SYNTHETIC PULSE METHODS FOR ULTRASONIC NONDESTRUCTIVE EVALUATION (NDE)

LARGE-GRAIN MATERIALS ARE DIFFICULT TO INSPECT WITH CONVENTIONAL ULTRASONIC NONDESTRUCTIVE EVALUATION (NDE) METHODS. THIS IS PARTICULARLY TRUE OF THE CEN- TRIFUGALLY CAST STAINLESS STEEL USED FOR COOLANT PIPING IN PRESSURIZED WATER REACTORS (PWR). REDUCED TEST FREQUENCIES MUST BE USED TO PENETRATE THE MATERIAL. HOWEVER, A CORRESPONDING DECREASE IN NEAR-SURFACE RESOLUTION IS INCURRED RESULTING IN A MARGINAL TEST FOR WELD FLAWS. THE PLANNED WORK WILL EVALUATE A POTENTIAL TECHNIQUE FOR COMBINING DEEP PENETRATION WITH EXCELLENT NEAR-SURFACE RESOLUTION. THIS TECHNI- QUE SYNTHESIZES A BROADBAND IMPULSE BY TESTING THE PART WITH A SERIES OF DISCRETE TEST FREQUENCIES. THE FOURIER COEFFICIENTS OF EACH FREQUENCY ARE STACKED TOGETHER TO BUILD A CONTROLLED SPECTRUM. TAKING THE INVERSE FOURIER TRANSFORM RECONSTRUCTS A BROADBAND PULSE THAT SHOULD CONTAIN THE DESIRED FLAW INFORMA- TION. AN OUTSTANDING ADVANTAGE OF THE TECHNIQUE IS THAT THE INDIVIDUAL SPECTRAL COMPONENTS MAY BE AD- JUSTED TO OPTIMIZE THE OUTPUT PULSE.