Tomography

Paul S. Fisk, President NDT Corporation

Pier in the power plant.

Integrity Testing of Switch Yard Piers

NDT Corporation conducted nondestructive sonic/ultrasonic measurements on 22 Piers in the switch yard of a Power Plant. The objective of this investigation was to obtain data to assist engineers in evaluating the structural integrity of the top 3 to 4 feet of the switch yard piers. Compressional wave velocity tomography was used for this investigation. This technique is used to construct a two-dimensional cross-section (slices) of the measured compressional waves through the interior of a concrete structure (see below). These tomograms can be used to locate and qualify local high and low velocity anomalies. Low velocity anomalies are indicative of zones of cracking, honeycombing, low strength concrete, and or voiding. The best results for this technique are obtained by numerous individual measurements with crossing wave-paths. Field recordings are obtained by position sensors on one side of a concrete structure and generating a signal with a projectile impact at multiple locations (independently) on the top and or opposing sides of a structure. This procedure is repeated switching the sensor array and energy source to the opposing side of the structure until multiple crossing signal wave paths have been obtained for the area of interest.

Tomography results: Pier with weak areas

Tomography results: Pier with weak areas