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Radiography, the use of ionizing electromagnetic radiation for object imaging, can be used for the nondestructive testing of subjects in many industries. Radiographic inspection methods are employed for flaw detection in castings, weldments, solid propellants, missile hardware and finished assemblies, as well as many other applications. Test subjects can range in size from microminiature electronic parts to large rocket motors.
Radiographic inspection is useful for inspecting castings because it readily detects most flaws and discontinuities that can occur in ferrous and nonferrous castings, such as shrinkage, gas porosity, inclusion, hot tears, cold cracks and shuts, core shifts, and major surface irregularities. Radiographic inspection also can detect discontinuities that can occur in light metals such as aluminum and magnesium: gas holes, dross, inclusions, segregation, microshrinkage, hydrogen porosity, microporosity, shrinkage, sponge and cold shut, for example.
It also is used in the writing of welding procedures to qualify welders and to control quality of welded joints, and can be used to detect internal discontinuities in welds, such as porosity, cracks, lack of adequate penetration and fusion, undercut, and inclusions. The method can be used in the inspection of solid propellant rocket motors to detect cracks, voids, unbonded surfaces, foreign material inclusion and other anomalies. Radiographic inspection also can be used with missile hardware to detect cracks, unbonded surfaces and ensure internal conformance specifications.
Finished assemblies such as electronic devices, mufflers and fuel tanks can be subjected to radiographic testing for the inspection of electrical connections and the position of nuts and bolts, for example.
Modern radiographic inspection also allows for the inspection of forgings, powder metal parts and nonmetallic materials such as plastic, rubber and ceramics.
Radiographic inspection can be used with virtually all materials and reveals most discontinuities and assembly errors. However, it is a relatively expensive testing technique and safety concerns are always an issue when X-rays are used.
What follows are a number of radiographic inspection offerings for today’s nondestructive testing applications.
Metrotomography is a combination of computed tomography and traditional metrology. During the measurement process, a computer tomograph uses X-rays to nondestructively measure the interior and exterior of complex and small workpieces and then display the results as a 3-D image. The procedure is similar to the X-ray technology used in medicine. X-rays penetrate an object and display it on a detector. The details of the object appear as a 2-D image in varying intensity depending on the geometry and absorption properties. The 3-D image is created by rotating the object 360 degrees along its axis on a rotary table and then converting this data to a 3-D volume model.
Metrotomography can be used for assembly checks and damage analyses, material inspections, and porosity and defect analyses. Parts up to 350 millimeters can be inspected depending on the material-steel, alloys, ceramic and plastic, for example. The system is available with the company’s Calypso Metrology software. It supports comparisons to nominal geometries in which only visual inspections were possible in the past. It also allows for continuous monitoring of development up to the prototype. Workpieces, casting and assembly procedures can be modified during the development phase.
A Metrotom computer tomograph can generate a complete computer-aided design (CAD) data set of each metrotomographed workpiece. This can then be displayed in all standard formats, thus enabling generation of fast, highly accurate data during the development of the design.
The 49.2- by 49.2-millimeter sensing area consists of a 1,024- by 1,024-pixel CMOS photodiode array imager with pixels on 48-micrometer centers. The active area is obtained without the need for an optical interface. A Gd2O2S scintillator screen placed in direct contact with the photodiode array converts incident X-rays or energetic particles to visible light, which in turn is detected by the photodiode imager. Two models cover the energy range from 10 to 160 kilovolts.
The system includes digital X-ray images in three seconds; medical-grade flat panel amorphous silicon image receptor; 127-micron pixel pitch; advanced image processing software; the ability to interface with many portable and fixed X-ray sources; and no cassettes, film or chemicals.
Three stages of expansion allow adaptation to meet specific requirements: coordinate measuring machine (CMM) with tomography sensors based on proven software and machine components; raster tomography for measuring small features at high resolution, even on large parts; and expansion of the range of applications, through the combination of additional sensors.
The machines have a specification for contact and length measurement deviations, as is typical for CMMs. Complete software integration of all functions required for automatic measurement increases ease of use.
User interface translations are available in French, Italian, German and Spanish with the Kodak Industrex V2.0 multilingual software kit.
The system can examine test objects with a maximum weight of 30 kilograms and dimensions of 500 (H) by 335 (W) millimeters. The test object is attached to a manipulator that is situated in a protection cabin and consists of a rotary table. The test object is located between the X-ray tube and the detector. During the examination the test object is turned 360 degrees in small predefined steps. X-ray tubes are available with 225, 320 or 450 kilovolts.
The line detector offers a lateral resolution of 0.12 by 0.25 millimeter. The scan time is approximately 15 seconds, and the first reconstructed picture is delivered after 30 seconds.
Envision Product Design (www.cmosxray.com) introduces the LongSeam real-time system for inspection of welds in heavy wall pipe manufacturing. The LongSeam X-ray system automates pipe-seam weld inspection with 20- to 450-kilovolt X-ray systems capable of inspecting 40-foot pipe sections with 2-inch pipe wall thickness. Using CMOS X-ray technology, the image quality has 12-bit contrast resolution and 80-micron spatial resolution. The system includes an image software package with scrolling display combined with fully integrated pipe motion control, X-ray tube management and optional automatic defect recognition.
North Star Imaging Inc. (www.xviewct.com) introduces software for computed tomography acquisition and reconstruction, enabling the production of 3-D results in seconds. Acquisition times are as fast as six seconds and a 5123 voxel reconstruction is completed in as little as nine seconds.