Detection of stress concentrations around a defect by magnetic Barkhausen noise measurements

Abstract

The stress distribution around a 50% blind-hole pit in a steel pipe with a 9 mm wall has been studied using high-resolution magnetic Barkhausen noise (MBN) measurements. A magnetic disk read-head is used as the pick up coil in the MBN probe. The study shows a stress concentration factor of ∼2 at the defect edge perpendicular to the direction of applied stress and ∼−0.6 at the edge parallel to the same. The experimental results are consistent with the analytical solutions obtained by the Airy’s stress function approach.

Residual Magnetic Flux Leakage: A Possible Tool for Studying Pipeline Defects

“…The peak-to-peak value of the radial leakage flux (MFL pp ) is about 27.0 G. The shape of the flux pattern is well understood and has been reported by many workers. (12) Although the size and shape of the circular defect are not obvious from this contour map, some useful information can be obtained. For example, this type of circular defect is typically located between high positive and high negative flux regions, with its center almost on the zero flux line.…”

“…This is in spite of the fact that, even in the absence of applied stress, there exists a macroscopic easy axis that is parallel to the axis of the steel pipe section. (12,13) The active and residual MFL scans of the third defect, an irregular gouge, are shown in Figure 12. Although the actual length, width, and maximum depression of the gouge are about 125 mm, 26 mm, and 14 mm, respectively, the overall depression is not limited to an area of just 125 mm ϫ 26 mm because of depression of the surrounding region during the gouge formation.…”

A study of plastic deformation around a defect using the magnetic Barkhausen noise in ASTM 36 steel

“…These works document the dependence of the V rms of the MBN signal (measured in one point of the sample) with the plastic deformation. However, in some cases, it is important to know the deformation distribution around pits and cracks [17][18][19][20][21]. The analysis of pits in steel structures such as pipelines are usually performed using the magnetic flux leakage (MFL) method [17][18][19][20].…”

Factors Affecting Stress Concentrations Near Pit Defects, as Monitored by Magnetic Flux Leakage, Magnetic Barkhausen Noise, and Neutron Diffraction

“…This stress concentration around a defect can be measured directly by neutron diffi"action [2] and photo-elasticity measurements [3]. We also measure stress concentrations indirectly using the magnetic Barkhausen noise (MBN) technique [4].…”