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INTRODUCTION

After visual and optical testing (VT), the next method of nonde-structive testing (NDT) most commonly employed in industry isradiographic testing. Also simply referred to as radiography, it isperhaps the most versatile of the nondestructive testing meth-ods.[1] The basic radiographic process in use today is in large partstill the same as it was when it was introduced in the late 1800s.

Radiography uses radiation energy to penetrate solid objects inorder to assess variations in thickness or density. The second partof the process involves capturing a shadow image of the compo-nent being inspected on film using procedures similar to those thattechnicians used when the technology was firstdeveloped. Identifying density differences on an

X-ray, which indicate flaws or cracks, is still the

foundation of radiographic analysis.

PHYSICAL PRINCIPLESRadiography basically involves the projectionand penetration of radiation energy through thesample being inspected. The radiation energy isabsorbed uniformly by the material or compo-nent being inspected except where variations inthickness or density occur. The energy notabsorbed is passed through to a sensing mediumthat captures an image of the radiation pattern.The uniform absorption and any deviations inuniformity are subsequently captured on the

sensing material and indicate the potential pres-ence of a discontinuity.

Image Capturing MediaIn simple terms, a radiograph is a photographic record produced by the passage of X-rays or gamma rays through an object onto a filmor other recording medium (see Figure 1). The developing, fixing and washing of the film after exposure can be performed manual-ly or by automated processing equipment. The developmentprocess begins after the film is exposed to the radiation and aninvisible change called a latent image develops on the film emul-sion. These exposed areas become dark when the film is placed in

a developing solution. The degree of darkening that occurs during

this process depends on the amount of exposure that occurred. Thenext step is to place the film into a special bath and rinse it to stopthe development process. Lastly, the film is put into a fixing bathand then washed to remove the fixer solution. At this point thefilm is fully developed, the process is complete and the radiographis ready to be handled and analyzed.[1]

As the digital world has evolved, a quicker and much moreefficient alternative to the meticulous film development processhas also emerged to benefit the radiography NDT community.

Computed radiography, which is described inthe related article entitled “Computed Radiog-raphy in the Pacific Northwest: Benefits, Draw-backs and Requirements”, makes use of an

alternative image capturing media and develop-ment process.

Electromagnetic Radiation

Two types of electromagnetic radiation are usedto perform radiographic inspection: X-rays andgamma rays (see Figure 2). The primary distin-

guishing characteristic between these two typesof radiation is the different wavelengths of theelectromagnetic energy. Compared to other

types of radiation both X-rays and gamma rayshave relatively short wavelengths which allows

them to penetrate opaque materials. This

inherent capability is what enables their usefor nondestructive testing, as they can reveal

flaws embedded in visually non-transparent materials. The adventof radiography came quickly after the discovery of X-rays because

of the penetration properties of this electromagnetic energy.[3]

Types of Discontinuities A number of different types of discontinuities can be detected with radiographic NDT. Table 1 lists the suitability of traditionalradiographic NDT methods for identifying various types of discontinuities in several applications.

Brett J. Ingold

AMMTIAC

Rome, NYtechsolutions 5techsolutions 5

A Brief Introduction to Precious Metals

http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 2, Number 2

Selecting a Nondestructive Testing Method, Part IV: Radiography

This edition of TechSolutions is the fourth installment in a series dedicated to the subject of nondestructive testing.TechSolutions 1, published in Vol. 1, No. 2 of the AMMTIAC Quarterly , introduced the concept of nondestructive testing and provided brief descriptions of the various techniques currently available. TechSolutions 2 and 3, published in subsequent issues of the AMMTIAC Quarterly , focused on visual inspection and eddy current testing. The current article continues the series and provides a general and informative overview of the radiography nondestructive testing method. In addition, this article will highlight some of the physical principles, inspection requirements, and implementa-tion considerations involved in an effective radiographic inspection process.1 Once the series on nondestructive testing methods is complete, we will combine all of the articles into a valuable desk reference on nondestructive testing and place it on our website. – Editor

Figure 1. Diagram of Typical

Radiography Test Setup.[2]

Radiation Source

Beam

Flaw

Image of Flaw

Test Piece(Object)

Medium forConvertingthe Radiation

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techsolutions 5

The AMMTIAC Quarterly, Volume 2, Number 28

INSPECTION REQUIREMENTSSeveral critical elements are required to successfully analyze theresults of radiographic testing. Because of differences in density and variations in composition, different test pieces can absorbvarying amounts of radiation and therefore present a range of results. Technicians and radiologists each require several years of training to properly set up and administer tests and inspections

and to learn how to evaluate

and interpret the results. Also, as the industry contin-ues to develop, some fore-casts suggest that in thefuture X-rays will be readalmost exclusively by com-puters. This specific advance-ment, however, would notnecessarily eliminate thehigh costs associated withset up tasks, which con-sumes a significant portionof the total radiographic

inspection time.

SafetySafety is an important issueto consider when evaluating a new process for imple-

mentation, especially one such as radiography that requires theuse of radiation. Several governing bodies, including local andstate governments, work together to closely monitor anyone who

works with radiography equipment to ensure that the highestlevels of safety are consistently met.

The licensing and certification process for individuals working with radiography equipment, which emits radiation, requires

both a written examination and an assessment of specific skills while using the equipment. The primary governing body thatadministers the written examination is the American Society of Nondestructive Testing (ASNT). The practical skills evaluationcan be conducted by a variety of institutions that have approvalfrom ASNT. With successful completion of these safety require-ments, the applicant will be certified as an Industrial Radio-graphy Radiation Safety Personnel (IRRSP) member. ASNToffers more detailed information on the entire certificationprocess, including a more specific list of requirements.[4]

PRACTICAL CONSIDERATIONSThere are several factors to take into account when considering the implementation of a radiographic inspection program. Someof the most important factors include: cost, density, facility sizeand logistics. Compared to other nondestructive testing meth-ods, radiography is expensive. Relatively large costs can bereduced considerably when portable X-ray or gamma-ray sourcesare used in film radiography because this setup only requires

space for film processing and analysis. With real-time radiogra-phy, operating costs are usually much lower, because setup timesare shorter and there are no extra costs for processing or inter-pretation of film.

Advantages and DisadvantagesLike all other NDT methods, there are several advantagesand disadvantages that factor into deciding where and whenradiography is typically applied. In relation to other common-ly used NDT methods, the well-proven method of radiography has three main advantages: the ability to detect internalflaws, the ability to detect significant variations in composi-tion, and the abil-

ity to establish a permanent recordof raw inspectiondata. Radiogra-phy also presentstest results pictori-ally which can bemuch more readily interpreted thannumerical data.In addition, real-time radiography offers the ability

to rotate a testobject during inspection, which improves detection of bothinternal and external flaws due to the ability to find the opti-mum orientation.

On the negative side, orientation of the sample to beinspected is a key to successful radiographic inspection andtherefore can pose difficulties if the proper orientation is notfound. For example, radiography is not as effective at detecting flaws that are oriented in a planar direction with respect to theradiation source. Thick inspection samples are also problemat-

Figure 2. Electromagnetic

Spectrum Showing X-ray and

Gamma Ray Regions.[1]

X-Rays

Gamma Rays Ultraviolet Infrared

Visible

10-2 102 104 106100

A review of radiographs from an F -15 Eagle to

check for foreign object debris and cracks

in the aircraft's structure. (Photo taken by

Staff Sgt. Shelley Gill and provided courtesyof US Air Force)

A non-destructive inspection technician

(NDI) evaluates an X-ray image of

an A-10 Thunderbolt II aircraft noselanding gear door for cracks. NDI

technicians are tasked with finding

and confirming discontinuities on the

airframe and its parts using methodssuch as Eddy Current, Fluorescent

Penetrant, Magnetic Particles, Ultra

Sound and X-ray. (Photo taken byAirman 1st Class Alesia Goosic and

provided courtesy of US Air Force)

Wavelengths in angstrom units (A), where 1 A = 10-8 cm = 3.937x10 -9 in.





http://ammtiac.alionscience.com The AMMTIAC Quarterly, Volume 2, Number 2

AMMTIACA D V A N C E D M A T E R I A L S , M A N U F AC T U R I N G A N D T E S T I N G

ic for radiography methods. Radiation sources can pose healthand safety risks which is another disadvantage of the method.The tedious film processing requirement of radiography andassociated special facility requirements have traditionally beena distinct disadvantage; however, with the advent of digitalimaging and computed radiography many of these limitationshave been overcome.

CURRENT TRENDS AND FUTURE ADVANCEMENTSIn order to meet the constantly changing demands of industry,various new sources of radiation, such as neutron generatorsand radioactive isotopes, are continually being developed.Other ongoing advances also include improved X-ray films andautomatic film processors, as well as improved or specializedradiographic techniques.

Table 1. Suitability of Traditional Radiographic NDT Methods for Various Types of Discontinuities in Light and Heavy Metals.[3]

Suitability for Light Metals Suitability for Heavy Metals

Inspection Application Film Real-Time Film Film Real-Time Filmwith X-rays Radiography with γ-rays with X-rays Radiography with γ-rays

General

Surface cracks* 3 3 3 3 3 3

Internal cracks 3 3 3 3 3 3

Voids 4 4 4 4 4 4Thickness 3 4 3 3 4 3

Metallurgical variations 3 3 3 3 3 3

Sheet and plate

Thickness 4 4 4 4 4 4

Laminations 1 1 1 1 1 1

Voids 4 4 4 4 4 4

Bars and tubes

Seams 2 2 2 2 2 2

Pipe 4 4 4 4 4 3

Cupping 4 4 4 4 4 3

Inclusions 3 3 3 3 3 3

Castings

Cold shuts 4 4 4 4 4 4

Surface cracks 3 3 3 3 3 3

Internal shrinkage 4 4 4 4 4 4

Voids, pores 4 4 4 4 4 4

Core shift 4 4 4 4 4 4

Forgings

Laps 2 2 2 2 2 1

Inclusions 3 3 3 3 3 1

Internal bursts 4 4 4 3 3 4

Internal flakes 2 2 1 2 2 1

Cracks and tears 3 3 3 3 3 3

Welds

Shrinkage cracks 4 4 4 4 4 4Slag inclusions 4 4 4 4 4 4

Incomplete fusion 4 4 4 4 4 4

Pores 4 4 4 4 4 4

Incomplete penetration 4 4 4 4 4 4

Processing

Heat-treat cracks 1 1 1 2 1 1

Grinding cracks 1 1 1 1 1 1

Service

Fatigue and heat cracks 3 3 2 2 2 2

Stress corrosion 3 3 2 3 3 2

Blistering 2 2 2 2 2 2

Thinning 3 3 3 3 3 3

Corrosion pits 3 3 2 4 4 2

4 - Good, 3 - Average, 2 - Fair, 1 - Poor





The AMMTIAC Quarterly, Volume 2, Number 210

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However, with today’s technology it is now possible to gener-ate images of higher quality and sensitivity. The higher quality of radiographic images is primarily due to improved films that have

a wider variety of available grain sizes. Also, with the addition of computers and other advanced electronic systems to the process,the advent of digital radiography has proved to be a largeadvancement within the industry.

With the use of digital radiography, a radiographic image cap-tured today can theoretically be preserved forever and sent any-

where in the world almost instantly. In earlier cases, there had tobe concerns with deterioration of the image that no longer haveto be taken into account today. This ability to continually improve the process has led to growth of radiography intonumerous industries. Radiography has seen expanded use inindustry to inspect welds and castings, airbags and canned foods,to name a few. The area of metallurgical material identificationand security systems has also employed radiography NDT at air-ports and other facilities with security needs.[1, 5]

CONCLUSIONRadiography is a mature NDT method that can be used to effec-tively detect several types of discontinuities embedded within a variety of types of materials and components. Since the method

has been in use for many years, the drawbacks and shortcomingsare well-known. Some of these limitations have been overcome

with the rapid advancement of digital technology. Radiography

has continued to evolve by embracing certain aspects of thedigital era, and consequently it has become a more flexible andviable method for nondestructive evaluation.

REFERENCES[1] “Radiography in Modern Industry,” 4th Edition, R.A. Quinnand C.C. Sigl, Editors, Eastman Kodak Company, 1980, http://

www.kodak.com/eknec/documents/87/0900688a802b3c87/Radiogra phy-in-Modern-Industry.pdf [2] “Radiography Testing,” Engineer’s Handbook, http://www.engineershandbook.com/MfgMethods/ndtrt.htm[3] “Radiographic Inspection,” ASM Metals Handbook, NinthEdition, Vol. 17, Nondestructive Evaluation and Quality Control,

ASM International Metals Park, OH, pp. 296-357.[4] “Industrial Radiography Radiation Safety Personnel,” ASNTPractice No. ASNT-CP-IRRSP-1A, 2001 Edition, American Society for Nondestructive Testing, http://www.asnt.org/certification/irrsp/cp-irrsp-1a.pdf.[5] “Introduction to Radiographic Testing,” NDT Resource Center,http://www.ndted.org/EducationResources/CommunityCollege/Radiography/Introduction/presentstate.htm.

Table 1. Radiography Summary

Discontinuity types • Voids(e.g. what types the method can detect) • Inclusions

• Cracks• Non-uniformity of material

• Density changes• Weld defects

Size of discontinuities • Discontinuities that exhibit 1% or more absorption dif ference relative to surrounding region• Advanced systems can detect flaws as small as 0.001 inches

Limitations • Orientation of inspection sample• Not suitable for surface defects• As thickness increases, detection effectiveness decreases• Large amounts of equipment required for non-portable setup• Film limitations• Manual image interpretation

Advantages • Can be used to detect defects in a variety of materials• Can detect internal defects• Permanent inspection record• Objects radiographed range in size from micro-miniature electronic parts to

large missile components• Makes it easier to maintain a defect-free and uniform product line

Inspector training (level and/or availability) • Variety of programs available nationally to study the science of radiology

Inspector certification required • Radiation safety training is critically impor tant• ASNT offers certification for radiography safety

Equipment • Portable or fixed setups depending on industry/company requirements and desired function• Traditional radiography requires film development facilities and equipment

Relative cost of inspection • Depends on setup, but cost can be greatly reduced with the use of portable equipmentthat requires less space



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