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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 metalurgy tests.
Structural mechanics
Structures can be complex systems that undergo different loads during their lifetime.
Some complex structures, such as the turbo machinery in a liquid-fuel rocket, can also cost
millions of dollars. Engineers will commonly model these structures as coupled second-order
systems, approximating dynamic structure components with springs, masses, and dampers.
These sets of differential equations can be used to derive a transfer function that models the
behavior of the system.
In NDT, the structure undergoes a dynamic input, such as the tap of a hammer or a
controlled impulse. Key properties, such as displacement or acceleration at different points of
the structure, are measured as the corresponding output. This output is recorded and compared
to the corresponding output given by the transfer function and the known input. Differences
may indicate an inappropriate model (which may alert engineers to unpredicted instabilities or
performance outside of tolerances), failed components, or an inadequate control system.
NDT is used in a variety of settings that covers a wide range of industrial activity, with
new NDT methods and applications, being continuously developed. NDT services are not
only integrated with Asset Integrity Management (AIM) solutions, but also with Material
Testing laboratories and seamlessly fit into Supply Chain services.
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.
Radiography in medecine
Chest radiography indicates a peripheral bronchial carcinoma.
As a system, the human body is difficult to model as a complete transfer function.
Elements of the body, however, such as bones or molecules, have a known response to certain
radiographic inputs, such as x-rays or magnetic resonance. Coupled with the controlled
introduction of a known element, such as digested barium, radiography can be used to image
parts or functions of the body by measuring and interpreting the response to the radiographic
input. In this manner, many bone fractures and diseases may be detected and localized in
preparation for treatment. X-rays may also be used to examine the interior of mechanical
systems in manufacturing using NDT techniques, as well.

Notible events in early industrial NDT

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