Stage 1 Round-Robin Report: On the Use of Total Focusing Method for Sizing Flaws in Assessing Probability of Detection

Abstract

Reliability of non-destructive (NDT) procedures is usually assessed using probability of detection (POD). However, the reliability of the POD is rarely questioned. A POD usually produces a curve that relates the size of a defect to the likelihood that it will be detected by the NDT procedure. PODs are often used in conjunction with fracture mechanics that can relate the severity of a flaw to the service life of a component (Fitness for Service or FFS). To this end, it is the flaw vertical extent relative to the component thickness that is important. Closely related to the concern for flaw height is how close the flaw is relative to the surface of the component. Proximity to a surface can increase the stresses raised by the flaw and make it more critical to the fitness for service. Use of full matrix capture (FMC) techniques in ultrasonic testing, in conjunction with the postprocessing use of Total Focussing Method (TFM), has shown good potential to provide accurate flaw sizing. This paper examines the results of a round-robin trial using CIVA simulated data that were configured to assess flaw height and ligament in simulated welds. Results suggest that FMC with TFM post-processing can provide sizing estimates as good or better than manufacture estimates and can be used as the actual measured values for POD assessments.