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Pipelines are used extensively in industry for large-scale distribution of fluids such as crude oil and water. There are millions of miles of pipeline in the world for fluid distribution. Pipelines are a significant yet ageing asset. As pipelines age, corrosion flaws can develop, and it is therefore important to assess the structural integrity for its continuous operation. Defective pipelines can lead to fatalities, property damage, litigation and damage to the environment.

Conventional inspections techniques are expensive and time-consuming; hence Ultrasonic Guided Wave (UGW) inspection has attracted considerable interest as a Non-Destructive Testing (NDT) technique in the past two decades. UGW based techniques offer the advantage of full volumetric inspection of tens of metres of pipeline from a single test location. Initially, UGW was developed as a low-resolution rapid screening technique to find relatively large defects, i.e. patch of corrosion.

However, there is a need to expand the knowledge on the UGW inspection to allow more complex structures to be inspected and quantify smaller defects. If a flaw was detected in a pipe buried in the soil, it needs to be dug out and inspected using a high-resolution inspection technique to get quantitative information to state the health of the structure which is still a costly activity. The pipe inspection would be cost-effective if UGW can provide quantitative measurements of flaws.

This can be accomplished by introducing advance signal processing techniques and/or transducers development to enhance the resolution and sensitivity of the UGW inspection.

Contribution to the knowledge from this research project begins with the development of a sound energy focusing technique to enhance the resolution and the sensitivity of anomalies. The proposed technique is a hybrid sound energy focusing technique which combines numerical/analytical simulation with active focusing and the time-reversal concept. Performance of the proposed technique is compared against the sound energy focusing techniques described in the literature (i.e. active focusing, synthetic focusing and time-reversal focusing).

Then, the first longitudinal guided wave mode was studied with respect to adopting it as an incident mode. This enhances the resolution and sensitivity as it inherits a higher number of flexural modes in an operating frequency. Appropriate transduction techniques were suggested, and the resolution and sensitivity were compared to the existing probing modes.

Later on, the potential of flaw sizing was studied using the first longitudinal guided wave mode.