ASNT

National Safety Council, UL (formerly Underwriters Laboratories, Inc.), the United States Environmen- tal Protection Agency (EPA), the Federal Aviation Administration in the US, and the work of similar agencies abroad, are only a few of the ways in which this demand for safety is expressed. This demand for personal safety has been a strong force in the development of nondestructive tests. Costs of Failure Aside from awards to the injured and costs to the public for collateral effects of large system or structure failure, the cost of failure to a company is significant. Some important reasons are (1) costs of materials and labor; (2) costs of complex parts; (3) costs due to the complexity of assemblies; (4) risk that failure of one part will cause failure of others; and (5) part failure shutting down an entire high-speed, integrated production line. The economics of just-in-time and lean manufacturing place great emphasis on maintaining uninterrupted equipment performance. Loss of such production is one of the greatest losses from part failure. APPLICATIONS OF NONDESTRUCTIVE TESTING Nondestructive testing is a branch of the materials sciences concerned with all aspects of the uniformity, quality, and serviceability of materials and structures. The science of nondestructive testing incorporates all technology for detection and measurement of significant properties, including discontinuities, in items ranging from research specimens to finished hardware and products. By definition, nondestructive techniques are the means by which materials and structures may be inspected without disruption or impairment of serviceability. By using nondestructive testing, internal properties of hidden discontinuities are revealed or inferred through appropriate techniques. Nondestructive testing is vital in effective research, development, design, and manufacturing. Only with nondestructive testing can the benefits of materials science be realized. The information required to appreciate the scope of nondestructive testing is available in many publications.

CLASSIFICATION OF METHODS NDT method can be characterized in terms of five principal factors: (1) energy source or medium used to probe object (such as X-rays, ultrasonic waves, or thermal radiation); (2) nature of the signals, image, and/or signature resulting from interaction with the object (attenuation of X-rays or ref lection of ultrasound); (3) means of detecting or sensing resultant signals (photoemulsion, piezoelectric crystal, or inductance coil); (4) means of indicating and/or recording signals (meter reading, signal display, or image); and (5) basis for interpreting the results (direct or indirect indication, qualitative or quantitative, and pertinent dependencies). The objective of each method is to provide information about the following material parameters: 1. discontinuities and separations (cracks, voids, inclusions, delaminations, others); 2. structure or malstructure (crystalline structure, grain size, segregation, misalignment, others); 3. dimensions and metrology (thickness, diameter, gap size, discontinuity size, others); 4. physical and mechanical properties (reflectivity, conductivity, elastic modulus, sonic velocity, others); 5. composition and chemical analysis (alloy identification, impurities, elemental distributions, others); 6. stress and dynamic response (residual stress, crack growth, wear, vibration, others); 7. signature analysis (image content, frequency spectrum, field configuration, others). Terms in this block are defined in Table 1 with respect to specific objectives and specific attributes to be measured, detected, and defined. Methods that use electromagnetic radiation (Table 2) can be divided according to the segment of the spectrum each uses as interrogating energy: radar, thermography, visual testing, and X-radiography (Figure 3). Methods using vibration and ultrasound are in a different spectrum—the acoustic spectrum. The limitations of a method include conditions required by that method, conditions to be met for technique application (access, physical contact, preparation, or others), and requirements to adapt

CHAPTER 1

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Part 1