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Fundamentals of NDE-Radiographic Interpretation

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Issued: 12/14/98

Forward

This handbook is not under controlled distribution. It is intended to provide information to thoseindividuals who wish to obtain general information regarding the subject matter herein. Thishandbook has been developed to assist in the training and development of Bechtel personnel and

is intended to be part of Bechtel’s overall technical training program. The handbook is alsointended to provide useful guidelines, information, and data to assist personnel in making effectivedecisions. The appropriate Bechtel technical specialist(s) should be consulted wheneverquestions or concerns arise regarding the subject matter herein. All materials included in thishandbook are for reference purposes only and shall not be used for work execution. Thehandbook is not intended to replace or supercede codes, standards, procedures, or engineeringspecifications.




Issued: 12/14/98

Table of Contents

Section 1.0 Introduction

Section 2.0 Uses of Radiography

Section 3.0 Applicability

Section 4.0 Principles of Radiography

Section 5.0 Sources of Radiation

Section 6.0 Geometry of Exposure

Section 7.0 Principles of Shadow Formation

Section 8.0 Essential Variables of Exposure

Section 9.0 Radiographic Film Characteristics

Section 10.0 Scattered Radiation

Section 11.0 Radiographic Definition and Sensitivity

Section 12.0 Radiographic Techniques

Section 13.0 Elements of Radiographic Interpretation

Section 14.0 Viewing of Radiographs

Section 15.0 Penetrameters (Image Quality Indicators)

Section 16.0 Codes and Specifications

Section 17.0 Manufacturing Processes

Section 18.0 Welding Defects and Conditions

Section 19.0 Conclusion

Section 20.0 Glossary



Fundamentals of NDE-Radiographic Interpretation 1-1

Issued: 12/14/98

1.0 INTRODUCTION

Radiography is a nondestructive examination method used for inspection of components andassemblies that is based on differential absorption of penetrating radiation into the part or testpiece being examined. Radiographic testing usually requires exposing film to X or gamma rays

that have penetrated a specimen, processing the exposed film, and interpreting the resultantradiographic. There are many variables in these procedures and successful completion of any testis dependent upon understanding and control of variables.




Issued: 12/14/98

2.0 USES OF RADIOGRAPHY

Radiography is used to detect areas of a component or assembly that exhibit a difference inthickness or physical density, (such as internal flaws) as compared to the surrounding material.

Most metals are produced as a casting at some point in their processing. Other metals are workedand or shaped into desirable forms by some type of forging, usually at high temperatures. Duringthis heating and shaping process, stresses are often set-up by the contraction and expansion ofthe metal. This expansion and contraction of metal can result in cracks or tears at various points inthe metal. During the early stages of metal fabrication, radiography can be used to help locate andresolve these problems.

In the modern world of welding, radiography is a common nondestructive examination method forweld inspection. Radiography can be used to supplement other nondestructive examinationmethods, aiding in the detection and confirmation of internal and external discontinuities.




Issued: 12/14/98

3.0 APPLICABILITY

Radiography is a critical tool used to assure the integrity of many products and structural forms weencounter every day. Radiographic examinations can be applied to organic materials, inorganicmaterials, solids, liquids, and even gases.

Radiographic examination serves industry through its ability to detect flaws prior to expensivemachining or fabrication operations, as a check on manufacturing techniques, and as a means ofverifying quality.

3.1 Limitations of Radiography

Sensitivity of radiography to various types of flaws depends on many factors including type of flaworientation, material, thickness, and product form. Items to be radiographed must allow access toboth sides. Geometric exposure requirements make it impracticable to use radiography onspecimens of complex geometry.

Compared to other nondestructive methods, radiography is more costly. This is primarily due tothe radiation safety regulations and processing of the film prior to interpretation of the results. It ismost economical when it is used to inspect easily handled material of simple geometry with highrates of production testing. It becomes expensive when it is used to examine thick specimens thatrequire radiation sources of high energy potential.

Certain types of indications are difficult to detect by radiography. Relatively tight cracks are difficulto detect unless its major axis is essentially parallel to the radiation beam. Shallow tight cracks inthick sections seldom can be detected, even when properly oriented. Laminations are nearlyimpossible to detect with radiography due to their unfavorable orientation and because they do notyield sufficient differences in radiation absorption as compared to surrounding material. Thegreatest dimension of the discontinuity must be parallel to the radiation beam.

Personnel protection is of major importance. Safety requirements impose both economic andoperational restrictions on the use of radiography. Radiography sub-contractors are required tohave a radiation safety program in place to perform this type of examination.




Issued: 12/14/98

4.0 PRINCIPLES OF RADIOGRAPHY

4.1 Three Basic Elements of Radiography

4.1.1 Radiation or Electron Source

X-Radiation: Electromagnetic radiation that is electronically produced in a vacuum tube. Byplacing a positive charge on the anode of a x-ray tube and a negative charge on the cathode, freeelectrons are transferred from the cathode to the anode.

Gamma Rays: Short wave electromagnetic radiation emitted during the decay of unstable nuclei inatoms of certain elements. Gamma rays are produced by the nuclei of isotopes that areundergoing disintegration because of their instability. Because of this, the specific source activitymust be considered prior to performing radiography. As an isotope decays, the same exposurewill take increasingly longer. Isotopes are variations of the same element having different atomicweights. A parent element and it’s isotopes all have an identical number of protons in their nuclei

but a different number of neutrons. Among the known elements there are more than 800 isotopes;of which more than 500 are radioactive.

Throughout the electromagnetic spectrum, X and gamma radiation has the same characteristics.X and Gamma radiation of the same wave length has identical properties.

Particulate Emission: Particle emission such as alpha, beta, electron and neutron.

Note: The penetrating power of alpha and beta particles is relatively negligible, it is gamma raysthat are of use to the radiographer.

4.1.2 The object being evaluated

X-rays are generated whenever high velocity electrons collide with any form of matter, whethersolid, liquid, or gas. Since the atomic number of an element indicates its density, the higher theatomic number of the chosen target material, the greater the efficiency of X-ray generation.Hence, the greater the density of the material, the greater the number of X-ray generatingcollisions.

4.1.3 Recording medium

• Radiographic Film: Transparent or tinted base coated on both sides with an emulsioncontaining silver crystals.

• Photographic Paper: Paper base coated on one side with an emulsion containing silvercrystals.

• Digital imaging: Digital imaging equipment continues to have widespread industrialapplication, although not widely used on piping applications due to access and costlimitations. In this type of radiography, photo-stimulable phosphor plates are used in placeof industrial radiographic film. This type of imaging is currently the subject of many studiesand promises to play a significant role in the future of industrial radiography.




Issued: 12/14/98

4.2 Other Radiographic Principles

• Enhancement of Medium: In other methods of NDE, electronic amplification orenhancement may be used. For radiography, the amplification occurs in the filmdevelopment and also in the use of lead intensifying screens.

• Interpretation: Ability to interpret radiographs to various codes and customerspecifications or reference radiographs, if applicable.

• Disposition: After completion of an examination, a decision must be made as toacceptability or other disposition; i.e., reject, repair or scrap.




Issued: 12/14/98

5.0 SOURCES OF RADIATION

X and gamma radiation energies used in radiographic examination are a small portion of theElectromagnetic Radiation Spectrum. X and gamma energies are contained within the ultra highfrequency and extremely short wavelength end of the spectrum. It is this high frequency and short

wavelength that allows radiation to penetrate matter, even that which is opaque to visible light.Although it can penetrate opaque matter, electromagnetic radiation still follows most of the lawsapplied to visible light. The radiographic non-destructive examination method is based on thefollowing characteristics of X and gamma rays:

• They are electromagnetic with energy indirectly proportional to their wavelength.

• They have no electrical charge and no mass.

• They travel in straight lines at the velocity of light.

• They can penetrate matter, the depth of penetration being dependent upon the energy ofthe rays.

• They are absorbed and scattered by matter.

• They can ionize matter.

• They can expose film by ionization.

• They can produce fluorescence in certain materials.

• They are invisible and incapable of detection by any of the senses.

Particle emission is not electromagnetic radiation, but emission of particles such as alpha, beta,electron or neutrons. Alpha and beta particles are of concern to the radiation health physics, butare not useful for radiographic examination. Electron and neutron emissions are utilized inindustrial radiography in the following ways:

• Electrons provide intensification action when using lead screens in contact with the film,thus decreasing exposure time and improving radiographic definition.

• Neutrons are used in Neutron Radiography of explosives, nuclear fuel, and nuclearcomponents. Gamma rays are similar in characteristic to x-rays, but are distinguished fromx-rays by their origin rather than by their nature. The operator cannot control the quality ofgamma radiation in terms of wavelength and penetrating capabilities. Some gamma rayisotopes are natural sources, such as radium, whereas Cobalt 60 and Iridium 192 areartificially produced. Artificial isotopes are used almost exclusively as sources of gammaradiation for industrial radiography.

It is important to consider the source of radiation in radiography. Energy levels of gamma sourcesmake them more or less suitable for certain materials and thickness. X-ray energy levels must beselected such that the proper technique parameters are adhered to. Typically, a density range of2.0 to 4.0 at the penetrameter and area of interest is allowed for gamma sources and 1.8 to 4.0 forradiographs made with X-ray sources.




Issued: 12/14/98

6.0 GEOMETRY OF EXPOSURE

To produce a radiograph there must be a source of radiation, a specimen to be examined andradiographic film. "Geometric relationships" is a diagram of a radiographic exposure showingbasic geometric relationships between the radiation source, the object under examination

(specimen), and the film upon which the specimen image is recorded. The cause of enlargementof the image is the film not being in contact with the specimen. The ratio of the specimen diameter(Do) to the image diameter (Df) is equal to the ratio of the source-to-specimen distance (do) to thesource-to-film distance (df). For the radiographic image to be the same size as the specimen, thefilm is placed close to the specimen and the radiation source is placed as far from the film aspractical.

Geometric Relationships

The radiographer must be able to evaluate these geometrical relationships and apply aradiographic technique capable of achieving the necessary results. The interpreter must have a

full understanding of these relationships in order to properly evaluate the application of theradiographic technique.




Issued: 12/14/98

The following figures illustrate three important geometric relationships which must be understoodand considered by the radiographic interpreter. A thorough understanding of these principles willprovide for a better understanding of the resulting radiographic image thus an interpretation basedon all necessary considerations.

Geometry of Exposure

• "a" illustrates that portion (Ug) of a radiograph which exhibits a lack of definition, or "geometricunsharpness"

• "b" illustrates the principle by which an object appears larger than actual; commonly known asout of proportion, or "blown".

• "c" illustrates the importance of maintaining the greater axis of the component undergoingexamination and the film placement normal (perpendicular) to the radiation beam. As theillustration points out, distortion can lead to erroneous assumptions as to discontinuity size andposition.




Issued: 12/14/98

7.0 PRINCIPLES OF SHADOW FORMATION

The image formed on a radiograph is similar to a shadow cast on a screen by an opaque objectplaced in a beam of light. Although radiation used in radiography penetrates opaque objects,shadow formation remains basically the same. X, gamma, and light radiation all travel in straight

lines. Propagation in a straight line is the primary characteristic of radiation that enables theformation of sharply discernible shadows. The geometric relationships of source, object, andscreen to each other control the three main characteristics of the shadow imaged on the film.

7.1 Subject Enlargement

The amount of subject enlargement depends upon the distance of the object from the source aswell as the distance from the film to the object.

7.2 Distortion

When the true shape of an object is altered in the radiographic image, it is known as radiographicdistortion. If the plane of the object and the plane of the film are not parallel, image distortion willresult, as it will if the radiation beam is not directed perpendicular to the plane of the film.Whenever distortion of the film image is unavoidable, as a result of physical limitation, it should beremembered that all parts of the image are distorted; otherwise, an incorrect interpretation of theradiograph may be made.

7.3 Geometric Unsharpness

Fuzzy boundaries or lack of definition around the edges of an object or a specific feature of anobject on a radiograph are known as penumbral effects. When this effect is caused by theconfiguration of focal spot/specimen/film relationship it is called geometric unsharpness (Ug).

Limits as to the degree of geometric unsharpness are important as the radiographic definition isgreatly affected by these factors.

Factors Affecting Geometric Unsharpness




Issued: 12/14/98

The following is an example of Ug limits: You must not exceed a geometric unsharpness of .020"for material up to 2" in thickness and a geometric unsharpness of .070" for material thickness over4". Various fabrication codes impose different requirements on geometric unsharpness factors. Inno case is a geometric unsharpness greater than .070" acceptable. The formula for calculatinggeometric unsharpness is:

Ug = (Fd) / D

F = Effective source size, inches; the maximum projected dimension (diagonal) of theradiating source (or focal point). The effective size of the source is determined by theformula (square root of a2 + b2); where a = source diameter, and b = source length.

d = Thickness (inches) of the area of interest of the object being radiographed assumingthe film is against the object; otherwise, it is the thickness of the object plus the spacebetween the film and the object.

D = Distance (inches) from the source of radiation to the area of interest of object being

radiographed.




Issued: 12/14/98

8.0 ESSENTIAL VARIABLES OF EXPOSURE

The radiographic image is dependent upon the amount of radiation absorbed by the emulsion ofthe film. The amount of radiation absorbed by the emulsion of the film determines the degree ofblackening of the film after processing or the density of the radiograph. The amount of radiation

available for absorption by the film is dependent on the total amount of radiation emitted by thesource of radiation during exposure and the amount of radiation reaching the specimen andpassing through it.

8.1 Generation of X-Rays

Three factors determine the amount of radiation emitted by an x-ray tube are milliamperes (Ma),Kilovoltage (Kv), and Time (t).

The intensity of an x-ray beam is proportional to the milliamperage. Changes in Ma are reflected inproportionate changes in intensity. Intensity when used in reference to Ma defines the quantity of

x-rays produced. Higher Ma increases the quantity of x-rays than can be generated by a given x-ray unit in a given amount of time.

Kilovoltage controls the penetrating power of an x-ray unit. The higher the Kv, the shorter thewavelength of the x-rays generated, thus greater penetration is permitted.

The total amount of radiation produced by an x-ray tube operating at a given kilovoltage andmilliamperage is directly proportional to the time the x-ray tube is energized. The application ofMa, Kv, and time is referred to as exposure.

8.2 Gamma Rays

For a specific radioactive isotope, the intensity of the radiation is proportional to the curie strengthof the source. In comparison to x-ray tubes, source activity is not adjustable nor is it a constant.The total amount of radiation generated from a gamma source depends upon its intensity and theduration of the exposure. As in x-ray, the gamma ray output varies directly with both sourceactivity (intensity) and time. Gamma ray exposures may be specified in curie-minutes or curie-hours.

If a 50 curie source of Ir 192 produces an acceptable radiograph with an exposure time of twominutes, a 25 curie Ir 192 source will produce an acceptable radiograph with an exposure time offour minutes, when all other variables remain the same.

There is no variable in gamma radiography to correspond to the kilovoltage of an x-ray tube.Radiation energy, a factor in determining penetration, is determined by the nature of a givenisotope. A given isotope will have its own unique energy levels. For thicker specimens orspecimens which are radiographically more dense, isotopes with more penetrating power may benecessary.

Radiography performed with isotopes has the advantage of simplicity of equipment, portability,and no need for outside power. These advantages allow for the examination of pipe, pressurevessels, and other assemblies with access restrictions.




Issued: 12/14/98

8.3 Inverse Square Law

Gamma rays and x-rays have identical propagation characteristics because they both conform tothe laws of light. When the output of radiation emanating from a small area is constant, theintensity of the radiation varies inversely to the square of the distance from the radiation source at

any point along the beam of radiation. The reason for this is divergence as the distance from thesource of radiation is increased. The Inverse Square Law can be expressed mathematically by thefollowing equation:

I1 = Radiation Intensity at distance D1 (away from radiation source)

I2 = Radiation Intensity at distance D2 (away from radiation source)

The Inverse Square Law is of critical importance when used to establish radiation safety barriersat levels considered acceptable by Federal and State regulations.

8.4 RADIOGRAPHIC SCREENS

The film, in producing an image through ionization, absorbs less than one percent of the radiation.To convert the unused energy into a form that can be absorbed, radiographic screens are used.

Types of screens that can be used are:

• Lead Screens (Most Commonly Used)

• Fluorescent Screens (Seldom used)

It is important to remember that code requirements may specify the types of screens that may beused.

Lead and lead oxide screens are usually constructed of an antimony and lead alloy that is stiffer,harder, and more wear resistant than pure lead. The screens are used in pairs, on each side of,and in close contact with the film. Depending upon the specimen and the energy of radiation, thescreens may be of varying thickness. The front screen in most application is thinner than the backscreen. Front screens 0.005 inch thick and back screens 0.010 inch thick are commonly used.Most fabrication codes reference ASME section V Article 2 for performance of radiography which

specifies lead screen thickness to be used. Lead screens are particularly efficient because of theirability to absorb scattered radiation (soft radiation) in addition to increasing the ionizing effect onthe film. The increased ionizing effect is a result of the release of electrons from the lead atomswhen irradiated. Energy from the released electrons is readily absorbed by the film emulsion, andenhances film exposure. It is important to inspect the screens prior to film loading as damagedscreens can result in film anomalies, and re-performance of the exposure can result. Wrinkled,torn, or damaged screens can result in localized areas of reduced radiographic quality, thus poordefinition and sensitivity.




Issued: 12/14/98

The intensification factor of lead screens is much lower than that of fluorescent screens. Duringexposure using low energy radiation it is possible for the front screen absorption effect to be ofsuch magnitude that required exposure is greater than that without screens. However, due to theircapability for reducing the effects of scattered radiation and the resultant better contrast anddefinition of the radiographic image, lead screens are used whenever practicable. They are used

in almost all gamma ray applications. When using fluorescent screens, X or gamma radiationcauses the screens to emit visible light, which assists in exposing the film. Fluorescent screensare rarely used since they tend to decrease the sensitivity of the radiographic technique.




Issued: 12/14/98

9.0 RADIOGRAPHIC FILM CHARACTERISTICS

Radiographic density is defined as the degree of darkening of the film. Film density is measuredby the amount of visible light transmitted through the film and is measured as a logarithm (10x),where x equals the amount of transmitted light. The instrument used to measure density is the

densitometer. Two types are available, analog and electronic. Accuracy is a desirablecharacteristic, but more important is consistency. A good densitometer will give consistentreadings each time used.

Photographic density is expressed by the equation

D = Density

Io = incident light intensity

It = transmitted light intensity

Density vs Percent of Light that is Transmitted

Density Percent of Light Transmitted

0 100%

.3 50%

.6 25%

1.0 10%

2.0 1%

3.0 0.1%

4.0 0.01%

9.1 Radiographic Contrast

Radiographic contrast is defined as the difference of the various densities apparent on developedfilm. It is a combination of subject contrast and film contrast and, for any particular specimen,dependant upon radiation energy applied (penetrating quality), film contrast characteristics,exposure (the product of radiation intensity and time), use of screens, film processing, andscattered radiation.




Issued: 12/14/98

Factors of Radiographic Contrast

9.2 Subject Contrast

Subject contrast is the ratio of radiation intensities transmitted through any two selected areas ofthe object under examination. Subject contrast is dependent on thickness variations in the object,the radiation quality (lower Kv = higher contrast/ higher Kv = lower contrast), and scatteredradiation. As scattered radiation increases, radiographic contrast decreases.

9.3 Film Contrast

Film contrast refers to the slope of the characteristic curve of the film. Film contrast depends onthe type of film, the processing it receives (manual/automatic) and the density. The film contrastvalues of any particular film are usually expressed as a relationship between film exposure andthe resulting film density.




Issued: 12/14/98

9.4 Speed of Radiographic Film

Industrial radiographic film is commercially available from various manufactures. Each type andbrand of film has it’s own exposure factor which, in general terms, indicates the exposure requiredto produce a given density. High speed films need only low exposure while slow speed film

requires more exposure to attain the same film density. Radiographic film is divided into thefollowing four classifications:

9.4.1 Radiographic Film Classifications

• Type I - Extra fine grain, slow speed and very high contrast.

• Type II - Fine grain, medium speed and high contrast.

• Type III - Coarse grain, fast speed, medium contrast.

• Type IV - Very Coarse grain, very fast, low contrast.

9.5 Latitude

Latitude is the overall range of thickness (densities) that can be recorded on a radiograph withinthe useful density viewing range. A high contrast film is considered to have less latitude than a lowcontrast film.




Issued: 12/14/98

10.0 SCATTERED RADIATION

Scattered radiation is a factor that must be considered in most radiography. When a beam of x-rays or gamma rays strikes any object, some of the radiation is absorbed, some is scattered, andsome passes through the object. The wavelengths of the scattered radiation are lengthened and

therefore "softer" or less penetrating than the primary radiation. Any material, whether specimen,cassette, walls, or floor that is struck by the primary radiation is a source of scattered radiation.

As a rule, the largest portion of the scattered radiation affecting the film is generated from theobject being examined. The most common methods for reducing scatter are:

• Lead screens

• Masks and diaphragms

• Filters

Failure to reduce scattered radiation to acceptable levels can result in localized areas of over-exposure, lack of definition, and insufficient radiographic quality. The radiographic interpreter mustbe able to recognize this condition and be knowledgeable of control measures which can betaken.






Issued: 12/14/98

12.0 RADIOGRAPHIC TECHNIQUES

(B)(A)Film

Source Source

Film

IQIIQI

(C)Film

Source

(D)Film

Source

IQI IQI

(E)

Source

Film

(F)

Film

Source IQIIQI

Single-Wall Exposure, Single-Wall Viewing Techniques




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(B)(A)Film

Source

IQI Film

IQI

Source

(D)

IQI

Alternate Source

Locations

FilmIQI

Alternate Source

Locations

Film

(C)

(F)Film(E)

Source

IQI

Source

IQI

Film

Double-Wall Exposure, Single or Double-Wall Viewing




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12.1 Exposure / Viewing Techniques

12.1.1 Single wall exposure / single wall view (SWE/SWV); Figures a-f on Single-Wall Exposure,Single-Wall Viewing

12.1.2 Double wall exposure / single wall view (DWE/SWV); Figures a-d on Double-WallExposure, Single or Double-Wall Viewing

12.1.3 Double wall exposure / double wall view (DWE/DWV); Figures e-f on Double-WallExposure, Single or Double-Wall Viewing

12.2 Special Techniques

12.2.1 Multiple film radiography

Multiple film radiography is the use of more than one film loaded in the same cassette for thesame exposure. The films may be of the same speed or of different speeds. Films may be viewed

singly or superimposed as a composite radiograph. Each radiograph shall exhibit the requiredradiographic density and quality level. In the context of multiple film radiography, each exposuremay consist of more than one radiograph.

12.2.2 Duplicate Film Radiography

Duplicate film radiography or the use of two films of the same speed in one cassette is done forthe following reasons:

• To determine if an indication in a radiograph is a real defect or a film artifact.

•

To permit the use of the second film as the acceptance radiograph if the first film has arejectable artifact.

• Each film may be used as a separate radiographic record so that the manufacturer retainsa film and the customer retains a film.

• The two films may be superimposed and read as a composite radiograph.

NOTE: The radiographs (single or superimposed) shall exhibit the required radiographic qualitylevel and be within the specified density range as well as meeting any other requirements of theprocedure, specification, or governing code.

12.2.3 Double loading cassettes

Double loading of film cassettes of different speeds can also be done. This technique is commonlyused when performing radiography of objects with major differences in thickness. The fasterspeed film will result in acceptable densities for the thicker areas of the object, and the slowerspeed film will result in acceptable densities for thinner sections.




Issued: 12/14/98

12.2.4 Depth Localization of Defects

Two general methods are used to determine the depth of a defect from the surface of a specimenbeing radiographed.

•

Stereo-radiography is a method requiring two separate exposures on two separate filmsand a stereo viewer. This method is not normally used in industrial radiography.

• Double Exposure/Triangulation (parallax) Method: This technique requires two exposureson the same film. The first exposure is taken with the source centered over the area of thespecimen containing the defect. The second exposure is made with the source shiftedlaterally or at a right angle to the length of the defect. The shift should be offset enough toseparate the two defect images. Component thickness must be considered whendetermining this offset.

The following data should be recorded for use in making calculations:

• Source shift distance

• Source to film distance

• Specimen thickness

The following formula will give the distance of the defect from the film plane:

a = Source shift in inches

b = Change in position of defect image

d = Distance of defect above film plane

T = Source to film distance

The total exposure of the specimen should be as follows:

• 1st exposure is 3/5ths of the total exposure time.

• Move (offset) source.

• 2nd exposure is 2/5ths of the total exposure time.




Issued: 12/14/98

13.0 ELEMENTS OF RADIOGRAPHIC INTERPRETATION

The technical controls applied in radiography determine the amount and quality of information thatcan be obtained from a radiograph. Most specimens contain discontinuities of some degree. The

judgement as to whether a discontinuity meets pre-determined acceptance criteria is called

radiographic interpretation. Judgement varies from person to person and is based upon theknowledge, experience, and visual acuity of the interpreter.

Radiographic interpretation is comprised of many variables such as type, degree, severity, andlocation of discontinuities. All of these factors can vary due to differences in materials. Othervariables include the manufacturing process of the material form such as cast, wrought, or forged;and the method of joining such as welding, soldering, or brazing. Applicable codes, specifications,and standards must also be considered.

Generally, the reason for performing radiographic examination of a weld joint is to verify theintegrity and quality of the work and material. Other methods of quality control used prior to

nondestructive examination in assisting the film interpreter are:

• Qualification of welding procedures

• Qualification & certification of welders

• Visual Weld Inspection

With these quality control measures preceding the radiographic examination, the film interpreter isprovided with reassurance that surface irregularities have been corrected and will not interferewith interpretation of radiographic images.

In general, the following table illustrates the essential film viewing variables and their relationships

to each other.

Film Viewing Factors and Related Effects

↑

Kv,Mev

↓

FilmContrast

↑

Latitude

↓

Quality

↑

Graininess

↓

Sensitivity

↑ = increase ↓ = decrease

Film Viewing Factors and Related Effects

↓

Kv,Mev

↑

FilmContrast

↓

Latitude

↑

Quality

↓

Graininess

↑

Sensitivity

↑ = increase ↓ = decrease




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14.0 VIEWING OF RADIOGRAPHS

The evaluation of finished radiographs should be made under controlled darkroom conditions thatwill provide optimum viewing conditions for the interpreter.

To be satisfactory for use in viewing radiographs, a film viewer (illuminator) must meet two basicrequirements; it must provide light of an intensity that will illuminate the areas of interest in theradiograph, and it must diffuse the light evenly over the entire viewing area. It is imperative thatthe film interpreter know the examination area and that he does not let his focus be drawn toareas of lesser density in highly contrasting areas. A viewer which is capable of illuminatingdensities of 4.0 and which contains a rheostat is especially useful for the examination ofradiographs having a wide range of densities (wide latitude).

Adequately equipped film-viewing facilities must have a means of verifying density. A calibrateddensitometer capable of consistent reproducibility of readings should be part of every viewingfacility. As a minimum, a calibrated density strip must be used to ensure viewing of radiographs is

performed within an acceptable density range.

The contrast sensitivity of the human eye, which is the ability to distinguish small brightnessdifferences, is greatest when surroundings are of about the same brightness as the area ofinterest. Thus, to see the finest detail in a radiograph, the illuminator must be masked to avoidglare from the bright light at the edges of the radiograph or by the light transmitted from lowerdensity areas of the radiograph. Subdued lighting rather than total darkness is preferred in theviewing room. Room illumination should be arranged so that there are no interfering reflectionsfrom the surface of the radiograph.

Cleanliness is of great importance during the entire radiographic process. Film should be handled

with care. Cotton gloves should be used during loading and unloading of film holders as well asmounting of the film in processing hangers. Film holders, film, and screens should be handled onlyin clean surroundings. Images of dirt, lead chips, scratched or nicked screens, handling crimps,scratches, and nicks on the film result in an unacceptable radiograph. Similarly, chemical stainsand streaks can ruin a radiograph. The film processing area must be kept immaculately clean, andaccess limited to those who work in the area. It is critical to accurately maintain the temperature ofthe film loading darkroom and processing chemicals. A deviation in temperature of the developercan greatly affect processing results and result in a poor quality radiograph. Warmer developerthan recommended can overdevelop (increased density) a radiograph due to increased molecularactivity. Chemical contamination of the area can result in the loss of film, so it is advisable to storechemicals in a separate area until they are used. Floors must be kept clean and preferably dampto hold down dust. High humidity assists in preventing static electricity and static marks (sharp,bird-foot shaped marks) on film. Fabrics which encourage static electricity should be avoided bythe radiographer.




Issued: 12/14/98

15.0 PENETRAMETERS (IMAGE QUALITY INDICATORS)

Radiographs must contain the image of a penetrameter, or image quality indicator, as averification of the adequacy of the radiographic technique.

The penetrameter image on a radiograph is permanent evidence of the adequacy of theradiographic technique. This is a feature unique to radiography in comparison to othernondestructive examination methods. The radiographic interpreter must ensure that sourceplacement is over the area of interest and not the penetrameter. Generally, the penetrameter isplaced on the source side of the specimen. In some cases, placement of the penetrameter on thesource side is not possible, such as when radiographing a circumferential weld in a long tubularstructure. Under circumstances such as this, the penetrameter may be placed on the film side ofthe object being radiographed. Film side IQI shall not be used on welder’s qualification coupons assource side placement is easily performed. Placement of the penetrameter on the film side shallbe allowed only when access to the source side is not possible and must be indicated by thepresence of a lead letter "F" on the penetrameter.

In some instances, the geometry of the test specimen precludes placing the penetrameter directlyon it. When this occurs, the penetrameter may be placed on a block of radiographically similarmaterial. The block and the penetrameter should be placed as close as possible to the specimenwith the penetrameter to film distance equal to the source side of the object to film distance. Theinterpreter must ensure density requirements for viewing the area of interest fall within the limitsallowed based on the penetrameter density. For most codes this is -15% to +30% of thepenetrameter density. The weld reinforcement must be considered to permit viewing welddensities within the limits of penetrameter density. To ensure this, shims are used beneath thepenetrameter to compensate for the weld reinforcement and provide for acceptable radiographicdensity throughout the area of interest. The radiographic examination procedure should be

consulted to determine the acceptable range of viewing density when shims are used.

The ability to see a specified penetrameter hole on a radiograph does not indicate that adiscontinuity of equivalent diameter and thickness will also be discernible. Penetrameter holeshaving sharp boundaries result in abrupt changes in metal thickness and consequently filmdensity whereas a discontinuity can have more or less rounded sides causing a more gradualchange in film density. As a result, the image of the penetrameter hole is generally sharper andmore easily seen in the radiograph than is the image of a discontinuity. Similarly, a fine crack maybe of considerable extent, but if the x or gamma rays pass from the source to the film along thethickness of the crack, the image on the film may not be visible due to very gradual transitions ofdensity. Thus, a penetrameter is used to indicate the quality of the radiographic technique and not

to measure the size of discontinuities.

Penetrameter sensitivity is usually expressed in terms of penetrameter thickness as a percentageof test piece thickness that must be discernible on the radiograph. Quality or resolution isdetermined by the smallest hole size visible in the radiograph. Backing rings or strips are not usedin the selection of penetrameters. For example, an image quality level of 2-2T indicates that thethickness of the penetrameter equals 2% of the material thickness and the 2T is the penetrameterhole having a diameter twice the penetrameter thickness. The quality level of 2-2T is the mostcommon level generally specified in industrial radiography. Other radiographic quality levels are 1-2T, 1-1T, 2-4T and 4-4T.




Issued: 12/14/98

T

E

2 T dia (Minimum Size 0.020)

T dia (Minimum Size 0.010)

4 T dia (Minimum Size 0.040)

Place Identification

Numbers Here

A

F D

C

B

Design for IQIs to but notincluding 180.

Hole-Type IQI (See SE-1025 For Dimensions)

ENCAPSULATED BETWEEDTWO SHEETS OF .030 IN.CLEAR “VINYL” PLASTIC

MATERIAL

GRADE NUMBER

SET IDENTIFICATION LETTERS

FOR SETS A & B, THE

MINIMUM DISTANCE

BETWEEN THE AXIS

OF WIRES IS NOT LESS

THAN 3 TIMES THE

WIRE DIAMETER AND

NOT MORE THAN 0.2 IN.

FOR SETS C & D, THE

MINIMUM DISTANCE

BETWEEN THE AXIS

OF WIRES IS NOT LESSTHAN 3 TIMES THE

WIRE DIAMETER AND

NOT MORE THAN 0.75 IN.

LENGTH

MINIMUM 1 INCH

FOR SETS A & B,

MINIMUM 2 INCHES

FOR SETS C & D.

Wire-Type IQI (SE-747)

15.1 Identification and Location / Orientation Markers

15.2 To permit correct interpretation of the finished radiograph, the specimen and theradiograph must be so marked that the specimen and its location/orientation can beidentified from the radiograph. This is accomplished by affixing lead numbers or lettersadjacent to the specimen during exposure and marking the specimen in identical fashionwith a marking pen or by scribing. When performing radiography of welds, the locationmarkers shall not appear in the area of interest (weld). The lead numbers or letters, whichare attached with tape, appear as a radiographic image. Comparison of the radiographwith the marked specimen reduces the possibility of improperly establishing locations ofindications. Also, proper film identification should include component identification, nameof radiographic laboratory, etc., and date.




Issued: 12/14/98

16.0 CODES AND SPECIFICATIONS

Most radiography is performed in accordance with the provisions of specifications and codes.These may be in-house documents, purchase specifications set by the customer, or codes suchas the ASME Boiler and Pressure Vessel Codes.

Codes and specifications can establish certain factors for the radiographic technique such as theKv range or the use of a particular isotope, allowable geometric unsharpness, type of film,minimum/maximum densities, 100% or partial examination, and if partial examination, the extentor limits. Codes and specifications place requirements on the type, number, and placement ofpenetrameters in addition to the radiographic quality level. Codes and specifications establish theacceptance criteria for discontinuities that are revealed through radiography. Manycodes/specifications refer to reference radiographs produced by the American Society for TestingMaterials (ASTM).

The ASTM reference radiographs do not in themselves set acceptable levels for discontinuities

but they do provide a comparison by which the severity of a discontinuity can be judged orclassified. It is up to the purchaser and the seller to agree to acceptance levels for radiographicexamination as evaluated by comparison to the reference radiographs.

It is essential that the requirements of specifications and codes be followed closely. Productionradiographs can be rejected regardless of quality if they do not carry the proper identification or ifthe proper penetrameters are not used. Such rejections cause lost time and additional expenses.

Fabrication codes contain or reference the applicable acceptance criteria. The radiographicinterpreter must be completely familiar with and understand the acceptance criteria in order toproperly interpret the radiographic image and determine disposition.




Issued: 12/14/98

17.0 MANUFACTURING PROCESSES

It is of particular value to the radiographic interpreter to have knowledge of the manufacturingprocesses for the materials being radiographed. Discontinuities can be inherent to amanufacturing process or to a specific material type. Therefore, knowledge of the material and

manufacturing process is of great importance to the radiographic interpreter.

When performing radiographic interpretation of weldments, different welding processes such asMIG, TIG, and SMAW lend themselves to "typical" indications on weld radiographs. For thisreason, knowledge of welding processes is of significant benefit when viewing radiographs. TheVisual Examination Section contains further information relating to this topic.




Issued: 12/14/98

18.0 WELDING DEFECTS AND CONDITIONS

Some of the discontinuities that can be present in welds are cracks, voids in the weld metal, andinclusions which can be more or less dense than the surrounding weld metal. Radiographs mayshow both external and internal discontinuities in welds. It is important to note that not all

discontinuities that appear on a radiograph are cause for rejection of the weld.

Welding processes require that heat be carefully controlled to produce fusion to the parent metaland provide adequate penetration. Too much heat can cause porosity, cracks, and undercutting;too little heat can cause incomplete penetration and incomplete fusion. Stresses that areintroduced in the metal by welding but are not accompanied by a physical separation of materialwill not be detected by radiography. The Visual Examination Section contains further informationrelating to this topic.

18.1 Cracks; Star (Crater), Longitudinal, Transverse

A crack is defined as a fracture-type discontinuity characterized by a sharp tip and a high ratio ofarea-to-opening displacement. Cracks are linear ruptures of metal under stress. They are oftenvery narrow separations in the weld or adjacent base metal, and usually little deformation isapparent.

Weld metal cracks are the result of many factors. For example, cracking occurs when a joint ishighly restrained. Also, welds which are too small in size for the parts that are joined may crackwhen the shrinkage strains during cooling fracture at the least ductile location. Cracking alsoresults from poor welding practices, improper preparation of joints, or improper electrodes formatching base material. Inadequate preheat during welding of low-alloy carbon steel materialspromotes cracking of the weld metal or heat-affected zone (HAZ). Cracks in the HAZ are

promoted by high restraint of the joints and improper electrode control. Low-hydrogen proceduresare necessary for most low-alloy steels. High-alloy, austenitic materials such as stainless steel aremore crack resistant than low-alloy carbon steel. Contamination of the weldment with compoundssuch as sulfur or the selection of the wrong filler material can produce micro fissuring and / orcenterline cracking.

It must be recognized that other types of cracks can form during the service life of a component orweldment. Cracks can be generated by overloading, metal fatigue, intergranular and transgranularstress corrosion, and stress rupture mechanisms, to mention only a few. The radiographic andultrasonic examination response of such flaws is dependent upon the size and orientation of theflaw. Cracks in welds are usually produced by internal stresses caused by cooling of the weldmetal. Cracks may be oriented along the weld seam or they may be transverse to the weld seam.Transverse cracks can extend into the parent metal. Cracks are generally characterized by jaggedlines and may have fine hairline facets branching off from them.

The radiographic image of a crack defect is a dark narrow line that is usually irregular. If the planeof the crack is in line with the radiation beam, its image will be fairly defined. If the plane is notexactly in line with the radiation beam, a faint dark linear shadow may result. In this case,additional radiographs should be taken at other angles for accurate interpretation.




Issued: 12/14/98

Since cracks constitute a serious weld defect, additional radiographs and other NDE methodsshould be utilized when there is question as to their identity. Finer grain films may be used, theangle of the radiation beam should be changed, or other methods of nondestructive examinationused to supplement radiography.

Photomacrograph of Crack

18.2 Incomplete Penetration

Incomplete penetration occurs at the root of the weld groove (or at the center of the weld fordouble-v-groove welds). Incomplete penetration is caused by failure of the root pass to fuseproperly with the base metal at the root. A root opening is used to permit penetration and fusion atthe land area of a weld. When the root opening is too small for the electrode and/or inadequatewelding variables are used, incomplete penetration may result.

The radiographic image of lack of penetration appears as a straight dark line in the center of theweld. The width may vary from a thin sharp line to a broad line. Slag inclusions and gas holes maybe found in connection with a lack of penetration causing enlargement of the primary dark linemaking it appear broad and irregular.

A dark narrow line depicting lack of penetration on a radiograph may be caused due to the shiftingof plates as they are welded together. This cause of lack of penetration appears very distinctly onthe radiograph.

18.3 Root Conditions

18.3.1 Root Convexity

Root Convexity is a root pass that has excessively penetrated the joint. When this occurs, thewelder is moving or manipulating the weld rod too slowly or the current is too high.




Issued: 12/14/98

18.3.2 Root Concavity

Root concavity is a defect caused by excessive shrinkage of the weld deposited root bead. Aconcave root occurs when the molten weld solidifies without sufficient filler metal being added tothe molten zone to supply the volumetric shrinkage that takes place during solidification. Some

codes stipulate that the acceptability of concavity may be determined by comparing theradiographic film density. If the density of the concave area is the same as or less than (lighterthan) the adjacent base metal, the concave area is acceptable.

Radiographic Image of Root Concavity

18.3.3 Burn-Through

Burn-through appears on the radiograph as a relatively large round or oblong area in the root ofthe weld. When such an area appears as a circle with a light area at it’s center, the second pass

has filled the original defect. When a dark area appears, the interpreter can be sure that a void ofsome magnitude exists. Frequently the area will appear only slightly darker than the weld densitybut will contain a very black line in the center indicating that a second pass filled the original holein the root pass and a shrinkage crack has developed. Such a shrinkage crack can extend entirelythrough the second pass of the weld.

Radiographic Image of Burn-Through




Issued: 12/14/98

18.4 Porosity

Gas is sometimes formed during fusion welding due to improper control of arc current, technique,electrodes, or as a result of the quality of the parent metal. Porosity is gas inclusions that occur asspherical cavities in the weld metal. Gas inclusions may also occur as a tube-like cavity

sometimes referred to as worm hole porosity. Porosity may occur as single cavities in clusters oras randomly scattered cavities. Linear porosity may be associated with incomplete penetration asa series of cavities distributed along a line that runs lengthwise with the weld.

In a radiograph, porosity appears as round, dark spots with well defined contours and can be ofvarying sizes and distribution. Worm holes may appear as dark rectangles if the axis of thecylinder is perpendicular to the radiation beam and has two concentric circles; one darker than theother (if the axis is parallel to the radiation beam). Aligned porosity is indicated on radiographs asa series of round dark spots in line with the weld.

Radiographic Image of Scattered Porosity

Photomacrograph of Scattered Porosity




Issued: 12/14/98

18.5 Lack of Fusion (Incomplete Fusion)

18.6 Weld Slag Inclusions

Slags contain oxides produced during arc welding. Slag can be trapped in the weld metal if it fails

to remain molten long enough for the slag to rise to the surface. In welds requiring multiplepasses, slag may be left in early passes unless properly cleaned. Slag inclusions can be locatedalong the edges of the weld deposits and run in a line the length of the weld.

Since the oxides making up slag are usually less dense than the actual weld metal, it appears asdark irregular shapes on a radiograph. Slag inclusions can occur singly, in clusters, or scatteredrandomly throughout the weld. In some cases, slag may also occur in an aligned pattern. Slaginclusions generally have sharp pointed ends and can be of varying densities radiographically.

Slag lines may appear along the edge of a weld as an irregular or continuous dark line on theradiograph, caused by insufficient cleaning between weld passes. Voids left between passes byirregular deposits of metal can cause indications that have a similar radiographic appearance to

slag.

Radiographic Image of Slag




Issued: 12/14/98

18.7 Tungsten Inclusions

When using a tungsten electrode for arc welding, tungsten can become trapped in the depositedweld metal. Due to the high melting point of tungsten, fusion does not occur. Tungsten also has ahigher atomic weight than the weld metal resulting in higher radiation absorption. As a result of

having a higher density, tungsten inclusions appear as light spots on a radiograph. Tungsteninclusions may appear as single light spots or in clusters of small spots, usually irregular in shape.

Radiographic Image of Tungsten Inclusion

18.8 External Discontinuities

Various types of surface irregularities can result in density variations on a radiograph. To ensure

proper interpretation, surface irregularities should be removed prior to radiography. When it is notfeasible to remove surface irregularities, they must be considered by the interpreter to ensureindications are accurately identified and recorded. Surface irregularities must not preclude theinterpreter from making an accurate evaluation of the radiographic technique by obscuringpenetrameter images or indications of discontinuities. It is important to remember that all weldsshould be visually examined and accepted prior to radiography. Types of external discontinuitiesthat can affect radiographic interpretation are:

18.8.1 Incompletely filled weld grooves

18.8.2 Excessive reinforcement

18.8.3 Overlap

18.8.4 Excessive penetration

18.8.5 Longitudinal grooves






Issued: 12/14/98

19.0 CONCLUSION

The purpose of radiography is to provide visual information upon which judgements can be basedconcerning the quality level of a specimen. Accurate radiographic interpretation cannot be made ifinadequate information is presented in the image of the radiograph. It is imperative that those

involved with or overseeing the performance of radiography are familiar with the applicable coderequirements and technique parameters.

The following list can be used as a guideline to ensure that significant attributes of theinterpretation have been evaluated:

• Radiographic Review form annotated with applicable technique and acceptance criteria

• Radiation source applicable to component (thickness vs source limitation)

• Source physical size (mandatory to calculate Ug)

• Source to film distance (remember-AWS requires a minimum of 7 times the part thickness)

• Type of film (1 or 2)

• Set-up number (if a standard technique is used)

• Use of film side penetrameter justified

• Material thickness; nominal, actual, total (with internal and external reinforcement)

• Correct ID on radiograph, corresponds to review form and weld documentation

• Shim thickness (not to exceed thickness of reinforcement)

• Correct penetrameter selection and placement

• Location marker placement

• Any applicable notes concerning deviation from standard procedure




Issued: 12/14/98

Effective performance of radiography and the knowledge of a thorough radiographic filminterpreter can reduce or eliminate differences of opinion with client interpreters or theirrepresentatives. Typical sources of "difference of opinion" result from:

• Slag inclusions vs incomplete fusion

• Root concavity vs incomplete penetration

• Abrupt changes in density vs concavity

• Density readings (penetrameter vs area of interest)

• Length or diameter of indications

• Film artifacts vs discontinuities

As previously stated, fabrication codes contain or reference acceptance criteria. The radiographic

interpreter must be completely familiar with and understand the acceptance criteria in order toproperly interpret the radiographic image and determine disposition.

Since the radiographic interpreter’s decisions, directly or indirectly, determine the acceptance ofwelds; he must be knowledgeable of many requirements. His ability to make decisions is an assetto production and essential to assuring product quality levels. The interpreter has the overallresponsibility for the evaluation of radiographic quality as well as evaluatingdiscontinuities in welds!




Issued: 12/14/98

20.0 GLOSSARY

• absorption - The process whereby the particles or quanta (see photon) in a beam ofradiation are reduced in number or energy as they pass through some medium. Theparticles lose energy by interaction with either the nucleus (core) or electrons (shell) of the

atoms of the medium.• activity - A measure of how radioactive a particular radioisotope is. Activity is calculated by

the number of atomic disintegrations per unit of time. The unit of measurement is the curie.

• anode (target) - The positive terminal of an x-ray tube. It is a high melting point elementand receives the electron bombardment from the cathode or negative terminal.

• artifact - A mechanically produced, indication, a scratch, smudge, etc., on a radiographthat may be interpreted erroneously as a discontinuity.

• attenuation (radiographic) - Decrease of radiation caused by passage through material.

• back-scatter - Radiation scattered from the floor, walls, equipment and other items in the

area of a radiation source.• barium clay - A molding clay blocking material containing barium compounds placed round

a specimen to eliminate or reduce the amount of scattered or secondary radiation reachingthe film.

• blowhole - A hole in a casting or a weld caused by gas entrapped during solidification.

• calcium tungstate - A fluorescent chemical compound which emits visible blue violet lightwhen activated by either x- or gamma radiation.

• cassette - A light-proof container used for holding the radiographic films in position duringthe radiographic exposure. It may or may not contain intensifying screens.

• casting shrinkage - (l) "liquid shrinkage" - the reduction in volume of liquid metal as itcools to the liquids; (2) "solidification shrinkage" - the reduction in volume of metal from thebeginning to ending of solidification; (3) "solid shrinkage" - the reduction in volume of metalfrom the solidus to room temperature; (4) "total shrinkage" - the sum of the shrinkage in (l),(2) and (3).

• cathode - A negative electrode, as in an x-ray machine.

• cesium 137 - A radioactive isotope of the element cesium having a half-life of 30 years,plus or minus three years.

• cobalt 60 - A radioisotope of the element cobalt having a half life of approximately 5.3years.

•

cold shut - (l) A discontinuity that appears on the surface of cast metal as a result of twostreams of liquid meeting and failing to unite; (2) a portion of the surface of a forging that isseparated, in part, from the main body of metal by oxide.

• collimator - A device, made of lead, tungsten or spent uranium, used to surround aradiation source.

• contrast (radiographic) - The measure of difference in the film blackening resulting fromvarious x-ray intensities transmitted by the object and recorded as density differences in theimage. Thus, difference in film blackening from one area to another is contrast.




Issued: 12/14/98

• contrast (subject) - The ratio of radiation intensities passing through selected portions of aspecimen.

• crack - A discontinuity which has a relatively large cross-section in one direction and asmall or negligible cross-section when viewed in a direction perpendicular to the first.

• crater - (l) in machining, a depression in a cutting tool face eroded by chip contact; (2) inarc welding, a depression at the termination of a bead or in the weld pool beneath theelectrode.

• decay - The spontaneous change of a nucleus and emission of a particle or a photon. Forthe definite quantity of a nuclide, the rate of decay is usually expressed in terms of half-life.

• defect - A discontinuity the size, shape, orientation or location of which makes itdetrimental to the useful service of the part in which it occurs.

• definition - Sharpness of the outline of the image on a radiograph.

• densitometer - Instrument utilizing the photoelectric principle to determine the degree ofdarkening of developed photographic film.

• density - The degree of blackening of a film is density. Film blackening or density is usuallyexpressed in terms of the H & D curve (Hurter & Driffield) which is defined as the logarithmof the reciprocal of the transparency of the film. Blackening equals Log l/T. CT = LightTransmission). :

• developer - A chemical solution which reduces exposed silver halide crystals to metallicsilver.

• diffraction mottling - A diffuse diffraction pattern on a radiograph resulting from x-rayingthin sections of crystalline material.

• discontinuity - Any interruption in the normal physical structure or configuration of a part,such as cracks, laps, seams, inclusions or porosity. A discontinuity may or may not affect

the usefulness of a part.• electromagnetic radiation - Radiation consisting of electric and magnetic waves that

travel at the speed of light. Examples: light, radio waves, gamma rays, x-rays. All can betransmitted through a vacuum.

• emulsion - A gelatin and silver bromide crystal mixture coated onto a transparent filmbase.

• evaluation - The process of deciding as to the severity of the condition after the indicationhas been interpreted. Evaluation leads to the decision as to whether the part must berejected, repaired or accepted for use.

• false indication - In nondestructive examination, an indication that may be interpretederroneously as a discontinuity.

• film holder (cassette) - A light sealed carrier for films and screens.

• film speed - Relative exposure required to attain a specified density.

• filter - A layer of absorptive material that is placed in the beam of radiation for the purposeof absorbing rays of certain wavelengths and thus controlling the quality of the radiograph.

• fixer - A chemical solution which dissolves unexposed silver halide crystals from developedfilm emulsions.




Issued: 12/14/98

• fluorescence (radiographic) - The emission of electromagnetic radiation by a substanceas the result of the absorption of electromagnetic radiation having greater unit energy thanthat of the fluorescent radiation. Fluorescence is characterized by the fact that it occursonly so long as the stimulus responsible for it is maintained. The characteristic x-radiationemitted as a result of absorption of x-rays.

• fog - A darkening of the film resulting from chemical action of the developer, aging,scattered secondary radiation, pre-exposure to radiation or exposure to visible light.

• forward scatter - Radiation scattered in approximately the same direction as the primarybeam.

• fusion (incomplete, lack of) - Failure of deposited weld metal to fuse completely with thebase metal or preceding weld bead.

• gamma rays - High-energy, short wavelength electromagnetic radiation emitted by anucleus. Energies of gamma rays are usually between 0.010 and 10 Mev. Gamma rays arevery penetrating and are best attenuated by dense materials like lead and depleteduranium.

• gas holes - Holes created by a gas escaping from molten metal. Appear as round orelongated, smooth-edged dark spots, occurring individually, in clusters or distributedthroughout the casting.

• geometric unsharpness - The fuzziness or lack of definition on a radiograph

• graininess - A film characteristic resulting from the grouping or clumping together of thecountless small silver grains into relatively large masses visible to the naked eye or withslight magnification.

• grinding cracks - Shallow cracks formed in the surface of relatively hard materialsbecause of excessive grinding heat or the high sensitivity of the material.

•

half-life - The time in which half the atoms in a radioactive substance disintegrate. A half-life may vary from millionths of a second to billions of years.

• half value layer - The thickness of a material which absorbs 50 percent of the radiationwhich strikes it.

• hot cracks - Appear as ragged dark lines of variable width any numerous branches. Theyhave no definite line of continuity and may exist in groups. They may originate internally orat the surface.

• hot tear - A fracture formed in a metal during solidification because of hindered contraction

• icicles (drop through) - Metal which protrudes beyond the root of the weld.

• inclusion - Any foreign matter contained in welds or castings.

• incomplete penetration - Root penetration which is less than complete or the failure of aroot pass and a backing pass to fuse with each other.

• indication - In nondestructive examination, a response or evidence of a response, thatrequires interpretation to determine its significance.

• inherent defects - Discontinuities which are normal in the material at the time it originallysolidifies from the molten state.

• intensity - The amount of rays or particles emitted per unit of time.




Issued: 12/14/98

• inverse square law - At a distance from a point source of radiation, the intensity of energyreceived varies as the inverse square of the distance from the source.

• iridium 192 - A radioactive isotope of the element Iridium which has a half-life of 75 days. Itis used extensively as a source of gamma radiation in industrial radiography.

• irradiation - Exposure to radiation.

• isotope - Atoms with the same atomic number (same chemical element) but differentatomic weights. An equivalent statement is that the nuclei have the same number ofprotons but different numbers of neutrons.

• laminations - Metal defects with separation or weakness generally aligned parallel to theworked surface of the metal. May be the result of pipe, blisters, seams, inclusion orsegregation elongated and made directional by working.

• lap - A surface defect, appearing as a seam, caused by folding over hot metal or sharpcorners and then rolling or forging them into the surface, but not welding them.

• latitude (radiographic) - The range of thickness of material that can be recorded with the

useful reading range of film density. A high contrast film has little latitude and conversely alow contrast film has great latitude.

• penetrameter - A strip of metal the same composition as that of the metal being tested,representing a percentage of object thickness and provided with a combination of steps,holes or slots. When placed in the path of the rays, its image provides a check on theradiographic technique employed.

• personnel monitoring equipment - Devices designed to be worn or carried by anindividual for the purpose of measuring the dose received (e.g., film badges, pocketchambers, pocket dosimeters, film rings, etc.).

• pig - A container usually made of lead or U 238 used to shield radioactive sources when

not in use.• pipe - (1) The central cavity formed by contraction in metal, especially ingots, during

solidification: (2) the defect in wrought or cast products resulting from such a cavity (3) anextrusion defect due to the oxidized surface of the billet flowing toward the center of the rodat the back end.

• porosity - Holes or pores within a metal.

• primary radiation - Radiation arising directly from the target of an x-ray tube or from aradioactive source.

• radiation - The propagation of energy through matter or space in the form of waves. Inatomic physics the term has been extended to include fast-moving particles (alpha and

beta rays, free neutrons, etc.) Gamma rays and x-rays, of particular interest in atomicphysics, are electromagnetic radiation in which energy is propagated in packets calledphotons.

• radiation safety officer - An individual engaged in the practices of providing radiationprotection. He is the representative appointed by the licensee for liaison with the NuclearRegulatory Commission.

• radioactivity - Spontaneous nuclear disintegration with emission of electromagneticradiation.




Issued: 12/14/98

• radiographer - Any individual who performs or who, in attendance at the site where thesealed source or sources are being used, personally supervises radiographic operationsand who is responsible to the licensee for assuring compliance with the requirements ofthese regulations and the conditions of the licenses.

• radiographic exposure device - Any instrument containing a sealed source fastened or

contained therein, in which the sealed source or shielding thereof may be moved, orotherwise changed, from a shielded to unshielded position for purposes of making aradiographic exposure.

• radiographic interpretation - The determination of the cause and significance ofdiscontinuities indicated on the radiograph. The evaluation as to the acceptance of thematerial is based upon the application of the radiographic specifications and standardsgoverning the material.

• radiography - The use of radiant energy in the form of x-rays or gamma rays fornondestructive examination of opaque objects, in order to produce graphical records onsensitized films which indicate the comparative soundness of the object being tested.

• reference radiographs - A group of radiographs containing images of discontinuities.These can be used as comparison "standards" for acceptability of materials.

• reinforcement of weld - (1) In a butt Joint, weld metal on the face of the weld that extendsout beyond a surface plane common to the members being welded; (2) in a fillet weld, weldmetal that contributes to convexity; (3) in a flash, upset or gas- pressure weld, the originaldiameter or thickness.

• root crack - A crack in either the weld or heat-affected zone at the root of a weld.

• root penetration - The depth to which weld metal extends into the root of a joint.

• safelight - A special lamp used in the darkroom to provide working visibility withoutaffecting the photosensitive emulsion of the radiographic film.

• screen (intensifying) - A layer of material placed in contact with the film to increase theeffect of the radiation, thus shortening the exposure.

• sensitivity (radiographic) - The percent ratio of the thickness of the smallest detectabledefect to the thickness of the specimen being examined. It is a measure of the capability todetect a small discontinuity.

• shrinkage cavities - Cavities in castings caused by lack of sufficient molten metal as thecasting cools. A small bubble in metal that appears as a dendritic, filamentary, or jaggeddarkened area on a radiograph film.

• shrinkage cracks - Hot tears associated with shrinkage cavities.

• slag inclusions - Nonmetallic solid material entrapped in weld metal or between weldmetal and base metal.

• source - The origin of radiation: an x-ray tube or a radioisotope.

• source-film distance - The distance between the focal spot of an x-ray tube or radiationsource and the film; generally expressed in inches.

• step wedge - A device which is used with appropriate penetrameters on each step, for theinspection of parts having great variations in thickness or a complex geometry. The stepwedge must be made of material radiographically similar to that being radiographed.




• stress corrosion cracking - Failure by cracking under combined action of corrosion andstress, either external (applied) or internal (residual). Cracking may be either intergranularor transgranular, depending on the type of metal and corrosive medium it is exposed to.

• target - A material bombarded by any radiation, as the target is bombarded by

• toe crack -A base-metal crack at the toe of the weld

• tungsten inclusions - Inclusions in welds resulting from particles or splinters of tungstenwelding electrodes.

• underbead crack - A subsurface crack in the base metal near the weld.

• undercut - A depression or groove adjoining the toe of a weld in a metal object. Appearson a radiograph as a dark area.

• undercut (radiographic) - Excess blackening of the film within the image of any unblockededge due to radiation scattered, or passing around, not through, the object.

• weld bead - A deposit of filler metal from a single welding pass.

• weld metal - That portion of a weld which has been in a molten state during welding.

• worm holes (pipe) - Elongated or tubular cavities due to entrapped gas rising throughmolten metal prior to solidification.

• x-ray - Penetrating electromagnetic radiation emitted when the inner orbital electrons of anatom are excited and release energy. Thus, the radiation is non-nuclear in origin and isgenerated in practice by bombarding a metallic target with high-speed electrons.

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Hb Rt Interpretation