Advantage of Guided Wave Testing

    Guided waves are structure-borne ultrasonic waves that propagate along a structure confined and guided by its geometric boundaries. As shown in Figure 1, guided waves propagate along the pipe axis and are reflected from any local cross-sectional area change such as crack or corrosion defect. GWT is a technique for finding defect location and estimating the defect size using the arrival time and the amplitude of ultrasonic signal, respectively. The operating frequency of GWT is usually low (5 to 250 kHz) compared to ordinary ultrasonic testing. The low frequency operation helps to generate non-dispersive ultrasonic guided wave and to reduce the attenuation for long-range pipeline inspection.

How can an inspector perform Guided Wave Testing?

   Guided Wave Testing (GWT) and conventional ultrasonic testing (UT) follow the same exact testing/examination procedure:

1. Carry the GWT equipment
2. Select location to install probe
3. Install probe
4. Acquire data
5. Analyze data
6. Summarize findings in a report

    The inspection can be done at 4 to 30 locations per day depending on the accessibility and preparation of pipeline. The GWT data can be acquired by level I inspector for any kind of inspection situation by properly following the inspection procedure. However, the difficulty in guided wave testing arises from two specific areas which have a multitude of varieties: the pipe itself and the pipe condition(s). Varieties in pipe include the pipe size, surface corrosion, coating, insulation, geometric features of weld, pipe support, clamp, branch pipe, elbow, flange, valve, etc. Varieties in pipe condition include the content of pipe, buried or above ground, recording of geometric features along the length of pipe, probe installation on pipe, data analysis and reporting, etc. Due to these varieties, a guided wave Level I inspector needs to be properly trained and/or supported by a Level II or III guided wave inspector who has experience and solid knowledge in various field testing of the above mentioned arrears and combinations thereof.