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1、RADIOGRAPHIC TESTINGIntroductionThis module presents information on the NDT method of radiographic inspection or radiography.Radiography uses penetrating radiation that is directed towards a component. The component stops some of the radiation. The amount that is stopped or absorbed is affected by m
2、aterial density and thickness differences. These differences in “absorption” can be recorded on film, or electronically. OutlineElectromagnetic Radiation General Principles of Radiography Sources of Radiation Gamma Radiography X-ray RadiographyImaging Modalities Film Radiography Computed Radiography
3、 Real-Time Radiography Direct Digital Radiography Computed RadiographyRadiation SafetyAdvantages and LimitationsGlossary of TermsElectromagnetic RadiationThe radiation used in Radiography testing is a higher energy (shorter wavelength) version of the electromagnetic waves that we see every day. Visi
4、ble light is in the same family as x-rays and gamma rays.General Principlesof RadiographyTop view of developed film X-ray filmThe part is placed between the radiation source and a piece of film. The part will stop some of the radiation. Thicker and more dense area will stop more of the radiation. =
5、more exposure= less exposureThe film darkness (density) will vary with the amount of radiation reaching the film through the test object.General Principlesof Radiography The energy of the radiation affects its penetrating power. Higher energy radiation can penetrate thicker and more dense materials.
6、 The radiation energy and/or exposure time must be controlled to properly image the region of interest.Thin Walled AreaLow Energy RadiationHigh Energy RadiationIDL 2001Radiography has sensitivity limitations when detecting cracks. X-rays “see” a crack as a thickness variation and the larger the vari
7、ation, the easier the crack is to detect. Optimum AngleFlaw Orientation= easy to detect= not easy to detectWhen the path of the x-rays is not parallel to a crack, the thickness variation is less and the crack may not be visible. IDL 20010o10o20oSince the angle between the radiation beam and a crack
8、or other linear defect is so critical, the orientation of defect must be well known if radiography is going to be used to perform the inspection.Flaw Orientation (cont.)Radiation SourcesTwo of the most commonly used sources of radiation in industrial radiography are x-ray generators and gamma ray so
9、urces. Industrial radiography is often subdivided into “X-ray Radiography” or “Gamma Radiography”, depending on the source of radiation used.Gamma RadiographyGamma rays are produced by a radioisotope. A radioisotope has an unstable nuclei that does not have enough binding energy to hold the nucleus
10、together. The spontaneous breakdown of an atomic nucleus resulting in the release of energy and matter is known as radioactive decay.Gamma Radiography (cont.)Most of the radioactive material used in industrial radiography is artificially produced. This is done by subjecting stable material to a sour
11、ce of neutrons in a special nuclear reactor. This process is called activation.Gamma Radiography (cont.)Unlike X-rays, which are produced by a machine, gamma rays cannot be turned off. Radioisotopes used for gamma radiography are encapsulated to prevent leakage of the material. The radioactive “caps
12、ule” is attached to a cable to form what is often called a “pigtail.” The pigtail has a special connector at the other end that attaches to a drive cable.Gamma Radiography (cont.)A device called a “camera” is used to store, transport and expose the pigtail containing the radioactive material. The ca
13、mera contains shielding material which reduces the radiographers exposure to radiation during use. Gamma Radiography (cont.)A hose-like device called a guide tube is connected to a threaded hole called an “exit port” in the camera. The radioactive material will leave and return to the camera through
14、 this opening when performing an exposure!Gamma Radiography (cont.)A “drive cable” is connected to the other end of the camera. This cable, controlled by the radiographer, is used to force the radioactive material out into the guide tube where the gamma rays will pass through the specimen and expose
15、 the recording device.X-ray RadiographyUnlike gamma rays, x-rays are produced by an X-ray generator system. These systems typically include an X-ray tube head, a high voltage generator, and a control console. X-ray Radiography (cont.)X-rays are produced by establishing a very high voltage between tw
16、o electrodes, called the anode and cathode. To prevent arcing, the anode and cathode are located inside a vacuum tube, which is protected by a metal housing.X-ray Radiography (cont.)The cathode contains a small filament much the same as in a light bulb. Current is passed through the filament which heats it. The heat causes electrons to be stripp
