Nondestructive evaluation defects detected

Cross-linked polyethylene may include impurities and voids from which the major causes of premature failures (SCG in pipes, treeing in electric cables, and cracking in medical implants) can originate. Thus, nondestructive evaluation with effective techniques that can discover defects at the incipient stage, before the component is put in operation, is of vital importance. Conventional ultrasound (up to 10 MHz), which is the current technique for detection of flaws in metal piping and vessels, is limited by the attenuated nature of polymers. A scanning acoustic microscope with operating frequencies up to 100-150 MHz has been found to be more effective. 

In anticipation of the waiver, DOT requested assistance from NBS In evaluating the fracture mechanics analysis and the nondestructive evaluation methods used to detect and determine the dimensions of specific weld defects. The model used in the waiver request by Alyeska was actually more conservative than others that were generated In the evaltiation by NBS scientists. 

Nondestructive evaluation of ceramics is currently useful for process development and improvement, failure analysis, and detection of gross defects. At this time, there is no NDE technique to find critical volume flaws quickly in arbitrarily shaped technical ceramics. 

Defects are most often detected by visual inspection or automated optical inspection (AOI). Other means of nondestructive evaluation (NDE) include electrical testing, x-ray inspection, and ultrasonic inspection. The preferred NDE inspection technique for BGA and CSP solder joints is x-ray inspection. Automated x-ray inspection equipment is often placed directly into the assembly process line for circuit board products having a large number of area-array components. 

Unfortunately, most nondestructive evaluation techniques are not effective at finding encapsulation defects. Voids and density variations are not readily detectable by visual inspection or by x-ray analysis. In the case of x-ray, the inherently low density of encapsnlant foams limits the contrast between filled and unfilled (void) regions. Scanning aconstic microscopy (SAM) has had some limited success when the encapsulant layer is relatively thin, which is not often the case. Witness samples taken during the casting process are used to confirm foam density. 

Inspection techniques for the detection and measurement of corrosion range from simple visual examination to nondestructive evaluation. Significant technological advances have been made in the last decade. For example, the combined use of acoustic emission (AE) and ultrasonics (UT) can, in principle, allow an entire structure to be inspected and growing defects to be quantified in terms of length and depth. Advanced corrosion monitoring methods have been developed that have both online capabihty and the abihty to detect problems at an early stage. The oil and gas production and petrochemical industries have assumed a... 

Nondestructive testing (NDT) is the development and application of technical methods for the detection, location, measurement, and evaluation of discontinuities, defects and other imperfections, the assessment of integrity, the assessment of properties and composition, or the measurement of geometrical characters without impairing the intended use or application of the test object (31). 

---