Editing Nondestructive testing (section)

===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.