Zongqi Sun

Analysis of flexural mode focusing by a semianalytical finite element method

Focusing is one of the most promising techniques for the detection of small defects in pipe works, in which guided waves including longitudinal and flexural modes are tuned so that ultrasonic energy can be focused at a target point in a pipe, and analysis of reflected waves gives information on defects such as location and size. In this paper, the focusing technique is discussed by way of a simulation of guided wave propagation in pipe by a semianalytical finite element method (SAFE). Experiments and SAFE calculations were compared for waveforms transmitted by a single transducer and received at different circumferential positions initially, and then the focusing phenomena were experimentally observed using focusing parameters obtained by calculations. Calculation and visualization were conducted to clarify focusing phenomena in pipe in investigating the potential of the focusing technique. These results show that the time-reversal idea helps in understanding focusing and that resolution of focusing is strongly affected by incident waveforms as well as the number of channels available in an experiment.

Flexural Torsional Guided Wave Mechanics and Focusing in Pipe

Theoretical work on flexural torsional guided waves in pipe is presented along with angular profile experimental justification. Combined with previous work on flexural longitudinal modes and axisymmetric longitudinal and torsional modes, this work now forms a framework of nonuxisymmetric guided wave mechanics in pipe. Pipe inspection experiments are also carried out by flexural torsional. wave focusing to demonstrate the advantages of the focusing technique.

Guided Wave Focusing Mechanics in Pipe

Guided waves can be used in pipe inspection over long distances. Presented in this paper is a beam focusing technique to improve the S/N ratio of the reflection from a tiny defect. Focusing is accomplished by using nonaxisymmetric waveforms and subsequent time delayed superposition at a specific point in a pipe. A semianalytical finite element method is used to present wave structure in the pipe. Focusing potential is also studied with various modes and frequencies.

Ultrasonic Flexural Torsional Guided Wave Pipe Inspection Potential

The excitation and propagation characteristics of guided wave torsional flexural mode are exploited in this paper. Theoretical computations and experiments are carried out to show the angular profiles of the torsional flexural modes propagation characteristics and the subsequent natural focusing effects. Because of such inherent advantages as less mode conversion and high sensitivity to axial defects, torsional modes and focusing possibilities have great potential in pipe inspection. By combining longitudinal and torsional modes, defect characterizations including defect size, shape etc. can be determined by truly three-dimensional guided wave pipe inspection.© 2003 ASME

Flexural mode tuning in pipe inspection

The ability to carry out a complete pipe inspection with limited access to say 180 degree or less of the circumference is often necessary. Techniques are introduced to make this possible by flexural mode and focusing control via a four dimensional tuning process of adjusting circumferential loading length, position, phase and frequency. Theoretical experiments demonstrate the tuning process.

Non‐Axisymmetric Wave Focusing in Pipe Inspection

Non‐axisymmetric guided waves have been applied to pipe inspection recently. Due to the non‐axisymmetric characteristics of the waves, the circumferential displacement distribution is non‐axisymmetric. It shows a natural focusing phenomenon. With the aid of a circumferential transducer array, we developed an algorithm to focus wave energy at arbitrary locations. The algorithm is based on applying different amplitude and time delay to each of the excitation elements. A series of experiments were carried out to show the focusing effect.

Experimental Phased Array Focusing in Pipe Using Ultrasonic Guided Waves

The phased array focusing technique is being developed with the intent to inspect hundreds of feet of pipeline from a single array position. The single array position is beneficial if access to a pipe is limited, e.g. steam pipes onboard U.S. Naval ships, nuclear power plants, oil and gas pipelines, etc. From a single array position, ultrasonic guided waves propagate down the length of the pipe and return information about potential defects. Focusing the ultrasonic energy at a predetermined location along the length of the pipe enhances the ability to detect defects that current state of the art inspection systems cannot detect. In this paper, theoretical time delays are used to focus torsional ultrasonic guided waves in the frequency ranges of 30 to 130 kHz and 200 to 800 kHz. Results of the focusing experiments are presented along with some concluding remarks and future work.

Semi Analytical Finite Element Analysis for Ultrasonic Focusing in a Pipe

Guided wave focusing has been developed as a promising technique for defect detection in pipeworks, where non‐axisymmetric flexural modes are tuned so that ultrasonic energy can be focused at a target point in a pipe. If a defect is located at the target point, large amplitude reflected waves can be observed. In this study, the focusing phenomenon is analyzed using a semi‐analytical finite element method where a region of a pipe is divided in the thickness direction into the cylindrical subdivisions and is analytically treated in the circumferential and longitudinal directions. Visualization of the calculation results reveals that focusing occurs gradually in the vicinity of the target point.

Flexural Longitudinal and Torsional Mode Natural Focusing Phenomena in a Pipe

Non‐axisymmetric guided waves including flexural longitudinal and flexural torsional modes have shown natural focusing characteristics in pipe inspection. A flexural torsional mode theory was developed in this paper based on flexural longitudinal mode theory. Flexural mode experiments were then carried out to show the natural focusing phenomena.

Calculation of Guided Wave Scattering at a Defect in a Pipe

Guided wave calculation using a semi‐analytical finite element method is described in this study. Two dimensional discretization modeling and its optimization technique by the use of the symmetry of a pipe are developed for wave propagation in a pipe with a defect. The effect of guided wave focusing, having been developed by Penn State group, is investigated for torsional waves.