Study on echo characteristics of buried defects in fillet welds of small-diameter branch pipes of pressure vessels by phased array testing

Small-diameter branch pipes are crucial components of pressure vessels, with potentially serious consequences if they fail. Nondestructive testing of buried defects in fillet welds has been challenging in the industry. Presently, phased array nondestructive testing technology is commonly utilized, but further research is needed to characterize the defects accurately. The fillet weld model of the actual specifications of the small-diameter branch pipe of the pressure vessel was simulated and analyzed by the CIVA software in accordance with pressure vessel specifications. The echo response law and characteristics of typical defects such as spherical holes, transverse through holes, incomplete fusion, incomplete penetration, and cracks were studied. The results show that the echo intensity is different for various defects compared to the signal of the end corner structure. The echo intensity of area defects is greatest when they are at an angle of 90° to the sound beam. Echo intensity can vary considerably when the same type of defect is located at different positions, with a maximum difference of 13 dB. Simulated specimens with typical defects were designed and fabricated, and the testing results of five typical defects were analyzed. The results show that the defects in the specimen can be effectively detected. The changing patterns of echo characteristics of different defects, as summarized in this study, can provide a reference and basis for characterizing defects in field inspection.