The suspected circumferential weld defects found in the pipeline inspection process were tested and studied. It was found that there was slag inclusion in the girth weld at 9 o’clock, which had not been found in the early stage or in the laboratory nondestructive testing process. The defects are most likely due to incomplete slag removal between layers and low welding wire energy. There was a root crack at the 6 o’clock position of the weld, and the crack length was 10 mm, which was close to the original film and the detection result of excavation. The misjudgment of the field rebeat and the laboratory test results may be caused by the pits in the weld cover and the bottom weld. The crack is caused by the crystal crack formed along the middle of the columnar crystal during the solidification process of backing welding due to the increase of residual stress caused by the reduction of welding layers and the group stress caused by the steel tube.
In this study, the performance test and defect anatomy analysis were carried out for a girth weld of the pipeline. The results of the girth weld tensile test, groove hammer break test and Vickers hardness test showed no obvious abnormality, and the impact toughness and bending test results were not ideal. In the conventional inspection process, it was found that there were tiny unfused girth welds at 6 o 'clock and 9 o 'clock positions, and the maximum direction size of defects on the wall thickness section was 1.57 mm. The defects at the position from 6 o 'clock to 7 o 'clock found by on-site X-ray detection were identified as the existing non-fusion defects by anatomical analysis, and should be considered as the root of incomplete welding defects that could not be completely eliminated during repair welding. The length and height of the defects are 9 mm and 1.38 mm.
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