For several years, NDT has been a backbone in the aerospace, automotive, construction and other industries. It is a vital component in providing personal safety and maintaining reliability for the products tested with NDT. NDT (Non-Destructive Testing) also goes by NDE (Non-Destructive Evaluations) and NDI (Non-Destructive Inspection). It all means the same in what it does. It allows you to inspect a component without rendering the component unusable after the inspection.
There are a number of NDT inspection test methods and techniques available for use today. Here is a very basic summary of some of the more common NDT test methods:
Penetrant Inspection (PT): Allows surface inspections, generally for non-porous non-magnetic materials.
Magnetic Particle Inspection (MT): Allows both surface and sub-surface inspection of permimagnetic materials.
Radiography (RT): Allows inspection of internal areas of a broad spectrum of materials.
Ultrasonic Inspection (UT): Allows the inspection of internal and external surfaces of materials.
Eddy Current (ET): Allows inpection of materials to detect changes in material compositions, inspection of holes, and sorting of materials.
Visual Inspection: (VT) Allows surface inspection of materials where surface can be seen.
There are other methods of NDT available for special application such as Infrared, Thermography, etc. However, you will find more specific information about the commonly audited processes on this web site (i.e. MT,PT,RT,UT,ET) by clicking on the reference pages at the left.
There are a host of hard to control variables inherent to many of the testing methods. For example, parts are often rinsed differently by different operators in the penetrant process. Because these types of variables are hard to control, classifying NDT as a "process monitoring tool" instead of an absolute-will-find-all inspection should be considered. Complaints often surface because a part previously tested now has a defect, found by a subsequent inspection in the same test method. It is because of these currently inherent variables. Engineers should take note of this.
Reducing the possibility of missing a defect can be achieved by using more than one test method and striving to tighen process controls where possible. This could include thigs such as using digital controls to continual educationg and training of operators to reduce variables.
Performing inspections at multiple stages can also be helpful to in reducing losses and prevent missing critical discontinuities. However, it is recommended to use statistical data to drive choices when possible. If you have a very stable manufacturing process, you could considered reducing inspections needed. Unstable or poor processes would require more thorough inspection requirements.
Statistical tools for process improvement can be found here and here.
The Defect Detection link to the left will give you some suggestions for what type of test method to use for various types of disconinuities. More specific advantages and disadvantages to test methods can be found at the links for that process to the left of this page.