Influence of sensitivity direction and lift-off on weld macro defects by magnetic memory testing

In this study, the factors that affect macro defects in butt weld specimens of carbon steel detected using the magnetic memory method (MMM) are experimentally analysed. The characteristics of magnetic memory signals with different sensitivity directions and lift-off values are also studied. Test results show that the distribution laws of magnetic anomalies in different sensitivity directions under the same lift-off are consistent with one another. Under the same sensitivity direction and increase in lift-off value, the detection curve tends to flatten. The magnetic induction intensity at the position of the defect decreases, thereby impairing the analysis capability of the defect signal. When the lift-off value is less than 20 mm, the magnetic anomaly of the two defects presents a good resolution. Moreover, metal magnetic memory testing has a certain sensitivity direction for defect recognition. The characteristics of volumetric defects detected along the y-direction are evident, whereas planar defects are better judged in the z-direction.