Handbook ASNT vol 10 Tổng quan về kiểm tra không phá hủy (NDT Overview)

Sách Handbook của Hiệp hội kiểm tra không phá hủy Mỹ viết tổng quan về kỹ thuật kiểm tra không phá hủy (NDT) dùng để kiểm tra chất lượng mối hàn, chất lượng sản phẩm và rất nhiều ứng dụng phổ biến khác nữa. Đây là cuốn sách viết tổng quan mở đầu cho serie sách về NDT chi tiết về từng phương pháp.

Technical Editor Gary L Workman

Editor Patrick O Moore

American Society for Nondestructive Testing

American Society for Nondestructive Testing ISBN 978-1-57117-187-0

FOUNDE

D 1941

®

HANDBOOK NONDESTRUCTIVE TESTING

Volume 10

Nondestructive Testing Overview

It is often said that the world is changing

at a rapid pace, and this couldn’t be truer

than with respect to technology Our

profession of nondestructive testing and

the means by which the various methods

and techniques are applied has seen

significant change and new applications

in recent years Even as our team of

subject matter experts compiled the

informative sections of this publication,

new and emerging technologies have

arisen and are being refined for

application in industry It is refreshing to

know that we as NDT professionals have a

staple resource that we can turn to in

answering the day-to-day questions and

satisfying the needs of industry The NDT

Handbook has been the marquee of

resource for our industry The dedication

of unselfish volunteers and professionals

who step forward makes it possible for

publications like this to serve as the

benchmark for NDT

Our society continues to be a missionbased society With the rapidity of

technological advance, it is important

that publications such as this one truly

contribute to making the world a safer

place through the advancement of NDT

The knowledge herein will be shared bynot only the front line technician but alsoengineers and researchers, by not onlythose interested in the broad professionbut also those in a narrow specialty Iwould like to express my sincere gratitude

to the personnel that served ascontributors, editors and reviewers formaking this edition possible

As you are all aware, ASNT is avolunteer society and the effort that isrequired to see a result such as this isoften challenging The volunteers of ASNThave met this challenge for over a halfcentury, and the names of those whohave contributed to the development and

continued improvement of the NDT Handbook are etched into the foundation

of ASNT The handbooks, their media andarangement in which the information isshared with the NDT community,continue to evolve as fast as thetechnology that the books record It is ourgoal to continue to meet the needs of ourmembers in a timely manner

Robert PotterASNT President, 2011-2012

President’s Foreword

Aims of a Handbook

The volume you are holding in your hand

is the tenth in the third edition of the

Nondestructive Testing Handbook In the

beginning of each volume, ASNT has

stated the purposes and nature of the

NDT Handbook series.

Handbooks exist in many disciplines ofscience and technology, and certain

features set them apart from other

reference works A handbook should

ideally provide the basic knowledge

necessary for an understanding of the

technology, including both scientific

principles and means of application The

third edition of the NDT Handbook

provides this knowledge through method

specific volumes

The typical reader may be assumed tohave completed a few years of college

toward a degree in engineering or science

and has the background of an elementary

physics or mechanics course Additionally,

this volume allows for computer based

media that enhances all levels of

education and training

Standards, specifications,recommended practices and inspection

procedures are discussed for instructional

purposes, but at a level of generalization

that is illustrative rather than

comprehensive Standards writing bodies

take great pains to ensure that their

documents are definitive in wording andtechnical accuracy People writingcontracts or procedures should consultthe actual standards when appropriate

The NDT Handbook is widely used for

inspector training and qualification, yetits scope serves a broader audience,academic and industrial Noninspectorsuse it, too Those who design qualifyingexaminations or study material for themdraw on ASNT handbooks as a quick andconvenient way of approximating thebody of knowledge Committees andindividuals who write or anticipatequestions are selective in what they drawfrom any source The parts of a handbookthat give scientific background, forinstance, may have little bearing on apractical examination except to providethe physical foundation to assist handling

of more challenging tasks Other parts of

a handbook are specific to a certain

industry The NDT Handbook provides a

collection of perspectives on its subject tobroaden its value and convenience to thenondestructive testing community.The present volume is a worthyaddition to the third edition The editors,ASNT staff, contributors and reviewersworked together to bring the project tocompletion For their scholarship anddedication, I thank them all

Richard H BossiHandbook Development Director

Foreword

ASNT’s Nondestructive Testing Handbook

continues to include a broad range of

techniques and applications, as shown in

this final volume of the third edition The

primary intention in this NDT Overview

volume is to draw on the very extensive

and in-depth information contained in

the entire edition and to bring together

the core information into one volume

Thus this volume is able to provide key

information to allow scientists and

engineers to make the best choices across

the range of NDT methods

I was chairman of ASNT’s HandbookDevelopment Committee from 1996

through 2007 Those years saw the

publication of the first seven volumes of

the third edition Hundreds of experts

contributed, and it was my privilege to

meet the volume coordinators and

editors, the finest minds in our

technology

Many NDT concepts that wereprimarily research topics for the second

edition and some third edition volumes

have now matured into well defined

applications This volume offers

up-to-date techniques for signal

processing techniques as well as for a

broad range of applications in industries

such as welding, energy, petroleum andaerospace The series benefits frominternational contributions, providing alarger knowledge base for nondestructivetesting worldwide

This NDT Overview reflects changes in

the way inspections are performedbecause of advances in computertechnology These instruments andtechniques have improved data collectionand analysis, both in the laboratory and

in the field These advances in technologyalso provide improved imaging capabilityand better verification of measurementswith theory

This volume represents the work ofmany in the field who were able tocontribute their time and effort to providelatest state-of-the-art information Inaddition, volunteers were able to reviewand return comments in short order Weare indebted to both groups for bringingthis volume to publication We also wish

to express our gratitude to ASNT staff fortheir thoroughness, diligence andtimeliness in preparing this volume forpublication

Gary L WorkmanTechnical Editor

Preface

The book you are holding is the latest in a

series of attempts to do something almost

impossible: in a single volume to encapsulate

the technology of nondestructive testing

(NDT)

First Edition, 1959

Three years after its founding, the American

Industrial Radium and X-Ray Society’s

president, Maynard Evans, appointed a

Radiographer’s Handbook Committee,

authorized to prepare an applications manual

for distribution free to members

In 1951, the proposed handbook on

radiography was folded into plans for an NDT

manual covering radiographic, ultrasonic and

magnetic methods The change in content

echoed the change of society’s name to the

Society for Nondestructive Testing

In 1955, the Board of Directors agreed to

fund work on the Handbook of NDT Robert

McMaster was appointed editor The book was

expected to contain 500 pages, divided into

sections devoted to major fields of

nondestructive testing Within each section,

separate chapters covering separate methods

were to be written by individual authors

In 1958, the newly organized Technical

Council was given six primary functions,

including: “To conduct a continuing review of

the Handbook of Nondestructive Testing, directed

at the revision of subsequent editions.”

The book’s nearly 2000 pages would not fit

in a single cover, so it was published in two

volumes, in 1959

Second Edition, 1982-1996

The second edition was published in a series

of volumes appearing from 1982 to 1996 The

capstone was the edition’s tenth volume, NDT

Overview NDT Overview was composed almost

entirely of material that had appeared in the

previous volumes Some references had been

updated; some explanations were abridged;

and a comprehensive, multimethod glossary

was included

NDT Overview volume soon found its

audience: practitioners and students who

needed a comprehensive treatment of all

methods These readers would turn to method

volumes for details about specialties

Third Edition, 1998-2012

The third edition’s NDT Overview improves

over the second edition’s in several ways

1 The introduction’s treatment ofmeasurement units is more detailed andcomprehensive

2 There is a bibliography of NDT history,

15 pages that list publications, anauthoritative place for a technologyhistorian to start

3 References are updated since 1996, just asthe third edition has updated the second

4 The method chapters are updated to reflectnew techniques and technologies — inparticular, advances made possible bydigital processing and imaging Thischange is conspicuous in the chapters onthe visual, radiographic, ultrasonic andstrain measurement methods

5 The glossary in particular is updated andexpanded

The text in each method chapter is not merely

a revision of the second edition NDT Overview

but has been completely recreated from thirdedition files

Finally, and more than before, the volume’scontent is selected and edited with an eyetoward practicality The book can help aLevel III who specializes in one method andmay be confronted by a new inspectionproblem to determine what the othermethods offer Also, the examinee who studiesfor general NDT qualification will find much

of the body of knowledge here, in one book.(Such learners need other resources, of course,

in materials science and basic physics.)For these reasons, nearly everyone whopractices NDT needs this book

It has been an honor to work with GaryWorkman on this volume, and a pleasure tocollaborate again with the various chaptercoordinators Most of them were contributors

or editors in creating the original methodvolumes over the course of 16 years

It was also a pleasure to receive help andencouragement from ASNT staff, in particularTimothy Jones (senior manager, publications)for administrative support and Hollis

Humphries (technical publications supervisor)for graphics and editing at every stage ofproduction

Patrick O Moore

NDT Handbook Editor

Editor’s Preface

This book is made from the preceding

nine volumes of the third edition, and it

is impractical to list the hundreds of

contributors and reviewers

All chapter coordinators andcontributors are also reviewers but are

listed once, as contributors

Handbook Development

Committee

Michael W Allgaier, Mistras Group

Richard H Bossi, Boeing Research and

TechnologyLisa Brasche, Iowa State University

James R Cahill, GE Sensing and

Inspection TechnologiesRobert E Cameron

John S Cargill, Aerospace Structural

IntegrityNat Y Faransso, KBR

Gary Heath, All Tech Inspection

Dietmar F Henning, Level III Service

Eric v.K Hill, AURA Vector Consulting

James W Houf, American Society for

Nondestructive TestingMorteza K Jafari, Fugro South

Timothy E Jones, American Society for

Nondestructive TestingDoron Kishoni, Business Solutions USA

Richard D Lopez, John Deere Technology

and InnovationXavier P.V Maldague, University Laval

George A Matzkanin, Texas Research

InstituteCharles H Mazel, BlueLine NDT

Ronnie K Miller, Mistras Group

Scott D Miller

David G Moore, Sandia National

LaboratoriesPatrick O Moore, American Society for

Nondestructive TestingRobert F Plumstead, Municipal Testing

LaboratoryFrank J Sattler, Sattler Consultants

Todd E Sellmer, Washington TRU

SolutionsRoderic K Stanley, NDE Information

ConsultantsKenneth A Starry, IVC Technologies

Satish S Udpa, Michigan State University

Mark F.A Warchol, Texas Research

InstituteGlenn A Washer, University of Missouri

— ColumbiaGary L Workman, University of Alabama,

Huntsville

Contributors

Michael W Allgaier, Mistras GroupRichard H Bossi, Boeing Research andTechnology

John K Keve, AREVE Federal ServicesTimothy E Kinsella, Dassault Falcon JetDoron Kishoni, Business Solutions USARichard D Lopez, John Deere Technologyand Innovation

Xavier P.V Maldague, University LavalRonnie K Miller, Mistras GroupDavid G Moore, Sandia NationalLaboratories

John W Newman, Laser TechnologyEric I Schwartz, Trilion Quality SystemsRoderic K Stanley, NDE InformationConsultants

Kenneth A Starry, IVC TechnologiesMarvin W Trimm, Savannah RiverNational Laboratory

John Tyson II, Trilion Quality SystemsLalita Udpa, Michigan State UniversitySatish S Udpa, Michigan State UniversityGary L Workman, University of Alabama,Huntsville

Eric v.K Hill, AURA Vector ConsultingJames W Houf, American Society forNondestructive Testing

Doron Kishoni, Business Solutions USARavindran Krishnamurthy, SouthernInspection Services, Chennai, IndiaCharles P Longo, American Society forNondestructive Testing

Eugene A Mechtly, University of Illinois

at Urbana-ChampaignSteven M Shepard, Thermal WaveImaging

Flynn Spears, Laser Technology

Acknowledgments

Chapter 1 Introduction to

Nondestructive Testing 1

Part 1 Nondestructive Testing 2

Part 2 Management of Nondestructive Testing 13

Part 3 Measurement Units for Nondestructive Testing 19

References 30

Chapter 2 Bibliography of Nondestructive Testing History 31

Nondestructive Testing in General 32

Visual Testing 33

Liquid Penetrant Testing 35

Leak Testing 36

Infrared and Thermal Testing 36

Radiographic Testing 38

Electromagnetic Testing 40

Magnetic Testing 43

Ultrasonic Testing 44

Acoustic Emission Testing 45

Chapter 3 Visual Testing 47

Part 1 Introduction to Visual Testing 48

Part 2 Light and Vision 49

Part 3 Images 55

Part 4 Direct Visual Testing 63

Part 5 Indirect Visual Testing 69

Part 6 Visual Testing of Metals 75

Part 7 Visual Acceptance Criteria for Welds 87

References 94

Chapter 4 Liquid Penetrant Testing 95

Part 1 Elements of Liquid Penetrant Testing 96

Part 2 Liquid Penetrant Testing Processes 104

Part 3 Emulsification and Removal of Excess Surface Liquid Penetrant 110

Part 4 Application and Operation of Developers 117

Part 5 Interpretation of Liquid Penetrant Indications 121

Part 6 Field Techniques for Liquid Penetrant Testing 127

Part 7 Maintenance of Liquid Penetrant Test Systems 131

References 134

Chapter 5 Leak Testing 135

Part 1 Management of Leak Testing 136

Part 2 Selection of Leak Test Techniques 145

Part 3 Bubble Testing 153

Part 4 Mass Spectrometer Helium Leak Testing 156

Part 5 Leak Testing with Halogen Tracer Gases 158

Part 6 Other Techniques of Leak Testing 163

Part 7 Leak Testing of Hermetically Sealed Devices 167

Part 8 Other Applications of Leak Testing 170

References 173

Chapter 6 Infrared and Thermal Testing 175

Part 1 Management of Infrared and Thermal Testing 176

Part 2 Principles of Infrared and Thermal Testing 178

Part 3 Techniques of Infrared and Thermal Testing 187

References 198

Chapter 7 Radiographic Testing 199

Part 1 Radiographic Principles 200

Part 2 Radiation Sources 203

Part 3 Radiographic Imaging 215

Part 4 Radiographic Techniques 221

Part 5 Computed Tomography 227

Part 6 Neutron Radiography 230

Part 7 Radiographic Applications 232

References 241

Chapter 8 Electromagnetic Testing 243

Part 1 Introduction to Electromagnetic Testing 244

Part 2 Electromagnetic Techniques Other than Eddy Current Testing 246

Part 3 Eddy Current Testing 253

Part 4 Applications of Electromagnetic Testing 263

References 272

C O N T E N T S

Marvin W Trimm, Westinghouse Savannah River Company, Aiken, South Carolina (Part 2)

1

C H A P T E R

Introduction to Nondestructive Testing

Part 1 Nondestructive Testing, 2 Part 2 Management of Nondestructive Testing, 13 Part 3 Measurement Units for Nondestructive Testing, 19

References, 30

Scope of Nondestructive

Testing

Nondestructive testing is a materials

science concerned with many aspects of

quality and serviceability of materials and

structures The science of nondestructive

testing incorporates all the technology for

process monitoring and for detection and

measurement of significant properties,

including discontinuities, in items

ranging from research test objects to

finished hardware and products in service

Nondestructive testing examines materials

and structures without impairment of

serviceability and reveals hidden

properties and discontinuities

Nondestructive testing is becomingincreasingly vital in the effective conduct

of research, development, design and

manufacturing programs Only with

appropriate nondestructive testing can the

benefits of advanced materials science be

fully realized The information required

for appreciating the broad scope of

nondestructive testing is available in

many publications and reports

Definition

Nondestructive testing (NDT) has been

defined as those methods used to test a

part or material or system without

impairing its future usefulness The term

is generally applied to nonmedical

investigations of material integrity

Nondestructive testing is used toinvestigate specifically the material

integrity or properties of a test object A

number of other technologies — for

instance, radio astronomy, voltage and

amperage measurement and rheometry

(flow measurement) — are nondestructive

but are not used specifically to evaluate

material properties Radar and sonar are

classified as nondestructive testing when

used to inspect dams, for instance, but

not when used to chart a river bottom

Nondestructive testing asks “Is theresomething wrong with this material?” In

contrast, performance and proof tests ask

“Does this component work?” It is not

considered nondestructive testing when

an inspector checks a circuit by running

electric current through it Hydrostatic

pressure testing is a form of proof testingthat sometimes destroys the test object

A gray area in the definition of

nondestructive testing is the phrase future usefulness Some material investigations

involve taking a sample of the test objectfor a test that is inherently destructive Anoncritical part of a pressure vessel may

be scraped or shaved to get a sample forelectron microscopy, for example

Although future usefulness of the vessel isnot impaired by the loss of material, theprocedure is inherently destructive andthe shaving itself — in one sense the truetest object — has been removed fromservice permanently

The idea of future usefulness is relevant

to the quality control practice ofsampling Sampling (that is, less than

100 percent testing to draw inferencesabout the unsampled lots) is

nondestructive testing if the tested sample

is returned to service If steel bolts aretested to verify their alloy and are thenreturned to service, then the test isnondestructive In contrast, even ifspectroscopy in the chemical testing ofmany fluids is inherently nondestructive,the testing is destructive if the samples arepoured down the drain after testing.Nondestructive testing is not confined

to crack detection Other anomaliesinclude porosity, wall thinning fromcorrosion and many sorts of disbonds.Nondestructive material characterization

is a field concerned with propertiesincluding material identification andmicrostructural characteristics — such asresin curing, case hardening and stress —that directly influence the service life ofthe test object

Methods and Techniques

Nondestructive testing has also beendefined by listing or classifying thevarious techniques.1,2This approach to

nondestructive testing is practical in that it

typically highlights methods in use byindustry

In the Nondestructive Testing Handbook, the word method is used for a group of test

techniques that share a form of probingenergy The ultrasonic test method, forexample, uses acoustic waves at afrequency higher than audible sound.Infrared and thermal testing and

radiographic testing are two test methods

that use electromagnetic radiation, each

in a defined wavelength range The word

technique, in contrast, denotes a way of

adapting the method to the application

Through-transmission immersion testing

is a technique of the ultrasonic method,

for example

Purposes of

Nondestructive Testing

Since the 1920s, the art of testing without

destroying the test object has developed

from a laboratory curiosity to an

indispensable tool of fabrication,

construction, manufacturing and

maintenance processes No longer is

visual testing of materials, parts and

complete products the principal

nondestructive test for quality

Nondestructive tests in great variety are in

worldwide use to detect variations in

structure, minute changes in surface

finish, the presence of cracks or other

physical discontinuities, to measure the

thickness of materials and coatings and to

determine other characteristics of

industrial products Scientists and

engineers of many countries have

contributed greatly to nondestructive test

development and applications

How is nondestructive testing useful?

Why do thousands of industrial concerns

buy the test equipment, pay the

subsequent operating costs of the testing

and even reshape manufacturing

processes to fit the needs and findings of

nondestructive testing? Modern

nondestructive tests are used by

manufacturers (1) to ensure product

integrity and in turn reliability, (2) to

avoid failures, prevent accidents and save

human life (Figs 1 and 2), (3) to make a

profit for the user, (4) to ensure customer

satisfaction and maintain the

manufacturer’s reputation, (5) to aid in

better product design, (6) to controlmanufacturing processes, (7) to lowermanufacturing costs, (8) to maintainuniform quality levels and (9) to ensureoperational readiness

These reasons for widespread andprofitable nondestructive testing aresufficient in themselves but paralleldevelopments have contributed to thetechnology’s growth and acceptance

Increased Demand on Machines

In the interest of greater performance andreduced cost for materials, the designengineer is often under pressure to reduceweight Mass can be saved sometimes bysubstituting aluminum alloys, magnesiumalloys or composite materials for steel oriron but such light parts may not be thesame size or design as those they replace

The tendency is also to reduce the size

These pressures on the designer havesubjected parts of all sorts to increasedstress levels Even such commonplaceobjects as sewing machines, sauce pansand luggage are also lighter and moreheavily loaded than ever before The stress

to be supported is known as dynamic stress

or dynamic loading, as opposed to static

stress It often fluctuates and reverses atlow or high frequencies Frequency ofstress reversals increases with the speeds

of modern machines, so components tend

to fatigue and fail more rapidly

Another cause of increased stress onmodern products is a reduction in thesafety factor An engineer designs withcertain known loads in mind On thesupposition that materials andworkmanship are never perfect, a safetyfactor of 2, 3, 5 or 10 is applied However,

F IGURE 1 Fatigue cracks caused damage to aircraft fuselage,

causing death of flight attendant and injury to passengers

(April 1988)

F IGURE 2 Boilers operate with high internal steam pressure.

Material discontinuities can lead to sudden, violent failurewith possible injury to people and damage to property

a lower factor is often used that depends

on considerations such as cost or weight

New demands on machinery have alsostimulated the development and use of

new materials whose operating

characteristics and performances are not

completely known These new materials

could create greater and potentially

dangerous problems For example, an

aircraft part was built from an alloy whose

work hardening, notch resistance and

fatigue life were not well known After

relatively short periods of service, some of

the aircraft using these parts suffered

disastrous failures Sufficient and proper

nondestructive tests could have saved

many lives

As technology improves and as servicerequirements increase, machines are

subjected to greater variations and

extremes of all kinds of stress, creating an

increasing demand for stronger or more

damage tolerant materials

Engineering Demands for Sounder

Materials

Another justification for nondestructive

tests is the designer’s demand for sounder

materials As size and weight decrease and

the factor of safety is lowered, more

emphasis is placed on better raw material

control and higher quality of materials,

manufacturing processes and

workmanship

An interesting fact is that a producer ofraw material or of a finished product

sometimes does not improve quality or

performance until that improvement is

demanded by the customer The pressure

of the customer is transferred to

implementation of improved design or

manufacturing Nondestructive testing is

frequently called on to confirm delivery

of this new quality level

Public Demands for Greater Safety

The demands and expectations of the

public for greater safety are widespread

Review the record of the courts in

granting high awards to injured persons

Consider the outcry for greater

automobile safety as evidenced by the

required automotive safety belts and the

demand for air bags, blowout proof tires

and antilock braking systems The

publicly supported activities of the

National Safety Council, Underwriters

Laboratories, the Occupational Safety and

Health Administration, the Federal

Aviation Administration and other

agencies around the world are only a few

of the ways in which this demand for

safety is expressed It has been expressed

directly by passengers who cancel

reservations following a serious aircraft

accident This demand for personal safety

has been another strong force in thedevelopment of nondestructive tests

Rising Costs of Failure

Aside from awards to the injured or toestates of the deceased and aside fromcosts to the public (because of evacuationsoccasioned by chemical leaks, for

example), there are other factors in therising costs of mechanical failure

These costs are increasing for manyreasons Some important ones are(1) greater costs of materials and labor,(2) greater costs of complex parts,(3) greater costs because of the complexity

of assemblies, (4) a greater probability thatfailure of one part will cause failure ofothers because of overloads, (5) theprobability that the failure of one partwill damage other parts of high value and(6) part failure in an integrated automaticproduction machine, shutting down anentire high speed production line In thepast, when production was carried out onmany separate machines, the broken onecould be bypassed until repaired Today,one machine is often tied into theproduction cycles of several others Loss

of such production is one of the greatestlosses resulting from part failure

Classification of Methods

The National Materials Advisory Board(NMAB) Ad Hoc Committee onNondestructive Evaluation classifiedtechniques into six major methodcategories: visual, penetrating radiation,magnetic-electrical, mechanical vibration,thermal and chemical/electrochemical.2Amodified version of their system ispresented in Table 1

Each method can be completelycharacterized in terms of five principalfactors: (1) energy source or medium used

to probe the object (such as X-rays,ultrasonic waves or thermal radiation),(2) nature of the signals, image orsignature resulting from interaction withthe object (attenuation of X-rays orreflection of ultrasound, for example),(3) means of detecting or sensingresultant signals (photoemulsion,piezoelectric crystal or inductance coil),(4) means of indicating or recordingsignals (meter deflection, oscilloscopetrace or radiograph) and (5) basis forinterpreting the results (direct or indirectindication, qualitative or quantitative andpertinent dependencies)

The objective of each method is toprovide information about one or more ofthe following material parameters:

(1) discontinuities and separations (such

as cracks, voids, inclusions anddelaminations), (2) structure or

malstructure (such as crystalline structure,

grain size, segregation and misalignment),

(3) dimensions and metrology (such as

thickness, diameter, gap size and

discontinuity size), (4) physical and

mechanical properties (such as reflectivity,

conductivity, elastic modulus and sonic

velocity), (5) composition and chemical

analysis (such as alloy identification,

impurities and elemental distributions),

(6) stress and dynamic response (such as

residual stress, crack growth, wear and

vibration), (7) signature analysis (such as

image content, frequency spectrum and

field configuration) and (8) heat sources

Material characteristics in Table 1 arefurther defined in Table 2 with respect to

specific objectives and specific attributes

to be measured, detected and defined

Methods that use electromagneticradiation (Table 3) can be divided

according to the segment of the spectrum

each uses as interrogating energy: radar,

thermography, visual testing and

X-radiography (Fig 3) Methods using

vibration and ultrasound are in a different

spectrum: the acoustic

The limitations of a method includeconditions (such as access, physical

contact and surface preparation) and

requirements to adapt the probe to the

test object Other factors limit the

detection or characterization of

discontinuities or attributes and limit

interpretation of signals or images

Classification by Test Object

Nondestructive test techniques may beclassified according to how they detectindications relative to the surface of a testobject Surface methods include liquidpenetrant testing, visual testing and moirétesting Surface/near-surface methodsinclude tap, holographic, shearographic,magnetic particle and electromagnetictesting When surface or near-surfacemethods are applied during intermediatemanufacturing, they provide preliminaryassurance that volumetric methodsperformed on the completed object orcomponent will reveal few rejectablediscontinuities Volumetric methodsinclude radiography, ultrasonic testingand acoustic emission testing

Through-boundary techniques includeleak testing, some infrared thermographictechniques, airborne ultrasonic testingand certain techniques of acousticemission testing Other less easilyclassified methods are materialidentification, vibration analysis andstrain gaging

No one nondestructive test method isall revealing In some cases, one method

or technique may be adequate for testing

a specific object or component However,

in most cases, it takes a series of testmethods to do a complete nondestructivetest of an object or component Forexample, if surface cracks must bedetected and eliminated and if the object

T ABLE 1 Nondestructive test method categories.

Basic Categories

Mechanical and optical color; cracks; dimensions; film thickness; gaging; reflectivity; strain distribution and magnitude; surface

finish; surface flaws; through-cracksPenetrating radiation cracks; density and chemistry variations; elemental distribution; foreign objects; inclusions; microporosity;

misalignment; missing parts; segregation; service degradation; shrinkage; thickness; voidsElectromagnetic and electronic alloy content; anisotropy; cavities; cold work; local strain, hardness; composition; contamination;

corrosion; cracks; crack depth; crystal structure; electrical conductivities; flakes; heat treatment;hot tears; inclusions; ion concentrations; laps; lattice strain; layer thickness; moisture content;

polarization; seams; segregation; shrinkage; state of cure; tensile strength; thickness; disbonds; voidsSonic and ultrasonic crack initiation and propagation; cracks, voids; damping factor; degree of cure; degree of impregnation;

degree of sintering; delaminations; density; dimensions; elastic moduli; grain size; inclusions;

mechanical degradation; misalignment; porosity; radiation degradation; structure of composites;surface stress; tensile, shear and compressive strength; disbonds; wear

Infrared and thermal anisotropy; bonding; composition; emissivity; heat contours; plating thickness; porosity; reflectivity;

stress; thermal conductivity; thickness; voids; cracks; delaminations; heat treatment; state of cure;moisture; corrosion

Chemical and analytical alloy identification; composition; cracks; elemental analysis and distribution; grain size; inclusions;

macrostructure; porosity; segregation; surface anomalies

Auxiliary Categories

Image generation dimensional variations; dynamic performance; anomaly characterization and definition; anomaly

distribution; anomaly propagation; magnetic field configurationsSignal image analysis data selection, processing and display; anomaly mapping, correlation and identification; image

enhancement; separation of multiple variables; signature analysis

or component is made of ferromagnetic

material, then magnetic particle testing

would be the appropriate choice If the

material is aluminum or titanium, then

the choice would be liquid penetrant or

electromagnetic testing However, if

internal discontinuities are to be detected,then ultrasonic testing or radiographywould be chosen The exact technique ineach case depends on the thickness andnature of the material and the types ofdiscontinuities that must be detected

T ABLE 2 Objectives of nondestructive test methods.

Discontinuities and Separations

Surface anomalies roughness, scratches, gouges, crazing, pitting, imbedded foreign material

Surface connected anomalies cracks, porosity, pinholes, laps, seams, folds, inclusions

Internal anomalies cracks, separations, hot tears, cold shuts, shrinkage, voids, lack of fusion, pores, cavities, delaminations,

disbonds, poor bonds, inclusions, segregations

Structure

Microstructure molecular structure; crystalline structure and/or strain; lattice structure; strain; dislocation; vacancy;

deformationMatrix structure grain structure, size, orientation and phase; sinter and porosity; impregnation; filler and/or reinforcement

distribution; anisotropy; heterogeneity; segregationSmall structural anomalies leaks (lack of seal or through-holes), poor fit, poor contact, loose parts, loose particles, foreign objectsGross structural anomalies assembly errors; misalignment; poor spacing or ordering; deformation; malformation; missing parts

Dimensions and Measures

Displacement, position linear measurement; separation; gap size; discontinuity size, depth, location and orientation

Dimensional variations unevenness; nonuniformity; eccentricity; shape and contour; size and mass variations

Thickness, density film, coating, layer, plating, wall and sheet thickness; density or thickness variations

Physical and Mechanical Properties

Electrical properties resistivity; conductivity; dielectric constant and dissipation factor

Magnetic properties polarization; permeability; ferromagnetism; cohesive force, susceptibility

Thermal properties conductivity; thermal time constant and thermoelectric potential; diffusivity; effusivity; specific heatMechanical properties compressive, shear and tensile strength (and moduli); Poisson’s ratio; sonic speed; hardness; temper

and embrittlementSurface properties color, reflectivity, refraction index, emissivity

Chemical Composition and Analysis

Elemental analysis detection, identification, distribution and/or profile

Impurity concentrations contamination, depletion, doping and diffusants

Metallurgical content variation; alloy identification, verification and sorting

Physiochemical state moisture content; degree of cure; ion concentrations and corrosion; reaction products

Stress and Dynamic Response

Stress, strain, fatigue heat treatment, annealing and cold work effects; stress and strain; fatigue damage and residual lifeMechanical damage wear, spalling, erosion, friction effects

Chemical damage corrosion, stress corrosion, phase transformation

Other damage radiation damage and high frequency voltage breakdown

Dynamic performance crack initiation, crack propagation, plastic deformation, creep, excessive motion, vibration, damping,

timing of events, any anomalous behavior

Signature Analysis

Electromagnetic field potential; intensity; field distribution and pattern

Thermal field isotherms, heat contours, temperatures, heat flow, temperature distribution, heat leaks, hot spots, contrastAcoustic signature noise, vibration characteristics, frequency amplitude, harmonic spectrum, harmonic analysis, sonic

emissions, ultrasonic emissionsRadioactive signature distribution and diffusion of isotopes and tracers

Signal or image analysis image enhancement and quantization; pattern recognition; densitometry; signal classification, separation

and correlation; discontinuity identification, definition (size and shape) and distribution analysis;discontinuity mapping and display

Nondestructive Testing’s

Value

In manufacturing, nondestructive testing

may be accepted reluctantly because its

contribution to profits may not be

obvious to management Nondestructive

testing is sometimes thought of only as a

cost item and can be curtailed by industry

downsizing When a company cuts costs,

two vulnerable areas are quality and

safety When bidding contract work,

companies add profit margin to all cost

items, including nondestructive testing, so

a profit should be made on the

nondestructive testing The attitude

toward nondestructive testing is positive

when management understands its value

Nondestructive testing should be used

as a control mechanism to ensure that

manufacturing processes are within design

performance requirements When used

properly, nondestructive testing saves

money for the manufacturer Rather than

costing the manufacturer money,

nondestructive testing should add profits

to the manufacturing process

Nondestructive Test

Methods

To optimize nondestructive testing, it is

necessary first to understand the

principles and applications of all the

methods The following section brieflydescribes major methods and theapplications associated with them

Visual Testing

Principles Visual testing (Fig 4) is the

observation of a test object, either directlywith the eyes or indirectly using opticalinstruments, by an inspector to evaluatethe presence of surface anomalies and theobject’s conformance to specification

Visual testing is the first nondestructivetest method applied to an item The testprocedure is to clear obstructions from thesurface, provide adequate illumination

T ABLE 3 Nondestructive test methods and corresponding parts of electromagnetic spectrum.

X-rays or gamma rays radiography (RT) 10–16to 10–8 1024to 1017

Ultraviolet radiation various minor methodsa 10–8to 10–7 1017to 1015

Light (visible radiation) visual testing (VT) 4 × 10–7to 7 × 10–7 1015

Heat or thermal radiation infrared and thermal testing (IR) 10–6to 10–3 1015to 1011

Radio waves radar and microwave methods 10–3to 101 1011to 107

a Ultraviolet radiation is used in various methods: (1) viewing of fluorescent indications in liquid penetrant testing and

magnetic particle testing; (2) lasers and optical sensors operating at ultraviolet wavelengths.

F IGURE 3 Electromagnetic spectrum.

Photon energy (MeV)

F IGURE 4 Visual test using borescope to

view interior of cylinder

and observe A prerequisite necessary for

competent visual testing of an object is

knowledge of the manufacturing processes

by which it was made, of its service

history and of its potential failure modes,

as well as related industry experience

Applications Visual testing is widely used

on a variety of objects to detect surface

anomalies associated with various

structural failure mechanisms Even when

other nondestructive tests are performed,

visual tests often provide a useful

supplement When the eddy current

testing of process tubing is performed, for

example, visual testing is often performed

to examine the surface more closely The

following discontinuities may be detected

by a simple visual test: surface

discontinuities, cracks, misalignment,

warping, corrosion, wear and dents

Liquid Penetrant Testing

Principles Liquid penetrant testing (Fig 5)

reveals discontinuities open to the

surfaces of solid and nonporous materials

Indications of a wide variety of

discontinuity sizes can be found regardless

of the configuration of the test object and

regardless of discontinuity orientations

Liquid penetrants seep into various types

of minute surface openings by capillary

action The cavities of interest can be very

small, often invisible to the unaided eye

The ability of a given liquid to flow over a

surface and enter surface cavities depends

on the following: cleanliness of the

surface, surface tension of the liquid,

configuration of the cavity, contact angle

of the liquid, ability of the liquid to wet

the surface, cleanliness of the cavity and

size of the surface opening of the cavity

Applications The principal industrial uses

of liquid penetrant testing include

postfabrication testing, receiving testing,

in-process testing and quality control,

testing for maintenance and overhaul in

the transportation industries, in-plant and

machinery maintenance testing and

testing of large components The

following are some of the typicallydetected discontinuities: surfacediscontinuities, seams, cracks, laps,porosity and leak paths

Leak Testing

Principles Leak testing is concerned with

the flow of liquids or gases frompressurized components or into evacuatedcomponents The principles of leak testinginvolve the physics of liquids or gasesflowing through a barrier where a pressuredifferential or capillary action exists

Leak testing encompasses proceduresthat fall into these basic functions: leaklocation, leakage measurement andleakage monitoring There are severalsubsidiary methods of leak testing,entailing tracer gas detection (Fig 6),pressure change measurement,observation of bubble formation, acousticemission leak testing and other principles

Applications Like other forms of

nondestructive testing, leak testing affectsthe safety and performance of a product

Reliable leak testing decreases costs byreducing the number of reworkedproducts, warranty repairs and liabilityclaims The most common reasons forperforming a leak test are to prevent theloss of costly materials or energy, toprevent contamination of theenvironment, to ensure component orsystem reliability and to prevent anexplosion or fire

F IGURE 5 Liquid penetrant indication of

cracking

F IGURE 6 Leakage measurement dynamic leak testing using

vacuum pumping: (a) pressurized system mode for leaktesting of smaller components; (b) pressurized envelopemode for leak testing of larger volume systems

(a)

(b)

Leak detector Envelope

Source of tracer gas

Source of tracer gas

Envelope

Leak detector

System under test System under test

Infrared and Thermal Testing

Principles Conduction, convection and

radiation are the primary mechanisms of

heat transfer in an object or system

Electromagnetic radiation is emitted from

all bodies to a degree that depends on

their energy state

Thermal testing involves the

measurement or mapping of surface

temperatures when heat flows from, to or

through a test object Temperature

differentials on a surface, or changes in

surface temperature with time, are related

to heat flow patterns and can be used to

detect discontinuities or to determine the

heat transfer characteristics of an object

For example, during the operation of an

electrical breaker, a hot spot detected at

an electrical termination may be caused

by a loose or corroded connection (Fig 7)

The resistance to electrical flow through

the connection produces an increase in

surface temperature of the connection

Applications There are two basic

categories of infrared and thermal test

applications: electrical and mechanical

The specific applications within these two

categories are numerous

Electrical applications include

transmission and distribution lines,

transformers, disconnects, switches, fuses,

relays, breakers, motor windings,

capacitor banks, cable trays, bus taps and

other components and subsystems

Mechanical applications include

insulation (in boilers, furnaces, kilns,

piping, ducts, vessels, refrigerated trucks

and systems, tank cars and elsewhere),friction in rotating equipment (bearings,couplings, gears, gearboxes, conveyorbelts, pumps, compressors and othercomponents) and fluid flow (steam lines;

heat exchangers; tank fluid levels;

exothermic reactions; compositestructures; heating, ventilation and airconditioning systems; leaks above andbelow ground; cooling and heating; tubeblockages; environmental assessment ofthermal discharge; boiler or furnace airleakage; condenser or turbine systemleakage; pumps; compressors; and othersystem applications)

Radiographic Testing

Principles Radiographic testing (Fig 8) is

based on the test object’s attenuation ofpenetrating radiation — either

electromagnetic radiation of very shortwavelength or particulate radiation(X-rays, gamma rays and neutrons)

Different portions of an object absorbdifferent amounts of penetrating radiationbecause of differences in density andvariations in thickness of the test object

or differences in absorption characteristicscaused by variation in composition Thesevariations in the attenuation of thepenetrating radiation can be monitored

by detecting the unattenuated radiationthat passes through the object

This monitoring may be in differentforms The traditional form is throughradiation sensitive film Radioscopicsensors provide digital images X-raycomputed tomography is a three-dimensional, volumetric radiographictechnique

F IGURE 7 Infrared thermography of

automatic transfer switches for emergency

diesel generator Hot spots appear bright in

radiographic testing

Radiation source

Test object Void

Discontinuity images Image plane

Applications The principal industrial uses

of radiographic testing involve testing of

castings and weldments, particularly

where there is a critical need to ensure

freedom from internal discontinuities

Radiographic testing is often specified for

thick wall castings and for weldments in

steam power equipment (boiler and

turbine components and assemblies) The

method can also be used on forgings and

mechanical assemblies, although with

mechanical assemblies radiographic

testing is usually limited to testing for

conditions and proper placement of

components Radiographic testing is used

to detect inclusions, lack of fusion, cracks,

corrosion, porosity, leak paths, missing or

incomplete components and debris

Eddy Current Testing

Principles Based on electromagnetic

induction, eddy current testing is the best

known of the techniques in the

electromagnetic test method Eddy

current testing is used to identify or

differentiate among a wide variety of

physical, structural and metallurgical

conditions in electrically conductive

ferromagnetic and nonferromagnetic

metals and metal test objects The method

is based on indirect measurement and on

correlation between the instrument

reading and the structural characteristics

and serviceability of the test objects

With a basic system, the test object isplaced within or next to an electric coil in

which high frequency alternating current

is flowing This excitation current

establishes an electromagnetic field

around the coil This primary field causes

eddy currents to flow in the test object

because of electromagnetic induction

(Fig 9) Inversely, the eddy currents

affected by all characteristics

(conductivity, permeability, thickness,

discontinuities and geometry) of the test

object create a secondary magnetic field

that opposes the primary field This

interaction affects the coil impedance and

can be displayed in various ways

Eddy currents flow in closed loops inthe test object Their two most important

characteristics, amplitude and phase, are

influenced by the arrangement and

characteristics of the instrumentation and

test object For example, during the test of

a tube, the eddy currents flow

symmetrically in the tube when

discontinuities are not present However,

when a crack is present, then the eddy

current flow is impeded and changed in

direction, causing significant changes in

the associated electromagnetic field

Applications An important industrial use

of eddy current testing is on heat

exchanger tubing For example, eddy

current testing is often specified for thin

wall tubing in pressurized water reactors,steam generators, turbine condensers andair conditioning heat exchangers Eddycurrent testing is also used in aircraftmaintenance The following are some ofthe typical material characteristics thatmay affect conductivity and be evaluated

by eddy current testing: cracks, inclusions,dents and holes; grain size; heat

treatment; coating and material thickness;composition, conductivity or

permeability; and alloy composition

Magnetic Particle Testing

Principles Magnetic particle testing

(Fig 10) is a method of locating surfaceand near-surface discontinuities inferromagnetic materials When the testobject is magnetized, discontinuities thatlie in a direction generally transverse tothe direction of the magnetic field will

F IGURE 9 Electromagnetic testing:

(a) representative setup for eddy currenttest; (b) inservice detection of

discontinuities

Coil in eddy current probe

Primary electromagnetic

field

Direction of primary alternating current

Eddy current intensity decreases with increasing depth

Direction of eddy current Conducting

cause a magnetic flux leakage field to be

formed at and above the surface of the

test object The presence of this leakage

field and therefore the presence of the

discontinuity is detected with fine

ferromagnetic particles applied over the

surface, with some of the particles being

gathered and held to form an outline of

the discontinuity This generally indicates

its location, size, shape and extent

Magnetic particles are applied over a

surface as dry particles or as wet particles

in a liquid carrier such as water or oil

Applications The principal industrial uses

of magnetic particle testing include final,

receiving and in-process testing; testing

for quality control; testing for

maintenance and overhaul in the

transportation industries; testing for plant

and machinery maintenance; and testing

of large components Some discontinuities

typically detected are surface

discontinuities, seams, cracks and laps

Ultrasonic Testing

Principles In ultrasonic testing (Fig 11),

beams of acoustic waves at a frequency

too high to hear are introduced into a

material for the detection of surface and

subsurface discontinuities These acoustic

waves travel through the material with

some energy loss (attenuation) and are

reflected and refracted at interfaces The

echoes are then analyzed to define and

locate discontinuities

Applications Ultrasonic testing is widely

used in metals, principally for thickness

measurement and discontinuity detection

This method can be used to detect

internal discontinuities in most

engineering metals and alloys Bonds

produced by welding, brazing, soldering

and adhesives can also be ultrasonically

tested Inline techniques have been

developed for monitoring and classifying

materials as acceptable, salvageable or

scrap and for process control Also tested

are piping and pressure vessels, nuclear

systems, motor vehicles, machinery,

railroad stock and bridges

Acoustic Emission Testing

Principles Acoustic emissions are stress

waves produced by sudden movement instressed materials The classic sources ofacoustic emission are crack growth andplastic deformation Sudden movement atthe source produces a stress wave thatradiates out into the test object andexcites a sensitive piezoelectric sensor Asthe stress in the material is raised,emissions are generated The signals fromone or more sensors are amplified andmeasured to produce data for display andinterpretation

The source of acoustic emission energy

is the elastic stress field in the material

Without stress, there is no emission

Therefore, an acoustic emission test(Fig 12) is usually carried out during a

F IGURE 10 Test object demonstrating

magnetic particle method

F IGURE 11 Classic setups for ultrasonic

testing: (a) longitudinal wave technique;

(b) transverse wave technique

Transducer Crack

Bolt Time Crack

Back surface

Crack

Entry surface Crack

(a)

(b)

controlled loading of the test object This

can be a proof load before service; a

controlled variation of load while the

structure is in service; a fatigue, pressure

or creep test; or a complex loading

program Often, a structure is going to be

loaded hydrostatically anyway during

service and acoustic emission testing is

used because it gives valuable additional

information about the expected

performance of the structure under load

Other times, acoustic emission testing is

selected for reasons of economy or safety

and loading is applied specifically for the

acoustic emission test

Applications Acoustic emission is a

natural phenomenon occurring in thewidest range of materials, structures andprocesses The largest scale eventsobserved with acoustic emission testingare seismic; the smallest are microscopicdislocations in stressed metals

The equipment used is highly sensitive

to any kind of movement in its operatingfrequency (typically 20 to 1200 kHz) Theequipment can detect not only crackgrowth and material deformation but alsosuch processes as solidification, friction,impact, flow and phase transformations.Therefore, acoustic emission testing is alsoused for in-process weld monitoring, fordetecting tool touch and tool wear duringautomatic machining, for detecting wearand loss of lubrication in rotatingequipment, for detecting loose parts andloose particles, for preservice proof testingand for detecting and monitoring leaks,cavitation and flow

Other Methods

There are many other methods ofnondestructive testing, including opticalmethods such as holography,

shearography and moiré imaging; materialidentification methods such as chemicalspot testing, spark testing and

spectroscopy; strain gaging; and acousticmethods such as vibration analysis andtapping

F IGURE 12 Acoustic emission monitoring of floor beam on

suspension bridge

Sensor

In today’s world, industrial designers push

the limits of materials, engineering

knowledge and manufacturing processes

to produce system components More

than ever, component reliability at a

reduced cost is central in original designs

of most items Because nondestructive

testing can reveal, characterize and

quantify anomalies on the surface and

throughout a component’s volume, it has

become a major tool to ensure that raw

materials and fabricated components meet

design expectation for quality, reliability

and service life To reduce fabrication cost,

designers look for ways to conserve energy

and develop raw materials that allow

smaller, lighter components while

maintaining the strength and durability

to satisfy increased service demands

Nondestructive testing can provide data

to let engineers optimize safety factors

and cost

Engineers have long usednondestructive testing during component

fabrication, and codes and standards

require nondestructive testing to ensure

quality during fabrication Anyone

managing nondestructive testing will be

confronted with requirements that

originate in one or more national

standards Codes and standards require a

deep knowledge of both written

requirements and technique applications

Because of the success ofnondestructive testing in fabrication,

operation engineers use nondestructive

testing to locate and describe service

induced discontinuities and monitor their

growth Today’s nondestructive testing

technologies ensure structural integrity of

operating components and allow

continued service of critical components

Extended component life reduces

operational costs while ensuring

continued safe operation For this and

other reasons, national codes and

standards have also adopted

nondestructive testing in inservice

requirements The American Society of

Mechanical Engineers’ Boiler and Pressure

Vessel Code,3for example, has an entire

section dedicated to inservice inspection

of critical components That section uses

nondestructive testing as its primary tool

ASME Section V (Nondestructive

Examination) tells how to perform the

various nondestructive testing methods

Other sections of the Boiler Code also

specify requirements when nondestructivetesting techniques are to be used

Engineers use nondestructive testingfor plant life extension Most designsproject an expected life of operation Forexample, nuclear reactors at energygeneration stations in the United Stateswere designed originally for a service life

of forty years After their designed servicelife, the reactor would be shut down anddecommissioned However, because of thecritical need for energy, lead time for theconstruction of new power plants andenormous cost of construction, plantowners have commissioned studies todetermine if plant operations can safelycontinue beyond forty years Oncecomplete, the plant owner will submit aformal request to the appropriateregulatory authority (in this example, theNuclear Regulatory Commission) using astudy as a basis for continued service

Management of Nondestructive Testing Programs

Management of a nondestructive testingprogram requires consideration of manyitems to produce the desired results Thereare five basic questions

1 Do regulatory requirements mandateprogram characteristics?

2 What is the magnitude of the programfor desired results?

3 What is the date to fully implement aprogram?

4 What is the cost benefit ofnondestructive testing?

5 What resources in personnel andmoney are available?

Once these questions are answered,then a recommendation can be made todetermine the best path forward Threeprimary paths are (1) service companies,(2) consultants and (3) in-house programs

Though these are primary paths, someprograms may on a routine or onas-needed basis require support personnelfrom a combination of two or more ofthese sources Before a final decision ismade, advantages and disadvantages ofeach path must be considered Therefore,the following details must be considered

Service Companies

1 Who will identify the components to

be examined within the facility?

2 Will the contract be for time and

materials or have a specific scope of work?

3 If a time and materials contract is

awarded, who will monitor the timeand materials charged?

4 If a scope of work is required, who is

technically qualified to develop andapprove it?

5 After the inspection, what documents

(such as test reports, trending,recommendations and root causeanalysis) will the service companyprovide?

6 Who will evaluate and accept the

product (test reports, trending,recommendations, root cause analysisand other information) within yourcompany?

7 Do the service company workers

possess qualifications andcertifications required by contract and

by applicable regulations?

8 Do the service company workers

require training specific to the site,such as confined space entry, electricalsafety and hazardous materials? Dothey need clearance to enter and work

in the facility?

9 If quantitative tests are performed, do

program requirements mandateequipment calibration?

10 Does the service company retain any

liability for test results?

Consultants

1 Will the contract be for time and

materials or have a specific scope of work?

2 If a scope of work is required, who is

technically qualified to develop andapprove it?

3 Who will identify the required

qualifications of the consultant?

4 Is the purpose of the consultant to

develop a program or is it to overseeand evaluate the performance of anexisting program?

5 Will the consultant have oversight

responsibility for tests performed?

6 After the inspection, what documents

(such as trending, recommendationsand root cause analysis) will theconsultant provide?

7 What products (trending,

recommendations, root cause analysisetc.) are provided once the tests arecompleted?

8 Who will evaluate the consultant’s

performance (such as test reports,trending, recommendations, rootcause analysis) within your company?

9 Does the consultant possessqualifications and certificationsrequired by contract and by applicableregulations?

10 Does the consultant require trainingspecific to the site, such as confinedspace entry, electrical safety andhazardous materials? Do they needclearance to enter and work in thefacility?

11 Does the consultant retain anyliability for test results?

3 Who will develop a cost benefit

analysis for the program?

4 How much time and resources areavailable to establish the program?

5 What are the qualificationrequirements (including education,training and experience) forpersonnel?

6 Do program personnel requireadditional training (for safety orconfined space entry, for example) orqualifications?

7 Are subject matter experts required toprovide technical guidance duringpersonnel development?

8 Are procedures required to performwork in the facility?

9 If procedures are required, who willdevelop, review and approve them?

10 Who will determine the technicalspecifications for test equipment?

Test Procedures for Nondestructive Testing

The conduct of facility operations(in-house or contracted) should beperformed in accordance with specificinstructions from an expert Thiscompliance is typically accomplishedusing written instructions in the form of atechnical procedure In many cases, codesand specifications will require a technicalprocedure for required tests

The procedure process can take manyforms, including general instructions thataddress only major aspects of test

techniques Or a procedure may bewritten as a step-by-step process requiring

a supervisor’s initial or signature aftereach step The following list is typical for

an industrial procedure

1 The purpose identifies the intent of the

procedure

2 The scope establishes the latitude of

items, tests and techniques coveredand not covered by the procedure

3 References are specific documents from

which criteria are extracted or are

documents satisfied by

implementation of the procedure

4 Definitions are needed for terms and

abbreviations not commonly known

by people who will read the

procedure

5 Statements about personnel requirements

address requirements for performing

tasks in accordance with the procedure

— issues such as personnel

qualification, certification and access

clearance

6 Equipment characteristics, calibration

requirements and model numbers of

qualified equipment must be specified

7 The test procedure provides a sequential

process to be used to conduct

inspection activities

8 Acceptance criteria establish component

characteristics that will identify the

items suitable for service

9 Reports (records) provide the means to

document specific test techniques,

equipment used, personnel performing

activity, date performed and test

results

10 Attachments may include (if required)

items such as report forms, instrument

calibration forms, qualified equipment

matrices and schedules

Once the procedure is completed,

typically an expert in the subject matter

performs a technical evaluation If the

procedure meets requirements, the expert

will approve it for use Some codes and

standards also require the procedure to be

qualified — that is, demonstrated to the

Nondestructive testing specifications must

anticipate a number of issues that arise

during testing

Test Condition Requirements

1 What and where are the items to be

inspected?

2 What are the target discontinuities

and where in the item are they located

(surface, internal or both)?

3 Are there any environmental and

safety considerations (temperature,

ventilation or radiation, for example)

that must be addressed?

Selection of Nondestructive Testing Method/Technique

1 Does a code or standard dictate aspecific test technique?

2 Nondestructive test techniques must

be selected to detect the targetdiscontinuities The approaches may

be established by applicable codes andstandards If not, they must bedetermined by a subject matter expert

Subject matter experts document theirexpertise through established

Standards and Specifications for Nondestructive Testing

Standards have undergone a process ofpeer review in industry and can beinvoked with the force of law by contract

or by government regulation In contrast,

a specification represents an employer’sinstructions to employees and is specific

to a contract or work place Specificationsmay form the basis of standards through areview process Standards and

specifications exist in three basic areas:

equipment, processes and personnel

1 Standards for equipment and materialsinclude electronic and optical

equipment Standardized referenceobjects such as calibration blockswould also fit in this category

2 ASTM International (formerly theAmerican Society for Testing andMaterials) and other organizationspublish standards for test techniques.4Standards for quality assurance are notspecific to a test method or even toinspection in general

3 Qualification and certification of testpersonnel are discussed below, withspecific reference to recommendations

of ASNT Recommended Practice

No SNT-TC-1A.5

Personnel Qualification and

Certification

One of the most critical aspects of the test

process is the qualification of inspection

personnel Nondestructive testing is

sometimes referred to as a special process,

meaning simply that it is very difficult to

evaluate an inspection by merely

observing either the process or the

documentation generated at its

conclusion The quality of the test largely

depends on the skills and knowledge of

the inspector

The American Society forNondestructive Testing (ASNT) has been a

world leader in the qualification and

certification of nondestructive testing

personnel for many years By 1999, the

American Society for Nondestructive

Testing had instituted three major

programs for the qualification and

certification of nondestructive testing

personnel

1 ASNT Recommended Practice

No SNT-TC-1A provides guidelines for

personnel qualification andcertification in nondestructive testing

This recommended practice identifiesthe specific attributes that should beconsidered when qualifying

nondestructive testing personnel Itrequires the employer to develop and

implement a written practice

(procedure) that details the specificprocess and any limitation in thequalification and certification ofnondestructive test personnel.5

2 ANSI/ASNT CP-189, Standard for

Qualification and Certification of Nondestructive Testing Personnel, resembles SNT-TC-1A but also

establishes specific attributes for thequalification and certification ofnondestructive test personnel

However, CP-189 is a consensusstandard as defined by the AmericanNational Standards Institute (ANSI) It

is recognized as the American standardfor nondestructive testing It is not

considered a recommended practice; it is

a national standard.6

3 The ASNT Central Certification Program

(ACCP), unlike SNT-TC-1A and CP-189,

is a third party certification process

Currently it has identifiedqualification and certificationattributes for Level II and Level IIInondestructive test personnel TheAmerican Society for NondestructiveTesting certifies that the individual hasthe skills and knowledge for manynondestructive testing methodapplications It does not remove theresponsibility for the final

determination of personnelqualifications from the employer Theemployer evaluates an individual’s

skills and knowledge for application ofcompany procedures using techniquesdesignated and equipment identifiedfor specific tests.7

Sample Specifications from

SNT-TC-1A

To give an overview of the contents ofthese documents, the following items arespecified in the 2006 edition of

SNT-TC-1A (For this example, the

quantities cited are those that addressultrasonic testing only.)

Scope This recommended practice has been

prepared to establish guidelines for thequalification and certification ofnondestructive testing personnel whosespecific jobs require appropriate knowledge

of the technical principles underlying thenondestructive test they perform, witness,monitor or evaluate This documentprovides guidelines for the establishment of

a qualification and certification program

Written Practice The employer shall

establish a written practice (personnelqualification and certification procedure) forthe control and administration of

nondestructive testing personnel training,examination and certification Theemployer’s written practice should describethe responsibility of each level of

certification for determining theacceptability of materials or components inaccordance with applicable codes, standards,specifications and procedures

Education, Training, Experience Education,

training and experience requirements forinitial qualification are identified in each ofthe ASNT certification programs Candidatesfor certification in nondestructive testingshould have sufficient education, trainingand experience to ensure qualification inthose nondestructive testing methods forwhich they are being considered forcertification The employer’s written practicedocuments the training and experiencefactors for initial qualification of Level I and

II individuals

Training Programs Personnel being

considered for initial certification shouldcomplete sufficient organized training tobecome thoroughly familiar with theprinciples and practices of the specifiednondestructive testing method related tothe level of certification desired andapplicable to the processes to be used andthe products to be tested ANSI/ASNTStandard CP-1058provides topical outlinesfor training These outlines are establishedbase on certification level and NDT Method

Examinations For Level I and II personnel, a

composite grade should be determined by asimple averaging of the results of thegeneral, specific and practical examinationsdescribed below Examinations administeredfor qualification should result in a passingcomposite grade of at least 80 percent, with

no individual examination having a passinggrade less than 70 percent

Vision Examination The examination for

near vision acuity should ensure natural or

corrected near distance acuity in at least one

eye such that applicant can read a

minimum of jaeger size 2 or equivalent type

and size letter at a distance of not less than

305 mm (12 in.) on a standard jaeger test

chart This test should be administered

annually Note that some national codes

require different vision acuity (for example,

the ASME Boiler and Pressure Vessel Code3

requires jaeger size 1)

Written Examination for NDT Levels I and II.

The minimum number of questions that

should be administered in the written

examination for ultrasonic test personnel is

as follows: 40 questions in the general

examination and 20 questions in the specific

examination The number of questions is

the same for Level I and Level II

Practical Examination for NDT Level I and II.

The candidate should demonstrate

familiarity with the ability to operate the

necessary nondestructive test equipment,

record and analyze the resultant

information to the degree required At least

one selected specimen should be tested and

the results of the nondestructive test

analyzed by the candidate

Certification Certification of all levels of

nondestructive testing personnel is the

responsibility of the employer Certification

of nondestructive testing personnel shall be

based on demonstration of satisfactory

qualification in accordance with sections of

the appropriate ASNT Qualification and

Certification Program on education,

training, experience and examinations, as

modified by the employer’s written practice

Personnel certification records shall be

maintained on file by the employer

Recertification All levels of nondestructive

testing personnel shall be recertified

periodically in accordance with the

following: evidence of continuing

satisfactory performance or reexamination

in those portions of examinations (Section 8

of SNT-TC-1A) deemed necessary by the

employer’s NDT Level III

Recommended maximum

recertification intervals are five years for

all levels

These recommendations from

SNT-TC-1A are cited only to provide a

flavor of the specific items that must be

considered in the development of an

in-house nondestructive testing program

However, if an outside agency is

contracted for ultrasonic test services,

then the contractor must have a

qualification and certification program to

satisfy most codes and standards

Central Certification

Another standard that may be a source for

compliance is contained in the

requirements of the International

Organization for Standardization (ISO)

The International Organization for

Standardization is a worldwide federation

of national standards bodies (ISO member

bodies) The work of preparing

international standards is normally carriedout through technical committees of theInternational Organization for

Standardization Each member bodyinterested in a subject for which atechnical committee has been establishedhas the right to be represented on thatcommittee International organizations,governmental and nongovernmental, inliaison with the International

Organization for Standardization, alsotake part in the work The InternationalOrganization for Standardizationcollaborates closely with the InternationalElectrotechnical Commission (IEC) on allmatters of electrotechnical

“establishes a system for the qualificationand certification, by a certification body,

of personnel to perform industrialnondestructive testing (NDT) using any ofthe following methods: (a) eddy currenttesting; (b) liquid penetrant testing;

(c) magnetic particle testing;

(d) radiographic testing; (e) ultrasonictesting” and that the “system described inthis International Standard may alsoapply to visual testing (VT), leak testing(LT), neutron radiography (NR), acousticemission (AE) and other nondestructivetest methods where independentcertification programs exist.” Theapplicability of ISO 9712 to any methoddepends on activity of the nationalcertifying body

The American Society forNondestructive Testing has the ASNT NDTLevel III Certification Program thatincludes most nondestructive testmethods If industry requirements evolveand leaders of the industry request a thirdparty/ISO compliant certification, theAmerican Society for NondestructiveTesting is prepared to develop andimplement this certification within theASNT Central Certification Program(ACCP) for those methods currently notincluded in the program

Safety in Nondestructive Testing

To manage a nondestructive test program,

as with any test program, the firstobligation is to ensure safe workingconditions The following are components

of a safety program that may be required

or at least deserve serious consideration

1 Identify the safety and operational

rules and codes applicable to the areas,materials, equipment and processesbefore work is to begin

2 Provide proper safety equipment

(safety glasses, hard hat, safetyharnesses, steel toed shoes, hearingprotection, others)

3 If needed, obtain a qualified assistant

who knows the plant’s electrical,mechanical or process systems

4 Before the test, perform a thorough

visual survey to determine all thehazards and identify necessarysafeguards to protect test personneland equipment

5 Notify operative personnel to identify

the location and specific equipmentthat will be examined In addition,determine if signs or locks restrictaccess by personnel Be aware ofequipment that may be operatedremotely or may be started by timedelay

6 Be aware of any potentially explosive

atmospheres Determine whether it issafe to take your equipment into thearea

7 Do not enter any roped off or no entry

areas without permission andapproval

8 Determine if electrical safety courses

are required for the performance ofelectrical surveys

9 When working on or around electrical

equipment, remove pens, watches,rings or objects in your pockets thatmay touch (or fall into) energizedequipment

10 Know interplant communication and

evacuation systems

11 Never let unqualified personnel

operate equipment

12 Keep a safe distance between you and

any energized equipment In theUnited States, these distances can befound in documents from theOccupational Safety and HealthAdministration, the National Fire

Prevention Association (National Electric Code11), the Institute ofElectrical and Electronics Engineers

(National Electrical Safety Code12) andother organizations

13 Be aware of the personnel

responsibilities before entering a

confined space All such areas must be

tested satisfactorily for gas and oxygenlevels before entry and periodicallythereafter If odors are noticed, orunusual sensations such as ear aches,dizziness or difficulty in breathing areexperienced, leave the area

immediately

Most facilities in the United States arerequired by law to follow the

requirements in the applicable standard

Two Occupational Safety and Health

Standards in the United States that should

be reviewed are Occupational Safety and Health Standards for general industry13and

the Occupational Safety and Health Standards for the Construction Industry.14Toxic substances in systems inspectedand in the work site are also a

concern.14-17Safety considerations specific toparticular nondestructive test techniquesare covered in detail in method volumes

of the Nondestructive Testing Handbook.

Personnel safety is always the firstconsideration for every job

Ensuring Reliability of Test Results

When a test is performed, there are fourpossible outcomes: (1) a discontinuity can

be found when a discontinuity is present;(2) a discontinuity can be missed evenwhen a discontinuity is present; (3) adiscontinuity can be perceived when none

is present; and (4) no discontinuity isfound when none is present A reliabletesting process and a reliable inspectorshould find all discontinuities of concernwith no discontinuities missed (no errors

as in case 2, above) and no false callouts(case 3, above)

To achieve this goal, the probability offinding a discontinuity must be high andthe inspector must be both proficient inthe testing process and motivated toperform at maximum efficiency A recklessinspector may accept parts that containdiscontinuities, with the result of possibleinservice part failure A cautious inspectormay reject parts that do not containdiscontinuities, with the result ofunnecessary scrap and repair Neitherinspector is doing a good job

Summary

As noted in this discussion, many factorsmust be considered before a program ofnondestructive testing can begin at afacility To manage a nondestructivetesting program many options must beconsidered The final decision for a pathforward must be based on requirements(codes, standards and specifications) andwhat is best for the project If a customerlacks the expertise for this criticaldecision, the industry has many talentedindividuals that are willing to assist TheAmerican Society for NondestructiveTesting is a place to begin the decisionmaking process

International System

In 1960, the General Conference on

Weights and Measures established the

International System of Units Le Systéme

International d’Unités (SI) was designed so

that a single set of measurement units

could be used by all branches of science,

engineering and the general public

Without the International System of

Units, the Nondestructive Testing Handbook

series would contain a confusing mix of

obsolete centimeter gram second (CGS)

units, inch pound units and the units

preferred by certain localities or scientific

specialties

The International System of Units isthe modern version of the metric system

and ends the division between metric

units used by scientists and metric units

used by engineers and the public

Scientists have given up their units based

on centimeter and gram and engineers

have abandoned the kilogram-force in

favor of the newton Electrical engineers

have retained the ampere, volt and ohm

but changed all units related to

magnetism

Table 4 lists the seven base units of theInternational System of Units Table 5 lists

derived units with special names In the

International System of Units, the unit of

time is the second (s); the hour (h) is

recognized for use with the International

In science and engineering, very large

or very small numbers with units are

expressed by using multipliers, prefixes of

103intervals (Table 7) The multiplier

becomes a part of the SI symbol For

example, a millimeter (mm) is0.001 meter (m) The volume unit cubiccentimeter (cm3) is (0.01 m)3or 10–6m3.Unit submultiples such as the centimeter,decimeter, dekameter and hectometer areless common in scientific and technicaluses of the International System of Unitsbecause of their variance from theconvenient 103or 10–3intervals thatmake equations easy to manipulate

In the International System of Units,the distinction between upper and lowercase letters is meaningful and should beobserved For example, the meanings ofthe prefix m (milli) and the prefix M(mega) differ by nine orders of magnitude

For more information, the reader isreferred to the information availablethrough national standards organizationsand specialized information compiled bytechnical organizations.18-20

Nondestructive Testing

T ABLE 4 SI base units.

Catalytic activity katal kat s–1·mol

Magnetic flux density tesla T Wb·m–2

Radiation absorbed dose gray Gy J·kg–1

Radiation dose equivalent sievert Sv J·kg–1

a Hour and liter are not SI units but are accepted for use with SI.

b Number one (1) expresses a dimensionless relationship.

c Electromotive force.

Units for Visual Testing

Illumination

Many characteristics of light, light

sources, lighting materials and lighting

installations may be measured, including

illuminance, luminance, luminous

intensity, luminous flux, contrast, color

(appearance and rendering), spectral

distribution, electrical characteristics and

radiant energy

In visual testing, units expressmeasurements of visible light as part of

the electromagnetic spectrum In the

electromagnetic spectrum, radiometry is

the measurement of radiant energy, both

visible and invisible Photometry in Greek

means simply light measurement.

Radiometry measures all forms of

electromagnetic radiation, including light;

photometry measures light alone

Radiometry and photometry have the

same principles but different units of

measure (Table 8)

Vision requires a source ofillumination The luminous intensity in a

given direction is measured in candela

T ABLE 7 SI prefixes and multipliers.

T ABLE 6 Examples of conversions to SI units.

calorie (cal), thermochemical 4.184 joule (J)Power British thermal unit per hour (BTU·h–1) 0.293 watt (W)

Specific heat British thermal unit per pound 4.19 kilojoule per kilogram per kelvin (kJ·kg–1·K–1)

degree fahrenheit (BTU·lbm–1·°F–1)

Pressure pound force per square inch (lbf·in.–2) 6.89 kilopascal (kPa)

Luminance candela per square foot (cd·ft–2) 10.76 candela per square meter (cd·m–2)

candela per square inch (cd·in.–2) 1.550 003 × 10–3 candela per square meter (cd·m–2)footlambert (ftl) 3.426 candela per square meter (cd·m–2)lambert 3.183 099 × 10–3 candela per square meter (cd·m–2)

Ionizing radiation exposure roentgen (R) 0.258 millicoulomb per kilogram (mC·kg–1)

Temperature (increment) degree fahrenheit (°F) 0.556 kelvin (K) or degree celsius (°C)

Temperature (scale) degree fahrenheit (°F) (°F – 32) ÷ 1.8 degree celsius (°C)

Temperature (scale) degree fahrenheit (°F) (°F – 32) ÷ 1.8 + 273.15 kelvin (K)

Ultraviolet Radiation

Ultraviolet radiation is of concern to

visual inspectors because they are often

called on to document the vision acuity

and color discrimination of personnel

who use ultraviolet lamps to perform

liquid penetrant and magnetic particle

testing The term light is widely used for

electromagnetic radiation in the visible

part of the spectrum The term black light,

however, should not be used for

ultraviolet radiation, because (1) the term

has become ambiguous, denoting

sometimes the ultraviolet lamp and

sometimes its radiation, (2) the term black

here means merely invisible and not a

color and (3) ultraviolet radiation is not

truly light, any more than X-rays are

Although both light and ultravioletradiation are measured in watts per square

meter, their wavelengths have distinct

ranges Because ultraviolet radiation is

invisible, photometric measurement units

such as the lumen and lux should never

be applied to ultraviolet radiation

Ultraviolet radiation is divided intothree ranges: UV-A (320 to 400 nm), UV-B

(280 to 320 nm) and UV-C (100 to

280 nm) This is analogous to the

segmentation of visible light into the

wavelengths that produce the colors Blue

light, for example, generally has

wavelengths between 455 and 492 nm

Yellow light is between 577 and 597 nm

The analogy to visible radiation might

help those first learning to measure

ultraviolet radiation A certain intensity of

yellow light will produce on a surface a

certain illuminance measured in lux In

the same way, a certain amount of

ultraviolet radiation will produce an

irradiance on a test surface

Ultraviolet irradiance is a timedependent measure of the amount of

energy falling on a prescribed surface area

and is expressed in watts per square meter

(W·m–2) or (to avoid exponents)

microwatts per square centimeter

(µW·cm–2) One unit of irradiance

(1 µW·cm–2) is the power (microwatt)

falling on one square centimeter (cm–2) of

surface area At higher irradiance, the

milliwatt per square centimeter

found in literature about liquid penetrant

and magnetic particle testing

Units for Penetrant Testing and Leak Testing

The quantities of pressure, volume,viscosity and porosity are relevant for themethods of both penetrant testing andleak testing

Ultraviolet radiation is often used toreveal penetrant indications Itsmeasurement is discussed above, aftervisual testing

Pressure

The pascal (Pa), equal to one newton persquare meter (1 N·m–2), is used to expresspressure, stress and similar quantities It isused in place of units of pound force persquare inch (lbf·in.–2), atmosphere,millimeter of mercury (mm Hg), torr, bar,inch of mercury (in Hg), inch of water(H2O) and other units (Table 9)

Specifications must indicate whether

gage, absolute or differential pressure is

meant Negative pressures might be used

in heating duct technology and invacuum boxes used for bubble testing, but

in vacuums used in tracer leak testingabsolute pressures are used

Volume

The cubic meter (m3) is the volumemeasurement unit in the InternationalSystem of Units It takes the place of cubicfoot, cubic inch, gallon, pint, barrel andothers In the International System ofUnits, the liter (L) is also approved foruse The liter is a special name for cubicdecimeter (1 L = 1 dm3= 10–3m3) Only

the milli (m) and micro (µ) prefixes may be

used with liter

The fundamental units of time,temperature, pressure and volume areexpressed every time that a movement of

a fluid (liquid or gas) is measured

Viscosity

Dynamic viscosity is expressed in the

International System of Units by thepascal second An older unit is the

T ABLE 9 Factors for conversion of pressure values to pascal (Pa).

pound per square inch (lbf·in.–2) 6.8948 × 103

kilogram per square millimeter 9.8066 × 105

(kg·mm–2)atmosphere (atm) 1.01325 × 105

inch mercury (in Hg) 3.3864 × 103

poise (P), or centipoise (cP): 100 cP = 1 P =

0.1 Pa·s

Kinematic viscosity is expressed in the

International System of Units as square

meter per second, equivalent to the

dynamic viscosity divided by mass

density An older unit is the stokes (St):

1 cSt = 0.01 St = 1 mm2·s–1;

1 St = 0.0001 m2·s–1

Porosity

Porosity is reported as a ratio of volume to

volume and can be expressed as a

percentage For example, if hydrogen

content in aluminum is measured as

2.5 mm3·g–1, this value reduces to

2.50 mm3·(0.37 cm3)–1× 1000 mm3·cm–3=

0.675 or about 0.7 percent Therefore the

hydrogen content should be reported as

6.75 mm3·cm–3in volume, for a porosity

of 0.7 percent

Abrasives and Finish Treatment

Surface abrading is a matter of concern in

liquid penetrant testing because grinding,

shot peening and sand blasting can close

surface breaking cracks and so keep them

from being indicated in tests Finish also

affects adherence of materials to a surface

In preparation of test panels for

evaluation, the type and size of abrasive

blasting is often specified

Abrasive particle size (coarse versusfine) in the United States has traditionally

been specified using industry accepted

gage numbers that correspond to the

number of lines (or wires) per inch in

sieves used to sift the abrasive grit A

number of standards govern grit

specifications in the abrasive industries —

for example, ANSI B 74.16 for industrial

diamonds Table 10 shows several of the

many levels of grit designations based on

particle size.21

Organizations that issue standards inthis area include ASTM International, the

American National Standards Institute

(ANSI), the Federation of the European

Producers of Abrasives (FEPA) and the

International Standardization

Organization (ISO)

Quantitative Description of Leakage Rates

The significant quantitative measurementresulting from leak testing is the

volumetric leakage rate or mass flow rate

of fluid through one or more leaks

Leakage rate thus has dimensionsequivalent to pressure times volumedivided by time The units used previouslyfor volumetric leakage rate were standardcubic centimeter per second (std cm3·s–1)

In SI units, the quantity of gas ismeasured in units of pascal cubic meter(Pa·m3) The leakage rate is measured inpascal cubic meter per second (Pa·m3·s–1)

For this leakage rate to be a mass flow, thepressure and temperature must be atstandard values of 101 kPa (760 torr) and

0 °C (32 °F) Table 11 gives factors forconversion of leakage rates in variouscommon units, past and present Table 12provides leakage rate comparisons thatpermit a better understanding of the

T ABLE 10 Abrasive particle size and sieve apertures.

Pascal cubic meter per std cm3·s–19.87 (≅ 10)second (Pa·m3·s–1) mol·s–1 4.40 × 10–4

Standard cubic Pa·m3·s–1 1.01 × 10–1

centimeter per mol·s–1 4.46 × 10–5

second (std cm3·s–1)Mole per second Pa·m3·s–1 2.27 × 103

quantities involved, when leakage rates

are specified

Leakage is not simply the volume of airentering the vacuum chamber Instead,

the critical factor is the number of gaseous

molecules entering the vacuum system

This number of molecules, in turn,

depends on the external pressure,

temperature and the volume of gas at this

pressure that leaks into the vacuum

system The leakage rate is expressed in

terms of the product of this pressure

difference multiplied by the gas volume

passing through the leak, per unit of time

Thus, the leakage rate is directly

proportional to the number of molecules

leaking into the vacuum system per unit

of time

The molecular unit of mass flow usedfor gas by the National Institute of

Standards and Technology is mole per

second (mol·s–1), a mass flow unit

measured at standard atmospheric

pressure and standard temperature of 0 °C

(32 °F) A common unit of gas is the

standard cubic meter (std m3) This unit is

equivalent to one million units given as

atmospheric cubic centimeter (atm cm3)

Both units indicate the quantity of gas

(air) contained in a unit volume at

average sea level atmospheric pressure at a

temperature of 0 °C (32 °F) The average

atmospheric pressure at sea level is

101.3 kPa (760 mm Hg or 760 torr) The

SI unit of pressure, the pascal (Pa), is

equivalent to newton per square meter

(N·m–2)

Derived Units for Leak Testing

Gas Quantity The SI unit used for

measuring gas quantity is pascal cubic

meter (Pa·m3) The quantity of gas which

is stored in a container or which has

passed through a leak is described by the

derived SI unit of pascal cubic meter, the

product of pressure and volume To be

strict, the temperature should be specified

for the gas quantity or leakage

measurement to define the gas quantity

(sometimes loosely described as the mass

of gas) more precisely Often, gas quantity

is defined for standard temperature and

pressure, typically the standard

atmospheric pressure of 100 kPa (1 atm)

and a temperature of 0 °C (32 °F)

Temperature corrections are usually

required if temperature varies significantly

during leak testing However, small

changes in temperature may sometimes

be insignificant compared with many

orders of magnitude of change in gas

pressure or leakage quantity

Gas Leakage Rate The SI unit for leakage

rate is pascal cubic meter per second

(Pa·m3·s–1) The leakage rate is defined as

the quantity (mass) of gas leaking in one

second The unit in prior use was the

standard cubic centimeter per second(std cm3·s–1) Use of the word standard in

units such as std cm3·s–1requires that gasleakage rate be converted to standardtemperature and pressure conditions(293 K and 101.325 kPa), often evenduring the process of collecting dataduring leakage rate tests Leakage ratesgiven in units of std cm3·s–1can beconverted to SI units of Pa·m3·s–1at anytime by simply dividing the SI leakagerate by 10 or (more precisely) by 9.87

Gas Permeation Rate The compound unit

for permeation rate in SI is pascal cubicmeter per second per square meter permeter (Pa·m3·s–1)/(m2·m–1) Permeation isthe leakage of gas through a (typicallysolid) substance that is not impervious togas flow The permeation rate is largerwith an increased exposed area, a higherpressure differential across the substance(such as a membrane or gasket) and issmaller with an increasing thickness ofpermeable substance In vacuum testing,the pressure differential is usuallyconsidered to be one atmosphere (about

100 kPa) One sometimes findspermeation rate measured where the gasquantity is expressed in units of mass

Units for Infrared Thermography

Old units are converted (Table 6) Britishthermal unit (BTU) and calorie convert tojoule (J) British thermal unit per hourconverts to watt (W) For measurement ofwavelength, nanometer (nm) obviatesangstrom (Å): 10 Å = 1 nm

Volume

The cubic meter (m3) is the volumemeasurement unit in the InternationalSystem of Units It takes the place of cubicfoot, cubic inch, gallon, pint, barrel andmore In SI, the liter (L) is also approvedfor use The liter is a special name forcubic decimeter (1 L = 1 dm3 = 10–3m3)

Only the milli (m) and micro (µ) prefixes

may be used with liter

The fundamental units of time,temperature, pressure and volume areexpressed every time movement of a fluid(liquid or gas) is measured

Heat, Temperature and Thermal Radiation

Heat can be described as the energytransfer associated with the random andchaotic motions of the atomic particlesfrom which matter is composed The unit

of heat is the joule (J), equal to about0.24 calorie (cal) or 9.481 × 10–4Britishthermal units (BTUs)

Temperature is a measure of the

intensity of particle motion (or vibration)

in degrees celsius (°C) or fahrenheit (°F)

or, in the absolute scale, kelvin (K) or

rankine (°R), where per increment 1 K =

1 °C = 1.8 °R = 1.8 °F Fahrenheit and

rankine are obsolete units and never used

in scientific work

All materials (hot or cold) transfer heat

and radiate infrared energy As a material

is cooled, it continuously loses heat and

radiation power At absolute zero (0 K = 0

°R = –273.16 °C = –459.69 °F), all energy

content, radiation and particle motion

cease to exist It has been physically

impossible to create the temperature of

absolute zero

Quantities in infrared and thermal

testing are measured and expressed with a

variety of compound units Some of the

more common are listed in Table 13

Thermal conductivity is a body’s relative

ability to carry heat by conduction in a

static temperature gradient A material’s

thermal resistance is its resistance to the

flow of thermal energy and is inversely

proportional to the material’s thermal

conductance

Units for Radiography

The original discoveries of radioactivity

helped establish units of measurement

based on observation rather than precise

physical phenomena Later, scientists who

worked with radioactive substances (or

who managed to manufacture radioactive

beams) again made circumstantial

observations that were then used formeasurement purposes This practicalapproach was acceptable at the time, but

a broader understanding of physics andthe modern practice of using only oneunit for a quantity has led to themodification of many of the original units(Tables 14 to 16) In the InternationalSystem of Units, radiation units have beengiven established physical foundationsand new names where necessary

Physical Quantities

Three physical quantities in particular(Table 14) are widely used as measurementunits — the electronvolt (eV), the speed of

light (c) and the unified atomic mass unit

(u) Their precise values, however, areobtained experimentally

Electronvolt The electronvolt is the

kinetic energy acquired by an electron inpassing through a potential difference of

1 V in vacuum; 1 eV = 1.602 176 462 ×

10–19J with a combined standarduncertainty of 6.3 × 10–27J.20Theelectronvolt is accepted for use with SI

Speed of Electromagnetic Radiation The

quantity c represents the speed of light,

that is, the speed of electromagnetic

waves in vacuum; 1 c = 299 792 458 m·s–1exactly (670 616 629 mi·h–1) The speed oflight is a physical quantity but can beused as a unit of measure

Unified Atomic Mass Unit The unified

atomic mass unit (u) is 1/12 of the mass

of the atom of the nuclide carbon-12; 1 u

= 1.660 538 73 × 10–27kg with a combinedstandard uncertainty of ±1.3 × 10–34kg.20

T ABLE 13 Compound units used in infrared and thermal testing.

Heat capacity, or entropy joule per cubic meter kelvin J·m–3·K–1

Heat irradiance, or heat flux density watt per square meter W·m–2

Heat transfer coefficient watt per square meter kelvin W·m–2·K–1

Specific heat joule per kilogram kelvin J·kg–1·K–1

Thermal conductance watt per square meter kelvin W·m–2·K–1

Thermal conductivity watt per meter kelvin W·m–1·K–1

Thermal diffusivity square meter per second m2·s–1

Thermal expansion meter per meter kelvin m·m–1·K–1

Thermal resistance square meter kelvin per watt m2·K·W–1

Thermal transmittance watt per square meter kelvin W·m–2·K–1

a International System of Units (SI).

Radiation Measurement

Because of existing practice in certain

fields and countries, the International

Committee for Weights and Measures

(CIPM, Comité Internationale des Poids et

Mesures) permitted the units given in

Table 15 (curie, roentgen, rad and rem) to

continue to be used with the

International System of Units until

1998.18-20However, these units must not

be introduced where they are not

presently used The National Institute of

Standards and Technology strongly

discourages the continued use of curie,

roentgen, rad and rem.18-20ASTM

International, the American National

Standards Institute, the Institute of

Electrical and Electronics Engineers, the

International Organization

Standardization (ISO) and the American

Society for Nondestructive Testing all

support the replacement of older English

units with the International System of

Units

Becquerel Replaces Curie The original

unit for radioactivity was the curie (Ci),

simply the radiation of one gram of

radium Eventually all equivalent

radiation from any source was measured

with this same unit It is now known that

a curie is equivalent to 3.7 × 1010

disintegrations per second In SI, the unit

for radioactivity is the becquerel (Bq),

which is one disintegration per second

Because billions of disintegrations are

required in a useful source, the multiplier

prefix giga (10) is used and the unit isnormally seen as gigabecquerel (GBq)

Coulomb per Kilogram Replaces Roentgen The unit for quantity of

electric charge is the coulomb (C), where

1 C = 1 A × 1 s The original roentgen (R)was the quantity of radiation that wouldionize 1 cm3of air to 1 electrostatic unit

of electric charge, of either sign It is nowknown that a roentgen is equivalent to

258 microcoulombs per kilogram of air(258 µC·kg–1of air) This corresponds to1.61 × 1015ion pairs per 1 kg of air, whichhas then absorbed 8.8 mJ (0.88 rad, whererad is the obsolete unit for radiationabsorbed dose, not the SI symbol forradian)

Gray Replaces Rad The roentgen (R) was

an intensity unit but was notrepresentative of the dose absorbed bymaterial in a radiation field The radiationabsorbed dose (rad) was first created tomeasure this quantity and was based onthe erg, the energy unit from the oldcentimeter-gram-second (CGS) system Inthe SI system, the unit for radiation dose

is the gray (Gy) The gray is useful because

it applies to doses absorbed by matter at aparticular location It is expressed inenergy units per mass of matter or injoules per kilogram (J·kg–1) The mass isthat of the absorbing body

Sievert Replaces Rem The SI system’s unit

for the dose absorbed by the human body

(formerly rem for roentgen equivalent man; also known as ambient dose equivalent,

T ABLE 15 Conversion to SI radiographic units.

258 microcoulomb per kilogram µC·kg–1

a The abbreviation rd may be used for radiation absorbed dose where there is possibility of confusion with radian

(rad), the SI unit for plane angle.

T ABLE 14 Physical quantities used as units Values of physical quantities are experimentally obtained and may only be approximated in SI Conversions are provided here for descriptive purposes.

Speed of electromagnetic waves in vacuum c 2.997 924 58 × 108 meter per second m·s–1

a Approved for use with SI.

b Mass of unified atomic mass unit is 12 –1 of the mass of the atom of the nuclide carbon-12.

directional dose equivalent, dose equivalent,

equivalent dose and personal dose equivalent)

is similar to the gray but includes quality

factors dependent on the type of

radiation This absorbed dose has been

given the name sievert (Sv) but its

dimensions are the same as the gray, that

is, 1 Sv = 1 J·kg–1

Compound Units

Exposure to ionizing radiation could be

measured in roentgens with an ionization

chamber that, when placed 1 m (39 in.)

from the radiation source, provided

necessary information — one roentgen

per curie per hour at one meter (R·Ci–1·h–1

at 1 m), for example The numbers,

however, had limited physical meaning

and could not be used for different

applications such as high voltage X-ray

machines

The roentgen per hour (R·h–1) was used

to designate the exposure to an ionizing

radiation of the stated value Because the

radiation received from 1 R·h–1was

considered about equal to 1 rem, the

relationship is approximated as 1 R·h–1 =

0.01 Gy·h–1= 10 mGy·h–1

A previously popular unit, roentgen percurie per hour at one meter (R·Ci–1·h–1at

1 m), is expressed in the International

System of Units as millisievert per

gigabecquerel per hour at one meter

(mSv·GBq–1·h–1at 1 m), such that

1 mSv·GBq–1·h–1at 1 m = 3.7 R·Ci–1·h–1at

1 m In this relationship, roentgen

converts to millisieverts on a one-to-ten

basis

Exposure charts were often made byusing curie minutes at a source-to-film

distance in inches squared This was

written Ci·min·in.–2 Exposure charts

made in SI use gigabecquerel minutes for

a source-to-film distance in centimeters

squared, where 1 Ci·min·in.–2=

50 GBq·min·cm–2 Table 16 lists some of

these compound units

Units for Electromagnetic Testing

In this discussion, electromagnetic testingincludes techniques such as magneticparticle and eddy current testing

Radian

The radian (rad) is the international unitfor measurement of plane angle and isequal to the angle subtended by an arcfrom the center of a circle and equal to itsradius The radian is useful in theoreticalphysics, but physical measurements aretypically in degrees The degree (deg) isapproved for use with the InternationalSystem of Units

CGS Units

Centimeter-gram-second (CGS) units such

as the oersted, gauss and maxwell are notaccepted for use with the InternationalSystem of Units Furthermore, no otherunits of the various CGS systems of units,which includes the CGS electrostatic, CGSelectromagnetic and CGS gaussiansystems, are accepted for use with theInternational System of Units except suchunits as the centimeter (cm), gram (g) andsecond (s) that are also defined in theInternational System of Units

The oersted, gauss and maxwell arepart of the electromagnetic

three-dimensional CGS system Whenonly mechanical and electric quantitiesare considered, these three units cannotstrictly speaking be compared each to thecorresponding unit of the InternationalSystem of Units, which has fourdimensions The SI units include theweber (Wb) and the tesla (T)

Magnetic Field Intensity The ampere per

meter replaces the oersted Magnetic fieldintensity (magnetic field strength) isexpressed in ampere per meter (A·m–1)

One ampere per meter (A·m–1) equalsabout one eightieth of an oersted (Oe)

The relationship is 1 Oe = 1000·(4π)–1A·m–1= 79.57747 A·m–1 1 A·m–1=0.013 Oe = 13 mOe

Magnetic Flux Density The tesla replaces

the gauss Magnetic flux density isexpressed in weber per square meter(Wb·m–2), or tesla (T), to indicate flux perunit area One tesla equals ten thousandgauss (G): 1 T = 104G = 10 kG

1 G = 10–4T = 0.1 mT Tesla is a large unitand is often used with the multiplierprefixes (Table 7) in the InternationalSystem of Units

Magnetic Flux The weber replaces the

maxwell One weber (Wb) equals 108maxwell (Mx): 1 Wb = 100 MMx

1 Mx = 10–8Wb = 0.01 µWb = 10 nWb

T ABLE 16 Compound radiographic units.

Conductivity and Resistivity

In the twentieth century, the conductivity

of a given metal was conventionally

expressed as a percentage of pure copper’s

conductivity with reference to the

International Annealed Copper Standard

(IACS).22In the International System of

Units, conductivity is expressed in

siemens per meter (S·m–1) The

conductivity of pure copper (100 percent

IACS) is 58 MS·m–1

Resistivity is the inverse ofconductivity and is expressed in ohm

meter Table 17 gives the formulas for

conversion to and from units for

conductivity and resistivity

Units for Magnetic Testing

In magnetic testing, units are mainly for

magnetism, visible light and ultraviolet

radiation The units in the International

System of Units include the weber (Wb),

the tesla (T) and several derived units

Originally, these units were developed by

scientists using the CGS (centimeter gram

second) metric system For magnetic

theories, the introduction of SI meant the

removal of intermediate units (such as the

unit pole) and made possible a direct

conversion from flux per second to

voltage

Ultraviolet radiation is often used toreveal magnetic particle indications Itsmeasurement is discussed above, aftervisual testing

Units for Acoustics

In this discussion, acoustics includes themethods of ultrasonic testing and acousticemission testing

Pressure, Displacement and Related Quantities

Acoustic emission and ultrasound aremechanical waves inside a stressedmaterial, where a displacement ripplesthrough the material and moves itssurface A transducer on that surfaceundergoes this displacement as a pressure.The pressure is measured as force per unitarea in pascal (Pa), equivalent to newtonper square meter (N·m–2) The signal fromthe transducer is sometimes related tovelocity (m·s–1), displacement (m) oracceleration (m·s–2)

Properties of piezoelectric transducersare related to electric charge: a pressure onthe element creates a charge (measured incoulomb) on the electrodes A rapidlychanging pressure alters the charge fastenough to allow the use of either voltage

or charge amplifiers After this, signalprocessing may analyze and store data interms of distance in meter (m), velocity inmeter per second (m·s–1), acceleration inmeter per second per second (m·s–2),signal strength in volt·second (V·s),energy in joule (J), signal in volt (V) orpower in watt (W)

Hertz

Frequencies usually correspond tobandwidths for specific applications.Frequency is measured in hertz (Hz),where 1 Hz equals one cycle per second

Decibel

The term loudness refers to amplitude in

audible frequencies Some acoustic wavesare audible; others have frequencies above

or below audible frequencies (ultrasonic

or subsonic, respectively) A signal at aninaudible frequency has measurable

amplitude but is not called loud or soft.

A customary unit for measuring theamplitude of an acoustic signal is thedecibel (dB), one tenth of a bel (B) Thedecibel is extensively used in acousticsand electronics The decibel is not a fixedmeasurement unit but rather expresses alogarithmic ratio between two conditions

of the same dimension (such as voltage orenergy) In auditory acoustics, an arbitrarysound pressure such as 20 µPa can be used

T ABLE 17 Conversion of Units for

Conductivity σ and Resistivity ρ.

for the reference level of 0 dB In

acoustics, the reference level 0 dBAEis

defined as a signal of 1 µV at the

transducer before any amplification

Because they are ratios of reference

values, bel and decibel are not part of the

International System of Units There are

often two definitions given for the

decibel, so voltage decibel is sometimes

written dB(V).

Precision

In calculating and reporting

measurements, care must be given to

expressing values with a precision that

does not exceed the resolution of the

interrogating system This care requires

both a mathematical understanding of

significant digits and an appreciation of

what sort of data are needed and possible

from the sensors A reasonable and useful

number of significant digits should be

reflected in the instrument settings, and

this resolution may be specified in the

written test procedure

The mathematical concepts of accuracy

and precision are discussed in published

standards.18,23

1 Wenk, S.A and R.C McMaster.

Choosing NDT: Applications, Costs and Benefits of Nondestructive Testing in Your Quality Assurance Program Columbus,

OH: American Society forNondestructive Testing (1987)

2 TO33B-1-1 (NAVAIR 01-1A-16)

TM43-0103, Nondestructive Testing Methods Washington, DC: Department

of Defense (June 1984)

3 ASME Boiler and Pressure Vessel Code.

New York, NY: American Society ofMechanical Engineers

4 Annual Book of ASTM Standards:

Section 3, Metals Test Methods and Analytical Procedures Vol 03.03,

Nondestructive Testing WestConshohocken, PA: ASTMInternational (2009)

5 Recommended Practice

No SNT-TC-1A, Personnel Qualification and Certification in Nondestructive Testing Columbus, OH: American

Society for Nondestructive Testing(2006)

6 ANSI/ASNT CP-189, Standard for Qualification and Certification of Nondestructive Testing Personnel.

Columbus, OH: American Society forNondestructive Testing (2006)

7 ASNT Central Certification Program

(ACCP), Revision 4 (March 2005)

Columbus, OH: American Society forNondestructive Testing (2005)

8 ANSI/ASNT Standard CP-105, ASNT Standard Topical Outlines for

Qualification of Nondestructive Testing Personnel Columbus, OH: American

Society for Nondestructive Testing(2006)

9 ISO 9712, Nondestructive Testing — Qualification and Certification of Personnel Geneva, Switzerland:

International Organization forStandardization

10 ANSI/ASNT CP-106 (ISO 9712-2005,

modified), Non-Destructive Testing — Qualification and Certification of Personnel, third edition Geneva,

Switzerland: InternationalOrganization for Standardization(2008)

11 NFPA National Electric Code Quincy,

MA: National Fire PreventionAssociation

12 IEEE National Electrical Safety Code.

New York, NY: Institute of Electricaland Electronics Engineers

13 29 CFR 1910, Occupational Safety and Health Standards [Code of Federal Regulations: Title 29, Labor.]

Washington, DC: United StatesDepartment of Labor, OccupationalSafety and Health Administration

14 29 CFR 1926, Occupational Safety and Health Standards for the Construction Industry [Code of Federal Regulations: Title 29, Labor] Washington, DC:

United States Department of Labor,Occupational Safety and HealthAdministration

15 Documentation of the Threshold Limit Values for Physical Agents, seventh

edition Cincinnati, OH: AmericanConference of GovernmentalIndustrial Hygienists (2008;

supplements)

16 Guide to Occupational Exposure Values.

Cincinnati, OH: American Conference

of Governmental Industrial Hygienists(2011)

17 Threshold Limit Values [for Chemical Substances and Physical Agents] and Biological Exposure Indices Cincinnati,

OH: American Conference ofGovernmental Industrial Hygienists(2001; supplements)

18 IEEE/ASTM SI 10, Standard for Use of the International System of Units (SI): The Modern Metric System New York,

NY: IEEE (2011)

19 Thompson, A and B.N Taylor NIST

SP 811, Guide for the Use of the International System of Units (SI).

Washington, DC: United StatesGovernment Printing Office (2008)

20 Taylor, B.N and A Thompson NIST

SP 330, The International System of Units (SI) Washington, DC: United

States Government Printing Office(2008)

21 ANSI B 74.16, Checking the Size of Diamond and Cubic Boron Nitride Abrasive Grain New York, NY:

American National Standards Institute(2007)

22 IEC 60028, International Standard of Resistance for Copper Geneva,

Switzerland: InternationalElectrotechnical Commission (2001)

23 JCGM 200, International Vocabulary of Metrology — Basic and General Concepts and Associated Terms (VIM) Sèvres,

France: Bureau International des Poids

et Mesures (2008)

References