This month 50 Years of Quality takes a look at how nondestructive testing (NDT) has been covered throughout the years. NDT became such an important topic for our readers that a regular special section, NDT including Materials Test, launched in 2003. NONDESTRUCTIVE TESTING THROUGH ANNIHILATION, MAY 2003 Annihilation. The word itself brings to mind destruction and conflagration. In the atomic realm, however, the rules are different. One company has developed a way to play by those rules. It has developed a way to test materials nondestructively based on the physics of the subatomic world. In this technology, particles are created only to be destroyed. The technology, called Photon Induced Positron Annihilation (PIPA), was invented by scientists at the U.S. Department of Energy’s Idaho National Engineering and Environmental Laboratory (Boise, ID) and licensed to Positron Systems Inc. (Boise, ID) for commercial use. PIPA can detect component fatigue and embrittlement of materials based on the amount of energy created when positrons and electrons annihilate each other. The technology can identify defective materials or determine the remaining “life” of materials. It can identify atomic lattice defects smaller than 10 microns in size and measurement uncertainties of less than 1%. Measurements using this technique have been performed on a variety of materials, including titanium, aluminum, stainless steel, iron, copper, polymers and composites. The system can penetrate materials to different depths depending on the material’s density. For example, it can penetrate 2 inches into stainless steel, 3.5 inches into titanium and 4 inches into aluminum, says Curt Rideout, chemical and nuclear engineer who serves as Positron’s military marketing and sales manager. If desirable, measurements can be taken from both sides of a test material or part, doubling the depth-detection capability. The technology also can produce cross-sectional analyses, and assembled parts can be tested and analyzed. For instance, a titanium strut inside of an aluminum airplane wing can be tested without having to disassemble the structure. PRESERVE THE IMAGE, AUGUST 2006 Visual inspection is the oldest of all inspection techniques. Man has always trusted his eyes to assess the quality or fitness for purpose of objects ranging from artifacts and structures to precious stones and food. He also has always trusted his brain to provide him with analysis and management of the input data. However, as engineered products became increasingly complicated, it became necessary to devise other inspection methods. One of these is remote visual inspection (RVI), which still permits the human brain to make critical assessments but allows the eye to travel to previously inaccessible locations. Inspection, and specifically nondestructive testing (NDT) or examination, is a vital technology for the operation of any industrial plant and in the manufacture of any product. Inspection is carried out to assess the functional integrity of offshore oilrigs, nuclear power stations and aircraft. Inspection is carried out during the manufacture of capital and consumer products from children’s toys to autocanmobiles to ensure quality and fitness for purpose. There are many techniques available for such inspections. Radiography provides volumetric inspection of simple and complex geometry items by using high-energy radiation to penetrate the parts. Ultrasonic techniques, or sound waves much like sonar, can be used to detect and size defects in materials. Eddy current techniques are used to identify near-surface or surfacebreaking defects. Very often the first stage, and often the last stage, in any inspection will be a visual inspection. Because of the complexity of much of today’s plant and equipment, very often this inspection has to be carried out remotely. QUALITY 101: NONDESTRUCTIVE TESTING, MARCH 2008 Nondestructive testing (NDT), or nondestructive evaluation (NDE), is a method of materials testing that assesses the characteristics of a component without altering or destroying it. NDT is important in the materials testing industry where quick, dependable information on finished or raw material is needed. This may occur during the production stage, during the service life of a material or product, or as a diagnostic tool in the event of material failure. NDT is contrary to destructive testing such as stress or bend testing where critical material properties are determined through achieving specimen failure. While destructive testing is intrinsically more revealing, it is costly to a manufacturing operation due to material loss and, for obvious reasons, it is not suitable for in-service material testing. Application uses for NDT cover a comprehensive range of material and industries such as automotive, aerospace, construction and a multitude of manufacturing types. A classic example of NDT at work is testing for weld defects at manufacture and periodically during service life of the welded material. Other typical applications include crack detection in aircraft skins, surface flaws in pipes or bar, and evaluation of heat treating of product. NDT also has become a valuable tool in the research and development field where quick, reliable data can provide vital information on materials. Typical types of NDT include ultrasonics, eddy current, rebound and ultrasonic contact impedance. Hardness testing by diamond or ball indentation also is—although sometimes arguably— considered a form of NDT, as in most cases the material only is indiscernibly affected. The force applied in a hardness test correlated either with the depth of indent or with area of indent provides a measurement of hardness. Typically the properties and usefulness of the material is not compromised. Microhardness testing is the best example of a nondestructive hardness test. UNCONVENTIONAL NDT, JANUARY 2009 Robert Nath, chairman, and Mike Giannini, business development manager of Magnaflux Quasar (Albuquerque, NM), say that when customers approach them with a specific problem, they look at the application and then make recommendations to the customer. “Sometimes our recommendation is based on the physical properties required, sometimes it’s the economics of it, sometimes a combination,” Giannini says. “When it is possible to test between two different methods, our job is to recommend the most reliable means of testing and the most economical way for the customer.” Also, the method used depends on the industry. Liquid penetrant is heavily used in aerospace, but not widely used in automotive, where magnetic particle and resonance inspection would be more common. If ferrous materials are involved, magnetic particle inspection may be a good fit. If the customer is looking at areas with no surface imperfection and the potential for failure in service, resonant testing would be a solution. Though Magnaflux Quasar’s customers come from various industries, Giannini acknowledges that NDT is not widely known. “If you asked 10 people on street, ‘what is NDT?’ you would get blank stares,” he says. However, Giannini points out that almost everyone is affected by NDT technology. “Anybody who uses a vehicle for anything is made safer by these industries.” One recent example was an application for a high-end automobile engine manufacturer in Europe, for which Magnaflux successfully implemented resonant testing equipment. While the company has offered a magnetic particle method and liquid dye penetrant for more than 70 years, it began offering resonance testing equipment when it acquired Quasar in March of 2007. Unlike other testing methods, resonance testing equipment finds structural anomalies, and measures structural weaknesses and surface systems. Imagine driving to work, Giannini says, and the steering knuckle of the car breaks. “This would not be a good start to your day,” he says. These types of structural defects can be found with resonant testing, and it would take two to three seconds to test the knuckle. These results cannot be found with any other method, Giannini says. “What we’re doing is making sure you make it back and forth to work without the steering knuckle giving out on you,” Giannini says, as the company deals with safety critical and warranty critical parts. According to the company, Quasar process compensated resonant testing (PCRT) provides effective resonance inspection in the presence of typical manufacturing process variations. Using PCRT, defective parts can be reliably rejected on the production line because the results correlate directly to part performance. The resonant frequency of a part is based on its stiffness and mass. The Quasar method measures several resonances for each part and uses a proprietary pattern recognition algorithm to compensate for the acceptable process variations, according to Magnaflux.
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