Editing Nondestructive testing (section)

==Applications==
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. Nondestructive testing methods are routinely applied in industries where a failure of a component would cause significant hazard or economic loss, such as in transportation, pressure vessels, building structures, piping, and hoisting equipment.

===Weld verification===
[[Image:Ressuage principe 2.svg|thumb|250px|{{ordered list |1=Section of material with a surface-breaking crack that is not visible to the naked eye. |2=Penetrant is applied to the surface. |3=Excess penetrant is removed. |4=Developer is applied, rendering the crack visible.}}]]

In manufacturing, [[welding|welds]] are commonly used to join two or more metal parts. Because these connections may encounter loads and [[fatigue (material)|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.<ref name=UltrasonicMethods >{{cite book|last=Blitz|first=Jack|author2=G. Simpson |title=Ultrasonic Methods of Non-Destructive Testing|publisher=Springer-Verlag New York, LLC|year=1991|isbn=978-0-412-60470-6}}</ref> 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.

===Structural mechanics===
Structure can be complex systems that undergo different loads during their lifetime, e.g. [[Lithium-ion battery|Lithium-ion batteries]].<ref>{{cite journal
|author = Waldmann, T.
|year = 2014
|title = A Mechanical Aging Mechanism in Lithium-Ion Batteries
|journal = Journal of the Electrochemical Society
|volume = 161
|issue = 10
|pages = A1742–A1747
|doi = 10.1149/2.1001410jes
}}</ref> 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 [[spring (device)|springs]], [[mass]]es, and [[dashpot|dampers]]. The resulting sets of differential equations are then 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 (vector)|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]].

Reference standards, which are structures that intentionally flawed in order to be compared with components intended for use in the field, are often used in NDT. Reference standards can be with many NDT techniques, such as UT,<ref>{{cite web|url=https://customers.phtool.com/custom-reference-standards/edm-notch-reference-standards-gallery/|title=EDM Notch Reference Standards » PH Tool|website=customers.phtool.com}}</ref> RT<ref>{{cite web|url=https://customers.phtool.com/custom-reference-standards/radiography-rt-reference-standards/|title=Radiography (RT) Reference Standards » PH Tool|website=customers.phtool.com}}</ref> and VT.

===Relation to medical procedures===
[[File:Thorax pa peripheres Bronchialcarcinom li OF markiert.jpg|150px|thumb|Chest radiography indicating a peripheral [[Lung cancer|bronchial carcinoma]].]]

Several NDT methods are related to clinical procedures, such as radiography, ultrasonic testing, and visual testing.  
Technological improvements or upgrades in these NDT methods have migrated over from  medical equipment advances, including digital radiography (DR), phased array ultrasonic testing (PAUT), and [[endoscopy]] (borescope or assisted visual inspection).