NDT or Non destructive testing can be employed to check and test engineered parts such as welds. In manufacturing welds are commonly used to join two or more metal surfaces. Because these joints may encounter loads and fatigue during product life, there is a chance that it may fail if not created properly. An example of this would be the base metal which must reach a certain temperature during the welding process, and then must cool down at a certain rate, also it must be welded with compatible materials or the joint may not be strong enough to hold the two surfaces together, and 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 the 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 or via eddy current. In a good weld these tests would find a lack of cracks in the radiograph, show clear passage sound through the weld and back, or indicate a clear surface without penetrant captured in the cracks.