The basic concept of Acoustic Emission stimulation is to locate a yield point of the material where it can lead to a leakage or similar problems. Acoustic emission testing is normally practiced on welded piping and high energy steam piping in fossil power plants and it is now one of the most used non-destructive types of testing. The yield point causes a stress wave that propagates through the structure elastically. At some point, it reaches the surface and stimulates a piezoelectric sensor. This sensor will convert mechanical energy into an electrical signal, amplified to be able to perform the analysis process.
Acoustic Emission Applications
This non-destructive testing can be used in the following industries or applications:
- Pressure vessel testing
- Structural integrity testing
- Materials testing
- Concrete corrosion monitoring
- Pipeline monitoring
- Bridge monitoring
- Wind turbine monitoring
- Leak detection
There are other applications but they are still in the development process and for these newer applications, there are still certain areas for improvements and their results are not quite accurate as of today.
Why Is This Testing Different From Others?
The inspection by acoustic emission differs from other non-destructive inspections on the following points:
- The signal detected is generated by the same material
- The evaluation is comprehensive and not limited by its geometry
- The method is evaluating the response of the material to the application of effort; therefore, it is a dynamic technique
These factors provide the basic concept of Acoustic Emission as applied to a pressure tank or other structures including pipelines and even concrete.
Advantages of Acoustic Emission Testing
Acoustic Emission inspection is applied in three ways to pressure vessels:
- During the inspection phase of hydrostatic testing after being manufactured
- When the equipment has been re-certified for an alternative use
- Inspection when in service
Provides highly sensitive analyses
Acoustic Emission can assess the structural integrity of a pressure vessel in production, under controlled conditions of operation and their behavior while in use. This information on how the recipient is working in service and where degradation is occurring when in operation can help define when and where other non-destructive inspections should be performed. Their use can increase the time between inspections or other alerts to the presence of a potential weakness, for evaluation.
Acoustic Emission Results
Acoustic emission testing will provide you with the following information depending on the method or recipient that you are testing.
- Inspection of the entire structure - Following careful determination of the area where the sensor is to be fixed, the inspection can be done with a small number of sensors. This ability of the acoustic emission application is quite attractive to large structures (sausages), spheres, heat exchangers where access and inspection areas is difficult and takes too long.
- Find significant flaws - if Acoustic Emission is used under actual loading conditions of the structure, it can distinguish abnormalities that are growing and others that are structurally insignificant. With other techniques, it is possible to establish the presence of an anomaly, but it is difficult to assess the effect on the structure when it is in service.
- Structural severity measurement - Using the procedures of inspection and analysis of today, it is possible to give a measure of an active resource of a structure. The data is given with recommendations for follow-up inspections to be carried out periodically.
- Non-intrusive, using Acoustic Emission sensors that are installed on the outside of the vessel wall. This does not require access inside the vessel when the inspection is being performed. In insulated containers only one small manhole is needed for the installation of sensors and the rest of isolation remains unchanged.