05 May What is Acoustic Emission Testing ?

Acoustic emission testing is an NDT technique which is undergone when a material deforms under stress. AET detects and monitors the release of ultrasonic stress waves from the restricted sources.

When a piece of sample is subjected to an external stimulus, like change in pressure, temperature or load, this triggers the generation or release of energy in the form of stress waves and it is propagated to the surface which will be recorded by sensors. 

Acoustic emissions can come from certain natural sources, like rockbursts or earthquakes, or from the equipment itself like melting, phase transformations in metals and twinning. Using AE signals detection and analysis, information on the origin as well as importance of discontinuities in a material is gathered.

How does it work?

The term acoustic emission testing generally refers to the process of detecting and monitoring AE using specialized equipment. Sensors are used to detect the acoustic emissions and then it is converted to electric signals from the waves which are captured using external stimulus such as high temperatures, loads or pressure are being recorded. This record information is used to get the potential information which can give the valuable details on the origin and the significance of the defect in the sample.

There are mainly two methods of AE testing:-

• Transient
• Continuous

In the transient method, the acoustic emissions which are above the threshold level  are being captured and then extracted to get the features such as signal energy, peak amplitude and duration of the burst. The extracted features are then used to detect the condition of the sample.This method is mainly used for testing structures for the defects like cracks.

In the continuous method, AE are captured based on a set of  time periods, i.e like 1/10th of a second etc. In this method also some features like average signal level and RMS (root-mean squared) values are being extracted. This method is mainly used in applications where there needs a lot of background AE or in tests where the required low AE amplitude such as when detecting leaks or testing gearboxes.

Acoustic emission testing can be performed in a laboratory as well as in- field situations for both long and short periods of time even for a few months. In remote cases, data is analysed using wireless data relay methods.

Representation of a scheme clarifying AE testing Method

A – AE Transducer (Receiver 1)

B – AE Transducer (Receiver 2)

S1 – Distance between AE Source and Receiver 1

S2 – Distance between AE Source and Receiver 2

What are the advantages and disadvantages of Acoustic Emission Testing?

Advantages:

• Detect a range of damage mechanisms 
• Reduced costs
• Can locate damage sources 
• Shutdown is not required
• Assesses the structure under real operational conditions
• Minimal disruption to insulation
• Identification of only active defects
• Can be performed remotely
• Non-invasive method
• Global, simultaneous inspection of a structure
• Immediate indication of risk
• Operate in hazardous environments
• Early damage detection
• Compliance assistance

Disadvantages:

• Provide only qualitative results
• Limited to assessing structural integrity or machine health 
• Can find only active flaws
• Slower process
• Greater challenges in loud environments
• High skills and knowledge required
• Cannot detect defects which cannot be moved or cannot grow

What are its Applications of AET?

• Used in concrete structures such as buildings and bridges
• Monitor changes in phases and chemical reactions
• Used in the case of metallic structures such as pipelines, pressure vessels, aircraft structures, storage tanks and steel cables 
• Laboratory and research and development studies
• Composite structures like aircraft structures,composite beams and motorsport structures
• Weld quality monitoring
• In-field inspection
• Electrical machinery like detecting partial discharge in transformers and bushings
• Production quality control
• Additive manufacturing for assessing build quality during build
• Structural integrity evaluation
• Leak detection in pressure systems and pipelines 

Enrol for 1 month preparatory classes for Acoustic Emission testing exam

Gamma NDT academy offers NDT preparatory classes for candidates who intend to appear for the ASNT Level 3 Acoustic Emission testing certification exam. 

We will cover all the syllabus under ASNT for Acoustic Emission testing certification exam and conduct mock tests to prepare you for the exam. We will also share study materials and sample questions which you need to revise. We have a 100% success rate for NDT certification courses.

Gamma NDT academy training institute is located in Kerala, India. We provide online classes for candidates who cannot attend our training sessions in-person.