Time of flight diffraction technique TOFD - an alternative to radiography?

Review of a regional DGZfP working group meeting.

TOFD Lecture - Podium Discussion

By Rolf Diederichs

TOFD lecture:

O. A. Barbian - Heckhäuser - Prof. V. Deutsch - Dr. Bouma - K.-H Gischler

Podium Discussion:

    In the podium discussion, the majority of participants warned of disadvantages of the TOFD method. TOFD can solve specific problems but can not replace other established methods. The panel's major statements are summarized herein:

    O. A. Barbian , Pipetronix
    Cracks with cleft edges are almost impossible to see. TOFD is very undefined. It could be good applied as an in-service inspection but an exact protocol for all parameters must be established. TOFD is good for sizing. Generally speaking, the physics should be investigated first, and the standard developed after that.

    Heckhäuser , Gottfeld
    It's a good method for homogeneous materials. It was successfully applied for turbine blade testing. A precondition is that the crack edges are very clear. Since TOFD is fast it can be good for repeated testing.

    Prof. V. Deutsch , Karl-Deutsch
    TOFD works similar to the Delta Technique [6]. Some specific cracks can not be found. First comes the method and then we look for an application - that is not the right way; in the past it was the other way around.

    Dr. Bouma , RTD (NL)
    He has specialized in TOFD since 1993, and works with a team of 10 at RTD. He introduced the good results of the Netherlands welding institute (NIL) study. TOFD showed 90% POD in contrast to pulse echo, which showed only 50%. (The audience was critical of these results; the majority felt the study was not objective.) It is possible to test welds of 6 mm part wall thickness. The technique must be investigated more. TOFD is not a technique for all tasks.

    K.-H Gischler , Gischler
    He mentioned some bad experiences with tests performed on parts under 10 mm wall thickness. The method is a good add-on but can not replace other methods.

    Dr. Ewert , BAM
    The test standard should be fulfilled; that should be the priority, not "the cheaper method wins."



For more information see: TOFD in UTonline 09/97

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