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

Abstract

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 (EMATs). Two different defect depths are considered with different contrasts relative to the nominal wall thickness, both of which are smoothly varying and welldefined. The influence of areas with restricted surface access, support locations, pipe clamps and STOPAQ(R) coatings, are 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.

On-Line Corrosion Monitoring of Plate Structures Based on Guided Wave Tomography Using Piezoelectric Sensors

“…The thickness profiles of a deeper defect B after 110 h of corrosion are shown in Figure 8 d,f. It is clear that the reconstruction can still capture most features of the defect, although the discrepancy compared with the measured thickness profile is larger than the previous case, as the error of the reconstruction increases with the depth of the defect [ 19 ].…”

“…Ultrasonic non-destructive evaluation systems based on the guided waves generated by arrays of electromagnetic acoustic transducers (EMATs) have been applied to the corrosion monitoring of pipes and plate-like structures [ 17 ]. For example, the received signals from arrays of EMATs encircled the pipe were processed by using ultrasonic computerized tomography [ 18 , 19 ] to generate the maps of thickness loss. However, EMATs have a relatively low signal-to-noise ratio (SNR) and their performance relies on the electromagnetic properties of the tested objects such as the presence of a highly magnetostrictive oxide layer [ 20 ].…”

An improved gas kick detection method based on continuous Doppler ultrasonic wave in deep water drilling

“…Void fraction could be detected by amplitude of received signal frequency spectrum according to equation (22). In practice, it is greatly difficult to calibrate k s , A 0 , R, a, z r .…”

Guided wave tomography with an improved scattering model

“…It should be noted that this is a slightly artificial scenario as, in general, the locations will be calibrated beforehand (e.g. [41]) to ensure the effect of any Figure 11a-e shows the results from this scaling in a range of ±2%; for reference, a 2% error corresponds to around 20% of a wavelength for the through-transmission ray path, or 1.3 radians phase shift. It is clear that in this range the shape still remains well defined, and HARBUTISM, while inevitably being sensitive to the errors to an extent, does remain stable.…”