GWT is a non-destructive method for determination of the condition of elongated structures – commonly pipes, but rails etc. can also be tested.

A ring of transducers is attached around the circumference of the pipe to generate acoustic waves that propagates along the pipe in both directions from the transducer ring, while ‘guided’ by the boundaries of the pipe wall. Changes in cross section of the pipe, e.g. caused by metal loss due to corrosion or erosion, generate an echo, reflection, of the waves. This feature (defect) can be located relative to the transducer from the speed of the wave and time of arrival of the echo. The transducer ring is operated in ‘pulse-echo’ mode, i.e. it is also detects the echoes.

The waves travel metres to tens of metres. Thus the full area of the pipe wall can be tested for defects. This is a key advantage of the method – unlike with ultrasonic testing, in which only the area under the transducer is tested, it is not necessary to know in advance where the risk of corrosion / erosion is greatest. You do not need to get lucky in locating the transducer.

You can read a detailed description of how Guided Wave Testing works here.

Guided Wave Testing was developed as a practical method of testing of engineering structures at Imperial College, London in the 1990s, and proven in a wide range of industrial applications in the decade that followed 

If the transduction ring is permanently installed on the pipe, test data can be generated on an ongoing basis, at intervals of hours to days, enabling the condition of the structure to be monitored over time

• metal loss (corrosion / erosion) rates can be determined;
• the points in time at which these rates change can be correlated with changes in operating parameters – e.g. refining feedstock compositions, transmission pipeline ‘slugs’, sand holdup in risers – to contribute to generation of insights into the relationships between operating decisions and asset integrity.