Abstract: A new ultrasonic method for measuring wall thickness and detecting material flaws in natural-gas pipelines, risers, and similar structures. The method is inherently suitable for the task, because it relies on the use of the natural gas as the coupling fluid for transmitting the probing ultrasonic signals into and out of the pipe wall. Furthermore, the method facilitates the operation of the inspection from the inside of the pipe. An experimental apparatus used to demonstrate the technical feasibility of this approach and provide experimental and theoretical evidence that support the claims is described. Significantly, it is shown that by the use of a diplexer, the same transducer can be used to generate and detect the probing ultrasonic signals. The same configuration is used in commercial ultrasonic inspection of oil pipelines where oil is the coupling fluid; but until now this method could not be used in natural gas pipelines due to the low specific acoustic impedance of natural gas.

Abstract: An ultrasonic calibration block for standardizing an output of a pulse-echo ultrasonic inspection system is provided with an insonification surface for receiving ultrasonic pulses from the inspection system and a plurality of reflective interfaces stacked on top of one another and positioned at different distances from the insonification surface, each reflective interface having a different and characteristic reflectivity. A method of calibrating the output of the inspection system, using the calibration block, employs standard waveforms generated by insonifying the calibration block to generate a look-up table of standard waveform amplitudes related to a standardized output of the inspection system for a given material of a part to be inspected.

Abstract: An apparatus for characterizing a surface anomaly in an electrically conductive sample includes an oscillator with an amplifier for supplying gain to the oscillator, a feedback loop linking the input and output of the amplifier, a two port ferromagnetic resonator connected within the loop to modulate the level and frequency of oscillation of the oscillator in response to eddy currents induced in the surface of the sample by the resonator, a variable attenuator connected within the loop to adjust the power level of the oscillator, and an adjustable phase shifter connected within the loop for changing the total phase shift of the loop. A sensing circuit is operably connected to the output of the amplifier to monitor the resonance parameters of the oscillator.

Abstract: Disclosed is a method for generating an ultrasonic wave in a material, utilizing a transducer adapted to induce a higher than fundamental mode wave in the material and a signal generator adapted to drive the transducer at a frequency above the cutoff frequency below which the higher mode wave will not propagate. For a horizontal shear wave, optimal transducer efficiency is obtained by selecting a driven frequency between a minimum cutoff frequency f.sub.c =v.sub.s n/2t and an upper frequency sufficiently close to f.sub.c to drive the transducer with at least a preselected increase in efficiency.

Abstract: Disclosed is an electromagnetic acoustic transducer for generating and detecting an elliptically polarized ultrasonic wave in an electrically conductive material. The transducer includes a row of uniformly sized, adjacent, alternately oriented permanent magnets, which establish a periodic magnetic field. Coaxially wound around the row is a first coil for inducing an alternating current perpendicular to the field and perpendicular to the periodic direction, while a second coil is wound around the coil orthogonal to the first coil to induce an alternating current perpendicular to the field and parallel to the periodic direction. An ultrasonic ellipsometer includes such a dual coil transmitting transducer for generating an elliptically polarized wave and a dual coil receiving transducer for detecting the wave after it has propagated through an electrically conductive medium.

Abstract: A method and an apparatus are provided for ultrasonically inspecting a cylindrical object. The object is placed between the poles of a magnet to create a circumferential magnetic field in the object. A group of electromagnetic transducers (EMAT's) are placed adjacent the material so that the transducers scan the entire object when it is rotated. When an RF signal is applied to the transducers, elastic waves are generated in the material. These elastic waves reflect from defects in the material and these reflections are received by the transducers.

Abstract: A surface acoustic wave bridge for rotation measurement which uses acoustic waves propagated in opposite directions about the circumference of a rotor. The acoustic waves are generated by a transducer adjacent the rotor which is excited by an rf electric field. Clockwise and counterclockwise waves in the surface of the rotor interfere with each other adjacent the transducer to form a bridge system which produces a null when the waves are out of phase. The rf frequency of the electric field is varied to obtain the null and, thus, is a measurement of the rotation rate of the rotor.For the measurement of slow rotation rates two transducers are used to generate the counterrotating acoustic waves in a helical pattern such that the acoustic wave generated by one transducer is received by the other. The outputs of the transducers are detected and provide an approximately linear measurement of slow rotational rates.