Standard Practice for Flaw Sizing using Total Focusing Method

Importancia y uso:

5.1 Flaws that are made during manufacturing or that occur during service of a component have the potential to cause the component to fail. NDT methods such as described in Practice E2700 are intended to locate flaws that have the potential to result in component failure. Since not all flaws will result in failure, it is desirable to have a means of assessing the dimensions of flaws so that fracture-mechanics engineering calculations may be used to assess if the component is still fit for service if the flaw is left unrepaired.

5.2 When an NDT procedure is being evaluated for reliability using probability of detection (POD), standards such as Practices E2862 and E3023 can be used. These would require that flaws are intentionally placed in components. POD calculations require a high degree of accuracy of flaw sizes to ensure that the POD correctly indicates the reliability of the NDT procedure.

5.3 TFM has been demonstrated to provide accurate flaw sizes for both vertical extent and ligament to surface. In fine-grained steel, dimensional error can be less than 1 mm.

5.4 Although TFM has, on occasion, been used as a detection method, it can have limitations in that capacity. Without prior knowledge of flaw orientation, multiple combinations of mode-reconstruction are required. As well, the FMC method of data acquisition relies on single elements in transmit and receive mode, which for thicker section may result in weak signals due to attenuation and scatter noise. Using PWI instead of FMC as the acquisition mode can improve the strength of transmitted pulses; however, the resulting plane waves may not always provide the optimum angle to produce the required backscattered signals.

5.5 TFM reconstructions should always consider the modes that should be used to obtain optimum tip-diffraction signals for sizing and the best modes to obtain specular reflections to characterize flaw shapes.

5.6 TFM need not be limited to sizing flaws detected by just ultrasonic test methods. Where access permits, TFM may be an effective option for accurate sizing of flaws detected by other NDT methods.

Subcomité:

E07.06

Volúmen:

03.04

Palabras clave:

flaw sizing; full matrix capture; plane-wave imaging; total focusing method; ultrasonic;