Assessment of Stress-Strain State of Pipelines Based on the Measurements of Magnetic Characteristics in Field Conditions

A series of measurements on two pipeline sections made of 17G1S (17Г1С) steel using two measuring devices: magnetic multitester MMT-3 and magnetic analyser of structure KRM-C-K2M (КРМ-Ц-К2М) has been carried out. Maps of coercive force, residual magnetic induction and maximum magnetic induction on the pipes were obtained. The coefficient of loading for different cross-sections of the pipeline was calculated. Dependence of magnetic characteristics averaged over the cross-section on the coefficient of loading is plotted. It is revealed that the most dangerous for destruction cross-sections, in which the coefficient of loading exceeded the critical value of 1,2, correspond to the reduced values of coercive force and residual magnetic induction, obtained in the direction of measurement along the pipeline axis. It is shown that measurement along the axis at the top of the pipeline shows a similar relationship as for the cross-sectional averaged values, which means that in pipeline aerial crossings, measurement only at the top of the pipeline may be sufficient.