Acoustic Emission Capabilities
Acoustic Emission Technology also offers many unique capabilities. At the frequencies we use, the distance between the AE
source and the sensor could be as little as a few inches or as much as tens or even hundreds of feet. Sudden sub-critical local failures in materials under stress are the classic sources of Acoustic Emission.
Small-scale damage is detectable long before failure, so AE
can be used as a non-destructive technique to find defects during structural proof tests and plant operation. AE
also offers unique capabilities for materials research and development in the laboratory. Finally, AE
equipment is adaptable to many forms of production testing, including weld monitoring and leak detection.
Acoustic Emission In Field Testing
Many codes and standards exist for Acoustic Emission testing of vessels, from transportation gas cylinders and railroad tanks to thousands tons storage tanks. Because only active defects and deterioration produce Acoustic Emission no time is wasted on inactive defects which are not threatening structural integrity.
Global Monitoring - 100% Inspection of the Structure
A major advantage of Acoustic Emission inspection is that does not require access to the whole examination area. E.g. for covering a total area of a 16 meter diameter sphere approx. 30 +/- sensors are needed. Thus, the cost of the test is significantly less than inspection with conventional NDT
methods (for 100% inspection and scanning of the whole area). Identified problem areas can be inspected using conventional NDT
Testing with Insulation/High-Temperature Processes
In cases of insulation, only small holes in insulation are required for sensor mounting, resulting in increased cost savings. In cases of high temperature processes, wave-guides are used to guide the Acoustic Emission waves from the hot surface to the edge where the sensor is mounted. Finally, in large cryogenic vessels, permanent sensors are mounted under insulation for periodic inspection control.
As the method records defects in real time, it offers the possibility of on-line inspection, e.g. during hydrostatic testing. Other types of on-line stress application are introducing of gas into the upper vapor space, temperature control etc.
The actual Acoustic Emission test takes a matter of hours, and, in some cases, even less. There is no comparable technique which can provide 100% volumetric inspection.
The use of Acoustic Emission results in considerable reduction in plant maintenance costs, while increasing the available information about plant integrity. Plant downtime for inspection is also minimized.
Permanent Recording of Test
Acoustic Emission data are digitized and stored on a PC, providing permanent recording of the test to be used at any time for re-evaluation and post processing analysis.
When more than one sensor is used, the AE
source can be located and, thus, the defective area. Location is based on the wave propagation principles within the materials and is effectuated by measuring the signal's arrival time to each sensor. By comparing the signal's arrival time at different sensors, the flaw's location can be defined through triangulation. Linear location is used on long gas cylinders, planar (2-dimensional) location for thick walled and gas filled vessels, while 3-dimensional location is used for power transformers and concrete structures.