Acoustic measurements above a plate carrying Lamb waves

TL;DR

This study combines acoustic measurements and simulations to analyze Lamb wave propagation in a steel plate, providing insights into wave velocity and spreading characteristics relevant for oil well casing inspection.

Contribution

It presents experimental measurements and COMSOL simulations of Lamb waves in a steel plate resembling oil well casing, highlighting wave velocity and spreading behavior.

Findings

Fastest Lamb wave mode velocity: 3138.5 m/s

Wave spreading: 3.2 mm after 140 mm propagation

Agreement between measurements and simulations

Abstract

This article presents a set of acoustic measurements conducted on the Statoil funded Behind Casing Logging Set-Up, designed by SINTEF Petroleum Research to resemble an oil well casing. A set of simple simulations using COMSOL Multiphysics were also conducted and the results compared with the measurements. The experiments consists of measuring the pressure wave radiated of a set of Lamb waves propagating in a 3 mm thick steel plate, using the so called pitch-catch method. The Lamb waves were excited by a broadband piezoelectric immersion transducer with center frequency of 1 MHz. Through measurements and analysis the group velocity of the fastest mode in the plate was found to be 3138.5 m/s. Measuring the wave radiated into the water in a grid consisting of 8x33 measuring points, the spreading of the plate wave normal to the direction of propagation was investigated. Comparing the point where the amplitude had decreased 50 % relative to the amplitude measured at the axis pointing straight forward from the transducer shows that the wave spread out 3.2 mm after propagating 140 mm in the plate.