ASTM + AS Viewing and Interpretation of Radiographs. Дефектоскопия. Радиография

Viewing and Interpretation of Radiographs Topics Index 1. Back to Module Index 2. Introduction 3. Requirements for Inspecting Radiographs 4. Interpreting Weld Discontinuities 5. Surface Discontinuities for Welds 6. Internal Discontinuities for Welds 7. Interpreting Casting Discontinuities 8. Casting Discontinuities 9. Reporting Discontinuities 10. Summary – The Basic Steps in Interpreting a Radiograph 11. Check Your Progress 12. Your Task 13. Glossary

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Introduction The final stage in radiographic testing is the viewing, interpretation and reporting the results of a radiographic inspection. After all, the real purpose of a radiographic inspection is to provide information about the acceptability, or otherwise, of the product being tested. After compeleting this task, you should be able to: •

•

•

set up and check the conditions for properly viewing a radiograph interpret weld radiographs for defect in accordance with Australian Standards interpret casting radiographs in accordance with ASME and Australian Standards.

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Requirements for Inspecting Radiographs The viewer must include a uniformly illuminated diffusing screen AS2177 states that the examination of radiographs shall be carried out “by diffused light in a darkened room”. Most illuminators also include a rheostat that enables the brightness to be adjusted to accommodate radiographs of varying densities. In addition, it must be possible to mask the viewer so that bright, direct light is excluded from the eyes of the inspector.

Radiograph viewing illuminator (click photo to enlarge)

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A very important requirement is the brightness of the viewer AS3998 requires the minimum intensity of light transmitted through a radiograph being examined to be 30 candella per square meter (cd/m2). To achieve this, the brightness of the viewing facility must be at least that shown in the following table:

Minimum illuminator brightness required for radiograph density Density of Minimum Illuminator Brightness Radiograph (cd/m2) 1.5 1,000 2.0 3,000 2.5 10,000 3.0 30,000 3.5 100,000

It follows that the upper limit of film density is determined by the brightness of the available illuminator. The above values are the minimum brightness to view film, based on 30 cd/m2 intensity of transmitted light. The standard suggests that 100 cd/m2 is a more reasonable value. The brightness of an illuminator can be checked with a photographic light meter by following these steps:

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1. Set the film speed indicator to 100 ASA or 200 ASA 2. Place the sensitive element of the meter close to the screen of the illuminator 3. Record the ‘exposure’ in hundredths of a second against a camera aperture setting of f10, f14.3 or f20 4. Use the table below to relate photographic exposure time to screen brightness.

Photographic luminosity meter (click photo to enlarge)

The following table provides information on the relationship between screen brightness and the exposure reading obtained using the above method.

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Relationship between screen brightness and the exposure reading Screen brightness Exposure (cd/m2) f number (seconds) 100 ASA 200 ASA 10 1/100 1,000 2,000 10 1/500 5,000 10,000 10 1/1000 10,000 20,000 14.3 1/100 2,000 4,000 14.3 1/500 10,000 20,000 14.3 1/1000 20,000 40,000 20 1/100 3,000 6,000 20 1/500 15,000 30,000 20 1/1000 30,000 60,000 20 1/1500 45,000 90,000 20 1/2000 60,000 120,000

This illuminator must be used in a darkened room There should be only sufficient background light to enable recording of details on the viewing record. Too much background lighting may cause reflections off the film, effectively reducing contrast and making interpretation more difficult. Furthermore, the room used as a viewing room should be quiet and comfortable to avoid unnecessary distractions. Radiographs are veiwed for short intervals This practice is followed to prevent eye strain and maximise your concentration level. Although each interpreter will differ, it is recommended that no

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more than five minutes be spent viewing a radiograph. Upon commencing a viewing session, the interpreter must allow sufficient time for his or her eyes to become adjusted to the darkened conditions. Radiographs should be dried before viewing Wash water on a radiograph has a significant effect on sensitivity and increases the difficulty of detecting fine discontinuities. Be sure to dry you radiographs before viewing. Check the quality of the radiograph Before inspection proper can begin, the radiograph is checked for processing and handling artefacts and film density, and the IQI sensitivity is determined. The person interpreting the radiograph must be sure that the quality of the radiograph is adequate, and is in accordance with the requirements of the code or specification, so that relevant discontinuities can be detected. The results of these preliminary checks and measurements should be recorded on the viewing report. Assessing for discontinuities is done methodically You must resist the temptation to simply “spot the defect”. A thorough examination is achieved by carefully scanning the radiograph from one side to the other, concentrating on each area of the radiograph as it is viewed. To do this properly, the interpreter must understand:

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•

• • •

the product that has been radiographed, including the type of material the method of fabrication or casting the type of discontinuities that are likely to occur how the radiograph was produced.

The other very important criteria that the interpreter must clearly understand are the acceptance/rejection criteria for the area or part being inspected. This information is generally contained in specifications or codes, or sometimes in the customer’s own specification for the component. Radiographic interpretation is a skill that can only be mastered through knowledge of the material being tested and experience. Many indications produce subtle low contrast or unsharp images that can be difficult to interpret. Material knowledge and experience are the most valuable aids that an interpreter can draw on.

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Interpreting Weld Discontinuities Weld discontinuities are designated by standard abbreviations There is a standard set of abbreviations used to describe most weld discontinuities. These abbreviations are listed in AS4749-2001, “NonDestructive Testing –Terminology of and Abbreviations for Fusion Weld Imperfections as Revealed by Radiography”. Description of each discontinuity are provided, plus prints taken from an actual radiograph or a sketch to describe discontinuity. You are strongly advised to obtain a copy of this standard from Standards Australia if you are at all involved with weld radiography. Weld imperfections are either surface or internal There are two classes of weld discontinuities: • •

surface imperfections internal imperfections.

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Standard abbreviations for weld discontinuities are listed in the tables below. Abbreviations for surface imperfections Imperfection Code Excessive penetration SXP Incompletely filled groove SGI Undercut SUC Grinding mark SMG Hammer mark SMH Surface pitting SPT Linear misalignment HiLo Root Concavity SRC Shrinkage groove SGS Excessive dressing SED Tool mark SMT Torn surface STS Spatter SSP Abbreviations for internal imperfections Imperfection Code Longitudinal crack KL Crater crack KC Lack of root fusion LR Incomplete root penetration LP Linear inclusion IL Tungsten inclusion IT Gas pore GP Crater pipe CP Linear porosity PL Uniform porosity PU Diffraction mottling DM Transverse crack KT Lack of side fusion LS Lack of inter-run fusion LI

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Inclusion Oxide inclusion Copper inclusion Worm hole Localised porosity Elongated cavity Burn through

IN IO IC WH PG EC BT

All radiographs should be interpreted to determine their compliance with a code or standard A typical standard is Australian Standard AS4037 which includes acceptance levels for various weld imperfections in pressure vessels. It states: •

•

No planar imperfections (e.g. crack or lack fusion defects) are allowed. In main butt welds (class 1 vessels), slag inclusions can have: o a maximum length of 6 mm for thicknesses of up to 18 mm o a maximum length of T/3 for thicknesses between 18 mm and 60 mm o a maximum length of 20 mm for thicknesses greater than 60 mm.

Some standards include porosity charts which are typically illustrations to provide a visual comparison to help determine the acceptablility of porosity discontinuities. Porosity imperfections may be classified as: •

• • •

isolated pores (maximum diameter 0.3T but not greater than 6 mm) uniform porosity clustered porosity linear porosity.

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Surface Discontinuities for Welds

The following images have been provided courtesy of Agfa Gevaert Pty Ltd. These reproductions of radiographs show various weld defects as they might appear in a radiograph. Excessive penetration (SXP) Weld metal protruding through the root of the weld. Appears as a light continuous or more often intermittent, irregularly shaped band within the image of the weld.

Radiograph of Excessive Penetration (Courtesy Agfa NDT) (click radiograph to enlarge)

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Root concavity (SRC) Sometimes called suck-back. A shallow groove in the root of a butt weld. Appears as a dark area along the centre of the weld.

Radiograph of Internal (Root) Concavity (Courtesy Agfa NDT) (click radiograph to enlarge)

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Incompletely filled groove (SGI) A continuous or intermittent channel at the top surface of the weld and running along the length of the weld. It may be at the centre of the weld, where it is sometimes known as external concavity or insufficient fill, or may be at the edges of the weld where it is known as incompletely filled groove.

Radiograph of External Concavity (Courtesy Agfa NDT) (click radiograph to enlarge)

Incompletely Filled Groove

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Undercut (SUC) An irregular groove at the top edge (toe) of a weld caused by contraction of the weld metal, or by burning away (gouging) of the parent metal. Appears as a dark irregular band along the top edge of the weld metal. Radiograph of External Undercut (Courtesy Agfa NDT) (click radiograph to enlarge)

Undercut can also occur at the root of the weld, although this can easily be confused with lack of root fusion.

Radiograph of Internal Undercut (Courtesy Agfa NDT) (click radiograph to enlarge)

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Linear misalignment (HiLo) A planar misalignment of the two sides being welded. May appear as light and dark sides.

Radiograph of Linear Misaligment (Courtesy Agfa NDT) (click radiograph to enlarge)

Linear misalignment may have a linear indication associated with it caused by the protruding edge of one of the plates. This has the appearance of a lack of penetration indication.

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Radiograph of Lack of Penetration (Courtesy Agfa NDT) (click radiograph to enlarge)

Internal Discontinuities for Welds The following images have been provided courtesy of Agfa Gevaert Pty Ltd. These reproductions of radiographs show various weld defects as they might appear in a radiograph. Longitudinal Crack (KL) Cracks appear a fine dark lines, mostly jagged edges, sometimes discontinuous. Its detection is dependent on its orientation relative to the radiation beam. Radiograph of Longitudinal Crack (Courtesy Agfa NDT) (click radiograph to enlarge)

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Longitudinal root crack (KL) This form of crack occurs mostly in the parent metal adjacent to the root run of the weld. It appears as a fine dark line, mostly jagged edges, sometimes discontinuous. Its detection is dependent on its orientation relative to the radiation beam. Radiograph of Longitudinal Root Crack (Courtesy Agfa NDT) (click radiograph to enlarge)

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Transverse Crack (KT) A transverse crack runs across the weld bead and sometimes into the parent metal. It appears as a fine dark line, mostly jagged edges, sometimes discontinuous. Its detection is dependent on its orientation relative to the radiation beam. Radiograph of Transverse Crack (Courtesy Agfa NDT) (click radiograph to enlarge)

Lack of side fusion (LS) A lack of union between the weld metal and the parent metal at the side of a weld. Its image appears as a straight dark line or band, depending on the orientation of the beam of radiation. Its detection depends on its orientation relative to the beam orientation, and sometimes requires an additional exposure with the beam aligned parallel to the weld preparation face.

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Radiograph of Lack of Side Wall Fusion Crack (Courtesy Agfa NDT) (click radiograph to enlarge)

Lack of inter-run fusion (LI) A lack of union between adjacent weld runs in a multi-run weld. It appears as a faint dark line with sharply defined edges. Radiograph of Lack of Inter-run Fusion (Courtesy Agfa NDT) (click radiograph to enlarge)

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Lack of root fusion (LR) A lack of union of the weld metal with the parent metal at the root of a weld. Appears as a straight line or band at one or both edges of the weld root image. Lack of Root Fusion

Incomplete root penetration (LP) Failure of the weld metal to extend into the root area of a joint. Appears as a dark continuous or intermittent band with mostly straight edges. In close square butt joints it may appear as a continuous or broken line. There is often a line of fine porosity associated with this defect. Radiograph of Incomplete Root Penetration (Courtesy Agfa NDT) (click radiograph to enlarge)

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Inclusion (IN) Slag or other foreign matter trapped between weld runds or between the weld and the parent metal. Appears as mostly irregular shapes. Radiograph of Inclusion (Courtesy Agfa NDT) (click radiograph to enlarge)

Linear inclusion (IL) Also known as a slag line. Caused by lines of slag trapped, generally between the weld metal and parent metal, in a multi-run weld. Appears as one or more dark bands, mostly with irregular edges, running along a weld. Radiograph of Linear Inclusion (Courtesy Agfa NDT) (click radiograph to enlarge)

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Tungsten inclusion (IT) An inclusion of tungsten from a tungsten electrode used in the gas tungsten arc (GTAW) process. Appears as small white sharp edged images in the weld metal due to the fact that tungsten is much denser than steel or aluminium. Radiograph of Tungsten Inclusion (Courtesy Agfa NDT) (click radiograph to enlarge)

Gas pore (GP) A mostly spherical gas hole in the weld metal. Appears as one or more circular dark images. Radiograph of Scattered Porosity (Courtesy Agfa NDT) (click radiograph to enlarge)

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Linear porosity (PL) A line of mostly small round images aligned along a weld. Note that this can sometimes indicate a lack of fusion defect which may not be immediately obvious. Radiograph of Root Pass Aligned Porosity (Courtesy Agfa NDT) (click radiograph to enlarge)

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Localised porosity (PG) A group of gas pores confined to a small area of a weld. Appears as a cluster of small round indications. These discontinuities are sometimes elongated, where they are referred to as “worm holes”. Radiograph of Cluster Porosity (Courtesy Agfa NDT) (click radiograph to enlarge)

Burn through (BT) A localised collapse of the weld pool leaving a hole in the bottom of the weld run. Appears as an irregularly shaped globular dark area. Radiograph of Burn Through (Courtesy Agfa NDT) (click radiograph to enlarge)

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Interpreting Casting Discontinuities In the case of castings, there are two very different systems for interpretation: 1. The American (ASTM) system. 2. Australian standard AS3507 The American (ASTM) system This system relies on ‘reference radiographs’. These are sets of radiographs showing particular casting discontinuities at up to five levels of severity. A typical standard is ASTM E446 “Standard Reference Radiographs for Steel Castings up to two inches (51 mm) in Thickness”. This standard contains a number of reference radiographs showing particular casting discontinuities at different levels of severity. These discontinuities are categorised as gas porosity, shrinkage etc. The radiographs are each 5"× 7" (127 mm × 178 mm) and are used to compare with 5"× 7" areas of radiographs of actual castings. Acceptance is based on perceived severity of the particular discontinuity. The standards states “where a particular severity is called for, and the radiograph being evaluated is equal to or better than the reference radiograph, the casting shall be indicated as being radiographically acceptable. If the radiograph shows a discontinuity of greater severity than the reference radiograph, the casting shall be rejected” .

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The Australian standard The Australian standard for radiography of steel castings is AS3507, “Non-destructive testing – Radiography of steel castings and classification of quality”. This standard adopts a totally different approach in that discontinuities must be quantified (measured) and the acceptance or otherwise of the casting is based on these measurements. For gas porosity, inclusions and shrinkage discontinuities, the standard defines a viewing area that varies from 30 mm × 30 mm to 100 mm × 100 mm, depending on casting thickness. For gas defects (porosity) and inclusions, the standard assigns a ‘severity index’ depending on the diameter or size of the discontinuity. The total of the severity indexes in the viewing area must not exceed a particular limit, determined by the class of the casting.

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Example: The following porosity discontinuities were detected in the viewing area for a particular casting: Porosity discontinuities detected for a particular casting Number of Total of Discontinuity Severity Similar Individual Diameter Index Size Severity d (mm) Number Discontinuities Indexes d<2 1 5 5 2
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Casting Discontinuities The following images show various casting discontinuities as they might appear in a radiograph. Micro-porosity This is a very fine, but often extensive, discontinuity caused by evolution of gas whereby very fine gas pores form around grain boundaries or between dendrite arms. They present a somewhat mottled effect in a radiograph. Mainly effects non-ferrous metals such as magnesium and aluminium. Micro-porosity (click radiograph to enlarge)

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Pin-hole porosity Small rounded cavities, typically less than 1 mm diameter, caused by evolution of gas during solidification of the molten metal. Sometimes occurs just below the surface of the casting, where it is known as sub-cutaneous pinhole porosity. Appears in a radiograph as widely distributed small dark rounded images.

Pin-hole Porosity (click radiograph to enlarge)

Gas holes Rounded cavities generally greater than 1 mm diameter - they can be quite large - and often more randomly dispersed through the casting due to gas evolved from the metal during solidification or from the mould or core. Appears as dark areas with a smooth outline which may be circular or elongated in shape. Gas Holes (click radiograph to enlarge)

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Wormholes Tube-like cavities similar to gas holes, generally located just below the surface of a casting. Caused by progressive expansion of entrapped superheated steam from moisture in a mould or core. Wormholes (click radiograph to enlarge)

Airlock A large cavity formed by air entrapped in the mould during pouring of the metal. Appears as a generally smooth and often irregularly shaped image. Airlock (click radiograph to enlarge)

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Shrinkage cavity A discrete cavity caused by contraction of the metal during solidification. Generally rougher edges to the image and an irregular - often tapered - shape. Shrinkage cavity in casting feeder head (click radiograph to enlarge)

Filamentary shrinkage A fine to course form of shrinkage in which the cavities are branching, interconnected and extensive. Appears as a network of branched irregular shapes. Filamentary Shrinkage (click radiograph to enlarge)

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Hot tear A discontinuity caused by fracture of the metal during its contraction as it cools during the early stages after solidification. Appears as one or more dark, jagged, lines. Hot tears tend to be a planar type of discontinuity, so detection by radiography may depend on the plane of the crack relative to the direction of the radiation beam. Hot Tear (click radiograph to enlarge)

Stress crack A sharper, more well defined fracture of the metal that forms generally during the later stages of cooling from solidification. May appear as a slightly jagged or a smooth dark line. They can also form when the casting is cold or during subsequent heat treatment. Again, hot tears tend to be planar so detection will depend upon the viewpoint of the radiograph. Stress Crack (click radiograph to enlarge)

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Cold shut A discontinuity formed when a stream of liquid metal, as it flows through a mould, fails to fuse with other metal in the mould. Mostly a surface discontinuity, radiographically it appears as a smooth dark line. Being a basically planar type of discontinuity, its detection by radiography may depend on the plane of the discontinuity relative to the direction of the radiation beam. It is often detected visually. Cold Shut (click radiograph to enlarge)

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Unfused chaplet/unfused chill Chaplets and chills are metal inserts placed in a mould for various casting purposes. If the liquid metal fails to fuse to these devices, a planar discontinuity may result. The presence of rust on the chaplet or chill will generally give rise to porosity around the chaplet or chill. Unfused Chaplet

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Inclusion Sand from a mould, and slag or dross from a ladle of metal, can be washed into the stream of metal as it enters and flows through a mould, and become trapped in the metal as it solidifies. It may appear as a light or dark irregularly shaped image in a radiograph, and may be difficult to distinguish from a void. However, the outcome is the same this discontinuity is generally not acceptable. Inclusion (click radiograph to enlarge)

Segregation This discontinuity comprises particular components of the metal composition that have different solidification temperatures and so tend to be driven by solidifying metal and segregate at particular areas, particularly the central zones, of a casting. May appear as light or dark areas in a radiograph, or even as banded light and dark areas.

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Reporting Discontinuities All discontinuities are recorded on the viewing report In the case of welds, there is an accepted convention for the recording of discontinuity indications. This is described in AS4749, “NonDestructive Testing - Terminology of and Abbreviations for Fusion Weld Imperfections as Revealed by Radiography”. The code comprises of: •

•

•

•

a number to indicate the distance from the horizontal of vertical distance (mm) of the start of the discontinuity from the reference mark of the lowest number on the radiograph letters, using standard abbreviations, to denote the type of discontinuity a number to denote the length of the discontinuity (mm) over which the particular imperfection extends each code is separated by a dash ( - ).

Hence 48-PL-180 indicates linear porosity (PL), starting 48 mm from the reference mark and extending over a distance of 180 mm. The outcome of the viewing and interpretation is recorded in a report A typical viewing report should include the following information: • • • •

name of the test laboratory identification of the component product standard details of the material tested, including welding processes if relevant

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•

• •

• • •

• • •

the number of the test method standard (eg. AS2177.1/ AS3507) and designation of test method details of the area(s) tested details of surface imperfections and other artefacts noted in the radiograph type of IQI and calculated sensitivity film density range achieved a statement of compliance or non-compliance with the acceptance criteria date and place of testing identification of the radiographer and interpreter report number and date.

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Summary – The Basic Steps in Interpreting a Radiograph 1. Verify that the radiograph corresponds to the part being examined. 2. Verify that radiographic coverage is complete for the particular part. 3. Verify that the image quality indicators are correct and properly used and that the proper image quality level was achieved. 4. Verify that the film densities meet requirements of the standard. 5. Check for film artifacts and indications of surface phenomena and record any on the viewing record 6. Retake any indications that cannot be resolved as an artifact or discontinuity. 7. Visually check the surfaces of the part for surface discontinuities or contours that match the appearance of the discontinuity on the radiograph. 8. Evaluate the internal discontinuities to the applicable standards and accept, reject, or hold the part for further review. Record as ‘complies’ or ‘does not comply’ on the viewing record. 9. Mark the locations on the part of any noncomplying discontinuities. 10. Prepare a test report indicating the nature, extent, and disposition of all significant indications found on the radiographs.

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Check Your Progress 1. Radiographic viewing should be carried out in a: a. totally darkened room b. brightly lit room c. darkened room with sufficient indirect background light to enable details to be recorded Answer: c - Radiographic viewing should be carried out in adarkened room with sufficient indirect background list to enable details to be recorded. 2. The light intensity through a radiographic film should be: a. at least 30 cd/m2 b. at least 10 cd/m2 c. at least 100 cd/m2 d. bright enough to see the image of the IQI Answer: a - Light intensity through a radiographic film should be at least 30 cd/m2 3. The minimum brightness of an illuminator to view radiographic film of density 2.0 is: a. 30 cd/m2 b. 100 cd/m2 c. 1,000 cd/m2 d. 3,000 cd/m2 Answer: d - To view radiographic film of density 2.0, an illuminator of light intensity 3,000 cd/m2 is needed. 4. Radiographs should be viewed: a. immediately after the development phase b. immediately after the fixing phase c. immediately after the washing phase

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d. after the drying phase Answer: d - Radiographs should be dried before viewing. 5. When viewing a weld, a linear inclusion (code IL) located 54 mm from the left hand indicator and extending over a length 100 mm should be recorded on the viewing record as: a. IL-54-100 b. 54-IL-154 c. 54-IL-100 d. IL-54-154 Answer: c - 54-IL-100 6. A product code for a weld states “linear inclusions –maximum length T/3 in any 10T length”. An inclusion measuring 15 mm long in a 50 mm thick weld should be classified as: a. complies b. does not comply c. refer to customer Answer: a - complies 7. A casting shows 3 gas pores severity index = 1, 5 gas pores severity index = 3, and 2 gas pores severity index = 8. If the casting is 60 mm thick class 3, the maximum severity index for gas holes is 33. The above casting should be classified as: a. complies b. does not comply c. refer to customer Answer: b - does not comply

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8. Name five items that must be included on a viewing report. Answer: Choose any five of the following: • name of the test laboratory • identification of the component; product standard • details of the material tested (including welding processes if relevant) • the number of the test method standard (eg. AS2177.1/ AS3507) and designation of test method • details of the area(s) tested • details of surface imperfections and other artefacts noted in the radiograph • type of IQI and calculated sensitivity • film density range achieved • a statement of compliance or non-compliance with the acceptance criteria • date and place of testing • identification of the radiographer and interpreter • report number and date.

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In this task, you will identifiy some defects from radiographs. 1. What are the weld defects present in the following radiographs? You may click on each radiograph to examine it more closely. Radiographs of weld defects (click radiograph to enlarge)

a.

b.

c.

d.

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e. 2. What are the casting defects present in the following casting radiographs? You may click on each radiograph to examine it more closely. Radiographs of casting defects (click radiograph to enlarge) a.

b.

c.

d.

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e.

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Radiographic Testing Glossary Absorption The reduction in intensity of a beam of ionising radiation due to its passage through a material that blocks some of the incident radiation. Activity The number of atoms in a radioisotope that are decaying each second. Anode The positively charged electrode of an X-ray tube which contains the target and from which X-rays are emitted. Attenuation See absorption. Autoradiography Production of an image by the photographic recording of natural radiation. Back scatter That part of the scattered X-radiation or gamma radiation which is transmitted at an angle of more than 90 degrees in relation to the direction of the incident beam. Beam angle The angle between the central axis of the radiation beam and the plane of the radiographic film. Beam divergence The angle of the beam of radiation as it emerges from the X-ray tube or gamma ray source. Becquerel The unit of activity of a radioisotope. An isotope has an activity of one (1) becquerel if one (1) atom is decaying each second. Its unit symbol is Bq. Betatron

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A toroidal device in which electrons are accelerated using electromagnets to generate high energy X-rays. Cassette A light-tight container for holding a radiographic film during exposure. Cathode The negatively charged electrode of an X-ray tube carrying the filament and focusing cup and from which electrons are discharged towards the target contained in the anode electrode. Characteristic curve A curve showing the relation between the logarithm to the base 10 of the relative exposure and the photographic density of the film. Characteristic radiation X-radiation consisting of discrete wavelengths which are characteristic of the emitting material. Collimation The production of a near parallel beam of radiation by use of a slit or aperture in a shielding material. Constant potential circuit A circuit which is arranged to supply a substantially constant voltage across an X-ray tube. Coulomb per kilogram The metric unit of exposure. Its unit symbol is C/kg. Dark adaptation The process by which the eye adapts itself to a lower level of ambient illumination when entering a darkened room. Decay curve The activity of a radioactive source, measured in becquerels, plotted against time. Defect sensitivity

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The minimum size of a discontinuity, considered to be a defect, which can be detected under specified conditions. Densitometer An instrument for measuring light transmission density of film. Diffraction The phenomenon of the preferential scattering of a beam of radiation in certain directions when passing through a course grained absorber. Diffraction mottle A mottle superimposed on a radiographic image due to the diffraction of incident radiation. Dose A general term used to denote a quantity of radiation absorbed by living tissue. See also Gray. Dose equivalent A general term used to denote the biological effect of radiation absorbed by living tissue. See also Sievert. Dose rate The rate at which radiation is delivered or received. Dose rate meter See survey meter. Dosimeter A monitoring device used for measuring or evaluating the absorbed dose or exposure. It is normally worn by an operator to detect and record the radiation received. Effective source size The apparent dimensions as viewed along the beam axis of that portion of the source from which ionising radiation is emitted. Electromagnetic spectrum The broad range of wavelengths of radiation extending from very short wavelength cosmic rays to the very long wavelength radio waves that

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travel in straight lines and are characterised by a wave motion, and travel through a vacuum at the speed of light. Electron Very small negatively charged particles that orbit around the nucleus of an atom. Equilibrium half value layer The greatest thickness of materials required to reduce the intensity of a polychromatic beam of radiation by a factor of two. Exposure chart A chart on which is plotted one or more curves which indicate exposures for specified source or X-ray tube, product, film, film density and source to film distance for various product thicknesses. Exposure latitude The ability of a film to accommodate variations in density occurring as a result of differences in thickness of the test object. Filament The source of electrons in a Coolidge type X-ray tube. Film badge A film contained within a special holder worn by personnel to record the radiation received over a period of time. Largely replaced by the thermo-luminescent detector. Film base A flexible transparent or translucent support for the photographic emulsion. Film contrast The property of a film to record differences in density in relation to radiation intensity. It is dependent on the slope of the film's characteristic curve at the particular film density. Film processing The operations necessary to transform a latent image into a permanent visible image.

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Film speed A measure of the exposure required to produce a given density on a photographic emulsion under a particular set of conditions. Film unsharpness See inherent unsharpness. Filter A layer of absorptive material interposed in the path of radiation in order to reduce the intensity of longer wavelength radiation. Fixing The chemical removal of unexposed silver halides from emulsion after development. Flash radiography Radiography for the purpose of examining transient effects, such as moving objects in which the radiation intensity is relatively high and the exposure time is relatively short. Fluorescent screen A material which fluoresces in the visible region of the spectrum under the action of X-rays or gamma rays. Fluorometallic screen A support base to which is attached thin lead foil coated with a fluorescent material. Focal spot The area on the surface of the anode of an X-ray tube on which the electron stream impinges and from which the primary beam of X-rays is emitted. Fog A general term used to denote any increase in the density of a film arising from unwanted reduction of the silver halide during storage, use or processing. Full-wave rectification

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Rectification which reverses the negative half-cycle of an alternating supply allowing current to flow in only one direction during both half cycles of an alternating supply. Gamma radiation See gamma ray. Gamma radiography Radiography using a gamma ray source. Gamma ray Electromagnetic radiation emitted in the process of nuclear decay. There are also other nuclear processes that can give rise to gamma radiation. Gamma ray source A quantity of matter emitting gamma-radiation which is suitable for radiography (see sealed source). Geometric unsharpness Unsharpness caused by penumbra geometrically related to a finite source size and source to film distance Gradient The slope of a characteristic film curve at a specified density. It is represented by the symbol Gd. Graininess A visual effect due to the random distribution of groups of silver grains in the fixed emulsion layer. Gray The SI unit of absorbed dose of ionising radiation, equal to the joule per kilogram (J/ kg). Its unit symbol is Gy. Half-life The time taken for a radioisotope to decay to one half of its original activity. Half value layer

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See half value thickness. Half value thickness The thickness of an absorber that will reduce the intensity of ionising radiation to one half of its incident value half-life The time required for the activity of a radio-nuclide to be halved. Half-wave rectification Rectification which allows current to flow only during alternate half cycles of an alternating supply Hard radiation Radiation of relatively high penetrating power. Hardener A substance used to harden the gelatine in the emulsion on a radiographic film during fixing. Heel effect Reduction in intensity in X-radiation at the anode end of the radiation beam HVL The abbreviation for "half value layer". See also half value thickness. Image definition The sharpness of an image details in a radiograph. Image intensifier A device used improve the contrast of a fluoroscopic image and to render variations in X-ray intensity directly visible. Image quality indicator A device used for assessing the quality of a radiograph. Inherent filtration The filtration of an X-ray beam by any parts of the tube or tube shield. Inherent unsharpness

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Image spread caused by electron scatter through emulsion grains in the radiograph. Initial half value layer That thickness of material required to reduce the initial intensity of radiation passing through an absorber by a factor of two. Intensifying factor The ratio of the exposure time required without intensifying screens to that when screens are used. Intensifying screen A layer of material, which, when placed in close contact with a photographic emulsion, adds to the effect of the radiation on the film by reducing the exposure time. Ionisation A loss or gain of electrons from an atom, resulting in the formation of a positive or negative ion. Ionising radiation Radiation which produces ions when it passes through matter. IQI See image quality indicator. IQI sensitivity The sensitivity of a radiograph quantified in terms of the smallest IQI element seen on the radiograph. Isotope camera A device for housing radioisotopes which provides protection against radiation and permits controlled exposure of radiation. Also referred to as an "isotope container". Latent image A change produced in the emulsion of a film, paper or plate by exposure to radiation and capable of being converted into a visible image by development. Linear accelerator

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A straight-line particle accelerator used for the production of high energy X-rays. Mask A material used adjacent to a product during radiography to reduce the effect of scattered radiation, and/or minimize the effect on section differences on radiographic exposure. Masking The application of material which limits the area of irradiation to the region undergoing radiographic examination. Metal intensifying screen An intensifying screen of metal foil (usually lead) which emits secondary radiation under the influence of X-rays or gamma rays. Neutron Particles with zero electric charge located in the nucleus of an atom. Neutron radiography The use of a beam of neutrons to examine an object by producing a graphical record or image on sensitized film or on other recording or indicating media. Object-to-film distance The distance from the source side of the test object to the film surface, i.e. inclusive of object thickness. Penetrameter See image quality indicator. Photographic density The degree of blackening of a radiographic film expressed as the logarithm to base 10 of the opacity (blackness) of the film. Photographic development The conversion of a latent image into a visible image by a chemical process. Quality Factor

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A measure of the relative biological effect of radiation compared to other types of radiation. Also known as "radiation weighting factor". Xrays and Gamma rays have a quality factor of 1. Radioactive Decay Decrease of activity due to radioactive disintegration. Generally expressed as half life. Radioactivity The property of certain atoms to decay and emit particulate and/or gamma radiation. Radiograph A photographic image produced by ionizing radiation on a film or paper after passing through a material. Radiographic contrast The relative density or brightness between adjacent areas on an illuminated radiograph or a fluorescent screen or video device. Radiographic definition A measure of the sharpness of a radiographic image. Radiographic exposure The subjection of a recording medium to radiation for the purpose of producing a latent image. Radiographic exposure is commonly expressed in terms of milliampere minutes, or gigabequerel minutes. Radiographic film A photographic film which is usually coated on both sides with an emulsion designed for use with X-rays and gamma rays. Radiographic paper Photographic type paper suitable for the production of radiographs. Radiographic viewer Equipment incorporating a suitable area of diffuse illumination for viewing radiographs, the brightness of the illuminated area being appropriate to the density of the radiograph. Radiography

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The use of radiant energy in the form of X-rays or gamma rays, or neutrons, for non-destructive testing of opaque objects, to order to produce graphical records on sensitised film or as electronic or digital images on video devices, magnetic tape or computer disk. Radioisotope An isotope of an atom that undergoes a process of decay with the emission of ionising radiation. Reciprocity law A law which states that, all other conditions remaining constant, the time of exposure required to produce a given photographic density is inversely proportional to the intensity of radiation. Also known as the Bunsen-Roscoe Law. Rectification Any method by which a uni-directional voltage can be obtained from an alternating voltage supply. Reticulation A net-like structure appearing in an emulsion of a radiographic film as a result of buckling caused by difference in temperature between processing baths, or rinsing water. Safelight A source of filtered light of colour or waveband chosen to give insignificant fogging of a particular film type at intensity levels necessary for handling and processing films in a dark room. Salt intensifying screen An intensifying screen consisting of a substance which fluoresces in the visible or ultraviolet region of the spectrum under the action of radiation. Scattered radiation Secondary radiation which is emitted in all directions. Screen unsharpness Unsharpness caused by the use of intensifying screens or a fluorescent viewing screen. It may result from the scatter of light by the crystals of the fluorescent layer and poor contact between screens and films.

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Sealed source A radioactive source bonded or encapsulated to prevent the escape of the radioactive material under the conditions of use for which it was designed. Sensitivity The limiting amount of detail which can be seen on a radiograph. It can also be regarded as the smallest discontinuity which can be detected under given conditions. It is generally quantified as IQI sensitivity. Sensitometric curve See characteristic curve. SFD See source-to-film distance. Sievert The SI unit of absorbed radiation dose in biological matter equal to the absorbed dose in grays multiplied by the quality factor (QF) of the radiation. Its unit symbol is Sv. Soft radiation Radiation of relatively low penetrating power. Source The origin of radiation. Source shift radiography A method for determining the depth of a discontinuity by the use of two offset sources. Source-to-film distance The distance from the source of primary radiation to a film for a radiographic exposure. Specific activity The activity per unit mass of radio nuclide (see also activity). Step wedge

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A block of material in the form of a series of steps usually used for the preparation of exposure charts. Subject contrast The difference in radiation intensity between adjacent areas in a test object arising from differences in attenuation characteristics of those areas. Survey meter A device that provides an instant readout of radiation intensity. They are compulsory instruments for people working with X-ray and radioisotope equipment in industrial radiography. Target The metal (normally tungsten) insert in the anode of an X-ray tube on which the electron beam impinges. Tenth value layer See tenth value thickness. Tenth value thickness The thickness of an absorber that will reduce the intensity of ionising radiation to one tenth of its incident value. Thermo-luminescent detector A solid state device used to record the radiation received by an operator. Tomography The radiography of a predetermined layer of material. Tube current The current passing between the cathode and anode during the operation of an X-ray tube. Tube voltage The potential difference between the anode and the cathode of an Xray tube during operation. TVL

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Abbreviation for tenth value layer. See also tenth value thickness. Unsharpness Loss of image definition. Van de Graaf generator A high voltage generator for producing X-rays usually with energies of 1 MeV to 4 MeV. X-radiation See X-rays. X-ray film See radiographic film. X-ray paper See radiographic paper. X-ray tube An evacuated tube across which a high voltage is applied. Electrons are accelerated from the cathode to the anode and impact on a target, producing X-rays. X-rays Penetrating electromagnetic radiation originating in the extra-nuclear part of the atom and having wavelengths much shorter than visible light. Xero-radiography Radiography using a photo-conductive plate instead of radiographic film or paper that works on the same principles as a photocopier.

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