High temperature UT inspection techniques can be used to conduct random inspection on line on the key locations of pressure vessels and pipelines in operation so as to find out fresh defects in time and determine inspection time. It can also be used for real-time monitoring and control of defect-containing pressure vessels and pipelines and provide a basis for safety assessment of equipment so as to ensure safe operation of pressure vessels and pipelines. The propagation velocity of ultrasonic wave in metallic pressure-bearing equipment and its amplitude vary with temperature, therefore, the factors that influence UT inspection ability and measuring accuracy will be increased. In this paper the variation in sound velocity and attenuation law of ultrasonic shear wave in common pressure vessels and pipelines in the range of room temperature ∼ 450 °C is studied, the sound velocity decreases linearly as temperature rises and the attenuation coefficient α decreases as temperature rises, from 0.006 dB/mm at room temperature to 0.08dB/mm at 450 °C. The factors that influence inspection accuracy of ultrasonic shear wave are discussed, including variation in sound velocity, loss in interface sound pressure, thermal expansion, and so forth. The method for detection of weld defects within above temperature range using the ultrasonic shear wave is established, including scanning manner, measurement of defect height and length and their position correction, and so forth. The present situation of online high-temperature UT inspection technology for pressure vessels and pipelines in China is summarized through online UT inspection examples of petrochemical equipment under local high-temperature environment.

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