Experimental Studies of the Inspection of Areas With Restricted Access Using A0 Lamb Wave Tomography.

Corrosion damage in inaccessible regions presents a significant challenge to the petrochemical industry, and determining the remaining wall thickness is important to establish the remaining service life. Guided wave tomography is one solution to this and involves transmitting Lamb waves through the area of interest and, subsequently, using the received signals to reconstruct a thickness map of the remaining wall thickness. This avoids the need to access all points on the surface, making the technique well suited to inspection for areas with restricted access. The influence of these areas onto the ability to detect and size surface conditions, such as corrosion damage, using guided wave tomography is assessed. For that, a guided wave tomography system is employed, which is based on low-frequency A0 Lamb waves that are excited and detected with two arrays of electromagnetic acoustic transducers. Two different defect depths are considered with different contrasts relative to the nominal wall thickness, both of which are smoothly varying and well-defined. The influence of areas with restricted surface access, support locations, pipe clamps, and STOPAQ(R) coatings is experimentally tested, and their influence assessed through comparison to a baseline reconstruction without the respective restriction in place, demonstrating only a small influence on the detected value of the remaining wall thickness.