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Graphical method to asses the critical defect size of a linear indication found by UT/PAUT

Wednesday (27.05.2020)
10:20 - 10:40

Abstract for FDMD4 conference.

P.A. Deschênes, D. Thibault

Prior to the exploitation of new or repaired turbine runners, Ultrasonic Testing (UT) or Phased Array Ultrasonic Testing (PAUT) are commonly used as inspection methods to ensure no critical defects are present in welded regions. This work presents a new methodology to assess the acceptability of linear indication measured by UT/PAUT. This method allows engineers and UT technicians to diagnose any linear indication found in the bulk using a colored contour map of the inspected section specifying the local maximum permissible size defect, 2c. It can be constructed using any kind of vector field and type of defects. This method applies the stress field of a particular section of the bulk on a typical defect found in the majority of fracture mechanics handbooks. Two major steps must be performed prior to calculate the map: 1-extraction of the stress distribution on a plane within the bulk from the FEA model and 2- calculation of the severity of the crack-like defect using a Kitagawa diagram for each node of the stress distribution previously extracted. From this information, one can draw a map of the critical crack-like defect that can be embedded in the bulk at node locations, taking into account the stress gradient, if there is any, the stress field, the distance between the surface and the threshold value. The figure 1, shows a typical representation of the map obtained:

The method has been applied on the data collected during a turbine runner inspection. Both Hydro-Québec and GE collaborated during this investigation.


Additional Authors:
  • Dr. Denis Thibault