Application of the Barkhausen effect probe with adjustable magnetic field direction for stress state determination in the P91 steel pipe

The paper presents the results of application of a novel Barkhausen effect (BE) probe with adjustable magnetizing field direction for the stress level evaluation in ferromagnetic materials. The investigated sample was in a form of a pipe, made of P91 steel that was anisotropic due to the production process. The measurements were performed before and after welding, revealing the influence of welding process on the residual stress distribution. As was observed, the process introduced high tensile stresses in the normal to the weld direction (which can be interpreted as a decrease of strongly compressive residual stresses present in martensitic steels). In addition to that, the paper presents investigations of the measurement set performance corroborating its applicability for Barkhausen effect signal measurements in the magnetically anisotropic materials. The signals obtained during manual rotation of the probe (typical method of BE measurements) are very similar to those recorded during automatic field axis rotation.