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NDT is divided into various methods of nondestructive testing, each based on a particular
scientific principle. These methods may be further subdivided into various techniques. The
various methods and techniques, due to their particular natures, may lend themselves
especially well to certain applications and be of little or no value at all in other applications.
Therefore choosing the right method and technique is an important part of the performance of
NDT.

Acoustic emission testing (AE or AT)
The application of acoustic emission to non-destructive testing of materials in the
ultrasonic regime, typically takes place between 100 kHz and 1 MHz. Unlike conventional
ultrasonic testing, AE tools are designed for monitoring acoustic emissions produced within
the material during failure or stress, rather than actively transmitting waves, then collecting
them after they have traveled through the material. Part failure can be documented during
unattended monitoring. The monitoring of the level of AE activity during multiple load cycles
forms the basis for many AE safety inspection methods, that allow the parts undergoing
inspection to remain in service.
The technique is used, for example, to study the formation of cracks during the welding
process, as opposed to locating them after the weld has been formed with the more familiar
ultrasonic testing technique. In a material under active stress, such as some components of an
airplane during flight, transducers mounted in an area can detect the formation of a crack at
the moment it begins propagating. A group of transducers can be used to record signals, then
locate the precise area of their origin by measuring the time for the sound to reach different
transducers. The technique is also valuable for detecting cracks forming in pressure vessels
and pipelines transporting liquids under high pressures. Also, this technique is used for
estimation of corrosion in reinforced concrete structures.
In addition to non-destructive testing, acoustic emission monitoring has applications in
process monitoring. Applications where acoustic emission monitoring has successfully been
used include detecting anomalies in fluidized beds, and end points in batch granulation.

3 Make a written translation of the following:

In manufacturing, welds are commonly used to join two or more metal parts. Because these
connections may encounter loads and fatigue during product lifetime, there is a chance that
they may fail if not created to proper specification. For example, the base metal must reach a
certain temperature during the welding process, must cool at a specific rate, and must be
welded with compatible materials or the joint may not be strong enough to hold the parts
together, or cracks may form in the weld causing it to fail. The typical welding defects (lack
of fusion of the weld to the base metal, cracks or porosity inside the weld, and variations in
weld density) could cause a structure to break or a pipeline to rupture.
Welds may be tested using NDT techniques such as industrial radiography or industrial CT
scanning using X-rays or gamma rays, ultrasonic testing, liquid penetrant testing magnetic
particle inspection or via eddy current. In a proper weld, these tests would indicate a lack of
cracks in the radiograph, show clear passage of sound through the weld and back, or indicate
a clear surface without penetrant captured in cracks.
Welding techniques may also be actively monitored with acoustic emission techniques
before production to design the best set of parameters to use to properly join two materials. In
the case of high stress or safety critical welds, weld monitoring will be employed to confirm
the specified welding parameters (arc current, arc voltage, travel speed, heat input etc) are
being adhered to those stated in the welding procedure. This verifies the weld as correct to
procedure prior to nondestructive evaluation and metallurgy tests.

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