Building TFM Procedures for ERW Hook Crack, Girth Weld, HTHA, and Other Challenging Inspections

FMC and TFM have shown some improvement in specific applications in the past few years. However, inspectors using this method are often subject to a lot of trial-and-error to achieve the optimal results. Many challenges are still encountered when selecting a propagation mode in TFM inspection; for example, effectively preventing blind spots, confirming the angle of reflection, or optimizing for preferential gain direction, etc. The selection of the most appropriate mode of propagation (or, imaging path) is critical for an effective TFM inspection and is often problematic and still esoteric for the inspectors. Selecting the right mode of propagation requires extensive procedure development on simulation software to ensure proper detectability and perpendicularity of the beams with the reflectors (defects). The Acoustic Influence Map (AIM) simulator, is a theoretical amplitude representation (color map) of the region of interest, mode of propagation, and type of reflector selected for the TFM inspection. When the AIM tool is used, multiple imaging paths can be combined to obtain the optimal probability of detection (POD) for a given indication or damage mechanism. In this presentation, we will describe a wave propagation modeling technique that calculates the predicted signal response in the TFM zone created for both pulse-echo and self-tandem modes of propagation. Many applications will be covered to show the advantages and improvements offered for the detection for specific damage types, including hook cracks in electric resistance welding (ERW), defects that can appear parallel to the scanning surface, or in high temperature hydrogen attack (HTHA), a damage mechanism where the micro-fissuring can occur in different directions and locations within the part.