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Many defect-testing techniques exist and it may not be clear why one is used over the other. This article describes nine different testing methods explaining how they are used and what they can detect.
Nondestructive testing (NDT) methods are important tools help us assure product satety, qiuility and reliability. Finding detects, whether they are flaws or imperfections, during the manufacturing process or before a product is placed into service will decrease liability, increase productivity, save time and improve the bottom line. These techniques are also the first step in any "postmortem" failure analysis.
The most common types of NDT methods are:
* Visual inspection
* Dye (liquid) penetrant
* Magnetic particle inspection
* Radiographic (X-ray) testing
* Eddy current
* Ultrasonics
* Leak detection
* Acoustic emission
* Infrared thermography
Each method has advantages and limitations (Table 1), and often more than one technique is needed to identify the root cause and quantify the extent of the problem.
We will briefly review each of these methods with respect to how they work, where they are used and what can be found as a result of their use.
Visual Inspection
Visual inspection is the most basic and widely used method for the examination of parts. It is used to detect surface abnormalities (cracks and imperfections). Since it can be performed by virtually anyone and is subjective in nature, it is a good idea to develop standards or use comparative aids. It is useful in pinpointing areas that require closer inspection (perhaps by another NDT method) and is the place to start before performing any other type of NDT test.
Always begin by preparing an area where the visual inspection will take place. It should he well lit and allow easy manipulation of the part so that all surfaces can be easily viewed. Start by inspecting all surfaces in the "as received" condition. As the examination proceeds, the surface may need In he cleaned or treated in some manner to highlight a detect in more detail. All observations should be documented and adequate rime allowed to do a thorough inspection.
Visual inspection typically uses a wide variety of very simple tools such as:
* Lights - natural, fluorescent, black light, artificial light
* Magnifiers - loops...