FFS Forum: Acoustic Emission Testing - The Least Understood Inspection Technique (Part 2 of 2)

Editor’s Note: This is the second of a two-part column on Acoustic Emission Testing (AET). It addresses some of the advantages and disadvantages of AET and discusses a few examples of its typical applications. Part 1 of this series, published in the March/April 2021 issue of Inspectioneering Journal, presents a brief overview of the basic principles of AET and how it works. 

Introduction

In the last issue of Inspectioneering Journal (March/April 2021), we discussed the fundamentals of acoustic emission testing (AET), including the basic principles. In this issue, we will address some of the advantages and disadvantages of AET and a few examples of its typical applications.

Like all nondestructive testing (NDT) methods, there are some notable benefits and limitations of AET. An awareness of what it is good at, and its limitations, goes a long way to achieving a successful acoustic emission (AE) inspection.

The Advantages 

Active Flaws:  Acoustic emissions are produced by flaws that are stressed and experience local phenomena such as dislocation, plasticity, or crack extension. Components can have flaws that do not emit, however in most cases, this is a good thing because there is no value in identifying benign flaws that are not growing or increasing in damage. For example, consider a weld defect (e.g., porosity or undercut) that has been in place since fabrication many years ago. If the flaw is not “active” and not threatening the integrity of the structure, then it is beneficial that AET results screen out this benign flaw. 

Global Inspection:  With AET, an entire component can be tested at once. For example, an AE test of a large pressure vessel with many welds, nozzle connections, and other features can be...