2013 IR&D Annual Report

Guided Wave Imaging Technology Development, 18-R8289

Principal Investigators
Jay L. Fisher
Adam Cobb

Inclusive Dates: 02/01/12 – 11/01/12

Background — SwRI is a leader in developing and applying ultrasonic guided waves for nondestructive evaluation (NDE), particularly using its magnetostrictive sensors (MsS). One of the limitations of these sensors is that they must be bonded or otherwise well-coupled to the surface of the part being inspected to transfer mechanical wave motion directly to the part. The purpose of this project was to develop specific technical elements needed to advance SwRI's ultrasonic guided-wave technology for inspection of piping and plates, especially for cases where it is not feasible or desirable to bond MsS to the part under inspection. In particular, this project focused on developing electronics that could be used to operate electromagnetic acoustic transducer (EMAT) sensors. These sensors generate the wave motion directly in the part using electromagnetic forces, but they are much less efficient.

Image: Dual channel pulser/receiver board final design, before installation in enclosure
Figure 1. Dual channel pulser/receiver board final design, before installation in enclosure.

Approach — The primary goal was the design of a prototype high-power, low-frequency 2-channel pulser (for direction control or power doubling) and receiver electronics that could be used with new, low-frequency EMAT sensors to generate and receive ultrasonic guided waves. A secondary goal was to implement the beam-forming algorithm, critical to combining data from sensors at multiple positions around the pipe or plate being inspected into SwRI’s enhanced data acquisition system (EDAS®). The use of EMAT sensors that can be easily moved across the part surface enables the convenient collection of data for analysis with the beam-forming software.

Accomplishments — The high-power, low-frequency, 2-channel pulser and receiver electronics were developed by modifying an existing single-channel higher frequency design. Each channel provides multi-cycle tone bursts of more than 100 amperes into a 1-ohm load for use with low-frequency EMAT sensors. The two channels are delayed relative to one another to steer or increase the strength of the generated guided wave. The prototype unit will be used on at least one funded project and was the basis for the pulser design used in the MsSR4040SF, a pipeline inspection tool currently under development. The beam-forming algorithms were improved over previous implementations, and clearly improved SwRI's ability to localize flaws in the direction orthogonal to the beam direction. The signal-to-noise ratio (SNR) improvement was dramatic; in the case of a 1-percent cross-sectional area flaw, the SNR increased by a factor of more than four. The beam-forming algorithms were implemented in SwRI's EDAS software. This achievement will allow clients to use the beam-forming tool with existing EDAS analysis tools, including indication marking and reporting tools, for use with conventional (bulk wave) as well as guided wave transducers.

Image: Standard EDAS B-scan presentation for data obtained from scanning an MsS sensor circumferentially around a pipe
Figure 2.
(Left) Standard EDAS B-scan presentation for data obtained from scanning an MsS sensor circumferentially around a pipe, about 2 m axially distant from the flaw. The horizontal axis is in the circumferential direction, and the vertical axis is the waveform time (axial) direction. Only a small portion of the axial direction is shown in the color image; a complete waveform (A-scan) at one location is shown at the top (only the yellow portion of this waveform is displayed in the image below). The cursor box (rectangle) in the figure identifies the flaw location.

(Right) The pipe data shown after beam-forming is applied. The flaw is localized very well and the SNR is greatly increased. The synthetic waveform shown in the top portion includes the flaw location; the yellow portion of this waveform corresponds to the B-scan window length in the image.
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