Ultrasonic Stress Measurement and Material Characterization in Pressure Vessels, Piping, and Welds

Abstract

A pressure vessel has been constructed for demonstrating the LCR ultrasonic technique for indicating changes in wall and weld stress. A special contoured LCR probe was designed and constructed, and the pressure vessel was fitted with strain gauges for monitoring the wall stress. At low wall stresses, below 4 ksi (26 MPa), the ultrasonic data showed considerable scatter. There is similar scatter in the zero pressure travel-times at individual locations around the vessel. At wall stresses of 4 ksi (26 MPa) and above, however, there is an almost linear relationship of stress and travel-time change. Measurements adjacent to an end weld also showed very good trends. Plots of travel times approaching a weld predict −27.5 ksi (−190 MPa) at 1 in. (25 mm) from the weld, compared to zero stress at 5.6 in. (142 mm) away from the weld. These results are consistent with results obtained by others on a similar weld using the blind hole drilling method.