A New Insight on Phased Array Ultrasound Inspection in MIG/MAG Welding

Abstract

Weldment inspection is a critical process in the metal industry. It is first conducted visually, then manually and finally using instrumental techniques such as ultrasound. We made one hundred metal inert/active gas (MIG/MAG) weldments on plates of naval steel S275JR+N with no defects, and inducing pores, slag intrusion and cracks. With the objective of the three-dimensional reconstruction of the welding defects, phased array ultrasound inspections were carried out. Error-free weldment probes were used to provide the noise level. The results can be summarized as follows. (i) The top view obtained from the phased array provided no conclusive information about the welding defects. The values of the echo amplitudes were about 70 mV for pores and cracks, and greater than 150 mV for slag intrusion, all of which showed great variability. (ii) The sectional data did not lie at the same depths and they needed to be interpolated. (iii) The interpolated sectional views, or C-scans, allowed the computation of top views at any depth, as well as the three-dimensional reconstruction of the defects. (iv) The use of the simplest tool, consisting of the frequency histogram and its statistical moments, was sufficient to classify the defects. The mean echo amplitudes were 33 mV for pores, 72.16 mV for slag intrusion and 43.19 mV for cracks, with standard deviations of 8.84 mV, 24.64 mV and 12.39 mV, respectively. These findings represent the first step in the automatic classification of welding defects.

Advanced Comparison of Phased Array and X-rays in the Inspection of Metallic Welding

“…All weldments were visually inspected. The schematic cross-section is shown in Figure 1 , and it is basically the same as that used in [ 25 ].…”

“…When some very short copper or steel wires, with a fusion point much lower than the temperature of the torch, are added, a crack is induced. The qualitative analysis of the specimens can be found in [ 25 ].…”

“…Finally, three more runs for welding combing cord with 210 A, 26 V and the same gas shielding. All specimens were performed by a professional welder technician at the School of Naval and Ocean Engineering of the University of Cádiz [ 25 ]. All the specimens were inspected using PA and two specialists and a level III inspector in weld quality classified the different defects.…”

“…This means that the instrumental response was the same in any stage of the inspection. The setup of the equipment was carried out by InnerSpec [ 25 ].…”

“…Then, a quantitative comparison to compute how similar the top views from X-rays and PA are and to estimate the depth in the weldment where the PA inspection corresponds to the X-ray results. This is the main contribution of this study and most of the methodology follows [ 25 ].…”