Measurement and calibration of sound velocity for AUT in girth welds of pipelines

The measurement and calibration of sound velocity are the first step in conducting ultrasonic non-destructive testing for pipeline girth welds. Different materials, wall thickness, measurement direction, and waveform all have an impact on the sound velocity in steel. This paper discussed the equipment, sample preparation, and measurement procedures for automatic ultrasonic testing technology of sound velocity measurement based on GB/T 50818—2013 “Mechanized ultrasonic testing technology specification for oil & gas construction pipeline project”. According to the pulse reflection method and Snell′s law, a sound velocity measurement system was built by CPP-PRI-AUT system, shear wave probe and CPP-PRI upper computer program. The fast and slow shear horizontal waves of the sample in three directions of 0°, 70° and 90° were measured. The corresponding propagation velocity was calculated and the sound velocity calibration of the AUT system was carried out. Finally, on the basis of ensuring the focusing effect of the defect ultrasonic beam, the allowable error of pipeline steel sound velocity was analyzed.