Application of the Magnetoacoustic Emission Method for Estimation of Pipelines Material State

The influence of hydrogen factor and residual stresses on the sum of the magnetoelastic acoustic emission (MAE) signals amplitudes during magnetization of the oil and gas pipeline material is investigated. The regularities of change of the MAE signals parameters by the thickness of the pipe wall and around the longitudinal welded joint are established. The largest sum of the MAE signal amplitudes is recorded in the material from the internal layer of the pipe wall, which is evidently caused by the presence of hydrogen in the material that under long-term operation of the pipelines has penetrated into structural defects and facilitates jumping of the domain walls under samples magnetization. For the longitudinal welding of oil and gas pipelines, the MAE signals with the largest sum of amplitudes are generated in the material from the weld zone and the smallest—from the heat-affected zone. This effect is caused by the peculiarities of the restructure of the material structure under the influence of high-temperature fields under welding in different parts of the welded joint. It is found that residual stresses around the welded joints reduce the intensity of domain wall jumps and cause decrease in the sum of the MAE signals amplitudes. The use of the obtained research results in the newly developed methods of non-destructive testing makes it possible to quickly assess the local damage of the pipes of long-term operation.