Measurement of flaws to a precision of a few percent in a pipeline would allowrnpipeline engineers to accurately calculate the remaining pipe strength and to determinernwhat mitigating actions to take without investigative digs at pipeline flaw locations.rnMagnetic flux leakage, the most often used technique for pipeline inspection, will neverrnreach that precision. Ultrasonic inspection is precise enough but traditionally requires arncouplant of some kind between the transducer and the pipe wall. For liquid productrnpipelines, ultrasonic inspection is already commercially available for both remaining wallrnthickness measurement and crack depth measurement. Since it is undesirable to introducernliquids into a gas transmission pipeline, we have developed a gas coupled ultrasonicrninspection method that does not require a couplant in pressurized pipe. Although thernsignals are small, with improved transducers and low noise electronics enough of a signalrncomes back to the ultrasonic transducer to accurately measure flaw size.
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