rifi course

8/10/2019 Rifi Course

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The NDT Radiography Interpretation training course will provide theory lectures and practicaltraining to provide the candidate with full understanding of Radiography and film Interpretation.The course will encourage group discussions around practical problems and provide field

expertise on how to resolve them. At the end of this course the candidate will understand how toperform review of radiographic films and report the identified defects for corrective action. Thecourse will cover -

Basic principles on Radiography Testing. Equipment & Materials. Techniques and calibration Radiography InterpretationWelds Radiography Interpretation - Casting ASTM and ASME standards and specifications.

How will you and your company benefit from this course?

Qualified to review radiography films and evaluate results as per applicable codes, standards andspecifications. Should be familiar with radiography interpretation technique and report theresults.

What we will cover:

Radiography Interpretation (RI) Theory and Practical

Duration : 24 Hours (3 days ) with following topics for each day

Day 1

Manufacturing / Casting / Forging / Welding Process Discontinuities: Inherent, Processing and Service Fundamentals of RT Properties and production of X-rays and Gamma Rays


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X-ray Generators

The major components of an X-ray generator arethe tube, the high voltage generator, the controlconsole, and the cooling system. As discussed

earlier in this material, X-rays are generated bydirecting a stream of high speed electrons at atarget material such as tungsten, which has a highatomic number. When the electrons are slowed orstopped by the interaction with the atomicparticles of the target, X-radiation is produced.This is accomplished in an X-ray tube such as theone shown here. The X-ray tube is one of thecomponents of an X-ray generator and tubes comea variety of shapes and sizes. The image belowshows a portion of the Roentgen tube collection of

Grzegorz Jezierski, a professor at OpoleUniversity of Technology. For more informationon X-ray tubes visit Dr. Jezierski's website atwww.xraylamp.webd.pl

The tube cathode (filament) is heated with a low-voltage current of a few amps. The filament heatsup and the electrons in the wire become looselyheld. A large electrical potential is createdbetween the cathode and the anode by the high-voltage generator. Electrons that break free of

the cathode are strongly attracted to the anodetarget. The stream of electrons between thecathode and the anode is the tube current. Thetube current is measured in milliamps and iscontrolled by regulating the low-voltage, heatingcurrent applied to the cathode. The higher thetemperature of the filament, the larger thenumber of electrons that leave the cathode andtravel to the anode. The milliamp or currentsetting on the control console regulates thefilament temperature, which relates to the intensity of the X-ray output.

The high-voltage between the cathode and the anode affects the speed at which theelectrons travel and strike the anode. The higher the kilovoltage, the more speed and,therefore, energy the electrons have when they strike the anode. Electrons striking withmore energy results in X-rays with more penetrating power. The high-voltage potential ismeasured in kilovolts, and this is controlled with the voltage or kilovoltage control on thecontrol console. An increase in the kilovoltage will also result in an increase in theintensity of the radiation.
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A focusing cup is used to concentrate the stream of electrons to a small area of the targetcalled the focal spot. The focal spot size is an important factor in the system's ability toproduce a sharp image. See the information onimage resolutionandgeometricunsharpnessfor more information on the effect of the focal spot size. Much of the energyapplied to the tube is transformed into heat at the focal spot of the anode. As mentioned

above, the anode target is commonly made from tungsten, which has a high melting pointin addition to a high atomic number. However, cooling of the anode by active or passivemeans is necessary. Water or oil recirculating systems are often used to cool tubes. Somelow power tubes are cooled simply with the use of thermally conductive materials andheat radiating fins.

It should also be noted that in order to prevent the cathode from burning up and toprevent arcing between the anode and the cathode, all of the oxygen is removed from thetube by pulling a vacuum. Some systems have external vacuum pumps to remove anyoxygen that may have leaked into the tube. However, most industrial X-ray tubes simplyrequire a warm-up procedure to be followed. This warm-up procedure carefully raises the

tube current and voltage to slowly burn any of the available oxygen before the tube isoperated at high power.

The other important component of an X-raygenerating system is the control console. Consolestypically have a keyed lock to prevent unauthorizeduse of the system. They will have a button to start thegeneration of X-rays and a button to manually stopthe generation of X-rays. The three main adjustablecontrols regulate the tube voltage in kilovolts, thetube amperage in milliamps, and the exposure time inminutes and seconds. Some systems also have aswitch to change the focal spot size of the tube.

X-ray Generator OptionsKilovoltage- X-ray generators come in a largevariety of sizes and configurations. There are stationary units that areintended for use in lab or production environments and portablesystems that can be easily moved to the job site. Systems are availablein a wide range of energy levels. When inspecting large steel or heavymetal components, systems capable of producing millions of electronvolts may be necessary to penetrate the full thickness of the material.Alternately, small, lightweight components may only require a systemcapable of producing only a few tens of kilovolts.

Focal Spot Size- Another important consideration is the focal spotsize of the tube since this factors into the geometric unsharpness of theimage produced. Generally, the smaller the spot size the better. But asthe electron stream is focused to a smaller area, the power of the tubemust be reduced to prevent overheating at the tube anode. Therefore, the focal spot size
https://www.nde-ed.org/EducationResources/CommunityCollege/Radiography/TechCalibrations/imageconsiderations.htmhttps://www.nde-ed.org/EducationResources/CommunityCollege/Radiography/TechCalibrations/imageconsiderations.htmhttps://www.nde-ed.org/EducationResources/CommunityCollege/Radiography/TechCalibrations/imageconsiderations.htmhttps://www.nde-ed.org/EducationResources/CommunityCollege/Radiography/Physics/GeometricUnsharp.htmhttps://www.nde-ed.org/EducationResources/CommunityCollege/Radiography/Physics/GeometricUnsharp.htmhttps://www.nde-ed.org/EducationResources/CommunityCollege/Radiography/Physics/GeometricUnsharp.htmhttps://www.nde-ed.org/EducationResources/CommunityCollege/Radiography/Physics/GeometricUnsharp.htmhttps://www.nde-ed.org/EducationResources/CommunityCollege/Radiography/Physics/GeometricUnsharp.htmhttps://www.nde-ed.org/EducationResources/CommunityCollege/Radiography/Physics/GeometricUnsharp.htmhttps://www.nde-ed.org/EducationResources/CommunityCollege/Radiography/TechCalibrations/imageconsiderations.htm


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becomes a tradeoff of resolving capability and power. Generators can be classified as aconventional, minifocus, and microfocus system. Conventional units have focal-spotslarger than about 0.5 mm, minifocus units have focal-spots ranging from 50 microns to500 microns (.050 mm to .5 mm), and microfocus systems have focal-spots smaller than50 microns. Smaller spot sizes are especially advantageous in instances where the

magnification of an object or region of an object is necessary. The cost of a systemtypically increases as the spot size decreases and some microfocus tubes exceed$100,000. Some manufacturers combine two filaments of different sizes to make a dual-focus tube. This usually involves a conventional and a minifocus spot-size and addsflexibility to the system.

AC and Constant Potential Systems- AC X-ray systems supply the tube withsinusoidal varying alternating current. They produce X-rays only during one half of the1/60th second cycle. This produces bursts of radiation rather than a constant stream.Additionally, the voltage changes over the cycle and the X-ray energy varies as thevoltage ramps up and then back down. Only a portion of the radiation is useable and low

energy radiation must usually be filtered out. Constant potential generators rectify the ACwall current and supply the tube with DC current. This results in a constant stream ofrelatively consistent radiation. Most newer systems now use constant potentialgenerators.

Flash X-Ray Generators

Flash X-ray generators produce short, intense bursts of radiation. These systems areuseful when examining objects in rapid motion or when studying transient events such asthe tripping of an electrical breaker. In these type of situations, high-speed video is usedto rapidly capture images from an image intensifier or other real-time detector. Since theexposure time for each image is very short, a high level of radiation intensity is needed inorder to get a usable output from the detector. To prevent the imaging system frombecoming saturated from a continuous exposure high intensity radiation, the generatorsupplies microsecond bursts of radiation. The tubes of these X-ray generators do not havea heated filament but instead electrons are pulled from the cathode by the strong electricalpotential between the cathode and the anode. This process is known as field emission orcold emission and it is capable of producing electron currents in the thousands ofamperes.

Day 2

Basic Radiographic Principles Radiographs Radiographic Image Quality Film Handling, loading and processing Exposure Techniques


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Image Considerations

The usual objective in radiography is to produce an image showing the highest amount of detailpossible. This requires careful control of a number of different variables that can affect imagequality. Radiographic sensitivityis a measure of the quality of an image in terms of the smallest

detail or discontinuity that may be detected. Radiographic sensitivity is dependant on thecombined effects of two independent sets of variables. One set of variables affects the contrastand the other set of variables affects the definitionof the image.

Radiographic contrastis the degree of density difference between two areas on a radiograph.Contrast makes it easier to distinguish features of interest, such as defects, from the surroundingarea. The image to the right shows two radiographs of the same stepwedge. The upperradiograph has a high level of contrast and the lower radiograph has a lower level of contrast.

While they are both imaging the same change in thickness, the high contrast image uses a largerchange in radiographic density to show this change. In each of the two radiographs, there is asmall circle, which is of equal density in both radiographs. It is much easier to see in the highcontrast radiograph. The factors affecting contrast will be discussed in more detail on thefollowing page.


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Radiographic definitionis the abruptness of change in going from onearea of a given radiographic density to another. Like contrast, definitionalso makes it easier to see features of interest, such as defects, but in atotally different way. In the image to the right, the upper radiograph hasa high level of definition and the lower radiograph has a lower level of

definition. In the high definition radiograph it can be seen that a changein the thickness of the stepwedge translates to an abrupt change inradiographic density. It can be seen that the details, particularly thesmall circle, are much easier to see in the high definition radiograph. Itcan be said that the detail portrayed in the radiograph is equivalent tothe physical change present in the stepwedge. In other words, a faithfulvisual reproduction of the stepwedge was produced. In the lower image,the radiographic setup did not produce a faithful visual reproduction.The edge line between the steps is blurred. This is evidenced by thegradual transition between the high and low density areas on theradiograph. The factors affecting definition will be discussed in more detail on a following page.

Since radiographic contrast and definition are not dependent upon the same set of factors, it ispossible to produce radiographs with the following qualities:

Low contrast and poor definition High contrast and poor definition Low contrast and good definition High contrast and good definition

Controlling Radiographic Quality

One of the methods of controlling the quality of a radiograph is through the use of imagequality indicators (IQIs). IQIs, which are also referred to as penetrameters, provide ameans of visually informing the film interpreter of the contrast sensitivity and definitionof the radiograph. The IQI indicates that a specified amount of change in materialthickness will be detectable in the radiograph, and that the radiograph has a certain levelof definition so that the density changes are not lost due to unsharpness. Without such areference point, consistency and quality could not be maintained and defects could goundetected.Image quality indicators take many shapes and forms due to the various codes orstandards that invoke their use. In the United States, two IQI styles are prevalent: theplacard, or hole-type and the wire IQI. IQIs comes in a variety of material types so that

one with radiation absorption characteristics similar to the material being radiographedcan be used.


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Hole-Type IQIsASTM Standard E1025 gives detailed requirements for the design andmaterial group classification of hole-type image quality indicators.E1025 designates eight groups of shims based on their radiation

absorption characteristics. A notching system is incorporated into therequirements, which allows the radiographer to easily determine if theIQI is the correct material type for the product. The notches in the IQIto the right indicate that it is made of aluminum. The thickness inthousands of an inch is noted on each pentameter by one or more leadnumber. The IQI to the right is 0.005 inch thick. IQIs may also bemanufactured to a military or other industry specification and thematerial type and thickness may be indicated differently. Forexample, the IQI on the left in the image above uses lead letters toindicate the material. The numbers on this same IQI indicate thesample thickness that the IQI would typically be placed on when

attempting to achieve two percent contrast sensitivity.Image quality levels are typically designated using a two part expression such as 2-2T.The first term refers to the IQI thickness expressed as a percentage of the region ofinterest of the part being inspected. The second term in the expression refers to thediameter of the hole that must be revealed and it is expressed as a multiple of the IQIthickness. Therefore, a 2-2T call-out would mean that the shim thickness should be twopercent of the material thickness and that a hole that is twice the IQI thickness must bedetectable on the radiograph. This presentation of a 2-2T IQI in the radiograph verifiesthat the radiographic technique is capable of showing a material loss of 2% in the area ofinterest.It should be noted that even if 2-2T sensitivity is indicated on a radiograph, a defect of

the same diameter and material loss may not be visible. The holes in the IQI representsharp boundaries, and a small thickness change. Discontinues within the part may containgradual changes and are often less visible. The IQI is used to indicate the quality of theradiographic technique and not intended to be used as a measure of the size of a cavitythat can be located on the radiograph.

Wire IQIsASTM Standard E747 covers the radiographic examination of materials using wire IQIsto control image quality. Wire IQIs consist of a set of six wires arranged in order of


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increasing diameter and encapsulated between two sheets of clear plastic. E747 specifiesfour wire IQI sets, which control the wire diameters. The set letter (A, B, C or D) isshown in the lower right corner of the IQI. The number in the lower left corner indicatesthe material group. The same image quality levels and expressions (i.e. 2-2T) used forhole-type IQIs are typically also used for wire IQIs. The wire sizes that correspond to

various hole-type quality levels can be found in a table in E747 or can be calculated usingthe following formula.

Where:F = 0.79 (constant form factor for wire)d = wire diameter (mm or inch)l = 7.6 mm or 0.3 inch (effective length of wire)T = Hole-type IQI thickness (mm or inch)

H = Hole-type IQI hole diameter (mm or inch)Placement of IQIsIQIs should be placed on the source side of the part over a section with a materialthickness equivalent to the region of interest. If this is not possible, the IQI may be placedon a block of similar material and thickness to the region of interest. When a block isused, the IQI should be the same distance from the film as it would be if placed directlyon the part in the region of interest. The IQI should also be placed slightly away from theedge of the part so that at least three of its edges are visible in the radiograph.

Radiographic Film

X-ray films for general radiography consist of an emulsion-gelatincontaining radiation sensitive silver halide crystals, such as silverbromide or silver chloride, and a flexible, transparent, blue-tintedbase. The emulsion is different from those used in other types ofphotography films to account for the distinct characteristics ofgamma rays and x-rays, but X-ray films are sensitive to light.Usually, the emulsion is coated on both sides of the base in layersabout 0.0005 inch thick. Putting emulsion on both sides of the basedoubles the amount of radiation-sensitive silver halide, and thusincreases the film speed. The emulsion layers are thin enough sodeveloping, fixing, and drying can be accomplished in a reasonable


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time. A few of the films used for radiography only have emulsion on one side which producesthe greatest detail in the image.

When x-rays, gamma rays, or light strike the grains of the sensitive silver halide in the emulsion,

some of the Br-ions are liberated and captured by the Ag+ ions.This change is of such a small

nature that it cannot be detected by ordinary physical methods and is called a "latent (hidden)image." However, the exposed grains are now more sensitive to the reduction process whenexposed to a chemical solution (developer), and the reaction results in the formation of black,metallic silver. It is this silver, suspended in the gelatin on both sides of the base, that creates animage. See the page on film processing for additionalinformation.

Film Selection

The selection of a film when radiographing anyparticular component depends on a number ofdifferent factors. Listed below are some of the factors

that must be considered when selecting a film anddeveloping a radiographic technique.

1. Composition, shape, and size of the part beingexamined and, in some cases, its weight andlocation.

2. Type of radiation used, whether x-rays froman x-ray generator or gamma rays from aradioactive source.

3. Kilovoltages available with the x-rayequipment or the intensity of the gamma radiation.

4.

Relative importance of high radiographic detail or quick and economical results.

Selecting the proper film and developing the optimal radiographic technique usually involvesarriving at a balance between a number of opposing factors. For example, if high resolution andcontrast sensitivity is of overall importance, a slower and finer grained film should be used inplace of a faster film.

Film Packaging

Radiographic film can be purchased in a number of differentpackaging options. The most basic form is as individualsheets in a box. In preparation for use, each sheet must be

loaded into a cassette or film holder in the darkroom toprotect it from exposure to light. The sheets are available in avariety of sizes and can be purchased with or withoutinterleaving paper. Interleaved packages have a layer ofpaper that separates each piece of film. The interleavingpaper is removed before the film is loaded into the film holder. Many users find the interleavingpaper useful in separating the sheets of film and offer some protection against scratches and dirtduring handling.


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Industrial x-ray films are also available in a form in which each sheet is enclosed in a light-tightenvelope. The film can be exposed from either side without removing it from the protectivepackaging. A rip strip makes it easy to remove the film in the darkroom for processing. Thisform of packaging has the advantage of eliminating the process of loading the film holders in thedarkroom. The film is completely protected from finger marks and dirt until the time the film is

removed from the envelope for processing.

Packaged film is also available in rolls, which allows the radiographer to cut the film to anylength. The ends of the packaging are sealed with electrical tape in the darkroom. In applicationssuch as the radiography of circumferential welds and the examination of long joints on anaircraft fuselage, long lengths of film offer great economic advantage. The film is wrappedaround the outside of a structure and the radiation source is positioned on axis inside, allowingfor examination of a large area with a single exposure.

Envelope packaged film can be purchased with the film sandwiched between two lead oxidescreens. The screens function to reduce scatter radiation at energy levels below 150keV and as

intensification screens above 150 keV.

Film HandlingX-ray film should always be handled carefully to avoid physical strains, such as pressure,creasing, buckling, friction, etc. Whenever films are loaded in semi-flexible holders and externalclamping devices are used, care should be taken to be sure pressure is uniform. If a film holderbears against a few high spots, such as on an un-ground weld, the pressure may be great enoughto produce desensitized areas in the radiograph. This precaution is particularly important whenusing envelope-packed films.

Marks resulting from contact with fingers that are moist or contaminated with processing

chemicals, as well as crimp marks, are avoided if large films are always grasped by the edgesand allowed to hang free. A supply of clean towels should be kept close at hand as an incentiveto dry the hands often and well. Use of envelope-packed films avoids many of these problemsuntil the envelope is opened for processing.

Another important precaution is to avoid drawing film rapidly from cartons, exposure holders, orcassettes. Such care will help to eliminate circular or treelike black markings in the radiographthat sometimes result due to static electric discharges.

Film Processing

As mentioned previously, radiographic film consists of a transparent, blue-tinted base coated onboth sides with an emulsion. The emulsion consists of gelatin containing microscopic, radiationsensitive silver halide crystals, such as silver bromide and silver chloride. When x-rays, gammarays or light rays strike the the crystals or grains, some of the Br-ions are liberated and capturedby the Ag+ ions. In this condition, the radiograph is said to contain a latent (hidden) image


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because the change in the grains is virtually undetectable, but the exposed grains are now moresensitive to reaction with the developer.

When the film is processed, it is exposed to several different chemicalssolutions for controlled periods of time. Processing film basically

involves the following five steps.

Development - The developing agent gives up electrons toconvert the silver halide grains to metallic silver. Grains thathave been exposed to the radiation develop more rapidly, butgiven enough time the developer will convert all the silver ionsinto silver metal. Proper temperature control is needed toconvert exposed grains to pure silver while keeping unexposedgrains as silver halide crystals.

Stopping the development - The stop bath simply stops thedevelopment process by diluting and washing the developer

away with water. Fixing - Unexposed silver halide crystals are removed by the

fixing bath. The fixer dissolves only silver halide crystals,leaving the silver metal behind.

Washing - The film is washed with water to remove all theprocessing chemicals.

Drying - The film is dried for viewing.

Processing film is a strict science governed by rigid rules of chemicalconcentration, temperature, time, and physical movement. Whether processing is done by handor automatically by machine, excellent radiographs require a high degree of consistency and

quality control.

Manual Processing & DarkroomsManual processing begins with the darkroom. The darkroom should be located in a centrallocation, adjacent to the reading room and a reasonable distance from the exposure area. Forportability, darkrooms are often mounted on pickups or trailers.

Film should be located in a light, tight compartment, which is most often a metal bin that is usedto store and protect the film. An area next to the film bin that is dry and free of dust and dirtshould be used to load and unload the film. Another area, the wet side, should be used to processthe film. This method protects the film from any water or chemicals that may be located on thesurface of the wet side.

Each of step in the film processing must be excited properly to develop the image, wash outresidual processing chemicals, and to provide adequate shelf life of the radiograph. The objectiveof processing is two fold: first, to produce a radiograph adequate for viewing, and second, toprepare the radiograph for archival storage. Radiographs are often stored for 20 years or more asa record of the inspection.


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Automatic Processor EvaluationThe automatic processor is the essential piece of equipment in every x-ray department. Theautomatic processor will reduce film processing time when compared to manual development bya factor of four. To monitor the performance of a processor, apart from optimum temperature andmechanical checks, chemical and sensitometric checks should be performed for developer and

fixer. Chemical checks involve measuring the pH values of the developer and fixer as well asboth replenishers. Also, the specific gravity and fixer silver levels must be measured. Ideally, pHshould be measured daily and it is important to record these measurements, as regular loggingprovides very useful information. The daily measurements of pH values for the developer andfixer can then be plotted to observe the trend of variations in these values compared to thenormal pH operating levels to identify problems.

Sensitometric checks may be carried out to evaluate if the performance of films in the automaticprocessors is being maximized. These checks involve measurement of basic fog level, speed andaverage gradient made at 1 C intervals of temperature. The range of temperature measurementdepends on the type of chemistry in use, whether cold or hot developer. These three

measurements: fog level, speed, and average gradient, should then be plotted against temperatureand compared with the manufacturer's supplied figures.

Exposure Calculations

Properly exposing a radiograph is often a trial and error process, as there are many variables thataffect the final radiograph. Some of the variables that affect the density of the radiographinclude:

The spectrum of radiation produced by the x-ray generator. The voltage potential used to generate the x-rays (KeV). The amperage used to generate the x-rays (mA). The exposure time. The distance between the radiation source and the film. The material of the component being radiographed. The thickness of the material that the radiation must travel through. The amount of scattered radiation reaching the film. The film being used. The concentration of the film processing chemicals and the contact time.

The current industrial practice is to develop a procedure that produces an acceptable density bytrail for each specific x-ray generator. This process may begin using published exposure chartsto determine a starting exposure, which usually requires some refinement.

However, it is possible to calculate the density of a radiograph to a fair degree accuracy when thespectrum of an x-ray generator has been characterized. The calculation cannot completelyaccount for scattering but, otherwise, the relationship between many of the variables and theireffect on film density is known. Therefore, the change in film density can be estimated for any


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given variable change. For example, fromNewton's Inverse Square Law,it is known that theintensity of the radiation varies inversely with distance from the source. It is also known that theintensity of the radiation transmitted through a material varies exponentially with thelinearattenuation coefficient (m)and the thickness of the material.

A number of radiographic modeling program are available that make this calculation. Theseprograms can provide a fair representation of the radiograph that will be produce with a specificsetup and parameters. The applet below is a very simple radiographic density calculator. Theapplet allows the density of a radiograph to be estimated based on material, thickness, geometry,energy (voltage), current, and time. The effect of the energy and the physical setup are shown bylooking at the film density after exposure. Since the calculation uses a generic (and fixedcharacteristic) x-ray source, fixed film type and development, the applet results will differconsiderably from industrial x-ray configurations. The applet is design simply to demonstratethe affects of the variable on the resulting film density.

How To Use This Applet

First choose a material. Each material has a mass attenuation constant, mu. Next, the voltage tothe x-ray source needs to be set. Continue to fill in numbers for the rest of the variables. Thecurrent is the number of milliamps that flow to the source. After the Distance, Time, andThickness have been set, press the "Calculate" button.

Note, the Iofield has a number in it. This is the initial intensity of the x-ray beam. For largenumbers, it may be necessary to use the mouse to see the entire number. Click on the number andmove the mouse as if selecting it. The cyan pointer indicates the density on the resultantradiograph. The two other pointers represent under- and over-exposure by a factor of four. Thesemay be used to judge the degree of contrast in the resultant radiograph.

Try the following examples: material: aluminum, kV: 120, mA: 5, distance: 0.5 meter, time: 90seconds, thickness: 6.5 cm. The resultant density will be 2.959. As can be noted on thestepwedge, reducing the exposure by a factor of four will change the density to a value of 1.0,and increasing the exposure by a factor of four will result in a density of 5.0. Reduce the timefrom 90 seconds to 22.5 seconds (factor of four) and note the results.

Change the material to iron and press "Calculate". Note that not enough radiation is received togenerate an image. Change the following: kV: 320, mA: 10, time: 900 seconds, thickness: 1.25cm, and then click "Calculate". Note the resulting center density of 0.561. With aluminum, thetime was altered by a factor of four to change the density. With the iron, current (mA) must beincreased by a factor of four to produce an increase in density. Change the current from 10 to 40and calculate the results.

Caution:This applet does not have knowledge of the characteristics of any particular real-life x-ray source andshould NOT be used other than as a theoretical tool for making predictions of exposure and contrast.
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Day 3

Viewing of Radiographs Radiographic InterpretationWeld Radiographic InterpretationCasting

Practical Exercise Examination

Viewing Radiographs

Radiographs (developed film exposed to x-ray or gammaradiation) are generally viewed on a light-box. However, itis becoming increasingly common to digitize radiographsand view them on a high resolution monitor. Proper viewing

conditions are very important when interpreting aradiograph. The viewing conditions can enhance or degradethe subtle details of radiographs.

Viewing Radiographs

Before beginning the evaluation of a radiograph, theviewing equipment and area should be considered. The areashould be clean and free of distracting materials.Magnifying aids, masking aids, and film markers should be close at hand. Thin cotton glovesshould be available and worn to prevent fingerprints on the radiograph. Ambient light levels

should be low. Ambient light levels of less than 2 fc are often recommended, but subduedlighting (rather than total darkness) is preferable in the viewing room. The brightness of thesurroundings should be about the same as the area of interest in the radiograph. Roomillumination must be arranged so that there are no reflections from the surface of the film underexamination.

Film viewers should be clean and in good working condition. There are four groups of filmviewers. These include strip viewers, area viewers, spot viewers, and a combination of spot andarea viewers. Film viewers should provide a source of defused, adjustable, and relativity coollight as heat from viewers can cause distortion of the radiograph. A film having a measureddensity of 2.0 will allow only 1% of the incident light to pass. A film containing a density of 4.0

will allow only 0.01% of the incident light to pass. With such low levels of light passing throughthe radiograph, the delivery of a good light source is important.

The radiographic process should be performed in accordance with a written procedure or code,or as required by contractual documents. The required documents should be available in theviewing area and referenced as necessary when evaluating components. Radiographic filmquality and acceptability, as required by the procedure, should first be determined. It should beverified that the radiograph was produced to the correct density on the required film type, and


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that it contains the correct identification information. It should also be verified that the properimage quality indicator was used and that the required sensitivity level was met. Next, theradiograph should be checked to ensure that it does not contain processing and handling artifactsthat could mask discontinuities or other details of interest. The technician should develop astandard process for evaluating the radiographs so that details are not overlooked.

Once a radiograph passes these initial checks, it is ready for interpretation. Radiographic filminterpretation is an acquired skill combining visual acuity with knowledge of materials,manufacturing processes, and their associated discontinuities. If the component is inspectedwhile in service, an understanding of applied loads and history of the component is helpful. Aprocess for viewing radiographs (e.g. left to right, top to bottom, etc.) is helpful and will preventoverlooking an area on the radiograph. This process is often developed over time andindividualized. One part of the interpretation process, sometimes overlooked, is rest. The mind aswell as the eyes need to occasionally rest when interpreting radiographs.

When viewing a particular region of interest, techniques such as using a small light source and

moving the radiograph over the small light source, or changing the intensity of the light sourcewill help the radiographer identify relevant indications. Magnifying tools should also be usedwhen appropriate to help identify and evaluate indications. Viewing the actual component beinginspected is very often helpful in developing an understanding of the details seen in a radiograph.

Interpretation of radiographs is an acquired skill that is perfected over time. By using the properequipment and developing consistent evaluation processes, the interpreter will increase his or herprobability of detecting defects.

Radiograph Interpretation - Welds

In addition to producing high quality radiographs, the radiographer must also be skilled inradiographic interpretation. Interpretation of radiographs takes place in three basic steps: (1)detection, (2) interpretation, and (3) evaluation. All of these steps make use of the radiographer'svisual acuity. Visual acuity is the ability to resolve a spatial pattern in an image. The ability of anindividual to detect discontinuities in radiography is also affected by the lighting condition in theplace of viewing, and the experience level for recognizing various features in the image. Thefollowing material was developed to help students develop an understanding of the types ofdefects found in weldments and how they appear in a radiograph.

Discontinuities

Discontinuities are interruptions in the typical structure of a material. These interruptions mayoccur in the base metal, weld material or "heat affected" zones. Discontinuities, which do notmeet the requirements of the codes or specifications used to invoke and control an inspection, arereferred to as defects.

General Welding Discontinuities


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The following discontinuities are typical of all types of welding.

Cold lapis a condition where the weld filler metal does not properly fuse with the base metal orthe previous weld pass material (interpass cold lap). The arc does not melt the base metalsufficiently and causes the slightly molten puddle to flow into the base material without bonding.

Porosity is the result of gas entrapment in the solidifying metal. Porosity can take many shapeson a radiograph but often appears as dark round or irregular spots or specks appearing singularly,in clusters, or in rows. Sometimes, porosity is elongated and may appear to have a tail. This isthe result of gas attempting to escape while the metal is still in a liquid state and is calledwormhole porosity. All porosity is a void in the material and it will have a higher radiographicdensity than the surrounding area.

.

Cluster porosityis caused when flux coated electrodes are contaminated with moisture. The

moisture turns into a gas when heated and becomes trapped in the weld during the weldingprocess. Cluster porosity appear just like regular porosity in the radiograph but the indicationswill be grouped close together.


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Slag inclusionsare nonmetallic solid material entrapped in weld metal or between weld and basemetal. In a radiograph, dark, jagged asymmetrical shapes within the weld or along the weld jointareas are indicative of slag inclusions.

Incomplete penetration (IP) or lack of penetration (LOP)occurs when the weld metal fails topenetrate the joint. It is one of the most objectionable weld discontinuities. Lack of penetrationallows a natural stress riser from which a crack may propagate. The appearance on a radiographis a dark area with well-defined, straight edges that follows the land or root face down the centerof the weldment.


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Incomplete fusionis a condition where the weld filler metal does not properly fuse with the basemetal. Appearance on radiograph: usually appears as a dark line or lines oriented in the directionof the weld seam along the weld preparation or joining area.

Internal concavity or suck backis a condition where the weld metal has contracted as it coolsand has been drawn up into the root of the weld. On a radiograph it looks similar to a lack ofpenetration but the line has irregular edges and it is often quite wide in the center of the weldimage.


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Internal or root undercutis an erosion of the base metal next to the root of the weld. In theradiographic image it appears as a dark irregular line offset from the centerline of the weldment.Undercutting is not as straight edged as LOP because it does not follow a ground edge.

External or crown undercutis an erosion of the base metal next to the crown of the weld. Inthe radiograph, it appears as a dark irregular line along the outside edge of the weld area.

Offset ormismatchare terms associated with a condition where two pieces being weldedtogether are not properly aligned. The radiographic image shows a noticeable difference indensity between the two pieces. The difference in density is caused by the difference in materialthickness. The dark, straight line is caused by the failure of the weld metal to fuse with the landarea.


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Inadequate weld reinforcementis an area of a weld where the thickness of weld metaldeposited is less than the thickness of the base material. It is very easy to determine byradiograph if the weld has inadequate reinforcement, because the image density in the area of

suspected inadequacy will be higher (darker) than the image density of the surrounding basematerial.

Excess weld reinforcementis an area of a weld that has weld metal added in excess of thatspecified by engineering drawings and codes. The appearance on a radiograph is a localized,lighter area in the weld. A visual inspection will easily determine if the weld reinforcement is inexcess of that specified by the engineering requirements.


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Crackscan be detected in a radiograph only when they are propagating in a direction thatproduces a change in thickness that is parallel to the x-ray beam. Cracks will appear as jaggedand often very faint irregular lines. Cracks can sometimes appear as "tails" on inclusions orporosity.

Discontinuities in TIG welds

The following discontinuities are unique to the TIG welding process. These discontinuities occurin most metals welded by the process, including aluminum and stainless steels. The TIG methodof welding produces a clean homogeneous weld which when radiographed is easily interpreted.

Tungsten inclusions. Tungsten is a brittle and inherently dense material used in the electrode intungsten inert gas welding. If improper welding procedures are used, tungsten may be entrappedin the weld. Radiographically, tungsten is more dense than aluminum or steel, therefore it showsup as a lighter area with a distinct outline on the radiograph.


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Oxide inclusionsare usually visible on the surface of material being welded (especiallyaluminum). Oxide inclusions are less dense than the surrounding material and, therefore, appearas dark irregularly shaped discontinuities in the radiograph.

Discontinuities in Gas Metal Arc Welds (GMAW)

The following discontinuities are most commonly found in GMAW welds.

Whiskersare short lengths of weld electrode wire, visible on the top or bottom surface of theweld or contained within the weld. On a radiograph they appear as light, "wire like" indications.

Burn-Through results when too much heat causes excessive weld metal to penetrate the weldzone. Often lumps of metal sag through the weld, creating a thick globular condition on the backof the weld. These globs of metal are referred to as icicles. On a radiograph, burn-throughappears as dark spots, which are often surrounded by light globular areas (icicles).


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Radiograph Interpretation - Castings

The major objective of radiographic testing of castings is the disclosure of defects that adversely

affect the strength of the product. Castings are a product form that often receive radiographicinspection since many of the defects produced by the casting process are volumetric in nature,and are thus relatively easy to detect with this method. These discontinuities of course, arerelated to casting process deficiencies, which, if properly understood, can lead to accurateaccept-reject decisions as well as to suitable corrective measures. Since different types and sizesof defects have different effects of the performance of the casting, it is important that theradiographer is able to identify the type and size of the defects. ASTM E155, Standard forRadiographs of castings has been produced to help the radiographer make a better assessment ofthe defects found in components. The castings used to produce the standard radiographs havebeen destructively analyzed to confirm the size and type of discontinuities present. The followingis a brief description of the most common discontinuity types included in existing reference

radiograph documents (in graded types or as single illustrations).

RADIOGRAPHIC INDICATIONS FOR CASTINGS

Gas porosity or blow holesare caused byaccumulated gas or air which is trapped by the metal.These discontinuities are usually smooth-walledrounded cavities of a spherical, elongated or flattenedshape. If the sprue is not high enough to provide thenecessary heat transfer needed to force the gas or airout of the mold, the gas or air will be trapped as the

molten metal begins to solidify. Blows can also becaused by sand that is too fine, too wet, or by sandthat has a low permeability so that gas cannot escape.Too high a moisture content in the sand makes itdifficult to carry the excessive volumes of watervapor away from the casting. Another cause of blows can be attributed to using green ladles,rusty or damp chills and chaplets.


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Sand inclusions and drossare nonmetallic oxides,which appear on the radiograph as irregular, darkblotches. These come from disintegrated portions ofmold or core walls and/or from oxides (formed in themelt) which have not been skimmed off prior to the

introduction of the metal into the mold gates. Carefulcontrol of the melt, proper holding time in the ladleand skimming of the melt during pouring willminimize or obviate this source of trouble.

Shrinkageis a form of discontinuity that appears asdark spots on the radiograph. Shrinkage assumesvarious forms, but in all cases it occurs because molten metal shrinks as it solidifies, in allportions of the final casting. Shrinkage is avoided by making sure that the volume of the castingis adequately fed by risers which sacrificially retain the shrinkage. Shrinkage in its various formscan be recognized by a number of characteristics on radiographs. There are at least four types of

shrinkage: (1) cavity; (2) dendritic; (3) filamentary; and (4) sponge types. Some documentsdesignate these types by numbers, without actual names, to avoid possible misunderstanding.

Cavity shrinkageappears as areas with distinctjagged boundaries. It may be produced when metalsolidifies between two original streams of meltcoming from opposite directions to join a commonfront. Cavity shrinkage usually occurs at a time whenthe melt has almost reached solidificationtemperature and there is no source of supplementaryliquid to feed possible cavities.

Dendritic shrinkageis a distribution of very finelines or small elongated cavities that may vary indensity and are usually unconnected.

Filamentary shrinkageusually occurs asa continuous structure of connected lines orbranches of variable length, width and density, or

occasionally as a network.


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Sponge shrinkageshows itself as areas of lacytexture with diffuse outlines, generally toward themid- thickness of heavier casting sections.Sponge shrinkage may be dendritic or filamentaryshrinkage. Filamentary sponge shrinkage appears

more blurred because it is projected through therelatively thick coating between the discontinuitiesand the film surface.

Cracksare thin (straight or jagged) linearly disposeddiscontinuities that occur after the melt has solidified.They generally appear singly and originate at casting

surfaces.

Cold shutsgenerally appear on or near a surface ofcast metal as a result of two streams of liquid meetingand failing to unite. They may appear on a radiographas cracks or seams with smooth or rounded edges.

Inclusionsare nonmetallic materials in anotherwise solid metallic matrix. They may be less ormore dense than the matrix alloy and will appearon the radiograph, respectively, as darker orlighter indications. The latter type is morecommon in light metal castings.

Core shiftshows itself as a variation in sectionthickness, usually on radiographic views representing


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diametrically opposite portions of cylindrical casting portions.

Hot tearsare linearly disposed indications that represent fractures formed in a metal duringsolidification because of hindered contraction. The latter may occur due to overly hard

(completely unyielding) mold or core walls. The effect of hot tears as a stress concentration issimilar to that of an ordinary crack, and hot tears are usually systematic flaws. If flaws areidentified as hot tears in larger runs of a casting type, explicit improvements in the castingtechnique will be required.

Misrunsappear on the radiograph as prominent dense areas of variable dimensions with adefinite smooth outline. They are mostly random in occurrence and not readily eliminated byspecific remedial actions in the process.

Mottlingis a radiographic indication that appears as an indistinct area of more or less denseimages. The condition is a diffraction effect that occurs on relatively vague, thin-section

radiographs, most often with austenitic stainless steel. Mottling is caused by interaction of theobject's grain boundary material with low-energy X-rays (300 kV or lower). Inexperiencedinterpreters may incorrectly consider mottling as indications of unacceptable casting flaws. Evenexperienced interpreters often have to check the condition by re-radiography from slightlydifferent source-film angles. Shifts in mottling are then very pronounced, while true castingdiscontinuities change only slightly in appearance.

Radiographic Indications for Casting Repair Welds

Most common alloy castings require welding either in upgrading from defective conditions or in

joining to other system parts. It is mainly for reasons of casting repair that these descriptions ofthe more common weld defects are provided here. The terms appear as indication types in ASTME390. For additional information, see the Nondestructive Testing Handbook, Volume 3, Section9 on the "Radiographic Control of Welds."

Slagis nonmetallic solid material entrapped in weld metal or between weld material and basemetal. Radiographically, slag may appear in various shapes, from long narrow indications toshort wide indications, and in various densities, from gray to very dark.


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Porosityis a series of rounded gas pockets or voids in the weld metal, and is generallycylindrical or elliptical in shape.

Undercutis a groove melted in the base metal at the edge of a weld and left unfilled by weldmetal. It represents a stress concentration that often must be corrected, and appears as a dark

indication at the toe of a weld.

Incomplete penetration, as the name implies, is a lack of weld penetration through the thicknessof the joint (or penetration which is less than specified). It is located at the center of a weld and isa wide, linear indication.

Incomplete fusionis lack of complete fusion of some portions of the metal in a weld joint withadjacent metal (either base or previously deposited weld metal). On a radiograph, this appears asa long, sharp linear indication, occurring at the centerline of the weld joint or at the fusion line.

Melt-throughis a convex or concave irregularity (on the surface of backing ring, strip, fused

root or adjacent base metal) resulting from the complete melting of a localized region butwithout the development of a void or open hole. On a radiograph, melt-through generally appearsas a round or elliptical indication.

Burn-throughis a void or open hole in a backing ring, strip, fused root or adjacent base metal.

Arc strikeis an indication from a localized heat-affected zone or a change in surface contour ofa finished weld or adjacent base metal. Arc strikes are caused by the heat generated whenelectrical energy passes between the surfaces of the finished weld or base metal and the currentsource.

Weld spatteroccurs in arc or gas welding as metal particles which are expelled during welding.These particles do not form part of the actual weld. Weld spatter appears as many small, lightcylindrical indications on a radiograph.

Tungsten inclusionis usually more dense than base-metal particles. Tungsten inclusions appearvery light radiographic images. Accept/reject decisions for this defect are generally based on theslag criteria.

Oxidationis the condition of a surface which is heated during welding, resulting in oxideformation on the surface, due to partial or complete lack of purge of the weld atmosphere. Thecondition is also called sugaring.

Root edge conditionshows the penetration of weld metal into the backing ring or into theclearance between the backing ring or strip and the base metal. It appears in radiographs as asharply defined film density transition.

Root undercutappears as an intermittent or continuous groove in the internal surface of the basemetal, backing ring or strip along the edge of the weld root.


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rifi course

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