Session: 08 - 01 NDE for Civil Infrastructure

Paper Number: 117895

117895 - Time-of-Flight Diffraction Inspection Errors From Calibration 

This study addresses Time-of-Flight Diffraction (TOFD) sizing errors due to the differences between the calibration and the actual measurements. Probe center separation (PCS) and sound velocity are two parameters that may be calibrated for accurate measurement of the flaw depth and height in a test object. The investigated aspects are: difference between the calibration and the target depth in the test object, different sound velocities (due to different material properties and temperature between the calibration block and the test object) and a painting layer on the test object surface. The target inspection scenario is a steel test object with wall thickness 35-50mm and weld flaws located near the back wall. A calibration/inspection procedure and a TOFD instrument in accordance with ISO10863 and ISO16828 are assumed. The analysis method follows: 1) given a TOFD instrument with a PCS and a calibration block with a true sound velocity, times-of-flight (ToF) of the echoes are estimated using geometrical considerations. 2) The calibrated PCS and sound velocity are set close to the true values. 3) A test object is characterized by a true flaw depth and heigh, true sound velocity and an effective PCS that depends on the painting layer characteristics. This leads to ToFs of echoes in the test object. 4) The flaw depth and heigh are recalculated using the ToFs in the test object and the calibrated parameters. 5) The error is defined by the difference between the recalculated and the true flaw depths and heights. By varying individual parameters in steps 1) to 4), the sizing errors that originate from the calibration process are characterized. An inspection is simulated using a 2D numerical model to support the analysis. Among the addressed aspects, errors in sound velocity potentially lead the highest sizing errors. The accuracy of the flaw depth is more affected than the accuracy of the flaw height.

Presenting Author: Dênis Takeo Goto Eindhoven University of Technology

Presenting Author Biography: Dênis Goto is a PhD candidate in the field of ultrasonic non-destructive evaluation (NDE) at Eindhoven University of Technology. During his previous academic studies in the field of mechanical engineering, he worked with shearography, a non-destructive optical interferometry technique. He also worked with design of repairs for flaws inspected and sized using NDE in the aerospace industry.