Electromagnetic (EM) sensor measurement for residual stress characterisation in welded steel plates

Residual stresses can cause compromise in structural integrity; it is desirable to assess residual stresses using non-destructive testing so that effects on structural properties can be predicted. Electromagnetic (EM) sensors can be used to characterise residual stresses in steels accounting for, microstructure and geometry effects. Residual stress characterisation in welded EN S275 steel plates using EM sensors is reported. Low-frequency, low-magnetic field EM sensors were used to assess residual stresses in the plates. A finite element model for the sensor and sample was generated in COMSOL software so the influence of weld bead geometry and microstructure could be predicted and accounted for. This allowed residual stresses to be determined from EM sensor measurements, excluding the geometry and microstructure effects, XRD was used to verify EM sensor measurements. The highest residual stresses were found adjacent to the weld fusion zone, with magnitudes of, 170±5MPa, 120±20MPa and 42±10MPa for X-ray diffraction (XRD), a small EM sensor (U-12.7) and a big EM sensor (U-31) types, respectively. The differences are due to the volume of the material measured by each measurement type. It was shown that EM sensors are capable of measuring residual stress in welded plates to a good level of accuracy.