Abstract

4.1. State of the Art
Testing of austenitic and dissimilar metal welds is generally limited, since truly homogeneous ultrasound wave propagation does not exist. The testing and manufacturing methods must find economical solutions for achieving testability for those components. With today's advantages in forgings and welding processes a more homogeneous grain size could be achieved and the ultrasonic propagation will possibly be more quantifiable in the future. In practice, test examples show promising results for crack testing in the near surface and volume zones, this can be achieved by using Transmitter Receiver Longitudinal Probe Techniques (German term: SEL).

There are disadvantages for crack shaped reflectors in the probe far-surface area since the corner effect for longitudinal waves is weak. This disadvantage may be improved in the future by use of horizontal polarized shear waves (abbr. T_H or S_H) which can be generated with Electromagnetic Acoustic Transducers (EMAT or EMUS for the German term). Very early mechanized measurements in reference standards for composite welds show great potential for EMAT-S_H -Techniques. Test validation should be always checked by using the same type of reference standards.