Ultrasonic flaw detectors play a crucial role in pressure vessel testing, as they identify defects by emitting and receiving reflected waves based on the propagation characteristics of ultrasonic waves in materials. In pressure vessel inspection, this technology is mainly used for detecting internal defects in welds, such as cracks, lack of fusion, etc., especially suitable for the inspection of thick walled vessels (thickness exceeding 30mm).
Testing methods and advantages
The commonly used A-type pulse reflection method is suitable for detecting steel plates, forgings, and welds through longitudinal wave vertical detection and transverse wave oblique incidence detection, respectively. Compared with radiographic testing, ultrasonic testing has stronger penetration power for thick workpieces, can more sensitively detect area type defects (such as cracks), and more accurately locate defects in the thickness direction of the workpiece. In addition, ultrasonic testing has the advantages of fast speed, low cost, portable instrument, and no radiation, which is harmless to the operator's body and easy to use on site.
Practical cases and effects
During the regular inspection of pressure vessels in a certain chemical plant, ultrasonic testing found that the longitudinal weld seam of V-301 flash tank had an excessive defect (length 43mm, depth 13-20mm), while radiographic testing failed to detect it due to the small opening width of the defect (0.01-0.02mm). This indicates that ultrasonic testing has a stronger ability to detect planar defects, especially suitable for weld seam detection of thick walled containers. Through defect repair verification, the ultrasonic testing results are accurate, and the defect nature is white interlayer unmelted with signs of cracking, providing a reliable basis for the safety assessment of pressure vessels.
Operation points and precautions
When detecting, the detection surface should be selected according to the possible direction of the defect, so that the ultrasonic beam is perpendicular to the main reflection surface of the defect. At the same time, it is necessary to regularly check the status of the probe, replace worn probes in a timely manner, and pay attention to the use of coupling agents to eliminate air between the probe and the workpiece surface, ensuring the accuracy of the detection results.