Quantitative evaluation of ultrasonic techniques for the detection and monitoring of corrosion in pipes

Corrosion of the oil and gas pipeline infrastructure has the potential to lead to catastrophic consequences, including loss of life. By performing continual diagnostic non-destructive evaluation (NDE) assessments of the pipeline infrastructure, corrosion can be tracked, mitigated and controlled. However, the sheer scale of the modern pipeline networks around the world requires new innovative techniques to efficiently and cost-effectively monitor and screen for corrosion. Currently there are two well-established ultrasonic techniques for monitoring and screening corrosion. Spot measurements extract the pipe wall thickness at a single point location. This method can extract an accurate value of wall thickness, but the measurement is highly localised. In contrast, long range guided waves (LRGWs) screen for damage by exciting a pulse which travels axially down a pipe and will reflect off any large areas of corrosion. This method has a large coverage area, but is much less sensitive to corrosion than the spot measurement techniques. The first part of this thesis explores the sensitivity of a circumferential guided wave technique, which is suggested to mitigate against some of the disadvantages of existing methodologies. This method propagates a guided wave around the circumference of a pipe, and uses either the reflected pulse from the defect or the through transmitted pulse, to detect the presence of a defect. The viability of this method was assessed by modelling the ultrasonic response to a range of different defects and using probabilistic techniques. The S0, SH1 and SH0 modes were studied and it was revealed that in reflection the technique is able to detect narrow and deep defects, whereas in transmission wide defects are detectable. Wavelength normalised results are also presented. The second part of this thesis investigates the interaction between spot measurement (shear bulk waves) and hemispherical pits. This is with a view to further understanding the mechanics behind the interaction between shear waves and pitting corrosion, and to assessing current transducer types to the tracking and monitoring of individual pits. It was found that an anisotropic relationship exists between the pit’s location relative to the shearing direction of the bulk wave. This is due to either the inherent anisotropy of the transducer or the mode conversion of the shear wave.Open Acces