Magnetic methods for estimation of load and damage levels in X70 steel

The paper studies the magnetic, mechanical and structural characteristics of X70 steel after controlled rolling. The coercive force Hc, residual induction Br, maximum permeability μmax and maximum permeability field Hμmax measured in situ in the loaded or unloading steel magnetized in different directions about the pipe axis are analyzed for applicability as parameters from which the working tensile stress in a pipeline and its preceding overload with attendant transition to the plastic range can be determined. An approach is proposed for estimating the accumulated damage level in the steel under tension or torsion from the coercive force Hc and/or saturation magnetization Jmax.