NONDESTRUCTIVETESTING HANDBOOI{Second Edition

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VOLUME 10NONDESTRUCTIVE TESTING OVERVIEW

Stanley NessCharles N. SherlockTechnical Editors

Patrick O. MoorePaul McIntireEditors

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137 lAMERICAN SOCIETY FORNONDESTRUCTIVE TESTING

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Gopyright 1996AMERICAN SOCIETY FOR NONDESTRUCTrVE TESTING, INC.AU rights reserved.

No part of this book may be reproduced, stored in a retrieval system or transmitted, inany form Or by any means - electronic, mechanical, photocopying, recording orotherwise - without the prior written permission of the publisher.

Nothing contained in this book is to be construed as a grant of any right of manufacture,sale or use in connection with any method, process, apparatus, product or composition,whether or not covered by letters patent or registered trademark, nor as a defense againstliability for the infringement of letters patent or registered trademark.

The American Society for Nondestructive Testing, its employees and the contributors tothis volume are not responsible for the authenticity or accuracy of information herein, andopinions and statements published herein do not necessarily reflect the opinion of theAmerican Society for Nondestructive Testing or carry its endorsement orrecommendation.

The American Society for Nondestructive Testing, its employees, and the contributors tothis volume assume no responsibility for the safety of persons using the information in thisbook.

Library of Congress Cataloging-in-Publication Data

Nondestructive testing overview I Stanley Ness, Charles N, Sherlock, technical editors.Patrick 0, Moore, Paul M. Mcintire, editors.

p, em. - (Nondestructive testing handbook; v, 10)Includes bibliographie references and index.ISBN 1-57117-018-91. Non-destructive testing. 2. Non-destructive testing-Industrial applications,

3. Engineerinb1rl.sp~n, 1. Ness, Stanley. II. Sherlock, Charles N. III. Moore,Patrick 0, IV: Mcintire, Paul, v: American SOcietyfor Nondestructive Testing,VI. Series: Nondestructive testing handbook (2nd ed.) ; v 10 -TA418.2.N65 1996

620.1'1~7-dc20Pltblished by the American Society fOr Nondestructive Testing

1PRINTED IN THE UNITED STATES OF AMERICA

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PREFACE

The second edition of the Nondestructive Testing Hand-book comprises ten volumes, 17,000,000 characters, 6,573pages and more than 5,000 illustrations. Three HandbookDevelopment Directors (John Summers, Albert Birks andRoderic Stanley) managed progress of the edition throughthe Society's very .active Handbook Development Commit-tee. Fifteen technical editors undertook the task ofvalidatingthe technical content of documents covering dozens ofsophisticated nondestructive testing methods.' Key manu-scripts were. submitted by 104 lead authors, supported bymore than 750 contributing authors. Peer reviewers num-bered nearly 600. For the fIfteen years between 1981 and1996, three editors-in-chief labored to establish technicalprotocols and to give the series a consistency of style andvoice. Those editors were Robert C. McMaster (Volumes 1and 2), Paul McIntire (Volumes3 through 10) and Patrick O.Moore (Volumes 8, 9 and 10). Their work relied completelyon the efforts of those many volunteers and resulted in a sig-nificant contribution to the technical literature, at an impor-tant time for the American nondestructive testing industry.

The technical accomplishments of the NondestructiveTesting Handbook stand as a tribute to the volunteer spirit.ASNT could not have built the second edition without theunwavering commitment of its volunteer contributors.Experts in every field of nondestructive testing voluntarilydeveloped outlines to cover the science and use of theirnondestructive testing techniques, developed strategies for\vriting the chapters, reviewed, corrected and re-reviewedeveryone of those 17,000,000 characters. Volunteers haveofte~ expressed their reasons for doing this work: the over-whelming majority gave their personal time and knowledgebecause of their abiding concern for safety, scientific credi-bility, the quality of American industry and the value ofASNTs mission.

The Nondestructive Testing Handbook also validates thepeer review system and its ability to generate a high qualityproduct. It's true that manuscripts for the NondestructiveTesting Handbook arrived in all conditions within a broadrange of accuracy and consistency (one valuable contribu-tion comprised a two inch stack of yellow legal sheets hand-'written in what appeared to be lipstick). Yet, withoutexception, the positive criticism and constructive editing ofthe peel' reviewers molded the manuscripts into an accurateand practical finished product. -

The international stature of the Nondestructive TestingHandbook is reflected in its frequent citation in technical

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articles written and published in many other countries. Oneof the consistent themes in developing each volume wasmaintenance of the series' international value. Using SI asthe primary measurement system was one result of thisfocus, as was recruitment efforts for authors and reviewersoutside the United States. This international emphasisallowed the Nondestructive Testing Handbook to be writtenand reviewed by British, Canadian, Dutch, French, German,Greek, Japanese, Saudi Arabian and American volunteers.

Because of these skilled, high-reaching efforts, it turnedout that the second edition also showed how interestingnondestructive testing can be. There are uses of the tech-nology documented for virtually every industry and anastonishing range of materials. Here you can read aboutmicrowaving the pyramids (Vol. 4, P 546), listening to inte-grated circuit chips cracked in their substrates (VoL 5.,p 358), using alternating current underwater to do magneticparticle tests (VoL 6, p384), or applying ultrasonic waves toinspect the human abdomen and-other kinds of plumbing(Vol. 7, P 822 and 585). It's an impressive range of data for ahandbookseries.

Handbooks are expected to document the uses of theirtechnology and this field guide function may be supportedby text that details the pure science behind the applications.The second edition of the Nondestructive Testing Handbookdoes both of these things well, while at the same time repre-senting the dedication of its volunteer contributors, thevalue of the peer review system and the importance of itsinternational scope. With the publication of this, the secondeditions tenth and final volume, ASNT can rightly claim tohave documented a critical technology.

Thanks are due to Jack McElhaney, who helped in wordprocessing of much of the text, to Edwards Brothers forprinting and binding, to Kevin Mulrooney for indexing andto Hollis Humphries-Black, who prepared the art and layoutand made good things happen at every stage of production.

Thanks are due especially to Technical Editors StanleyNess and, Charles Sherlock for overseeing the technicalreview. The use of metric units in the text was reviewed hvHolger H. Streckert and Stanislav L [akuba, All the man)'volunteer contributors and reviewers deserve congratula-tions for what they have accomplished.

Paul MclntirePatrick MooreEditors

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ACKNOWLEDGMENTS

Nondestructive testing (NDT) continues to becomemore important in this age of increasing high technology.Materials with compositions of greater sophistication forhigher tensile strengths at lighter weights create the needfor NDT to be performed at higher sensitivities with moreaccuracy and more predictability than ever before. Contin-ued public demands for safer products at lower cost alsoincrease the need for better and more reliable NDT Thedevelopment of miniaturized computer chips and inte-grated circuits with power unthinkable just a few decadesago has, in tum, spurred development of electronic NDTequipment and helped create new NDT techniques. Thisadvancing technology and the need for increased sophistica-tion in NDT methods promote each other. The results areobserved every day in the more reliable and safer materialsand products used in the home, in automobiles, in aircraftand the space program.

Volume 10 of the Nondestructive Testing Handbook con-tains an overview of each of the major NDT methods widelyused by industry. In a single cover, Nondestructive TestingOverview provides students with an introductory text andmanagement with a readily portable reference publication.It provides NDT and quality assurance managers with gen-eral howledge and direction to ensure the specification ofthe most effective NDT for manufacturing and for in-ser-vice inspection of existing structures. Volume 10 will provevaluable to NDT practitioners whose work is limited to oneor two NDT methods but who must have a working famil-iarity with other methods, without requiring a separate vol-ume for each.

The second edition of AS:-H's Nondestructice TestingHandbook compiles the knowledge of many volunteerswithin the NDT communitv, both within and outside ASl\T.Single NDT method volu;nes require the input of manywithin that single NDT discipline. However, because Vol-ume 10 covers all the major NDT methods, it required thededication and voluntarv time and hard work of volunteersthroughout all the NDTdisciplines. The follov,ing acknowl-edgments indicate some of the hundreds of individuals andorganizations that contributed indirectly to the preparationof this book As technical co-editors, we thank all those whocontributed to this volume as writers and reviewers.

Stanlev NessCharles N. SherlockTechnical Editors

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Volume 10 of the Nondestructive TestingHandbook drawsextensively from the preceding nine volumes of the secondedition. Volunteers who were most active in the compilationof this volume are listed on the title page to each section.Additionally, the list of contributors below acknowledges con-tributors to the original sections in the second edition vol-umes from which Volume 10 was compiled. The reviewerslisted after the contributors below, however, are those whoparticipated in the preparation of Volume 10, not necessarilyother volumes in the second edition,

To acknowledge the support of scholarship by industry, aname of a contributor or reviewer is followed by his or heraffiliation at the time of most recent activity for the Nonde-structive Testing Handbook, even though that person mayhave changed employers since. Apologies are extended tocontributors, reviewers and others who helped to create thisvolume but may have been omitted from the list below.

Handbook DevelopmentCommitteeSreenivas Alampalli, New York State Department of

TransportationMichael W, Allgaier, GPU NuclearRobert A. Baker, Pennsylvania Power & Light CompanyAlbert S. Birks, AKZO Nobel ChemicalsRichard H. Bossi, Boeing Defense and Space GroupLawrence E. 'Bryant, [r., Los Alamos National LaboratorvJohn Stephen C~rgilI, Pratt & Whitney ,William C. Chedister, Circle Chemical CompanyWilliam D. Chevalier, Zetec, IncorporatedJames L. Doyle, Quest Integrated, -IncorporatedMatthew J. GolisAllen T. Green, Acoustic Technology GroupRobert E. Green. [r., Johns Hopkins UniversityGrover Hardv, Materials Directorate of Wright LaboratorvJames F. Jackson .. ~Stanislav I. Ja~llba, 51[akub AssociatesJohn K. Keve, Westinghouse HanfordIrvin R. Kraska. Martin MariettaLlovd P. Lemle, Jr.Rennie K. Miller. Physical Acoustics CorporationScott D. Miller, Aptech Engineering ServicesPhilip A. Oikle. Yankee Atomic Electric CompanyStanlev :\essRona!t! T. Nisbet

Donald J. Hagemaier, McDonnell Douglas AerospaceRichard L. Hannah, JF TechnologiesE. Blair HenryRoger F.Johnson, Quest Integrated, IncorporatedThomas S. Jones, Industrial Quality, IncorporatedSatish Nair, Karta Technology, San Antonio, TexasStanley NessDaniel Post, Virginia Polytechnic Institute and State

UniversityMartin]. Sablik, Southwest Research InstituteCesar A. Sclammarells, Illinois Institute of TechnologyPieter ]. Sevenhuijsen, National Aerospace LaboratoryJohn R. Snell, [r., John Snell and AssociatesRoderic K. Stanley, Quality Tubing, IncorporatedJohn Scott Steckenrider, Argonne National LaboratoryPeter K. Stein, Stein Engineering ServicesColleen M. Stuart, TechnicorpWalter Tomasulo, TechnicorpAlex Vary, NASA Lewis Research Center

Volume 10 ReviewersMichael W Allgaier, GPU NuclearRobert A. BakerYoseph Bar-Cohen, Jet Propulsion LaboratoryHarry Berger, Industrial Quality, IncorporatedAlbert S. Birks, AKZO Nobel ChemicalsBernard BoisvertRichard H. Bossi, BoeingDefense and Space GroupRonald J. Botsko, NDT Systems, IncorporatedJohn Stephen Cargill, Pratt & WhitneyFrancis H. Chang, Lockheed Martin Technical Aircraft

SystemsWilliam C. Chedister, Circle Systems, IncorporatedEugene J. Chemma, Bethlehem Steel CorporationThomas F. Drouillard].C. Duke, Jr., Virginia Polytechnic Institute and State

UniversityGary R. Eld~r, Gary Elder & AssociatesTodd S. Fleckenstein, Moody International

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Timothy J. Fowler, Felicity Group, IncorporatedMatthew J. Golis .Allen T. Green, Acoustic TechnologyGroupRobert E. Green, Jr., Johns Hopkins UniversityPaul E. Grover, Infraspection InstituteDonald J. Hagemaier, McDonnell Douglas AerospaceGrover Hardy, Materials Directorate of 'Wright LaboratoryE.G. Henneke, II, Virginia Polytechnic and State

UniversityNathan Ida, Akron UniversityFrank A. Iddings[amesF, JacksonStanislav L Jakuba, SI Jakub AssociatesThomas S. Jones, Industrial Quality, IncorporatedJohn K. Keve, Westinghouse HanfordIrvin R. Kraska, Martin MariettaDavid S. Kupperman, Argonne National LaboratoryRonnie K. Miller, Physical Acoustics CorporationScott D. Miller, Aptech Engineering ServicesRonald T. Nisbet, Ronan CorporationPhilip A. Oikle, Yankee AtomicEmmanuel P. Papadakis, Quality Systems ConceptsMorteza Safar, Q-uest Integrated, IncorporatedRam P. Samy, The Timken CompanyEdward R. Schaufler, Infra Red Scanning ServicesJ. Thomas Schmidt, J. Thomas Schmidt AssociatesPaul B. Shaw, Chicago Bridge and Iron, IncorporatedAmos G. Sherwin, Sherwin NDT SystemsKermit Skeie, Kermit Skeie AssociatesJohn R. Snell, Jr., John Snell and AssociatesRoderic K. Stanley, Quality Tubing, IncorporatedPhil Stolarski, California Department of TransportationHolger H. Streckert, General AtomicsColleen M. Stuart, TechnicorpStuart A. Tison, National Institute of Standards and

TechnologyNoel A. Tracy, Universal Technology CorporationMark F.A. Warchol, Aluminum Company of AmericaRandall D. Wasberg, American Society for Nondestructive

TestingCarl Waterstrat, Varian Vacuum ProductsGeorge C. Wheeler, Wheeler NDT, Incorporated

CONTENTS

SECTION 1: INTRODUCTION TONONDESTRUCTIVE TESTING

PART 1: NATURE OF NONDESTRUCTIVETESTING .

Definition of Nondestructive Testing . .Purposes of Nondestructive Testing .Rapid Growth and Acceptance of

Nondestructive Tests . . . . . . . . . . . . . . . . .PART 2: QUALITY ASSURANCE .

Basic Concepts of Quality Assurance .Quality Control and Quality Assurance .Establishing Quality Levels .

PART 3: TEST SPECIFICATION .Management Policies .Sources of Information .SpecifYing Sensitivity and Accuracy in Tests ..Establishing the Reliability.of Tests .Scheduling Tests for Maximum

Effectiveness and Economy .Applications of Nondestructive Testing .Mode of Presentation ~ .

PART 4: UNITS OF MEASURE FORNONDESTRUCTIVE TESTING .

Origin and Use of the SI System .SI Units for Radiography .Fundamental S1 Units Used for Leak testing ..SI Units for Electrical and Magnetic Testing ..SI Units for Other Nondestructive Testing-

Methods , .Prefixes for SI Units .. , , .

BIBLIOGRAPHY , , .

SECTION 2: LEAK TESTING .

PART 1: MANAGEMENT A1'\D APPLICATIONSOF LEAK TESTING , ,.

Functions of Leak Testing , ,Relationship of Leak Testing to Product

Serviceability . , , .Determination of Overall Leakage Rates

through Pressure Boundaries , ,Measuring Leakage Rates to Characterize

Individual Leaks " ' .Quantitative Description of Leakage Rates '.Examples of Practical Units Used Earlier for

Measurement of Leakage .Units for Leakage Rates of Vacuum Systems .

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Ensuring System Reliability through LeakTesting .

Leak Testing to Detect Material Flaws . . .SpecifYing Desired Degrees of Leak

Tightness .Avoiding Impractical Specifications for

Leak Tightness .SpecifYing Leak Testing Requirements to

Locate Every Leak .SpecifYing Sensitivity of Leak Testing for

Practical Applications - .Definition of Leak Detector and Leak Test

Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . ..Example of Sensitivity and Difficulty of

Bubble Leak Testing .Relation of Test Costs to Sensitivity of

Leak Testing '. .Selection of Specific Leak Testing Technique

for Various Applications .Basic Categories of Leak Testing .Selection of Tracer Gas Technique for Leak

Location Only .Factors Influencing Choice between,

Detector Probe and Tracer Probe Tests ..Selection of Technique for Leakage

Measurement .Practical Measurement of Leakage Rates with

Gaseous Tracers - .Leakage Measurements of Open Test Objects

Accessible on Both Sides .Selection of Test Methods for Systems

Leaking to Atmospheric Pressure .Purposes of Leak Testing to Locate

Individual Leaks .Classification of Methods for Locating and

Evaluating Individual Leaks .Techniques for Locating Leaks 'With

Electronic Detector Instruments .Coordinating Overall Leakage Measurements

with Leak Location Tests , .Laser Based Leak Imaging .Training of Leak Testing Personnel .

PART 2: SAFETY 11'\ LEAK TESTING .General Safety Procedures for Test PersonnelPsvchologicalFactors and the Safety ProgramControl of Hazards from Airborne Toxic

Liquids. Vapors and Particles .""""Control of Hazards of Flammable Liquids

and Vapors ' .

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Control of Electrical and Lighting Hazards .. 44Safety Precautions with Leak Testing Tracer

Gases. . . . . . . . . .. . . . . . . . . . . . . . . . . . . 45Safety Precautions in Pressure and Vacuum

Leak Testing 45Safety Precautions with Compressed Gas

Cylinders .. :............. 47PART 3: HALOGEN TRACER GAS

TECHNIQUES AND LEAK DETECTORS ... 48Halogen Vapor Tracer Gases and Detectors . . 48Pressure Leak Testing with Halogen (Sniffer)

Detector Probe 48PART 4: REFERENCE LEAKS 49

Terminology Applicable to Reference,Calibrated or Standard Leaks 49

Classification of Common Types of Calibratedor Standard Physical Leaks 49

Modes of Gas Flow through Leaks . . . . . . . . . 49PART 5: PRESSURE CHANGE TESTS FOR

MEASURING LEAKAGE RATES........... 50Functions of Pressurizing Gases in

Leak Testing 50Conversion of Pressure Measurements

to Svsteme Internationale d'Unites(SI 'Units) 50

Compressibility of Gaseous and LiquidFluids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Pressure Change Tests for MeasuringLeakage Rates in Pressurized Systems . . . . 50

Pressure Change Tests for MeasuringLeakage in Evacuated Systems 52

PART 6: LEAK TESTING OF VACUUMSySTEMS.............................. 54

The Nature of Vacuum . . . . . . . . . . . . . . . . . . 54Leak Testing of Vacuum Systems with

Mass Spectrometer Leak DetectorTechniques . . . . . . . . . . . . . . . . . . . . . . . . . 55

PART 7: BUBBLE LEAK TESTING " . . . 57Introduction to Bubble Techniques 57Bubble Testing by Liquid Film Application

Technique ,........... 57Bubble Testing by the Vacuum Box

Technique .. ,...................... 58PART 8: HELIUM MASS SPECTROMETER

LEAK TESTING......................... 59Basic Techniques for Leak Detection "ith

Helium Tracer Gas .59PART 9: ACOUSTIC LEAK TESTING. . . . . .. . . . . 61

Principles of Acoustic: Leak Testing 61Instrumentation for Ultrasonic Detection of

Leaks. . . . . . . . . . . . . . . . . . . . . . . . . . 61Techniques of Leakage Monitoring with

Multiple Acoustic Emission Sensors ..... 62

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PART 10: LEAK TESTING OF STORAGETANKS 65

Detection of External Leaks in UndergroundStorage Tanks . . . . . . . . . . . . . . . . . . . . . . . 65

Leak Testing of Aboveground StorageTanks with Double Flat Bottoms ..... , . . 65

Comparison of Quantitative Leak TestingTechniques ' , . , . . 68

BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . 71

SECTION 3: LIQUID PENETRANTTESTING.......................... 75

PART 1: DEFINITION AND PURPOSE OFLIQUID PENETRANT TESTING 76

History ",.,.....,.,...........".... 76Basic Penetrant Testing Process ,'......... 76Reasons for Selecting Liquid Penetrant

Testing . . . . . . . . . . . . . . , : , . , , , ' , . . . . . 77Disadvantages and Limitations of Liquid

Penetrant Testing . . . . . .. . . . . . . . . . . . . . . 78Equipment Requirements '.............. 79Personnel Requirements , . . . . . . 80

PART 2: CLASSIFICATIONS OF PENETRANTS. 81Classification of Penetrants by Dye Type .... 81Classification of Penetrants by Removal

Method , ',....... 81Types of Developers . , , , , , , . . . . . . . . . . . . . 82Qualified!Approved Penetrant Materials .... 83Sensitivity , . , . . . . . . . . . . . 83

PART 3: PENETRANT TESTING PROCESSES. , 84Selection of a Penetrant Material/Process .. , 84Control of a Penetrant Process ... , . . . . . . . . 85Advantages and Limitations of Penetrant

Materials and Techniques ... ,......... 85Pretesting. Cleaning and Postcleaning .,.... 86Summary , , , , , , . . . 88

BIBLIOGRt\PHY , . . . . . . . . . . . . . 89

SECTION 4: RADIATION PRINCIPLESAND SOURCES , 91

PART 1: ELECTROMAGNETIC RADIATION . . . 92The Photon , . . . . 92X-Rays and Gamma Ravs ,."... 92

Gen~ration ofX-Ravs ~ ,.......... 93PART 2: RADIATION ABSORPTION ' 95

Categories of Absorption ,........ 95Absorption of Photons , , ,. 9.5Scattering of Photons " ".... 96Attenuation Coefficients of the Elements . . . . 98Neutron Irradiation , ,.... 98

PART 3: BASIC GENERATORCONSTRUCTION ., , ,. 99

X-Ray Tubes , ,... 99High Energy Sources 103Control Units under 500 keY . . . . . . . . . . . .. 108

PART 4: X-RAY OPERATINGRECOMMENDATIONS 110

Baseline Data .,....................... 110Selecting a Unit 110Tube Warmup , " .. , .. , IIIMaintenance . . . . . . . . . . . . . . . . . . . . . . . . ., IIIElectrical Safety 112X-Ray Safety , , Il2

PART 5: ISOTOPES FOR RADIOGRAPHY .. , . .. 114Radioactivity , . . . . . . . . . . . . . . . .. 114Selection of Radiographic Sources 114

PART 6: SOURCE HANDLING EQUIPMENT .. 120Requirements .. , , 120Classification . . . . . . . . . . . . . . . . . . . . . . . . .. 120Manual Manipulation of Sources 120Remote Handling Equipment 120Safety Considerations , . . . . . . .. 122

BIBLIOGRAPHY ' , . . . . .. 129

SECTION 5: FILM RADIOGRAPIIT 131

PART I: FILM EXPOSURE ,.,... 132Making a Radiograph ' '........ 132Factors Governing Exposure ,.'., 133Geometric Principles ,., , ,... 134Relations of Milliamperage (Source

Strength), Distance and Time 139The Reciprocity Law ' , 140Exposure Factor .. , . ' , .. , 141Determination of Exposure Factors 141Contrast ... '......................... 142Choice of Film ' ' 142Radiographic Sensitivity ..' , ' ' ' '. 143

PART 2: ABSORPTION AND SCATTERING 144Radiation Absorption in the Specimen ' " 144Scattered Radiation. . . . . . . . . . . . . . . . . . . .. 146Reduction of Scatter . ' , ' , . , , . .. 146Mottling Caused by X-ray Diffraction , 151Scattering in High Voltage Megavolt

Radiography , ,. 151PART 3: RADIOGRAPHIC SCREENS, ' . '. 152

Functions of Screens ., , .. '........ 152Lead Foil Screens , .. ' ' , ' . .. 152Fluorescent Screens .. , ' . , , 154

PART 4: INDUSTRIAL RADIOGRAPHIC FILMS, 157Selection of Films for Industrial Radiography. 158Photographic Density , ' ' , . . .. 158Densitometers , "... 158X-Ray Exposure Charts, , " ., .. , ... ' 159

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Gamma Ray Exposure Charts , 161The Characteristic Curve 161

PART 5: RADIOGRAPHIC IMAGE QUALITYAND DETAIL VISIBILITY ., ,....... 164

Controlling Factors , 164Subject Contrast , , 164Film Contrast . . . . . . . . . . . . . . . . . . . . .. 164Film Graininess and Screen Mottle 166Penetrameters . . . . . . . . . . . . . . . . . . . . . . . .. 166Viewing and Interpreting Radiographs. . . . .. 169

PART 6: FILM HANDLING AND STORAGE 170IdentifYing Radiographs 170Shipping of Unprocessed Films .. '........ 170Storage of Unprocessed Film , , 170Storage of Exposed and Processed Film , 171

SECTION 6: RADIOSCOPY ANDTOMOGRAPIIT . . . . . . . . . . . . . . . . . . . .. 173

PART 1: FUNDAMENTALS OF RADIOSCOPY.. 174Principles , ,.................. 174Background , . . . . . . . . . . . . . .. 174Basic Technique .,...............'...,. 175Recommended Practice 175Image Intensifiers ' . ' ' 175Spectral Matching , 177Statistics 178Television Cameras, Image Tubes and

Peripherals. . . . . . . . . . . . . . . . . . . . . . . .. 178Optical Coupling , ., 182Viewing and Recording Systems , . . . .. 183

PART 2: RADIOSCOPIC IMAGEENHANCEMENT '" , ' 184

Digital Techniques 184Pseudocolor , '., .. ',.............. 187Other Techniques ' ... ' . ' ..... ' . . . .. 187

PART 3: X-RAYCOMPUTED TOMOGRAPHY . " 188Introduction , 188Computed Tomography Systems ., '.... 191Computed Tomography Applications , .. , 195

SECTION 7: ELECTROMAGNETIC TESTING 199PART 1: INTRODUCTION TO

ELECTROMAGNETIC TESTING . ' " 200Typical Uses of Eddv Current

Nondestructive Tests. . . . . . . . . . . . . . . .. 200Method of Induction of Eddv Currents in

Materials ' ..... , .. ,. ,'. , ' ... ' , ... , .' 200Test Material Properties Influencing Eddy

Current Tests . ' ' ... ' .... ' ... ,. .".. 200Methods for Detection of Eddv Current

Intensities and Flow Patteri'ls '. 201Analysis of Eddy Current Test Signals

(Amplitudes and Phase Angles) , " 201

Selection of Optimum Eddy Current TestFrequencies '" 201

Control of Eddy Current PenetrationDepths in Test Materials 202

Limitations of Eddy Current Tests 202Correlation of Eddy Current Test

Indications with Material Properties andDiscontinuities :. 202

Typical Industrial Applications of EddyCurrent Tests . . . . . . . . . . . . . . . . . . . . . .. 202

Eddy Current Transducers , 203Factors Affecting Eddy Current Transducers. 204

PART 2: REMOTE FIELD LOW FREQUENCYEDDY CURRENT INSPECTION . . . . . . . . . .. 206

Remote Field Zone . . . . . . . . . . . . . . . . . . . .. 206Eddy Currents in Pipe Wall Applications . . .. 207Example Applications . . . . . . . . . . . . . . . . . .. 208Conclusions ~. . . . . . . . . . . . . . . . . . .. 211

PART 3: ELECTROMAGNETIC SORTINGTECHNIQUES . . . . . . . . . . . . . . . . . . . . . . . . .. 212

Eddy Current Impedance Plane Analysis . . .. 212Impedance Plane 212Liftoff and Edge Effects on Impedance

Plane -. . . . . . . . . . .. 213Conductivity and Permeability Loci on

Impedance Plane . . . . . . . . . . . . . . . . . . .. 213PART 4: EDDY CURRENT APPLICATIONS IN

THE STEEL INDUSTRY. .. . . . . . . . . . . . . . . .. 218Eddy Current Systems That Rotate the

Product at Ambient Temperatures 218Eddv Current SYstems That Rotate the

Sensors . . . .'. . . . . . . . . . . . . . . . . . . . . . .. 222Tests at Elevated Temperatures 223

PART 5: EDDY CURRENT INSPECTION OFBOLT HOLES. . . . . . . . . . . . . . . . . . . . . . . . . .. 228

Eddy Current Bolt Hole Inspection . . . . . . .. 228Reference Standards for Bolt Hole Inspection. 229Procedure for Bolt Hole Inspection 230Automated Bolt Hole Inspection 231

PART 6: AUTOMOTrVE APPLICATIONS OFEDDY CURRENT TESTING 232

Hardness and Case Depth Inspection ofAxle Shafts . . . . . . . . . . . . . . . . . . . . . . . .. 232

Crack and Porosity Detection andMachined Hol~ Presence in MasterBrake Cylinders . . . . . . . . . . . . . . . . . . . .. 234

Tin Plate Thickness on Diesel Engine Piston. 235Cold Headed Pinion Gear Blank Crack

Detection . . . . . . . . . . . . . . . . . . . . . . . . .. 235Hub and Spindle Hardness and Case Depth

Inspection 236Camshaft Heat Treat Inspection . . . . . . . . . 237

PART 7: MULTIFREQUENCY TESTING. . . . . .. 239Requirements for Multifrequency Testing '" 239Physical Basis of the Multifrequency Process. 239

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PART 8: MAGNETIC FLUX LEAKAGETESTING 242

Types of Parts Inspected by Magnetic FluxLeakage . . . . . . . . . . . . . . . .. 242

Types of Discontinuities Found byMagnetic Flux Leakage 245

Effects of Discontinuities . . . . . .. 246Sensors Used in Magnetic Flux Leakage

Inspection 246Typical Magnetic Flux Leakage Applications .. 250

BIBLIOGRAPHY " 256

SECTION 8: MAGNETIC PARTICLETESTING ...................... , 257

PART I: INTRODUCTION. . . . . . . . . . . . . . . . . .. 258Capabilities and Limitations of MagneticParticle Techniques . . . . . . . . . . . . . . . . . . . .. 258Principles of Magnetic Particle Testing. .. . . .. 258

PART 2: FABRICATION PROCESSES ANDMAGNETIC PARTICLE TESTAPPLICATION 259

Basic Ferromagnetic Materials Production. .. 259Inherent Discontinuities 259Primary Processing Discontinuities 260Forging Discontinuities 262Casting Discontinuities : . . . . . . . . . .. 263Weldment Discontinuities 263Manufacturing and Fabrication

Discontinuities . . . . . . . . . . . . . . . . . . . . .. 263Service Discontinuities . . . . . . . . . . . . . . . . .. 266Corrosion 266

PART 3: MAGNETIC FIELD THEORY 267Magnetic Domains 267Magnetic Poles .. . . . . . . . . . . . . . . . . . . . . .. 267Types of Magnetic Materials . . . . . . . . . . . . .. 268Sources of Magnetism . . . . . . . . . . . . . . . . . .. 268

PART 4: MAGNETIC FLUX AND FLUXLEAKAGE 270

Circular Magnetic Fields 270Longitudinal Magnetization 270Magnetic Field Strength . . . . . . . . . . . . . . . .. 271Subsurface Discontinuities . . . . . . . . . . . . . .. 271Effect of Discontinuity Orientation 272Formation of Indications 272

PART 5: ELECTRICALLY INDUCEDMAGNETISM. . . . . . . . . . . . . . . . . . . . . . . . . .. 273

Circular Magnetization . . . . . . . . . . . . . . . . .. 273Magnetic Field Direction . . . . . . .. 273Longitudinal Magnetization 274Multidirectional Magnetization. . . . . . . . . .. .. 275

PART 6: MAGNETIC PARTICLE TESTSYSTEMS 276

Stationary Magnetic Particle Test Systems .,. 277Power Packs 277

JMobile and Portable Testing Units, , ' 277Prods and Yokes ., , , ,.. 278

PART 7: FERROMAGNETIC MATERIALCHARACTERISTICS , ,. 278

Magnetic Flux and Units of Measure . . . . . .. 278Magnetic Hysteresis .......,............ 278Magnetic Permeability ,.......... 280

PART 8: TYPES OF MAGNETIZING CURRENT. 281Alternating Current ,............. 281Half-Wave Direct Current 281Full-Wave Direct Current ,....... 282Three-Phase Full-Wave Direct Current .... , 282

PART 9: DEMAGNETIZATION PROCEDURES. 284Justification for Demagnetizing ,.... 284Methods of Demagnenzanon , " 284Demagnetization Practices .. . , . . . . . . . . . ., 286

PART 10: MEDIA AND PROCESSES INMAGNETIC PARTICLE TESTING ,.. 288

Magnetic Particle Properties , ... ,'....... 288Effects of Particle Size ,..,....,.......... 289Effect of Particle Shape ,....... 289Visibility and Contrast. . . . . . . . . . . . . . .. . . .. 290Particle Mobility , . . . . . . . . .. 290Media Selection .. ,.................... 291Magnetic Particle Testing Processes .. ,.... 291Conclusion , ,.. 292

BIBLIOGRAPHY , , . . . . . .. 294

SECTION 9: ACOUSTIC EMISSIONTESTING . . . . . . . . . . . . . . . . . . . . . . . .. 297

PART 1: FUNDAMENTALS OF ACOUSTICEMISSION TESTING , ... , ... ,........... 298

The Acoustic Emission Phenomenon . . . . . . 298Acoustic Emission Nondestructive Testing. .. 298Application of Acoustic Emission Tests ..... 300Successful Applications .... , . . . . . . . . . . . .. 300Acoustic Emission Testing Equipment . . . . .. 301Microcomputers in Acoustic Emission

Test Svstems 302Characteristics of Acoustic Emission

Techniques " 302Acoustic Emission Test Sensitivity 303Interpretation of Test Data ' , , 303The Kaiser Effect ., " 304

PART 2: BUCKET TRUCK AND LIFTINSPECTION , . . .. 30.5

Acoustic Emission Inspection Development . 30,5Instrumentation for Bucket Truck Inspection. 306Test Procedure for Bucket Truck Inspection . 307T:pical Test Data ,............... 308Acceptance Criteria 309

PART 3: ACOUSTIC EMISSIO\, TESTS OFFIBER REINFORCED PLASTIC VESSELS .. 310

xiv

Testing Procedures for Pressure, Storageand Vacuum Vessels , , , . . . .. 310

Applications in the Chemical Industries . .. 310Composite Pipe Testing Applications , 312Effect of Acoustic Emission Tests of Fiber

Reinforced Plastic Structures .,........ 314Zone Location in Fiber Reinforced Plastics ,. 314Felicity Effect in Fiber Reinforced Plastics .. 316Acceptance of Acoustic Emission Techniques

for Testing of Fiber Reinforced Plastics ,. 317PART 4: INDUSTRIAL GAS TRAILER TUBE

APPLICATIONS " 318Recertification of Gas Trailer Tubing . . . . . .. 318Test Procedure for Trailer Tubing Tests ..... 319Advantages of Acoustic Emission Testing of

Trailer Tubes , , ,.. 321PART 5: RESISTANCE SPOT WELD TESTING . 322

Resistance Spot Welding , ,. 322Principles of Acoustic Emission Weld

Monitoring , 323Weld Quality Parameters That Produce

Acoustic Emission .. ,................ 324Acoustic Emission Instrumentation for

Resistance Spot Welding , . . . . . .. 324Typical Applications of the Acoustic

Emission Method. , , ,. 326Monitoring Coated Steel Alternating Current

Welds............. 327Alternating Current Spot Welding

Galvanized Steel 327Detecting the Size of Adjacent Alternating

Current Welds , " 329Control of Spot Weld Nugget Size .. . . . . . .. 329Conclusions : . , ,. 330

PART 6: ACOUSTIC EMISSION APPLICATIONSIN UNDERSEA REPEATERMANUFACTURE , , . . . . . . . . . . . .. 331

High Voltage Capacitor in the RepeaterCircuitry Unit , ,.............. 331

Instrumentation and Analvsis .. 332Tubulation Pinchweld on the Repeater

Housing , , .. " 334BIBLIOGRAPHY , , . . . . .. 339

SECTION 10: INTRODUCTION TOULTRASONIC TESTING . . . . . . . . .. . . . .. 345

PART 1: BASIC ULTRASONIC TESTING 346Advantages of Ultrasonic Tests ,. 346

Limitati~ns of Ultrasonic Tests " 347Criteria for Successful Testing 348

PART 2; ULTRASONIC WAVES IK ~IATERIALS. :349Definition of Wave and Wave Properties .... 350Ultrasonic Attenuation , ,............. 3.50Nonlinear Elastic Waves , .. 350

PART 3: IMPLEMENTATION OF ULTRASONICTESTING 351

Transmission and Reflection Techniques 351Ultrasonic Test Systems 351Ultrasonic Sources 352Typical Transducer Characteristics . . . . . . . .. 353Through-Transmission Systems . . . . . . . . . . .. 354Pitch and Catch Contact Testing 354Amplitude and Transit Time Systems . . . . . .. 356B-Scan Presentation 358C-Scan Presentation . . . . . . . . . . . . . . .. 359System Calibration 359Major System Parameters ' 361

PART 4: ULTRASONIC TESTING EQUIPMENT. 363Basic Ultrasonic Test Systems . . . . . . . . . . . .. 363Portable Instruments 364Capabilities of General Purpose Ultrasonic

Test Equipment . . . . . . . . . . . . . . . . . . . .. 367Modular Ultrasonic Equipment 367Special Purpose Ultrasonic Equipment 368Operation in Large Testing Systems . . . . . . .. 369

PART 5: OTHER ULTRASONIC TECHNIQUES. 370Optical Generation and Detection of

Ultrasound . . . . . . . . . . . . . . . . . . . . . . . .. 370Optical Generation of Elastic Waves 370Optical Detection of Ultrasound. 370Future Developments in Laser Ultrasonics .. 371Air Coupled Transducers . 371Low Frequency Transducers 371High Frequency Transducers 372Electromagnetic Acoustic Transducers . . . . .. 373

BIBLIOGRAPHY. . . . . . . . . . . . . . . . . . . . . . . . . .. 378

SECTION 11: ULTRASONIC PULSE ECHOTECHNIQUES. . . . . . . . . . . . . . . . . . . . .. 379

PART 1; ULTRASONIC TESTINGTECHNIQUES . . . . . . . . . . . . . . . . . . . . . . . . .. 380

The A-Scan Method 380The B-Scan Method . . . . . . . . . . . . . .. 380The C-Scan Method .. . . . . . . . . . . . . . . . . .. 380

PART 2: STRAIGHT BEAM PULSE ECHOTESTS. . . :382

Instrumentation for Straight Beam Tests 382Straight Beam Test Procedures. . . . . . . . . . .. 382Applications of Straight Beam Contact Tests. :384Discontinuity Discrimination :38.5Discontinuities Detected by the Straight

Beam Method . ~. . . . . .. 386Sizing Discontinuities . . . . . . . . . . . . . . . . . .. 386Mechanical Scanning 3Ell)Selection of Ultraso~ic Test Frequencies 388Effects of Ultrasonic Transducer Diameter .. 388Transducer Near Field 389

Divergence of Ultrasonic Beams in theFar Field 389

Focused Beam Immersion Techniques. . . . .. 390Ultrasonic Beam Attenuation by Scattering .. 392Selection of Test Frequencies . . . . . . . . . . . .. 393Effect of Discontinuity Orientation on

Signal Amplitude 394Effect of Geometry of Discontinuity on Echo

Signal Amplitude " 394Data Presentation . . " . . . . . . . . . . . . . . . . .. 395Tests of Multilayered Structures and

Composites 395Dual-Transducer Methods 395

PART 3: ANGLE BEAM CONTACT TESTING. " 397Verification of Shear Wave Angle 397Ranging in Shear Wave Tests. . . . . . . . . . . .. 397Ultrasonic Tests of Tubes 398Weld Testing . . . . . . . . . . . . . . . . . . . . . . . . .. 398

PART 4: COUPLING MEDIA FORCONTACT TESTS 400

Use of Transducer Shoes 400Use of Couplant and Membranes . . . . . . . . .. 400Use of Delay Lines 401Selection and Use of Coupling Media 401Selection of Couplants 402Operator Techniques to Ensure Good

- Coupling 402PART 5: IMAGING OF PULSE ECHO

CONTACT TESTS 404Ultrasonic Imaging Procedures . . . . . . . . . . .. 404Contact Weld Tesis . . . . . . . . . . . . . . . . . . . .. 405

PART 6: ULTRASONIC PULSE ECHO WATERCOUPLED TECHNIQUES .. . . . . . . . . . . . . . .. 407

Immersion Coupling . . . . . . . . . . . . .. ..... 407Immersion Coupling Devices . . . . . . . . . . . .. 408Pulse Echo Immersion Test Parameters . . . .. 410Test Indications Requiring Special

Consideration. . . . . . .. 411Location of Discontinuities. . . . . . . . . . . . . .. 412Grain Site Discontinuities 413Interpretation of Indications from Rotor

Wheels. . . . . . . . . . . . . . . . . . . . . . . . . . .. 414PART 7: IMMERSION TESTING OF

COMPOSITE MATERIALS . . . . . . . . . . . . . . .. 419Discontinuities in Composite Laminates .... 419Ultrasonic Testing of Composite Laminates .. 419Tests of Composite Tubing . . . . .. . . . . . . . . .. 420Laminate Test Indications. . . . . . . . . . . . . . 423Conclusion 423

SECTION 12: VISUAL TESTI:'\1G , 425PART 1: DESCRIPTION OF VISUAL .AND

OPTICAL TESTS .' ' 426

SECTION 14: NONDESTRUCTIVE TESTINGGLOSSARy.. . . . . . . . . . . . . . . . . . . . ... 515

Manual Systems 465System Selection and Application . . . . .. . . . .. 466

PART 7: MACHINE VISION TECHNOLOGY ... 468Lighting Techniques . . . . . . . . . . . . . . . .. . .. 468Optical Filtering. . . . . . . . . . . . . . . . . . . . . .. 470Image Sensors. . . . . . . . . . . . . . . . . . . 470

SECTION 13: THERMOGRAPHY ANDOTHER SPECIAL METHODS ........ 473

PART 1: THE SPECIAL NONDESTRUCTIVETESTING METHODS . . . . . . . . . . . . . . . . . . .. 474

Relationship between Material Property andMaterial Behavior 475

PART 2: PRINCIPLES OF INFRAREDTHERMOGRAPHY 478

Heat Transfer . . . . . . . . . . . . . . . . . . .. 478Instrumentation and Techniques 482

PART 3: THERMOGRAPHIC APPLICATIONS .. 486Composite Materials and Structures . . . . . . .. 486Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 490Electric Power Distribution and

Transmission Systems 491Pavement, Bridge Decks and Subterranean

Surveys ' . . . . . . . . .. 491Automotive Applications . . . . . . . . . . . . . . . .. 492Bonded Materials and Structures ... . . . . . .. 493Diverse Applications . . . . . . .. . . . . . . . . . . . .. 495

PART 4: OPTICAL METHODS 497Grid and Moire Nondestructive Testing. . . .. 49iHolography . . . . . . . . . . . . . . . . . . . . . . . . . .. 498Shearography 500Point Triangulation Profilometry 500

PART 5: OTHER SPECIAL METHODS 503Alloy Identification . . . . . . . . . . . . .. 503Electromagnetic Special Methods 503Acoustic Methods .. . . . . . . . . . . . . . . . . . . .. 505Resistance Strain Gaging 506

Luminous Energy Tests 426Geometrical Optics . . . . . . . . . . . . . . . . . . . .. 426

PART2: VISION AND LIGHT . . 428The Physiology ~{s.ight .:::::::::::::::: 428Vision Acuity . . . . . . . . . . . . . . . . . . . . . . . . .. 429Vision Acuity Examinations . . ., . . . . . . . . . . .. 430Visual Angle 432Color Vision 432Fluorescent Materials . . . . . . . . . . . . . . . . . .. 435

__ Safety for Visual and Optical Tests 435PART 3: BASIC VISUAL AIDS . . . . . . . . . . . . . . .. 440

Environmental Factors .. , . . . . . . . . . . . . . .. 440Effects of the Test Object . . . . . . . . . . . . . . .. 441Magnifiers . . . . . . . . . . . . . . . . . . . . . . . . . . .. 443Low Power Microscopes . . . . . . . . . . . . . . . .. 445Photographic Techniques for Recording

Visual Test Results . . . . . . . . . .....' . . . .. 446Image Enhancement. . . . . . . . . . . . . . . . . . .. 447

PART4: BORESCOPES 449Fiber Optic Boresoopes 449Rigid Boreseopes 450Special Purpose Borescopes . .. 452Typical Industrial Borescope Applications ... 452Borescope Optical Systems . . . . . .. . . . . . . . .. 453Borescope Construction 454

_ ..Photographic Adaptations . . . . . . . . . . . . . . .. 455PART5: VIDEO TECHNOLOGY 457

Photoelectric Devices : : : : : : : : : : : : :: 457Phctoemissive Devices 457Photoconductive Cells or Photodiodes 457Photovoltaic Devices . . . . . . . . . . . . . . . . . . .. 457Uses of Photoelectric Detectinz and

MeasuringDevices ..... ~............. 458Photoelectric Imaging Devices . . . . . . . . . . .. 458Video Borescopes 459Video Borescope Applications. . . . . . . . . . . .. 461Principles ofScanning 461Television Camera Tubes 462Cathode Ray ViewingTube . . . . . . . . . . . . . 462Video Resolution . . . . . . . . . . . . . . . . . . . . . .. 463

PART 6: REMOTE POSITIOI'\ING ANDTRANSPORT SYSTEMS 46.5

Fixed Systems ... : : : : : : : : : : : : : : : : : .: 465Automated Systems 465

xvi

INDEX .............. ,.~~ ~ .. 567

SECTION 1INTRODUCTION TONONDESTRUCTIVE TESTING

2 / NONDESTRUCTIVE TESTING OVERVIEW

PART 1NATURE OF NONDESTRUCTIVE TESTING

Definition of NondestructiveTesting

Nondestructive testing (NDT) has been defined as com-prising those test methods used to examine or ins-pect a partor material or system without impairing its future useful-ness. The term is generally applied to nonmedical investiga-tions of material integrity. . -

Strictly speaking, this definition of nondestructive test-ing does include noninvasive medical diagnostics. Xvrays,ultrasound and endoscopes are used by both medical andindustrial nondestructive testing. In the 1940s, many mem-bers of the American Society for Nondestructive Testing(then the Society for Industrial Radiography) were medicalX-ray professionals. Medical nondestructive testing, how-ever, has come to be treated by a body of learning so sepa-rate from industrial nondestructive testing that today mostphysicians never use the word nondestructive.

Nondestructive testing is used to investigate specificallythe material integrity of the test object. A number of othertechnologies - for instance, radio astronomy, voltage andamperage measurement and rheometry (flow measure-ment) - are nondestructive but are not used to evaluatematerial properties specifically. Nondestructive testing isconcerned in a practical way with the performance of thetest piece - how long may the piece be used and when doesit need to be checked again? Radar and sonar are classifiedas nondestructive testing when used to inspect dams, forinstance, but not when they are used to chart a river bottom.

Nondestructive testing asks "Is there something wrongwith this material?" Various performance and proof tests, incontrast, ask "Does this component work?" This is the rea-son that it is not considered nondestructive testing when aninspector checks a circuit by running electric currentthrough it. Hydrostatic pressure testing is usually proof test-ing and intrinsicallv not nondestructive~ but acoustic: emis-sion testing used to monitor changes in a pressure vessel'sintegrity dt!ring hydrostatic testing is nondestructive testing.

Another gray area that invites various interpretations indeHning non-destructive testing is that of future usefulness.Some material investigations involve taking a sample of theinspected part for testing that is inherently destructive. Anoncritical part of a pressure vessel ma>' be scraped orshaved to get a sample Tor electron microscopy. for example.Although future usefulness of the vessel is not impaired b>"

the loss of material, the procedure is inherently destructiveand the shaving itself --in one sense the true test object"- has been removed from service permanently.

The idea of future usefulness is relevant to the qualitycontrol practice of sampling. Sampling (that is, the use ofless than 100 percent inspection to draw inferences aboutthe unsampled lots) is nondestructive testing if the testedsample is returned to service. If the steel is tested to verifythe alloy in some bolts that can then be returned to service,then the test is nondestructive. In contrast, even if spec-troscopy used in the chemical testing of many fluids isinherently nondestructive, the testing is destructive if thesamples are poured down the drain after testing.

Hardness testing by indentation provides an interestingtest case for the definition of nondestructive testing. Hard-ness testing machines look somewhat like drill presses. Theapplied force is controlled as the bit is lowered to make asmall dent in the surface of the test piece. Then the diame-ter or depth of the dent is measured. The force applied iscorrelated with the dent size to provide a measurement ofsurface hardness. The future usefulness of the test piece isnot impaired except in rare cases when a high degree of sur-face quality is important. However, because the piece's con-tour is altered, the test is rarely considered nondestructive.A nondestructive alternative to this hardness test could beto use electromagnetic nondestructive testing. .

Nondestructive testing is not confined to crack detec-tion, Other discontinuities include porosity, wall thinningfrom corrosion and manv sorts of disbonds. Nondestructivematerial characterizatio~ is a grov\ling field concerned withmaterial properties including material identification andmicrostructural characteristics - such as resin curing, casehardening and stress - that have a direct influence on theservice life of the test object.

Nondestructive testing has also been defined by listingor dassif}ing the variousmethods, 1.2 This approach is prac"tical in that it typically highlights methods in use by industry.

Purposes of Nondestructive TestingSince the 1920s, the art of testing without destroying the

test object has developed from a laboratorv curiosity to anindispensable tool of production. No longer is visual exarni-nation of materials, parts and complete products the princi-pal means of determining adequate quality. Nonclestmc:tive

tests in great variety are in worldwide use to detect varia-tions in -structure, minute changes in surface finish, thepresence of cracks or other physical discontinuities, to mea-sure the thickness of materials and coatings and to deter-mine other characteristics of industrial products. Scientistsand engineers of many countries have contributed greatly tonondestructive test development and applications.

The various nondestructive testing methods are coveredin detail in the literature but it is always wise to considerobjectives before plunging into the details of a method.What is the use of nondestructive testing? Why do thou-sands of industrial concerns buy the testing equipment, paythe subsequent operating costs of the testing and evenreshape manufacturing processes to fit the needs and find-ings of nondestructive testing?

Modem nondestructive tests are used by manufacturers(1) to ensure product integrity, and in turn, reliability; (2) toavoid failures, prevent accidents and save human life (seeFigs. 1 and 2); (3) to make a profit for the user; (4) to en-sure customer satisfaction and maintain the manufacturer'sreputation; (5) to aid in better product design; (6) to control

INTRODUCTION TO NONDESTRUCTIVE TESTING I 3

manufacturing processes; (7) to lower manufacturing costs;(8) to maintain uniform qualitylevel; and (9) to ensure oper-ational readiness.

Ensuring the Integrity/Reliability of a Product

The user of a fabricated product buys it with everyexpectation that it will give trouble-free service for a reason-able period of usefulness. Few of today's products areexpected to deliver decades of service but they are requiredto give reasonable unfailing value. Year by year the publichas learned to expect better service and longer life, despitethe increasing complexity of our everyday electrical andmechanical appliances.

America has always been a nation on the move. Todayour railroads, automobiles, buses, aircraft and ships carrypeople to more places faster than ever before. And peopleexpect to get there without delays due to mechanical failure.Meanwhile factories tum out more products, better, fasterand with more automatic machinery. Management expectsmachinery to operate continuously because profits depend

FIGURE 1. Fatigue cracks caused damage to the fuselage of this Aloha Airlines aircraft, causing thedeath of a flight attendant and injury to many passengers (April 1988)

4 I NONDESTRUCTIVE TESTING OVERVIEW

on such sustained output. The complexity of present-dayproducts and the machinery which makes and transportsthem requires greater reliability from every part.

If a product has one part that has a probability of failureof 1 in 1,000 before it has served a reasonable life, it may besatisfactory. This seems to be a very low chance of failure.Now suppose that a product is assembled from 100 criticalparts of various kinds and that each part has a failure possi-bility of 1 in 1,000. 'What then is the possibility of failure ofthe assembled item? The overall reliability of any assemblyis the mathematical product of the component reliabilityfactors. Overall reliability of this example is then:

or almost 1 in 10. It is certain that the user of this productwill be highly dissatisfied if lout of every 10 units failsprematurely. The point is that component integrity, and inturn, reliability must be immensely greater than the requiredreliabilityof the assembled product. -

Consider the ordinary V-8automobile engine. It has onlyone crankshaft but eight connecting rods, sixteen valvesprings and hundreds of other parts. Theoretically, failure ofanyone of these could make the motor useless. Yet how fre-quently does the car owner experience a part failure? Thisamazingly low incidence of service failure during the normallife of an automobile is a great tribute to the ability of theautomotive engineers to design well, of metallurgists todevelop the right materials, of production personnel to cast,

R = 0.999100 '" 0.9057

The possibility of failure of the assembly is then:

(Eq. 1)

1.00 - 0.9057 ;;;;;; 0.0943 (Eq.2)

FIGURE 2. Boilers operate with high internal steam pressure; material discontinuities can lead tosudden, vio'entfallure with possible injury to people and property

FROM BEN BAILEY. USEO WITH PERMISSION.

roll, forge, machine and assemble correctly, and of inspec-tors and quality control staff to set standards and see thatthe product meets those standards.

Preventing Accidents and Saving Lives

Ensuring product reliability is necessary because of thegeneral increase in performance expectancy of the public. Ahomeowner expects the refrigerator to remain in uninter-rupted service, indefinitely protecting the food investment,or the power lawnmower to start with one pull of the ropeand to keep cutting grass for years on end. The manufac-turer expects the lathe, punch press Or fork lift to stand upfor years of continuous work even under severe loads.

But reliability merely for convenience and profit is notenough. Reliability to protect human lives is a valuable endin itself. The railroad axle must not fail at high speed. Thefront spindle of the intercity bus must not break on thecurve. The aircraft landing gear must not collapse on touch-down. The mine hoist cable must not snap with people inthe cab. Such critical failures are rare indeed. And this ismostcertainly not the result of mere good luck. In large partit is the direct result of the extensive use of nondestructivetesting and of the high order of nondestructive testing abil-ity now available.

Ensuring Customer Satisfaction

While it is true that the most laudable reason for the useof nondestructive tests is that of safety, it is probably alsotrue that the most comnwn reason is that of making a profitfor the user. The sources of this profit are both tangrble andintangible.

Toe intangible source of profit is ensured customer satis-faction. Its corollary is the preservation and improvement ofthe manufacturer's reputation. To this obvious advantagemay be added that of maintaining the manufacturer's com-petitive position. It is generally true that the user sets thequality level, It is set in the market place when choosingamong the products of several competing manufacturers.Certainly the manufacturer's reputation for high quality isonly one factor. Others may be function, appearance, pack-aging, service and price. But in todays highly competitivemarkets, actual qualityand reputation for quality stand highin the consumer's mind.

Aiding in Product Design

Nondestructive testing aids Significantly in better prod-uct design. For example, the state of physical soundness as

INTRODUCTION TO NONDESTRUCTIVE TESTING I 5

revealed by such nondestructive tests as radiography, mag-netic particle or penetrant inspection of a pilot run of cast-ings often shows the designer that design changes areneeded to produce a sounder casting in an important sec-tion. The design may then be improved and the patternmodified to increase the quality of the product. This exam-ple is not academic; it occurs almost daily in many plants.

Somewhat outside the scope of discontinuity detectionare nondestructive tests to determine the direction, amountand gradient of stresses in mechanical parts, as applied inthe field of experimental stress analysis. These play a veryimportant part in the design of lighter, stronger,-less costlyand more reliable parts.' -

Controlling Manufacturing Processes

Control is a basic concept in industry. Engineers, inspec-tors, operators .and production personnel know the prob-lems of keeping any manufacturing process under control.The process must he controlled, and the operator must betrained and supervised. When any element of a manufactur-ing operation gets out of control, quality of the affectedproduct is compromised and waste may be produced.

Almostevery nondestructive testing method is applied inone wayor another to assist in process control and so ensurea direct profit for the manufacturer. As one example ofthousands which could he cited, consider a heat treatingoperation. The metallurgist sets up a procedure based onsound material of a given analysis. One nondestructive test,applied to all parts or to a few from each batch of parts, tellswhether the chemical analysis of the material is so erraticthat the procedure will fail to produce the desired hardnessor induce cracking. A second test may show when andwhere cracking has occurred, Another test may show thatthe desired hardness has not been developed. If so, processvariables may be corrected immediately. In these ways, costand processing time are saved for the manufacturer.

Lowering Manufacturing Costs

There are many other examples of both actual andpotential cost savings possible through the use of nonde-structive tests. Most manufacturers could cut manufactur-ing costs by deciding where to apply the following costreduction principle: A nondestructive test can reduce manu-facturing cost when it locates undesirable characteristics ofa material or component at an early stage, thus eliminatingcosts offurther processing or assembly. -An example of thisprinciple is the testing of forging blanks before the forgingoperation. The presence of seams, large inclusions or cracksin the blanks may result in a woefully defective product.

(, I NONDESTRUCTIVE TESTING OVE~V1EW

Using such a blank would waste all the labor and forge ham-mer time involved in forming the material into the product.

Another profit making principle is that a nondestructivetest may save manufacturing cost when it produces desirableinformation at lower cost than some other destructive ornondestructive tests. An example of this principle is the sub-stitution of a magnetic particle nondestructive test for acidpicklingto detect seams or cracks. Asit has in many plants, astraightforward economic study of comparative costs of thetwo methods may showthe cost savingadvantage of the non-destructive test over the pickling examination. -

Maintaining Uniform Quality Level

It seems obvious that improved product quality shouldbe an invariable aim and result of nondestructive testing.Yetthis is not always the case, for there is such a thing as toohigh a quality level. The true function of testing is to controland maintain the quality level that engineers or design engi-neers establish for the particular product and circum-stances. Quality conscious engineers and manufacturershave long recognized that perfection is unattainable andthat even the attempt to achieve perfection in production isunrealistic and costly Sound management seeks not perfec-tion but pursues excellence in management of workmanshipfrom order entry to product delivery. The desired qualitylevel is the one which is most worthwhile, all things consid-ered. Quality below the specified requirement can ruin salesand reputation. Quality above the specified requirementcan swallow up profits through excessive production andscrap losses. Management must decide what quality level itwants to produce and support

Once the quality level has been established, productionand testing personnel should aim to maintain this level andnot to depart from it excessively either toward lower orhigher quality. In blunt language, a nondestructive test doesnot improve quality. It can help to establish the quality levelbut only management sets the quality standard.1f manage-ment wants to make a nearly perfect product or wants at theother extreme to make junk, then nondestructive tests willhelp make what is wanted, no more and no less.

In making a drawing for a part, the designer sets toler-ances on dimension and finish. If a drawing specifies a cer-tain dimension as 31.8 mm (1.25 in.) but failsto specify thetolerance, the machine shop supervisor rejects the drawingas incomplete or assumes the standard tolerance. In nonde-structive testing, a quality tolerance (the tolerance on thecharacteristic being determined) or criteria for acceptanceor rejection must also be specified. The lack of appreciationfor this obvious requirement has caused more misunder-standing of nondestructive testing and more objections tonondestructive tests than any other factor. Perhaps it is thecause of more confusion than all other factors combined.

Rapid Growth and Acceptance ofNondestructive Tests .

The foregoing tangible and intangible reasons forwidespread profitable use of nondestructive tests are suffi-cient in themselves. But parallel developments have con-tributed to their growth and acceptance.

Increased Complexity of Modern Machinery

Consider the present-day automobile. First, the manualchoke became obsolete. The old rod from the dashboard toa butterfly valve in the carburetor has been replaced bymore reliable and efficient metered fuel injection. Themechanically connected brake pedal and brake shoe havegiven way to hydraulic and antiloek braking systems.The oldmanual windshield wipers are now powered by vacuum Orelectricity and complicated by washer jets and variabletimers. Today's components include complex ventilation,heating, defrosting and air conditioning systems, powerseats, power actuated windows and sun roofs, expandedelectronics, emission controls, cruise controls, stereo equip-ment, digital gaging and automatic transmissions. The auto-mobile industry, while carrying design complexity to greatlengths, has also tremendously raised component reliability.Otherwise, most people would never dare to take their carfrom the garage for fear of serious failure.

As an even more startling example of component relia-bility arithmetic, consider computers. They require complexmicroprocessors, chips, resistors, wire connections, coun-ters and other parts whose functioning demands operationalreliability in each component. The automobile and the elec-tronic instrument industries are examples of complexity thatcould never have been achieved without parallel advances innondestructive testing.

Increased Demand on Machines

Within a lifetime, average speeds of railway passengerand freight trains have doubled. The speed of commercialair transport has quintupled. Transonic speeds for rocketpowered missiles and for piloted aircraft are not unusual.Automobile. bus and truck speeds have increased and theirengines tum twice as fast. Elevators in tall buildings arefully automatic and much faster.with speeds limited only bythe comfort of the passengers. The stress applied to parts inthese vehicles often increases as the square or cube of theincreased velocitv,

In the interest of greater speed and rising costs of mate-rials, the design engineer is always under pressure to reduce

weight. This can sometimes be done by substituting alu-minum or magnesium alloys for steel or iron, but such lightalloyparts are not of the same size or design as those theyreplace. The tendency is also to reduce the size.These pres-sures on the designer have subjected parts of all sorts toincreased stress levels. Even such commonplace objects assewing machines, sauce pans and luggage are also lighterand more heavily loaded than ever before. The stress to besupported is seldom static. It often fluctuates and reversesat low or high frequencies. Frequency of stress reversalsincreases with the speeds of modem machines and thusparts tend to fatigue and fail more rapidly.

Another cause of increased stress on modem products isa reduction in the safety factor. An engineer designs withcertain known loads in mind. On the supposition that materi-alsand workmanship are never perfect, a safety factor of 2,3,.5 or 10 is applied. Because of other considerations though, alower factor is often used, depending on the importance oflighter weight or reduced cost or risk to consumer.

New demands on machinery have also stimulated thedevelopment and use of new 'materials whose operatingcharacteristics and performance are not completely known.These new materials create greater and potentially danger-ous problems. As an example, there is a record of an air-craft's being built from an alloy whose work hardening,notch resistance and fatigue life were not well known. Afterrelativelyshort periods of service some of these aircraft suf-fered disastrous failures. Sufficient and proper nondestruc-tive tests could have saved manv lives.

As technology improves and as service requirementsincrease, machines are subjected to greater variations and towider extremes of all kinds of stress, creating an increasingdemand for stronger materials.

Engineering Demands for Sounder Materials

Another justification for the use of nondestructive testsis the designer's demand for sounder materials. As size andweight decrease and the factor of safety is lowered, moreand more emphasis is placed on better raw material controland higher quality of materials, manufacturing processesand workmanship.

An interesting fact is that a producer of raw material orof a finished product frequently does not improve quality orperformance until that improvement is demanded by thecustomer. The pressure of the customer is transferred toimplementation .ofimproved design or manufacturing. Non-destructive testing is frequently caned on to deliver this newqualitv level.

Public Demands for Greater SafetyThe demands and expectations of the public for greater

safety are apparent evervwhere, Review the record of the

INTRODUCTION TO NONDESTRUCTIVE TESTING I 7

courts in granting higher and higher awards to injured per-sons. Consider tne outcry for greater automobile safety, asevidenced by the required use of auto safety belts and thedemand for air bags, blowout proof tires and antilock brak-ing systems. The publicly supported activities of theNational Safety Council, Underwriters Laboratories, theEnvironmental Protection Agency and the Federal AviationAdministration in the United States, and the work of similaragencies abroad, are only a few of the ways in which thisdemand for safety is expressed. It has been expresseddirectly by the many passengers who cancel reservationsimmediately following a serious aircraft accident. Thisdemand for personal safety has been another strong force inthe development of nondestructive tests.

Rising Costs of Failure

Aside from awards to the injured or to estates of thedeceased, consider briefly other factors in the rising costs ofmechanical failure. These costs are increasing for many rea-sons. Some important ones are:

L greater costs of materials and labor;2. greater costs of complex parts;3. greater costs due to the complexity of assemblies;4. greater probability that failure of one part will cause

failure of others, due to overloads;5. trend to lower factors of safety;6. probability that the failure a'f one part will damage

other parts of high value; andI. failure of a part within an automatic production

machine may shut down an entire high speed, inte-grated, production line. '\.Then production was car-ried out on many separate machines, the broken onecould be bypassed until repaired. Today, one machineis tied into the production of several others. Loss ofsuch production is one of the greatest losses resultingfrom part failure.

Responsibilities of Production Personnel andInspectors

Labor today often means a machinery operator. For-merly, a laborer in a shop manually made a part and thework piece received individual attention. Today the laborermay be just as skilled but the skill is directed toward theoperation of a machine. The machine requires attentionrather than the work piece, Production rates are also higher.This prevents paying personal attention to individual parts.

Formerly everyone who worked on a part gave it somesort of inspection. even if cursory. Today that is seldom thecase. Many production operations are covered hy hoods,

8 I NONDESTRUCTIVE TESTING OVERVIEW

FIGURE 3. Industrial organization chart with channels of responsibility for Inspection areas {chartshows only departments involved with testing or inspection}

CHIEFINSPECTOR

QUALITYSPECIFICATIONS

!---------..f

IIII!

__ J

SAFETYENGINEEr

PART 2QUALITY ASSURANCE

Basic Concepts of QualityAssurance

To avoid misunderstanding, it is important to discuss themeaning, interrelation and interpretation of some widelyused expressions. It is not uncommon to think of inspectionas a nonproductive operation. As such, it is viewed as lessvaluable than direct labor. Again, it is not uncommon tothink of testing as a laboratory operation, comparable topulling of tensile test bars to determine physical properties.It is sometimes imagined that quality is something injectedinto a product by the qesigner.

In certain situations, these concepts may be true or par-tiallv true. Actuallv these terms have little real meaning

unl~ss their place in the overall scheme of production anduse of a product is understood.

Product ReliabilityFirst and foremost, the goal for any product is a useful

life. This may be termed reliability, quality (usually meaninghigh quality), good value, performance and so on. Considerthe word reliability. The maker of the product generallyagrees that it should be reliable. But how reliable? Thatanswer is the manufacturer's responsibility. The degree ofreliability must be defined as closely as possible. Thedemands of customers, the reliability of competitive prod-ucts and the market price of similar products are weighed.Extensiveexperience and the expert advice of all depart-ments within the organization guide the decision. Finally, aquality level becomes company policy. H:;1ving set policy, itis management's responsibility to monitor performance. Itwants assurance that its policy is being followed, It wants toknow that the operation is under control or, if not, whereand how it is out of control. It wants assurance of quality.

Quality Control and QualityAssurance

Quality assurance is the establishment of a program toguarantee the desired quality level of

10 I NONDESTRUCTIVE TESTING OVERVIEW

5. Auditing. The quality assurance program must con-tain provisionsfor unbiased, independent audits of allaspects of the program, including supplied materialsor components. Audits can be made on either ascheduled or random basis. Quality supervisors musthave management support to audit anything, anytime and anywhere in the manufacturing cycle and toinitiate timely corrective action.

Ouality Centro:Seeking quality assurance, management sets up a mech-

anism for obtaining it, a quality control department. Qualitycontrol is a more inclusive term than testing or inspection.Notably it implies a responsibility for the control of thequality of the product. In the older concept, the inspectiondepartment was responsible for checking certain aspects ofthe product against given specifications. Such inspection isonlypart of quality control. For example, the inspector maysay, "The requirements for hardness (or surface finish, free-dom from inclusions, or electrical conductivity) seem veryhard for our suppliers or for our own factory to meet." Aquality controller would then ask, "Is the tight specificationnecessary? Can we change it? Can we do it a different wayand yet keep the required quality?" When inspectors thinkbeyond the specification to the why's and wherefore's, thenthey enter into the decision about how to make a product ofthe required quality easier, cheaper and better and they maytruly be called quality control engineers.

Establishing Quality LevelsOne of the toughest problems of managers and design

engineers is to determine and then to define desired qualitylevel in any product. This problem hasno purely math-emat-icalsolution. It is not a problem for the engineer to solvenora standard for production personnel to establish. Yetit mustbe defined as clearly and as accurately as possible.

Too often management leaves this problem solely to thedesign engineer, the inspector or to production, by default.When that happens, the result is often less profit thanexpected. The designer usually wants a higher quality levelthan necessary. The inspector often agrees with the designer,Production usually focuses on producing a predeterminednumber of units within a specific time. All are sincere. allare trying to do a good job but each is affected by differentpressures. What management wants is quality assurancewithin a certain range or tolerance. Once that is made clear.

the functions of design, production, inspection and qualitycontrol can take over. In any case, recognition of the cus-tomer's stated and implied needs must be considered mini-mum requirements.

Practical Quality Levels

No product is perfect, whatever that word may mean.The characteristics of a perfect part, material or productmay be defined, but as knowledge increases, it becomesnecessary to add definitions of more characteristics. Totalperfection is never the true goal of nondestructive testing ormanufacturing. Industry desires a certain quality levelbelow perfection and will even tolerate some deviation fromthat level within an economic tolerance, plus or minus.

Range of Test Sensitivity

Manydo not realize the wide range of sensitivitypossiblein each nondestructive test. Radiography may be madesuperficial or very sensitive to many minute discontinuitiesby variations in X-ray tube voltage, type of film, distancefrom the tube to the part and other factors, Magnetic parti-cle test sensitivity varies widely with changes in type andmagnitude of current or with concentration and grade of theparticles themselves. If it is desired to locate grinding crackstwo hundredths of a millimeter deep, it can be done_-On theother hand, if nothing less than 2.5 mm (0.1 in.) deep is con-sidered important, the test can be made that insensitive.

Ouality Specifications

It should not be inferred that the depth of a discontinu-ity is a common or desirable specification. It maybe used onprimary or intermediate mill items, such as billets orsemirolled steel, or on manufactured parts in the roughstate where a known amount of surface material is to beremoved after inspection. Most commonly, a specification isconcerned with the direction, location or shape of a discon-tinuitv in the critical areas. These considerations determinethe importance of a discontinuity in causing the fatigue fail-ures common in mechanical parts of assemblies. Control oftest sensitivity in accordance with such specifications ispractical and should be practiced, For example, \>vith mag-netic particle testing. the direction of magnetization, fieldstrength, bath type, concentration and other factors cancontrol such sensitivity to desired limits.

PART 3TEST SPECIFICATION

Management PoliciesTo achieve the maximum value from any nondestructive

testing operation, it is essential to set up proper policiesregarding its use. These policies include:

L statements of the aims of management for develop-ment, management and assessment of quality systems;

2. an organization chart of the entire quality manage-ment system;

3. description in chart or word form of the interrelationamong all departments of the company; and

4. establishment of skills needed for each person assignedresponsibility within the quality system.

Objectives of Nondestructive TestingAstatement of the aims for a nondestructive test depart-

ment may be based on one or more of the previously dis-cussed broad reasons for use of these methods:

L to ensure the reliability of the end product;2. to save lives or prevent accidents; and3. to save money for the user.Such a statement should, however. go into much more

detail to make the wishes of management very clear to alllevelsof the organization.

Receiving InspectionConsider a well integrated metal goods manufacturing

company. It receives raw-material such-asbars, plate, shapescastings, forgings, fasteners and other forms. It may have areceiving inspection department. The aims of such an oper-ation may include establishing standards and saving moneyfor the company by:

1. testing incoming material to ensure that defectivematerial does not go to the shop;

2. keeping quality records for each supplier and noti~i"ing the-purchasing department of the various suppli-ers' quality perfonnance (the lowest cost supplier ona per-piece basis may not give the lowest overall costif the quality level is much lower than that of a sup-plier whose piece price is higher);

3. advising the purchasing department to inform suppli-ers of variations in packing. surface protection or othermeans that may reduce discontinuities or costs; and

INTRODUCTION TO NONDESTRUCTIVE TESTING I 11

4. consulting with suppliers' inspection or test person-nel on the types of tests or the standards or tolerancesused, to the end that both supplier and purchaser arefully informed of the quality level required.

This receiving inspector would report to the chiefinspector, as shown on the accompanying organization chart(Fig. 3). Similar definitions of aims and responsibility arethen set up for inspection operations followingparts manu-facture, assembly and final tests.

In the function of chief inspector. the head of these oper-ations uses standards furnished by the company. The chiefinspector reports to a quality manager, one of whose func-tions is aSSisting in setting up realistic, well defined qualityspecifications. In some plants with fewer people, the chiefinspector mayalso act as quality manager by establishing thespecifications. These quality specifications (which includemore than the nondestructive testing standards) must bedrawn up with the cooperation of management, sales, engi-neering and production, and must be thoroughly under-stood by purchasing. All departments must agree to them.Thus Fig. 3 showsa dotted communication line between thequality manager. chief engineer. chief inspector, plant man-ager and purchasing agent.

Department of Testing or Inspection

In Fig. 3. the letter T associated with stores. parts manu-facturing. tools. maintenance .and the safety engineer indi-cates such departments may have their own nondestructivetest eqUipment, not under supervision of the chief inspec-tor. A lathe operator may have a micrometer and may peri-odically check dimensions of the product to keep theoperation within control limits. In the same manner. theremay be a magnetic particle inspection unit in the heat treatdepartment to ensure control of heating and quenchingoperations. That unit may be under direct control of the heattreat foreman. Other production departments, too, may havetheir own test equipment for internal control purposes.

Similarly. in the tool room a penetrant inspection mayensure that tools are reground or that new carbide tips aresound and ready for use in the machine shop. Such inspec-tion is commonly placed under the foreman of that depart-ment. Also. the maintenance department may have its ownequipment for testing the production machinery in theplant. The safety engIneer may have similar equipment.Failure of such equipment may be very dangerous to allplant personnel.

12 I NONDESTRUCTIVE TESTING OVERVIeW

Management of Inspection

Inspection performed by personnel from departmentssuch as maintenance or the tool room is managed by thedepartment manager. Production line inspection functionsare, however, under the chief inspector. These inspectionsare in the nature of audits and must be performed by per-sonnel who are not responsible to the operation that is beingaudited. Therefore, the chief inspector (or quality manager)should not report to the plant manager but to a generalexecutive who may be responsible not only for manufactur-ing but also for engineering or other operations that have abroad bearing on the entire company performance. This isthe general manager. In some situations, the title may bemanufacturing manager or president. In this way, the policyof management may be directly applied to the determina-tion and surveillance of the quality of the product.

Peer Contact

It is highly desirable for quality control and supervisorypersonnel to have contacts both inside and outside the com-pany organization. Ashas been stated, liaison with engineer-ing and production is essential in the development ofstandards.for test methods and the test interpretation. Inaddition, frequent contacts with the sales or service depart-ments will bring field reports into consideration so that test-ing specifications can be adjusted to meet serviceconditions.

It is essential that other outside contacts be maintained.Contacts with customers give excellent information. Con-tacts with suppliers are also important. A supplier with adefinite understanding of the standards and requirementsof the customer may provide better standards or a lessexpensive product.

Last, but alsoimportant, is.peer contact for inspection andtesting personnel of all levels. Attendance and membershipin technical societies such as the American Society for Non-destructive Testing is a valuable method of maintaining suchcontacts and working toward better, more accurate andmore valuable quality assurance. Committee E-7 on Nonde-structive Testing of the American Society for Testing andMaterials also serves the nondestructive testing field. Manyother technical and industrial societies include committeesand research groups devoted to the application of nonde-structive tests in their fields.

Sources of InformationNondestructive test management engineers require full

information concerning service loads and conditions of usein order to design or sped!)- a useful nondestructive test fora particular part. They also need clearly established limits of

acceptability or rejectability, or at least a statement of theaccuracy with which discontinuities must be detected. Fur-thermore, it is necessary to prove that the properties to bemeasured by the nondestructive tests are a reliable means ofdetecting discontinuities or of predicting strength or ser-viceability properties. In the absence of these necessarydata, it is not usually possible to intelligently specify a reli-able nondestructive test.

Design Engineer and Stress Engineer

The design engineer and stress engineer should supplythe necessary data on service loads, operating conditionsand the limits of performance acceptability. They shouldidentify the critically stressed regions of the material andthe probable points and types of failure to be expected inservice.

Materials or Process Engineer

The knowledge of the design engineer may be sup-plemented by destructive tests on critical materials andcomponents. Determination of the correlation between(1) strength or serviceability and (2) the discontinuities orproperties measured nondestructively usually requires theaid of a materials or process engineer. Often an extensiveseries of controlled destructive tests is required to provethat the test indications are a complete and reliable indica-tion of serviceability.

Nondestructive Test Engineer

Finally the job of finding a sensitive and reliable methodof measuring the correlated property nondestructively is theresponsibility of the nondestructive test engineer. The non-destructive test program must be the result of workingclosely with the customer, the design engineer, the stressengineer and a materials or process engineer, in addition tothe basic job of designing, developing and applying suitablenondestructive tests. As a result, nondestructive testingdevelopments will provide valuable data to design engineersand manufacturers. The nondestructive test must be a reli-able measurement of properties it is designed to measure.

Specifying Sensitivity and Accuracyin Tests

Special care and caution should be used in speci!)ing thelimits of sensitivity and accuracy required or expected innondestructive tests. The sensitivityof every type of nonde-structive test is limited. Sensitivity adequate for testing ofone part may be totally inadequate for another test object,or for a more severe service condition on the same part. In

general, more sensitive tests require more elaborate equip-ment and cost more. The cost of developing, proving andapplying a suitable nondestructive test must be consideredin each application. Nondestructive tests which cannot beapplied economically in specific applications will usually beabandoned, even when technically adequate.

Reasonable Tolerances

There are no-simple rules for determining the most eco-nomical sensitivity and accuracy of such tests. In somecases, it is not economical to require that the accuracy ofnondestructive tests exceed the accuracies of the bOWDnumber and magnitude of service loads. Similarly, it is notalwavs economical to exceed the accuracv within which thedeSign assumptions predict true stresses or performance.Alternatively, it may sometimes be reasonable to limit thespecified test sensitivity to some fraction of the tolerancelimits in strength or serviceability.

Interpretati0 n Limitati0 ns

Even well established methods of nondestructive testingare subject to limitations. Radiography, for example, mayreliably reveal porosity,shrinkage, inclusions, dross and mis-runs in castings, lack of penetration in welds and similar dis-continuities. But few indeed are the cases in which theactual service life or load for failure can be predicted quan-titatively from radiographic testing. This would be difficultto do even if the parts' were destructively sectioned fordetailed internal visual examination.

Similarly, magnetic particle inspection of ferrous materi-als reveals surface cracks and discontinuities reliablv, How-ever, there are very few cases in which the fatigue ~trengthor the number of load applications required to producefatigue failure can be predicted from these test indications.However, recognition that a surface crack or stress concen-tration may lead to premature failure under repeated load-ing is generally sufficient basis for rejecting the material orpart f~r such s'ervice. ~

Geometric Limitations

In designing. specifyingor applying nondestructive tests,it is important to recogniie certain geometric limitations intheir scope and sensitivity. Some test methods are specifi-cally limited to test objects with reasonably flat or parallelsurfaces, or even to constant thickness sections. Ultrasonicresonance thickness gaging is naturally limited to walls orplates with nearly parallel surfaces. in order that echoes mayreturn to the sensing probe.

A few t}l)es of nondestructive tests arc applicable only tospecirnens of exactly identical geometry. Some electromag-netic induction or eddy current test devices can onlv detect

. .

INTRODUCTION TO NONDESTRUCTIVE TESTING I 13

discontinuities in symmetrical rods or bars of given shapeand diameter.

Accessibility Limitations

Some test methods require access to both sides of thetest specimen. In many tests, the source of the probingmedium is located on one side of the test object and thedetector on the opposite side, such as the X-ray tube (orgamma ray source) and fUm in through-wall radiography.. Other methods are designed or can be modified for useas Single-Side tests. Magnetic particle inspection, ultrasonicreflection techniques and many liquid penetrant tests maybe performed with Single-side access,

Size and Shape Limitations

Some test methods may be applied to parts of almost anyshape or size. Portable apparatus can be used to examinelarge, fixed structures in the field. Other tests involve use ofmassive testing units on fixed foundations with limitedmaneuverability within a confined testing area. Their use islimited to test objects that can be brought into the test areaand positioned properly with respect to the test apparatus.

Other tests nave definite thickness limits. Beta-ray thick-ness gages, for example, can penetrate only Very thin laversof m~stmaterials. Contact probe ultrasoni~pul~e refledtiontests require sufficient material thickness above discontinu-ities to permit the pulse from the source to attenuate beforethe discontinuity sIgnal returns.

Material Limitations

A few tests are limited to certain kinds of materials. Mag-netic particle tests, for example. are useful only with ferro-magnetic materials. Thev cannot be used for nonferrous

all~)'s or for nonmagnetic, austenitic stainless steel alloys.Scanning Limitations

Some nondestructi