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Radiography in NDT
Radiography for non-destruction testing
| Question | Answer |
|---|---|
| What is attenuation of radiation? | Absorbed rays of radiation |
| What are 6 advantages of radiographic testing? | 1) compatible with most materials 2) permanent record 3) reveal internal discontinuities 4) allows internal inspection 5) discloses fabrication errors 6) reveals assembly errors |
| What are 5 limitations of radiographic testing? | 1) accessibility to both sides of test object are required 2) expensive 3) time consuming 4) depth to discontinuity may be difficult to determine 5) small discontinuities that are not parallel with the radiation beam are difficult to detect (image) |
| What are the basic principles to minimize radiation exposure in industrial radiography? | 1) minimize time duration working with radiation sources 2) increase distance between the source of radiation and the technician 3) provide suitable shielding |
| How many basic levels of qualification are there for non-destructive personnel? | 3 |
| How do you become qualified in non-destructive testing in accordance with SNT-TC-1A? | 1) training 2) experience 3) vision test 4) color test |
| What is non-destructive testing certification? | Personnel may be certified when they have completed the initial training, experience, and examination requirements. |
| How does test object thickness variations affect film density on a radiograph? | Less absorption occurs where the test object is thin or where a void is present. Thicker portions of the test object or dense inclusions will appear lighter because of more absorption of the radiation. |
| What is another name for the shadow of geometric unsharpness? | Penumbra |
| What 3 items determine the sharpness of an image on a radiograph? | 1) Size of the radiation source 2) Ratio of the (OFD) object-to-film distance 3) Ratio of the (SOD) source-to-film distance |
| What is the darkest part of the shadow on a radiograph? | The umbra |
| What 3 factors would achieve optimum geometrical sharpness of a radiographic image? | 1) Radiation source is small 2) Distance from the source to test object is relatively great 3) The distance from the test object to film is small |
| What is the formula to determine geometric unsharpness in a radiograph? | |
| Ug = Fd/D--- Ug = geometric unsharpness F = source size D = the distance from the source of radiation to the test object (OFD) d = the distance from the source side of the test object to the film (OFD OR material thickness) | |
| How do you get the optimum geometrical sharpness of an image in a radiograph? | Optimum geometrical sharpness of the image is obtained when the radiation source is small, the distance from the source to the test object is relatively great, and the distance from the test object to the film plane is small. |
| What are the two possible causes of image distortion? | 1) the plane of the test object and the film planes are not parallel 2) the radiation beam is not directed perpendicular to film plane |
| In what spectrum do X-rays and gamma-rays overlap? | Electromagnetic spectrum (EMR) |
| What are the characteristics of X-rays and gamma-rays? | 1)wavelength inversely proportional to their energy 2)travel in straight lines 3)travel in a vacuum at the speed of light 4)have no electrical charge/no rest mass 5)not detectable by human senses 6)penetrates matter 7)absorbed, scattered,& ionize matter |
| What is the difference between X-rays and gamma rays? | Their origin, an x-ray is an atomic phenomenon, gamma rays are a nuclear phenomenon |
| What is Bremsstrahlung radiation? | Electromagnetic radiation produced when electrons path and kinetic energy brings them close to the positive fields of atomic nuclei- as when electrons strike a Target provided for this purpose. The electrons slow down, giving up kinetic energy as X rays |
| What 3 terms is Bremsstrahlung radiation also known as? | 1) continuous radiation 2) braking radiation 3) white radiation |
| Energies of the electrons and x-rays are usually given in what? | Kiloelectronvolts (keV), which correspond to the amount of kinetic energy that an electron would gain when moving between two points that Dipper in voltage . megaelectrinvolts (MeV) |
| What does the anode side of an x-ray tube contain and what charge does it have? | The anode side of an x-ray tube contains the Target, and it is positively charged |
| In an x-ray tube, what is the source of electrons known as? | The cathode |
| What does the cathode side of an x-ray tube contain and what charge does it have? | 1) focusing cup 2) filament 3) has a negative charge |
| In an x-ray tube, what does the intensity depend on? | By increasing the kilovolts this increases the current through the tube filament, which increases the cathode temperature, and causes more emission of electrons, therefore increasing the intensity of the x-ray beam. |
| How is the intensity of the generated beam (in an x-ray) measured? | It is measured in volts (either kV or MeV) |
| What mathematical law do you use in Computing radiographic exposures and safety procedures? | Inverse Square law. ( the intensity of an x-ray beam varies inversely with the square of the distance from the radiation source) |
| What happens if you increase the voltage in an x-ray? | The x-rays will have a shorter wavelength (more energy) |
| What are hard x-rays? | High energy, short wave length, more punching power (high kilovoltage) |
| What are soft x-rays? | Low energy, longer wavelength, weaker x-ray |
| What are the effects of kilovolts in an x-ray? | (Low amperage) Low-intensity soft x-ray (low kilovoltage). Low-intensity hard x-ray (high kilovoltage) |
| What are the effects of amperage in an X-ray? | (High amperage) High-intensity soft x-ray (low kilovoltage). High-intensity hard x-ray (high kilovoltage) |
| What are the three types of scatter? | 1) internal scatter. 2) sidescatter. 3) backscatter |
| What is internal scatter? | It is the scattering that occurs in the object being radiographed, it is reasonably uniform throughout a test object of one thickness but affects definition by blurring the image outline |
| What is buildup of internal scatter? | Buildup is the increase in radiation passing through matter caused by scatter in the forward Direction |
| What is sidescatter? | It is the scattering from walls of an object in the vicinity of the test object or from portions of the test object that cause rays to enter the side of the object being tested. |
| What is Backscatter and what does it do to the image of the test object on a radiograph? | It is the scattering of rays from surfaces or objects beneath or behind the object being tested. It also obscures the test object image. |
| What are the methods in controlling scatter in it test object? | Lead screens can reduce or eliminate the problem of internal scatter. To control or limit Backscatter and sidescatter, diaphragms, collimators, cones, masking material, and area shielding equipment are used. |
| What are the three basic requirements for generating x-rays? | 1) source of free electrons 2) means of moving the electrons rapidly in the desired directions 3) suitable materials for the electrons to strike |
| What two electrodes are contained in the high vacuum envelope of an x-ray tube? | 1) Anode 2) Cathode |
| The filament of an x-ray tube emits what, which strike what to generate x-rays? | Free electrons leave the filament in the cathode striking a Target in the anode |
| What function does the focusing cup perform? | The focusing cup is an electrostatic lens in which to direct the electrons in a beam towards the anode. |
| The filament and Target are usually made of what material? | Tungsten |
| What application to the filament controls the intensity of the x-rays generated? | Amperage / current |
| What factor limits the size to which a focal spot can be reduced, on an X-ray tube Target? | The size to which the focal spot can be reduced is limited by the heat generated in Target bombardment. |
| The majority of energy spent, an x-ray generation, is lost in the form of what? | Heat |
| In radiography, what is the phenomenon known as heel effect? | The intensity of the beam rapidly diminishing from a central Ray towards the anode side and slightly increasing towards the cathode side. |
| What factor determines the penetrating ability of an x-ray machine? | Operating voltage (kilovolts) |
| What is the thin, flexible plastic sheet that is support for the other material in the cross-section of radiographic film? | The base ( made of acetate or polymers) |
| What does the Emulsion, in radiographic film, contain that forms a visible latent image after exposure and processing? | Silver bromide crystals in gelatin |
| What is radiographic "definition"? | The sharpness of any change in density |
| Radiographic contrast is a combination of what two types of contrast? | Subject contrast and film contrast |
| What three factors does subject contrast depend on? | 1) type/configuration of test object 2) energy & wavelength of the radiation used or type of isotopic source 3) intensity & amount of the scattered radiation. |
| The ability of film to detect and record different radiation exposures as differences in density is called what? | Film contrast |
| What six factors determine film contrast? | 1)grain size/type of film 2-3)chemistry/concentration of the film processing chemicals 4) development time 5) development temperature 6) type of agitation |
| What are the ISO and equivalent ATSM film classes, listed from the slowest to fastest? | 1) class C1-ASTM class special 2) class C2, C3 & C4-ASTM class I 3) class C5-ASTM class II 3) class C6-ASMT class III |
| How does film speed relate to film grain size? | Fast films have larger grains which may cause blurry of the outline of discontinuities. |
| What are the five separate steps, and proper order, and tank processing? | 1) developer 2) stop bath 3)fixing 4) washing 5) drying |
| What step, in tank processing, does the silver bromide crystals on the film get reduced to metallic silver? | Developing |
| What function does the stop bath perform in manual processing? | The stop bath neutralizes the alkaline remnants of the developer, permitting the acid in the fixer solution to function in the desired manner. ( it removes the residual developer solution from the film to prevent film streaking) |
| Excessive film density may be caused by what? | 1) over exposure to radiation 2) overdevelopment of film 3) film fog |
| What are causes for over development? | 1) too long a development time 2) too warm a developer solution 3) possibly both |
| What is the definition of fog, related to radiographic film? | The increase of film density caused by sources other than from the intended primary beam exposure. Heat, humidity, pressure, and scatter radiation can all cause fogging of the film. |
| What is a double exposure? | Exposing the same film twice, resulting in the presence of two images on the film. |
| What three factors may cause inadequate film density? | 1) underexposure 2) under development 3) the presence of foreign materials between the lead screen and the film |
| Excessive radiographic contrast may result from what two factors? | 1) high subject contrast 2) high film contrast |
| What three ways could you correct for high subject contrast? | 1) increase kilovoltage 2) use a filter at the X-ray tube 3) use masking to lessen the thickness range |
| How would you correct a high film contrast? | Use film with a lower contrast |
| What are the possible causes for poor radiographic definition? | 1) geometric exposure factors 2) poor contact between film and intensifying Screen 3) graininess of fluorescent intensifying screens 4) graininess of film |
| What three causes of fog, on a radiograph, are attributed to improper film processing? | 1) overdevelopment 2) contaminated developers solution usually incorrectly mixed 3) prolonged inspection of film |
| Causes of streaking of radiographic films may be associated with what? | 1) development 2) stop bath and fixer 3) film drying |
| Sources of spotting include what? | Water, developer, air bubbles, inopportune splashing of stop bath or fixer, or dirt |
| What are several forms of damage to film emulsion? | Including reticulation, frilling, scratches, & lead oxide |
| Define reticulation | A puckered ornette like film service that can result from a sudden extreme temperature change in processing. |
| Define frilling | A loosening of film Emulsion from the base that can result from warm or exhausted fixer solution |
| Various artifacts, due to improper film handling, include... | 1) pressure 2) static 3) crimp marks |
| What will a pressure mark look like on a developed radiograph? | The radiograph will appear as a lower density compared to the adjacent area. |
| What will static marks resemble on a developed radiograph? | Tree-like or branching on the developed radiograph |
| What will crimp marks resemble, before and after exposure, on a developed radiograph? | Before the developed radiograph, you will see a white, Half-Moon shaped mark. After the radiograph, you will see a black, Half-Moon shaped mark. |
| What characteristics do diaphragms, collimators, and Cones all share? | 1) They limit the area of radiation 2) decrease the scatter by limiting the beam of radiation to a desired test object. |
| What purposes can filters accomplish in radiography? | 1)reduce subject contrast giving you a more latitude on the film 2) absorb soft radiation 3) reduce scatter caused by Soft radiation 4) permits a wide range of test object thickness to be recorded |
| What are two types of radiographic screens? | Fluorescent screen and LEAD screen |
| Lead screens are particularly efficient because of their ability to... | 1) absorb scatter radiation 2) increase the photographic action of the primary radiation on the film |
| What is an advantage of fluorescent screens under LEAD screens? | Fluorescent screens expose the film faster than lead screens |
| What is masking in radiographic testing? | Masking reduces the subject contrast by eliminating side scatter |
| What is the image quality indicators (IQI) used to check in radiography? | The adequacy of the radiographic technique |
| What are the 2 types of IQIs utilized in radiography? | 1) hole type 2) wire type |
| When utilizing a hole type IQI, what do the numbers and letters mean for a 2-2 T quality requirement? | T = thickness; 2T = 2*thickness: 2 = % of material thickness |
| What are the sets for wire type IQIs, and what is the difference between the sets? | A-D and the difference between the sets is the wire diameters. |
| What is a shim stock? | It is a thin piece of material identical to the test object. Shims are used in radiography of test objects such as welds, where the area of interest is thicker than the nearby test object thickness. |
| What are shims used for in radiography and where do you place them on the test object? | Shims are used to make the metal the same thickness as the weld. |
| What must a film cassette keep the film protected from? | 1) Light 2) moisture 3) contaminants |
| What is a densitometer? | An instrument that measures the intensity of light transmitted through a radiograph, providing a density value. |
| What 3 items does x-ray exposure chart plot the relationship of? | 1) material thickness 2) kilovoltage 3) exposure |
| Define film latitude... | The variation in material thickness that can be radiographed with 1 exposure while maintaining film density within acceptable limits. |
| What is a dated decay curve? | Computer generated tables of date verses source activity |
| What is plotted on the X and Y axis of an x-ray and gamma ray exposure chart? | X = Thickness of the material; Y = exposure |
| What are 3 exposure factors in X-radiography? | 1) kilovoltage 2) milliamperage 3) time |
| What are 3 exposure factors in gamma radiography? | 1) source energy 2) source strength 3) time |
| What is the equation used in the Reciprocity Law and what do the variables represent? | M1 * T1 = M2 * T2____ M = milliamps ___ T = time. T1/T2 = M2/M1 |
| What are 4 radiograph technique arrangements? | 1) Single Wall/Single Image (SWSI) 2) Double Wall/Single Image (DWSI) 3) Double Wall/Double Image (DWDI) or elliptical 4) Double Wall Superimposed |
| In the SWSI technique, where is the IQI placed? | On the source side of the test object |
| What are two methods of determining depth of a discontinuity? | 1) stereoradiography 2) parallax |
| All circular test objects should be numbered in what direction? | Clockwise |
| Lead location markers should be placed adjacent to the weld, but never within the what? | .125 in from the heat affected Zone |
| In the DWSI technique, what is the IQI thickness based on? | The thickness of a single wall |
| In the DWSI technique, where is the IQI placed and what is required to be placed along with the IQI? | The IQI is placed on the film along with the letter "F" |
| What is fluoroscopy? | The process in which an x-ray image is observed on a fluorescent screen. |
| What are two radiographic techniques used to determine depth of a discontinuity? | 1) Stereoradiography 2) double exposure (parallax) |
| What does stereo radiography use to give the viewer a three-dimensional effect? | To radiographs are made with two different positions of the X-ray tube. The viewer looks at them like you would 3D viewer. |
| How would you determine depth using the Double Exposure(parallax) technique? | d = bt/a+b |
| Flash radiography permits the observation of what? | High-speed events in opaque material. It is primarily used for observation of explosive or ruptured processes. |
| Describe in-motion radiography... | Any radiographic technique where the source of radiation, the test object, or the film is moving during the exposure |
| How does Backscatter Imaging work? | It collects scattered radiation (from one side) instead of the transmitted radiation to form an image. |
| Does the image of indications on a radiograph appear lighter or darker? | It shows up as a difference in the pattern of Darkness, so the image could be either lighter or darker. |
| What are relevant discontinuities? | Any unintended disruption in the physical structure or makeup of a material or part. |
| List the discontinuities that are relevant indicators... | 1) porosity, hot tears and cracks in casting 2) laps and bursts in forgings 3) stringers and laminations (rolled) 4) Chevron cracks (extruded products) 5) incomplete penetration, root concavity and undercut (welds) |
| What are non-relevant indications? | Any induced acceptable break in the physical structure of an object. |
| List 4 examples of non-relevant discontinuities... | 1) keyway 2) hole drilled in flange 3) two different thickness joined in welding process 4) a raised part in a casting |
| What is a discontinuity? | A break in the test objects structural continuity |
| What is a defect? | Any condition that renders the part unsuitable for the intended services. |
| What are true indications? | A change in thickness or atomic number due to differential absorption. |
| What are false indications? | Indications with no relevance to a defect or discontinuity. Usually associated with screen problems, fog, scatter, molting, Etc. |
| What are artifacts? | A false indication |
| What are the three General categories of discontinuity types? | 1) inherent 2) processing 3) inservice |
| What are inherent discontinuities? | Inherent discontinuities are nonmetallic inclusions, originating in the casting process. |
| What are processing discontinuities? | Discontinuities caused by Rolling, forging, and Welding |
| What are in-service discontinuities? | Discontinuities that occur during the service life of a part. |
| Discontinuities caused by gases entrapped during solidification of molten metal are called what? | 1) gas holes 2) wormhole 3) porosity 4) blowhole |
| Describe the image porosity produces on a radiograph... | They are generally spherical and sometimes elongated. They can be individually identified and defined on a radiograph as distinct globular gas voids. The most serious gas voids are referred to as gas holes, wormholes, porosity, or blowholes. |
| What is the difference between a hot tear and a crack? | Hot tears have jagged edges whereas cracks are smooth in appearance. |
| What are three types of inclusions? | 1) sand 2) slag 3) dense inclusions |
| What are 4 forging discontinuities? | 1) laps 2) bursts 3) pipe 4) cracks |
| What are 3 rolling discontinuities? | 1) stringers 2) laminations/laminar discontinuities 3) seams |
| What are the 5 most common fusion welding techniques? | 1) shielding metal arc welding (SMAW) 2) submerged arc welding (SAW) 3) gas tungsten arc welding (GTAW) 4) gas metal arc welding (GMAW) 5) flux-cored arc welding (FCAW) |
| What are the main discontinuities found in fusion welding, associated with the weld root? | 1) incomplete fusion 2) incomplete penetration 3) root concavity 4) root undercut |
| Describe the image of incomplete penetration in a radiograph.... | A distinct, geometrically perfect projection of a darker, straight-line image at the middle of the weld bead, only if the source is in line with the film, perpendicular to the discontinuity |
| Describe the image of incomplete fusion on a radiograph.... | This shows a darker image with a straight line on one side of the root run. |
| Describe the image of root concavity on a radiograph... | This shows a darker area than the surrounding weld metal, forming a broad, dark image with unsharp edges at the root of the weld |
| Describe the image of root undercut on a radiograph.... | This produces a sharp notch and may detrimental in service |
| Describe the image of lack of fusion on a radiograph... | This presents a faint, darker linear indication, away from the weld root. |
| What is a slag inclusion? | Any nonmetallic inclusion entrapped in the weld metal |
| What causes slag inclusions? | * entrapped slag not properly removed between passes * oxide gases, namely nitrogen in the arc & atmospheric gases reacting with iron manganese, or silicon in the molten metal * improper manipulation of the electrode |
| Describe the image of a slag inclusion on a radiograph... | Slag is less dense than the weld bead or parent metal which creates a darker image with wavy edges. |
| What causes tungsten inclusions? | * They occur with GTAW (gas tungsten arc welding) when a portion of the tungsten electrode chips or breaks off * drops in the weld & becomes entrapped |
| Describe the image of a tungsten inclusion on a radiograph. | Tungsten inclusions have a higher density than the weld metal and appear as light or white spots in the radiograph. |
| List six types of cracks that occur in weld metals. | *longitudinal *root *heat affected *transverse *toe *crater |
| What causes porosity in welds? | Entrapped gas pocket, generally less than 1/16 inch. |
| Describe the image of porosity on a radiograph. | Porosity produces a darker image, typically spherical in shape because it has less density than the weld metal. |
| What are the three types of digital imaging techniques? | * (CR) computed radiography * (DR) digital detector array * (CT) computed tomography |
| List the advantages of digital radiography. | *more efficient, no cassettes to use * immediate preview/transfer * lower radiation exposure * wider dynamic range * reduced cost compared to traditional radiography |
| How many times can Imaging plates be used before they need to be replaced? | Theoretically, thousands of times. However, IP handling under industrial conditions may result in damage after a few hundred uses. |
| What Greek word does the term tomography derive from and what does it mean? | Greek- Tomos which means "cut" or "slice" |
| What digital technique uses a collimated fan beam and a linear detector array to acquire data and reconstruct the cross-section of the object? | Computed tomography |
| Computed tomography was adapted to Industrial applications for its ability to virtually slice open a test object to do what three inspections? | *examine its internal features *perform dimensional inspection or measurements * identify any material or structural anomalies that may exist |
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