from zero up to about 20% strain. The outcomes evidence that the metal magnetic memory gradient index m can be used to evaluate the stress-strain state of ferromagnetic materials under tensile stresses. The tensile stress effect on the gradient index in significantly in elastic stage, but the gradient index in remained unchanged in the plastic deformation stage.