The indications are classified in three categories.
- Surface-breaking. The indication can be breaking the top surface or the bottom surface
- Embedded. The indication is entirely within the part
- Unclassified. Indications that cannot be classified in the two previous categories and need further testing and analysis
- To classify an indication, the following features are analysed:
- The lateral wave
- The backwall signal
- Signals between the lateral wave and the backwall
- Phase of the signals
- Signals between the backwall and the mode converted backwall
In TOFD, traditional classification like lack of side wall fusion or centerline crack are not used because it is very difficult to distinguish between them.