[3A4] Integrated modelling of guided wave reflections from defects in pipes
A M Qadri¹, P Huthwaite¹, M Lowe¹ and T Vogt²
¹Imperial College London, UK
²Guided Ultrasonics Ltd, UK
Computational modelling is increasingly utilised for the qualification and design of ultrasonic inspections applied to pipelines in the petrochemical industry. Numerical methods, and particularly the finite element method, facilitate the simulation of ultrasonic inspection with realistic geometries. However, their computational memory and processing requirements limit their usage for large structures such as long lengths of pipe. This work presents a methodology for integrating analytical dispersion curves, obtained from Disperse, with finite element modelling: it uses dispersion curves to model guided wave propagation over long lengths where the pipe geometry is unchanged and finite element modelling where it contains a feature, for example a defect. This integrated model allows the full potential of numerical modelling to be realised without restricting computational and memory requirements. A numerical finite element study of the scattering of the torsional T(0,1) mode from defects in straight pipes is carried out using Pogo, a graphical processing unit-based solver. Both axisymmetric and non-axisymmetric defects have been considered. The results show that there is excellent agreement in the displacement profiles between the integrated model and the full numerical model for the axisymmetric case whereby no mode conversion is seen. With non-axisymmetric defects, mode conversion to the F(1,2), F(2,2) and higher-order flexural modes is generally seen. A mode separation technique based on a guided wave reciprocity relation is applied and analytical techniques are applied to propagate the separated waveforms in the pristine pipe length. It is shown that there is good agreement for the integrated model with full numerical results when applying this mode separation technique. The results indicate the viability of the integrated approach, thereby permitting the inspection of thick-section components with large propagation distances.
