Automotive Engineering

PhD Eng. Marcin Korzeniowski

Non Destructive Evaluation in Contemporary Manufacturing Systems

Lecture 7Radiography Testing

Radiography TestingX-rays are electromagnetic waves with an energy that is 100100,000 times higher than visible light, Like visible light, X-rays can be scattered and absorbed by materials,X-rays have a much higher energy, these rays tend to pass through materials that block visible light, Xray scan see through objects that are opaque to the naked eye,

The electromagnetic spectrumX-radiation (composed of X-rays) is a form of electromagnetic radiation.

X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies from 3 1016 Hz to 3 1019 Hz and energies in the range 120 eV to 120 keV.

They are shorter in wavelength than UV rays and longer than gamma rays. In many languages, X-radiation is called Rntgen radiation,

in the English language includes the variants x-ray(s) and X ray(s).

The radiation sourcesX ray radiationgenerated by Xray tube, radiation,generated by isotopic sources,

The scheme of radiographic testing

The X-ray tube

Isotopic sources

Detection of the radiation

Analog detectors (film)

During irradiation a changes in film structure of silver compounds appears. Latent image is formed, which can be detected only photochemical methods (developing). During develeloping of the film the granules of black silver are formed.

Detection of the radiationEmulsion layer on both sides of the film surface (1) is divided into two layers (2 +3). This increases the uniformity of the distribution of grains in the film and makes an excellent uniformity of density.

To protect protect film from the stresses the coatings are covered by two separate layers (4 +5). To achieve the matte surface of the radiographic image, the outer layer contains a matting agent.

Intensifying screenOnly about 1% of the X-ray and radiation incoming to the film is absorbed by the photographic emulsion. The rest passes through the membrane and is not used.To increase the impact of radiation on the radiographic film intensifying screens are used: metal (usually lead with thicknesses 0.02, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.40, 0.50mm), fluorescent, fluorometalic.

Radiographic film is placed between two intensifying screens. The thickness of the screen is chosen according to the radiation energy.

Lead screenthe effect of enhancing the exposure of photographic emulsion is reached by knocking out of the electron, for which emulsion is sensitive, the front screen absorb some rays, are so filters, enhanced contrast of the radiographs because of reduction of scattered radiation, exposure time significantly reduced, the effect of strengthening ca . 5 timesIntensifying screen

Fluoroscent screens

contain the phosphor (luminophor) layer (mainly calcium tungstate CaWO4), under the influence of X-ray and phosphor emits visible and ultraviolet light, the effect of the gaining 10 - 100X, worse quality than using radiographic images (compared with lead screens), is the result of the much larger grains than a grain of phosphor films.Intensifying screen

Detection of the radiationDigital detectorsphotodiode coupled linear array

Radiographic examination techniques

by one wallsSourcesradiographic filmradiographic film

Sourceobject to be inspexted (f.ex. gas pipe under the pressure)Radiographic examination techniques

by two walls (f.ex. pipes)radiographic film

Exposure diagrams

Made for each type of films and materials.

The value of exposure is unit: mA minVoltage [kV]the thicknes of the plate [mm]

radiographic film for aluminum and aluminum alloysExposure diagramsradiographic film for steel and iron matrices alloys

X-Ray imagetaken with high class film (D2)150 kV, 5 mA, Pb Filter, 1000 mm FFD, Exposure time 330 s Scanned with Primescan 7100 (10 m pixel distance, aperture 21 m, averaged to 50 m acc. to ISO 14096; 16 Bit gray values

Detail of welding seamwith XRD 1620 and 3 x geom. Magn. SNRnorm 1040

Detail of welding seamwith XRD 1620 and 3 x geom. Magn.

Resolution of longitudinal objects like cracksOrange marked zones of cracks that can be seenSmalles visible defect

Whole crack can be seenSmalles visible defectResolution of longitudinal objects like cracks

Resolution of circular objects like holes (porosities)Smalles visible defect

Smalles visible defectResolution of circular objects like holes (porosities)

Better defect recognition through better signal-to-noise rationD2 film, class C1 EN 584-1330 s exposure time PE XRD1620 detector (200 m SRB), magnification of 3.0 100 s exposure time

Radiography TestingAdvantages and disadvantages

References:ASM Handbook Volum 17 - Nondestructive Evaluation and Quality Control, 5th Edition 1997.Shull P.J. Non Destructive Evaluation. Theory, Techniques and Applications., Marcel Dekker 2001.Lewinska-Romicka A. Badania nieniszczace podstawy defektoskopi, WNT 2001,http://www.ndt-ed.org ,http://www.asnt.orghttp://www.acndt.comhttp://www.ndt-instruments.comhttp://engineering.indiabizclub.comhttp://www.envirocoustics.grwww.ndt.pl/http://www.ndt.org/

Source of informationThe Collaboration for NDT Education www.ndt-ed.orgThe American Society for Nondestructive Testing www.asnt.org

IDL 2001Radiography has sensitivity limitations when detecting cracks. X-rays see a crack as a thickness variation and the larger the variation, 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 2001Since the angle between the radiation beam and a crack 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 sources. Industrial radiography is often subdivided into X-ray Radiography or Gamma Radiography, depending on the source of radiation used.

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 capsule 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 camera contains shielding material which reduces the radiographers exposure to radiation during use.

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 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 two 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 stripped off. The high voltage causes these free electrons to be pulled toward a target material (usually made of tungsten) located in the anode. The electrons impact against the target. This impact causes an energy exchange which causes x-rays to be created.

Imaging ModalitiesSeveral different imaging methods are available to display the final image in industrial radiography:Film RadiographyReal Time RadiographyComputed Tomography (CT)Digital Radiography (DR)Computed Radiography (CR)

Film Radiography (cont.)Film must be protected from visible light. Light, just like x-rays and gamma rays, can expose film. Film is loaded in a light proof cassette in a darkroom. This cassette is then placed on the specimen opposite the source of radiation. Film is often placed between screens to intensify radiation.

Film Radiography (cont.)In order for the image to be viewed, the film must be developed in a darkroom. The process is very similar to photographic film development.Film processing can either be performed manually in open tanks or in an automatic processor.

Film Radiography (cont.)Once developed, the film is typically referred to as a radiograph.

Digital RadiographyOne of the newest forms of radiographic imaging is Digital Radiography.Requiring no film, digital radiographic images are captured using either special phosphor screens or flat panels containing micro-electronic sensors.No darkrooms are needed to process film, and captured images can be digitally enhanced for increased detail.Images are also easily archived (stored) when in digital form.

Computed RadiographyComputed Radiography (CR) is a digital imaging process that uses a special imaging plate which employs storage phosphors.

Computed Radiography (cont.)CR Phosphor Screen StructureX-rays penetrating the specimen stimulate the phosphors. The stimulated phosphors remain in an excited state.

Computed Radiography (cont.)After exposure:The imaging plate is read electronically and erased for re-use in a special scanner system.

MotorA/DConverterImaging PlateOptical ScannerPhoto-multiplier Tube110010010010110Laser BeamComputed Radiography (cont.)As a laser scans the imaging plate, light is emitted where X-rays stimulated the phosphor during exposure. The light is then converted to a digital value.

Computed Radiography (cont.)Digital images are typically sent to a computer workstation where specialized software allows manipulation and enhancement.

Computed Radiography (cont.)Examples of computed radiographs:

Real-Time RadiographyReal-Time Radiography (RTR) is a term used to describe a form of radiography that allows electronic images to be captured and viewed in real time. Because image acquisition is almost instantaneous, X-ray images can be viewed as the part is moved and rotated.Manipulating the part can be advantageous for several reasons:It may be possible to image the entire component with one exposure.Viewing the internal structure of the part from different angular prospectives can provide additional data for analysis.Time of inspection can often be reduced.

Real-Time Radiography (cont.)The equipment needed for an RTR includes:X-ray tubeImage intensifier or other real-time detectorCameraComputer with frame grabber board and softwareMonitorSample positioning system (optional)

Direct Radiography Direct radiography (DR) is a form of real-time radiography that uses a special flat panel detector.The panel works by converting penetrating radiation passing through the test specimen into minute electrical charges. The panel contains many micro-electronic capacitors. The capacitors form an electrical charge pattern image of the specimen.Each capacitors charge is converted into a pixel which forms the digital image.

Computed TomographyComputed Tomography (CT) uses a real-time inspection system employing a sample positioning system and special software.

Computed Tomography (cont.)Many separate images are saved (grabbed) and complied into 2-dimensional sections as the sample is rotated.2-D images are them combined into 3-dimensional images.

Real-Time CapturesCompiled 2-D ImagesCompiled 3-D Structure

Image QualityImage quality is critical for accurate assessment of a test specimens integrity. Various tools called Image Quality Indicators (IQIs) are used for this purpose.There are many different designs of IQIs. Some contain artificial holes of varying size drilled in metal plaques while others are manufactured from wires of differing diameters mounted next to one another.

Image Quality (cont.)IQIs are typically placed on or next to a test specimen.Quality typically being determined based on the smallest hole or wire diameter that is reproduced on the image.

Radiation SafetyUse of radiation sources in industrial radiography is heavily regulated by state and federal organizations due to potential public and personal risks.

Radiation Safety (cont.)There are many sources of radiation. In general, a person receives roughly 100 mrem/year from natural sources and roughly 100 mrem/year (1mSiwert/year) from manmade sources.

Radiographic Images

Radiographic ImagesCan you determine what object was radiographed in this and the next three slides?

Radiographic Images

Radiographic Images

Radiographic Images

********Within a CR reader, the IP is scanned with a laser beam in order to initiate the emission of light from the storage phosphors (photostimulated luminescence). The intensity of light emitted from the IP is proportional to the amount of radiation absorbed by the storage phosphor.

The laser scans across the surface of the IP in a raster pattern. During the reading process, the light that is emitted from the IP is collected by a light guide & sent to a photomultiplier tube (PMT). The signal coming from the PMT is amplified, spatially sampled, & then sent to be converted to a digital signal (in an analog to digital converter). The resultant digital information can now be electronically transmitted, manipulated, & more efficiently stored.