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Defect Depth Calculation

The depth of a object such as a defect can be determined by taking two exposures with the source shifted in second exposure.  As shown in the image, a marker is placed on the surface of the component.  Two radiographs are produced with the alignment between the source and the specimen different for each exposure.  Using the following equation, the depth of the defect can be determined by relating the shift of the defect to the shift in the marker in the two radiographs.  

     

      Where: D = Defect depth
                    t = thickness of the component
                 SD = Shift of defect in the radiographs
                 SM = Shift of marker in the radiographs

Example Calculation
When radiographing a component with a thickness of 1.5 inches, a defect is detected.  A second radiograph is produced with sample shifted relative to the center of the source cone beam.  A penetrameter on the surface of the component is found to shift 0.45 inch between the two radiographs.  The defect is found to shift 0.18 inch between the two radiographs.  Determine the depth of the defect.

Substitute known values into the equation and solve for defect depth.