Guided waves are structure-borne ultrasonic waves that propagate along a structure confined and guided by its geometric boundaries. As shown in the figure below, 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 areas.

What are the other names for Guided Wave Testing?

Guided wave testing (GWT) has many different names: LRUT (Long-Range Ultrasonic Testing), MsS Testing (Magnetostrictive Sensor Testing), GUL Testing (Guided Ultrasonic Limited Testing), Guided Wave UT (Ultrasonic Testing), Guided Wave Ultrasonic Long Range Inspection, Long-range guided wave testing, Guided Ultrasonic Long Range Inspection, and Long-range guided UT. But its name was discussed in ASNT and BINDT meeting.

ASNT selected its name as “Guided Wave Testing” in 2009 ICPIIT committee meeting at Houston. BINDT selected Guided Wave Testing (GWT) as a method in its own right and not a sub technique of UT. Therefore, guided wave testing (GWT)will be proper terminology for describing the activity of low-frequency ultrasonic testing for finding defects in the long-length of pipe with a local probe location.