Acoustic emission wave propagation in pipeline sections and analysis of the effect of coating and sensor location

This paper presents an experimental investigation in which acoustic emission (AE) wave was generated through a pencil lead break (PLB) as a point source on two pipeline sections made of mild steel and titanium. The pipelines (bare, epoxy phenolic coated) were of same length but had two different diameters and wall thicknesses. The investigation included an analysis of the effects of coating, pipeline materials, pipe wall thicknesses and significance of sensor placement on monitoring. The recorded AE signals were analysed using time and frequency domain signals, energy levels and wavelet transform (WT) to explore time-frequency features for the identification of wave-modes. It is concluded that the damping behaviour of coating restricts the peaks of waves, and decreases the decay time of waves, and reduces the energy level in the coated pipeline. Based on the sensor location-based results, it is concluded that monitoring of coated pipeline wave propagation could be done effectively with sensor placement directly on the pipeline surface compared to sensor placement on the coating surface. A high wall thickness of pipeline results in a higher number of reflected waves and increases the decay time of waves. The coating on pipeline resists wave propagation, and different density of coating layer and pipeline affects the velocity of the wave. These findings could be useful to providing a greater understanding of recorded data, improving the current abilities to identify, locate, and characterise degradation occurring in single and multilayer conditions. Particularly, this experimental work and its results advancing toward designing a potential alternative way to monitor changes in coated pipeline structure, for example, in corrosion under insulation (CUI) applications.