Calibration and flaw detection method for ultrasonic inspection of acoustically noisy materials
First Claim
1. In a nondestructive testing system for performing ultrasonic inspections, including a processor for controlling the positioning of at least one ultrasonic transducer element with respect to a surface of a specimen under test, acquiring, digitizing and preserving ultrasonic measurement data produced at least in part from internal scattering of ultrasonics signals in the specimen, and performing calculations based on said data, a method for dynamic automatic adjustment of a flaw/defect detection threshold, comprising the steps of:
- (a) scanning a surface of a specimen under test in a predetermined pattern with at least one transducer and operating at least one transducer that is used for said scanning to acquire groups of ultrasonic measurement signal data corresponding to a plurality of ultrasonic test data points arranged within distinct planes, said distinct planes defined substantially parallel to the scanned surface of said specimen;
(b) calculating a unique signal-to-noise (S/N) ratio value corresponding to each test point of said plurality of ultrasonic test data points in a particular plane of said distinct planes based on a rolling average of signal levels measured over an area localized about each of said plurality of ultrasonic test data points acquired in step (a); and
(c) setting a flaw/defect detection threshold level for said particular plane in said specimen based on a predetermined function of a standard deviation value of all S/N values calculated for said particular plane in step (b).
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Abstract
A method and apparatus for the ultrasonic inspection of acoustically "noisy" specimens, such as those having intrinsically coarse grain structure (e.g., turbine rotor parts made of superalloy compositions) employs several types of ultrasonic diagnostic measurement techniques, including at least: "Pitch-Catch" analysis and "Pulse-Echo Axial Long-Wave" analysis. When a Pitch-Catch technique is utilized, a "through-transmitted" sound wave is acquired for each specimen tested and used as a calibration standard to normalize ultrasonic inspection test data for that specimen prior to any automated defect/flaw detection and sizing processing. The through transmitted sound wave is also used to equate the amplitude of "indications" (i.e., significant detected ultrasonic reflections) to that of a standardized theoretical reflector of known size (e.g., an equivalent "flat bottom hole" or EFBH reflector) so that the test sensitivity or "size of indications" can be uniquely determined for each specimen on which the test is performed. When a Pulse-Echo technique is utilized, a through-transmitted sound wave is not used (since this technique employs only a single transducer) and inspection data is instead normalized by a "back wall" reflection signal. Once ultrasonic inspection test data is obtained and digitized, a "rolling average" of the data is used to estimate the localized noise level within the material under test. For every transducer pulse data point obtained, a unique signal-to-noise (S/N) ratio is computed. Variations in S/N ratio for the material are measured at each axial slice of material volume inspected. A function of the standard deviation of the S/N values is then used to automatically adjust a detection amplitude threshold to optimize the flaw detection process and minimize false alarms.
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Citations
20 Claims
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1. In a nondestructive testing system for performing ultrasonic inspections, including a processor for controlling the positioning of at least one ultrasonic transducer element with respect to a surface of a specimen under test, acquiring, digitizing and preserving ultrasonic measurement data produced at least in part from internal scattering of ultrasonics signals in the specimen, and performing calculations based on said data, a method for dynamic automatic adjustment of a flaw/defect detection threshold, comprising the steps of:
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(a) scanning a surface of a specimen under test in a predetermined pattern with at least one transducer and operating at least one transducer that is used for said scanning to acquire groups of ultrasonic measurement signal data corresponding to a plurality of ultrasonic test data points arranged within distinct planes, said distinct planes defined substantially parallel to the scanned surface of said specimen; (b) calculating a unique signal-to-noise (S/N) ratio value corresponding to each test point of said plurality of ultrasonic test data points in a particular plane of said distinct planes based on a rolling average of signal levels measured over an area localized about each of said plurality of ultrasonic test data points acquired in step (a); and (c) setting a flaw/defect detection threshold level for said particular plane in said specimen based on a predetermined function of a standard deviation value of all S/N values calculated for said particular plane in step (b). - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. An automatic flaw/defect indication and dynamic detection threshold adjustment technique for ultrasonic inspection of acoustically noisy materials, comprising the steps of:
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(a) scanning a surface of a specimen under test in a predetermined pattern with at least one transducer and operating said transducer to acquire groups of ultrasonic measurement signal data corresponding to a plurality of ultrasonic test data points arranged within a plane within said specimen; (b) calculating a unique signal-to-noise (S/N) ratio value corresponding to each test point in said plane based on a local noise level proximate to each test point wherein said local noise level is computed as a rolling average of ultrasonic measurement signal levels proximate each test data point of measurement data acquired in step (a); (c) defining a flaw/defect detection threshold level for said plane based on a predetermined function of a standard deviation value of all S/N values calculated in step (b); (d) repeating steps (a) through (c) for each plane inspected within said specimen, whereby said flaw/defect detection threshold level is dynamically reset for each plane; (e) indicating a flaw/defect condition at a test point whenever a measured signal level at said test point is substantially equal to or greater than twice said flaw/defect detection threshold set in step (c). - View Dependent Claims (17, 18, 19, 20)
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Specification