NDT HandBook Volume 10

NONDESTRUCTIVE TESTING HANDBOOI{ Second Edition T

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VOLUME 10 NONDESTRUCTIVE TESTING OVERVIEW

Stanley Ness Charles N. Sherlock Technical Editors Patrick O. Moore Paul McIntire Editors

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AMERICAN SOCIETY FOR NONDESTRUCTIVE TESTING

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Gopyright © 1996 AMERICAN SOCIETY FOR NONDESTRUCTrVE TESTING, INC. AU rights reserved. No part of this book may be reproduced, stored in a retrieval system or transmitted, in any form Or by any means - electronic, mechanical, photocopying, recording or otherwise - 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 against liability for the infringement of letters patent or registered trademark.

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The American Society for Nondestructive Testing, its employees and the contributors to this volume are not responsible for the authenticity or accuracy of information herein, and opinions and statements published herein do not necessarily reflect the opinion of the American Society for Nondestructive Testing or carry its endorsement or recommendation. The American Society for Nondestructive Testing, its employees, and the contributors to this volume assume no responsibility for the safety of persons using the information in this book.

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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 1-57117-018-9 1. 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 96-25138 TA418.2.N65 1996 CIP 620.1'1~7-dc20 Pltblished by the American Society fOr Nondestructive Testing

1 PRINTED IN THE UNITED STATES OF AMERICA

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PREFACE The second edition of the Nondestructive Testing Handbook comprises ten volumes, 17,000,000 characters, 6,573 pages and more than 5,000 illustrations. Three Handbook Development Directors (John Summers, Albert Birks and Roderic Stanley) managed progress of the edition through the Society's very .active Handbook Development Committee. Fifteen technical editors undertook the task ofvalidating the technical content of documents covering dozens of sophisticated nondestructive testing methods.' Key manuscripts were. submitted by 104 lead authors, supported by more than 750 contributing authors. Peer reviewers numbered nearly 600. For the fIfteen years between 1981 and 1996, three editors-in-chief labored to establish technical protocols and to give the series a consistency of style and voice. Those editors were Robert C. McMaster (Volumes 1 and 2), Paul McIntire (Volumes3 through 10) and Patrick O. Moore (Volumes 8, 9 and 10). Their work relied completely on the efforts of those many volunteers and resulted in a significant contribution to the technical literature, at an important time for the American nondestructive testing industry. The technical accomplishments of the Nondestructive Testing Handbook stand as a tribute to the volunteer spirit. ASNT could not have built the second edition without the unwavering commitment of its volunteer contributors. Experts in every field of nondestructive testing voluntarily developed outlines to cover the science and use of their nondestructive testing techniques, developed strategies for \vriting the chapters, reviewed, corrected and re-reviewed everyone of those 17,000,000 characters. Volunteers have ofte~ expressed their reasons for doing this work: the overwhelming majority gave their personal time and knowledge because of their abiding concern for safety, scientific credibility, the quality of American industry and the value of ASNTs mission. The Nondestructive Testing Handbook also validates the peer review system and its ability to generate a high quality product. It's true that manuscripts for the Nondestructive Testing Handbook arrived in all conditions within a broad range of accuracy and consistency (one valuable contribution comprised a two inch stack of yellow legal sheets hand'written in what appeared to be lipstick). Yet, without exception, the positive criticism and constructive editing of the peel' reviewers molded the manuscripts into an accurate and practical finished product. The international stature of the Nondestructive Testing Handbook is reflected in its frequent citation in technical

articles written and published in many other countries. One of the consistent themes in developing each volume was maintenance of the series' international value. Using SI as the primary measurement system was one result of this focus, as was recruitment efforts for authors and reviewers outside the United States. This international emphasis allowed the Nondestructive Testing Handbook to be written and reviewed by British, Canadian, Dutch, French, German, Greek, Japanese, Saudi Arabian and American volunteers. Because of these skilled, high-reaching efforts, it turned out that the second edition also showed how interesting nondestructive testing can be. There are uses of the technology documented for virtually every industry and an astonishing range of materials. Here you can read about microwaving the pyramids (Vol. 4, P 546), listening to integrated circuit chips cracked in their substrates (VoL 5., p 358), using alternating current underwater to do magnetic particle tests (VoL 6, p384), or applying ultrasonic waves to inspect the human abdomen and-other kinds of plumbing (Vol. 7, P 822 and 585). It's an impressive range of data for a handbook series. Handbooks are expected to document the uses of their technology and this field guide function may be supported by text that details the pure science behind the applications. The second edition of the Nondestructive Testing Handbook does both of these things well, while at the same time representing the dedication of its volunteer contributors, the value of the peer review system and the importance of its international scope. With the publication of this, the second editions tenth and final volume, ASNT can rightly claim to have documented a critical technology. Thanks are due to Jack McElhaney, who helped in word processing of much of the text, to Edwards Brothers for printing and binding, to Kevin Mulrooney for indexing and to Hollis Humphries-Black, who prepared the art and layout and made good things happen at every stage of production. Thanks are due especially to Technical Editors Stanley Ness and, Charles Sherlock for overseeing the technical review. The use of metric units in the text was reviewed hv Holger H. Streckert and Stanislav L [akuba, All the man)' volunteer contributors and reviewers deserve congratulations for what they have accomplished. Paul Mclntire Patrick Moore Editors

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ACKNOWLEDGMENTS

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Nondestructive testing (NDT) continues to become more important in this age of increasing high technology. Materials with compositions of greater sophistication for higher tensile strengths at lighter weights create the need for NDT to be performed at higher sensitivities with more accuracy and more predictability than ever before. Continued public demands for safer products at lower cost also increase the need for better and more reliable NDT The development of miniaturized computer chips and integrated circuits with power unthinkable just a few decades ago has, in tum, spurred development of electronic NDT equipment and helped create new NDT techniques. This advancing technology and the need for increased sophistication in NDT methods promote each other. The results are observed every day in the more reliable and safer materials and products used in the home, in automobiles, in aircraft and the space program. Volume 10 of the Nondestructive Testing Handbook contains an overview of each of the major NDT methods widely used by industry. In a single cover, Nondestructive Testing Overview provides students with an introductory text and management with a readily portable reference publication. It provides NDT and quality assurance managers with general howledge and direction to ensure the specification of the most effective NDT for manufacturing and for in-service inspection of existing structures. Volume 10 will prove valuable to NDT practitioners whose work is limited to one or two NDT methods but who must have a working familiarity with other methods, without requiring a separate volume for each. The second edition of AS:-H's Nondestructice Testing Handbook compiles the knowledge of many volunteers within the NDT communitv, both within and outside ASl\T. Single NDT method volu;nes require the input of many within that single NDT discipline. However, because Volume 10 covers all the major NDT methods, it required the dedication and voluntarv time and hard work of volunteers throughout all the NDT disciplines. The follov,ing acknowledgments indicate some of the hundreds of individuals and organizations that contributed indirectly to the preparation of this book As technical co-editors, we thank all those who contributed to this volume as writers and reviewers.

Volume 10 of the Nondestructive Testing Handbook draws extensively from the preceding nine volumes of the second edition. Volunteers who were most active in the compilation of this volume are listed on the title page to each section. Additionally, the list of contributors below acknowledges contributors to the original sections in the second edition volumes from which Volume 10 was compiled. The reviewers listed after the contributors below, however, are those who participated in the preparation of Volume 10, not necessarily other volumes in the second edition, To acknowledge the support of scholarship by industry, a name of a contributor or reviewer is followed by his or her affiliation at the time of most recent activity for the Nondestructive Testing Handbook, even though that person may have changed employers since. Apologies are extended to contributors, reviewers and others who helped to create this volume but may have been omitted from the list below.

Handbook Development Committee Sreenivas Alampalli, New York State Department of Transportation Michael W, Allgaier, GPU Nuclear Robert A. Baker, Pennsylvania Power & Light Company Albert S. Birks, AKZO Nobel Chemicals Richard H. Bossi, Boeing Defense and Space Group Lawrence E. 'Bryant, [r., Los Alamos National Laboratorv John Stephen C~rgilI, Pratt & Whitney , William C. Chedister, Circle Chemical Company William D. Chevalier, Zetec, Incorporated James L. Doyle, Quest Integrated, -Incorporated Matthew J. Golis Allen T. Green, Acoustic Technology Group Robert E. Green. [r., Johns Hopkins University Grover Hardv, Materials Directorate of Wright Laboratorv . ~ James F. Jackson Stanislav I. Ja~llba, 51 [akub Associates John K. Keve, Westinghouse Hanford Irvin R. Kraska. Martin Marietta Llovd P. Lemle, Jr. Rennie K. Miller. Physical Acoustics Corporation Scott D. Miller, Aptech Engineering Services Philip A. Oikle. Yankee Atomic Electric Company Stanlev :\ess Rona!t! T. Nisbet

Stanlev Ness Charles N. Sherlock Technical Editors

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Timothy J. Fowler, Felicity Group, Incorporated . Matthew J. Golis Allen T. Green, Acoustic TechnologyGroup Robert E. Green, Jr., Johns Hopkins University Paul E. Grover, Infraspection Institute Donald J. Hagemaier, McDonnell Douglas Aerospace Grover Hardy, Materials Directorate of 'Wright Laboratory E.G. Henneke, II, Virginia Polytechnic and State University Nathan Ida, Akron University Frank A. Iddings [amesF, Jackson Stanislav L Jakuba, SI Jakub Associates Thomas S. Jones, Industrial Quality, Incorporated John K. Keve, Westinghouse Hanford Irvin R. Kraska, Martin Marietta David S. Kupperman, Argonne National Laboratory Ronnie K. Miller, Physical Acoustics Corporation Scott D. Miller, Aptech Engineering Services Ronald T. Nisbet, Ronan Corporation Philip A. Oikle, Yankee Atomic Emmanuel P. Papadakis, Quality Systems Concepts Morteza Safar, Q-uest Integrated, Incorporated Ram P. Samy, The Timken Company Edward R. Schaufler, Infra Red Scanning Services J. Thomas Schmidt, J. Thomas Schmidt Associates Paul B. Shaw, Chicago Bridge and Iron, Incorporated Amos G. Sherwin, Sherwin NDT Systems Kermit Skeie, Kermit Skeie Associates John R. Snell, Jr., John Snell and Associates Roderic K. Stanley, Quality Tubing, Incorporated Phil Stolarski, California Department of Transportation Holger H. Streckert, General Atomics Colleen M. Stuart, Technicorp Stuart A. Tison, National Institute of Standards and Technology Noel A. Tracy, Universal Technology Corporation Mark F.A. Warchol, Aluminum Company of America Randall D. Wasberg, American Society for Nondestructive Testing Carl Waterstrat, Varian Vacuum Products George C. Wheeler, Wheeler NDT, Incorporated

Donald J. Hagemaier, McDonnell Douglas Aerospace Richard L. Hannah, JF Technologies E. Blair Henry Roger F. Johnson, Quest Integrated, Incorporated Thomas S. Jones, Industrial Quality, Incorporated Satish Nair, Karta Technology, San Antonio, Texas Stanley Ness Daniel Post, Virginia Polytechnic Institute and State University Martin]. Sablik, Southwest Research Institute Cesar A. Sclammarells, Illinois Institute of Technology Pieter ]. Sevenhuijsen, National Aerospace Laboratory John R. Snell, [r., John Snell and Associates Roderic K. Stanley, Quality Tubing, Incorporated John Scott Steckenrider, Argonne National Laboratory Peter K. Stein, Stein Engineering Services Colleen M. Stuart, Technicorp Walter Tomasulo, Technicorp Alex Vary, NASA Lewis Research Center

Volume 10 Reviewers Michael W Allgaier, GPU Nuclear Robert A. Baker Yoseph Bar-Cohen, Jet Propulsion Laboratory Harry Berger, Industrial Quality, Incorporated Albert S. Birks, AKZO Nobel Chemicals Bernard Boisvert Richard H. Bossi, BoeingDefense and Space Group Ronald J. Botsko, NDT Systems, Incorporated John Stephen Cargill, Pratt & Whitney Francis H. Chang, Lockheed Martin Technical Aircraft Systems William C. Chedister, Circle Systems, Incorporated Eugene J. Chemma, Bethlehem Steel Corporation Thomas F. Drouillard ].C. Duke, Jr., Virginia Polytechnic Institute and State University Gary R. Eld~r, Gary Elder & Associates Todd S. Fleckenstein, Moody International

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CONTENTS SECTION 1: INTRODUCTION TO NONDESTRUCTIVE TESTING PART 1: NATURE OF NONDESTRUCTIVE TESTING . 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 FOR NONDESTRUCTIVE 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 TestingMethods ,. Prefixes for SI Units .. , ,. BIBLIOGRAPHY ,,.

SECTION 2: LEAK TESTING

Ensuring System Reliability through Leak Testing . 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 Personnel PsvchologicalFactors and the Safety Program Control of Hazards from Airborne Toxic Liquids. Vapors and Particles ."""" Control of Hazards of Flammable Liquids and Vapors ' .

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PART 1: MANAGEMENT A1'\D APPLICATIONS OF 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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Control of Electrical and Lighting Hazards .. Safety Precautions with Leak Testing Tracer Gases. . . . . . . . . .. . . . . . . . . . . . . . . . . . . Safety Precautions in Pressure and Vacuum Leak Testing Safety Precautions with Compressed Gas Cylinders .. :............. PART 3: HALOGEN TRACER GAS TECHNIQUES AND LEAK DETECTORS ... Halogen Vapor Tracer Gases and Detectors . . Pressure Leak Testing with Halogen (Sniffer) Detector Probe PART 4: REFERENCE LEAKS Terminology Applicable to Reference, Calibrated or Standard Leaks Classification of Common Types of Calibrated or Standard Physical Leaks Modes of Gas Flow through Leaks . . . . . . . . . PART 5: PRESSURE CHANGE TESTS FOR MEASURING LEAKAGE RATES........... Functions of Pressurizing Gases in Leak Testing Conversion of Pressure Measurements to Svsteme Internationale d'Unites (SI 'Units) Compressibility of Gaseous and Liquid Fluids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pressure Change Tests for Measuring Leakage Rates in Pressurized Systems . . . . Pressure Change Tests for Measuring Leakage in Evacuated Systems PART 6: LEAK TESTING OF VACUUM SySTEMS.............................. The Nature of Vacuum . . . . . . . . . . . . . . . . . . Leak Testing of Vacuum Systems with Mass Spectrometer Leak Detector Techniques . . . . . . . . . . . . . . . . . . . . . . . . . PART 7: BUBBLE LEAK TESTING ". . . Introduction to Bubble Techniques Bubble Testing by Liquid Film Application Technique ,........... Bubble Testing by the Vacuum Box Technique .. ,...................... PART 8: HELIUM MASS SPECTROMETER LEAK TESTING......................... Basic Techniques for Leak Detection "ith Helium Tracer Gas PART 9: ACOUSTIC LEAK TESTING. . . . . . . . . . Principles of Acoustic: Leak Testing Instrumentation for Ultrasonic Detection of Leaks. . . . . . . . . . . ............... Techniques of Leakage Monitoring with Multiple Acoustic Emission Sensors .....

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PART 10: LEAK TESTING OF STORAGE TANKS Detection of External Leaks in Underground Storage Tanks . . . . . . . . . . . . . . . . . . . . . . . Leak Testing of Aboveground Storage Tanks with Double Flat Bottoms ..... , . . Comparison of Quantitative Leak Testing Techniques ' ,.,.. BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . .

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SECTION 3: LIQUID PENETRANT TESTING..........................

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PART 1: DEFINITION AND PURPOSE OF LIQUID PENETRANT TESTING History ",.,.....,.,...........".... Basic Penetrant Testing Process ,'......... Reasons for Selecting Liquid Penetrant Testing . . . . . . . . . . . . . . , : , . , , , ' , . . . . . Disadvantages and Limitations of Liquid Penetrant Testing . . . . . . . . . •. . . . . . . . . . . Equipment Requirements '.............. Personnel Requirements ,...... PART 2: CLASSIFICATIONS OF PENETRANTS. Classification of Penetrants by Dye Type .... Classification of Penetrants by Removal Method , ',....... Types of Developers . , , , , , , . . . . . . . . . . . . . Qualified!Approved Penetrant Materials .... Sensitivity ,.,........... PART 3: PENETRANT TESTING PROCESSES. , Selection of a Penetrant Material/Process .. , Control of a Penetrant Process ... , . . . . . . . . Advantages and Limitations of Penetrant Materials and Techniques ... ,......... Pretesting. Cleaning and Postcleaning .,.... Summary , , , ,,,... BIBLIOGRt\PHY ,.............

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SECTION 4: RADIATION PRINCIPLES AND SOURCES

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PART 1: ELECTROMAGNETIC RADIATION . . . The Photon ,.... X-Rays and Gamma Ravs ,."... Gen~ration ofX-Ravs ~ ,.......... PART 2: RADIATION ABSORPTION ' Categories of Absorption ,........ Absorption of Photons , , ,. Scattering of Photons " ".... Attenuation Coefficients of the Elements . . . . Neutron Irradiation , ,....

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PART 3: BASIC GENERATOR CONSTRUCTION ., , ,. X-Ray Tubes , ,... High Energy Sources Control Units under 500 keY . . . . . . . . . . . .. PART 4: X-RAY OPERATING RECOMMENDATIONS Baseline Data .,....................... Selecting a Unit Tube Warmup , " .. , .. , Maintenance . . . . . . . . . . . . . . . . . . . . . . . . ., Electrical Safety X-Ray Safety , , PART 5: ISOTOPES FOR RADIOGRAPHY .. , . .. Radioactivity , . . . . . . . . . . . . . . . .. Selection of Radiographic Sources PART 6: SOURCE HANDLING EQUIPMENT .. Requirements .. , , Classification . . . . . . . . . . . . . . . . . . . . . . . . .. Manual Manipulation of Sources Remote Handling Equipment Safety Considerations , . . . . . . .. BIBLIOGRAPHY ' , . . . . ..

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SECTION 5: FILM RADIOGRAPIIT

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PART I: FILM EXPOSURE ,.,... Making a Radiograph ' '........ Factors Governing Exposure ,.'., Geometric Principles ,., , ,... Relations of Milliamperage (Source Strength), Distance and Time The Reciprocity Law ' , Exposure Factor .. , . ' , .. , Determination of Exposure Factors Contrast ... '......................... Choice of Film ' ' Radiographic Sensitivity ..' ,' '' '. PART 2: ABSORPTION AND SCATTERING Radiation Absorption in the Specimen ' " Scattered Radiation. . . . . . . . . . . . . . . . . . . .. Reduction of Scatter . ' ,' , . , , . .. Mottling Caused by X-ray Diffraction , Scattering in High Voltage Megavolt Radiography , ,. PART 3: RADIOGRAPHIC SCREENS, ' . '. Functions of Screens ., , .. '........ Lead Foil Screens , .. ' ', ' . .. Fluorescent Screens .. , '., , PART 4: INDUSTRIAL RADIOGRAPHIC FILMS, Selection of Films for Industrial Radiography. Photographic Density , ' ' , . . .. Densitometers , "... X-Ray Exposure Charts, , " ., .. , ... '

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Gamma Ray Exposure Charts , The Characteristic Curve PART 5: RADIOGRAPHIC IMAGE QUALITY AND DETAIL VISIBILITY ., ,....... Controlling Factors , Subject Contrast , , Film Contrast . . . . . . . . . . . . . . . . . . . . .. Film Graininess and Screen Mottle Penetrameters . . . . . . . . . . . . . . . . . . . . . . . .. Viewing and Interpreting Radiographs. . . . .. PART 6: FILM HANDLING AND STORAGE IdentifYing Radiographs Shipping of Unprocessed Films .. '........ Storage of Unprocessed Film , , Storage of Exposed and Processed Film ,

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SECTION 6: RADIOSCOPY AND TOMOGRAPIIT . . . . . . . . . . . . . . . . . . . .. 173 PART 1: FUNDAMENTALS OF RADIOSCOPY.. Principles , ,.................. Background , . . . . . . . . . . . . . .. Basic Technique .,...............'...,. Recommended Practice Image Intensifiers '.' ' Spectral Matching , Statistics Television Cameras, Image Tubes and Peripherals. . . . . . . . . . . . . . . . . . . . . . . .. Optical Coupling , ., Viewing and Recording Systems , . . . .. PART 2: RADIOSCOPIC IMAGE ENHANCEMENT '" , ' Digital Techniques Pseudocolor , '., .. ',.............. Other Techniques ' ... ' . ' ..... ' . . . .. PART 3: X-RAY COMPUTED TOMOGRAPHY . " Introduction , Computed Tomography Systems ., '.... Computed Tomography Applications , .. ,

139 140 141 141 142 142 143 144 144 146 146 151

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SECTION 7: ELECTROMAGNETIC TESTING 199 PART 1: INTRODUCTION TO ELECTROMAGNETIC TESTING . ' " Typical Uses of Eddv Current • Nondestructive Tests. . . . . . . . . . . . . . . .. Method of Induction of Eddv Currents in Materials ' ..... , .. ,. ,'. , ' ... ' , ... , .' Test Material Properties Influencing Eddy Current Tests . ' ' ... ' .... ' ... ,. .".. Methods for Detection of Eddv Current Intensities and Flow Patteri'ls '. Analysis of Eddy Current Test Signals (Amplitudes and Phase Angles) , "

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Selection of Optimum Eddy Current Test Frequencies '" Control of Eddy Current Penetration Depths in Test Materials Limitations of Eddy Current Tests Correlation of Eddy Current Test Indications with Material Properties and Discontinuities :. Typical Industrial Applications of Eddy Current Tests . . . . . . . . . . . . . . . . . . . . . .. Eddy Current Transducers , Factors Affecting Eddy Current Transducers. PART 2: REMOTE FIELD LOW FREQUENCY EDDY CURRENT INSPECTION . . . . . . . . . .. Remote Field Zone . . . . . . . . . . . . . . . . . . . .. Eddy Currents in Pipe Wall Applications . . .. Example Applications . . . . . . . . . . . . . . . . . .. Conclusions ~. . . . . . . . . . . . . . . . . . .. PART 3: ELECTROMAGNETIC SORTING TECHNIQUES . . . . . . . . . . . . . . . . . . . . . . . . .. Eddy Current Impedance Plane Analysis . . .. Impedance Plane Liftoff and Edge Effects on Impedance Plane -. . . . . . . . . . .. Conductivity and Permeability Loci on Impedance Plane . . . . . . . . . . . . . . . . . . .. PART 4: EDDY CURRENT APPLICATIONS IN THE STEEL INDUSTRY. .. . . . . . . . . . . . . . . .. Eddy Current Systems That Rotate the Product at Ambient Temperatures Eddv Current SYstems That Rotate the Sensors . . . .'. . . . . . . . . . . . . . . . . . . . . . .. Tests at Elevated Temperatures PART 5: EDDY CURRENT INSPECTION OF BOLT HOLES. . . . . . . . . . . . . . . . . . . . . . . . . .. Eddy Current Bolt Hole Inspection . . . . . . .. Reference Standards for Bolt Hole Inspection. Procedure for Bolt Hole Inspection Automated Bolt Hole Inspection PART 6: AUTOMOTrVE APPLICATIONS OF EDDY CURRENT TESTING Hardness and Case Depth Inspection of Axle Shafts . . . . . . . . . . . . . . . . . . . . . . . .. Crack and Porosity Detection and Machined Hol~ Presence in Master Brake Cylinders . . . . . . . . . . . . . . . . . . . .. Tin Plate Thickness on Diesel Engine Piston. Cold Headed Pinion Gear Blank Crack Detection . . . . . . . . . . . . . . . . . . . . . . . . .. Hub and Spindle Hardness and Case Depth Inspection Camshaft Heat Treat Inspection . . . . . . . . . PART 7: MULTIFREQUENCY TESTING. . . . . .. Requirements for Multifrequency Testing '" Physical Basis of the Multifrequency Process.

PART 8: MAGNETIC FLUX LEAKAGE TESTING Types of Parts Inspected by Magnetic Flux Leakage . . . . . . . . . . . . . . . .. Types of Discontinuities Found by Magnetic Flux Leakage Effects of Discontinuities . . . . . .. Sensors Used in Magnetic Flux Leakage Inspection Typical Magnetic Flux Leakage Applications .. BIBLIOGRAPHY "

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SECTION 8: MAGNETIC PARTICLE

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TESTING .........•.......•..•.... , 257 PART I: INTRODUCTION. . . . . . . . . . . . . . . . . .. Capabilities and Limitations of Magnetic Particle Techniques . . . . . . . . . . . . . . . . . . . .. Principles of Magnetic Particle Testing. . . . .. PART 2: FABRICATION PROCESSES AND MAGNETIC PARTICLE TEST APPLICATION Basic Ferromagnetic Materials Production. .. Inherent Discontinuities Primary Processing Discontinuities Forging Discontinuities Casting Discontinuities : . . . . . . . . . .. Weldment Discontinuities Manufacturing and Fabrication Discontinuities . . . . . . . . . . . . . . . . . . . . .. Service Discontinuities . . . . . . . . . . . . . . . . .. Corrosion PART 3: MAGNETIC FIELD THEORY Magnetic Domains Magnetic Poles .. . . . . . . . . . . . . . . . . . . . . .. Types of Magnetic Materials . . . . . . . . . . . . .. Sources of Magnetism . . . . . . . . . . . . . . . . . .. PART 4: MAGNETIC FLUX AND FLUX LEAKAGE Circular Magnetic Fields Longitudinal Magnetization Magnetic Field Strength . . . . . . . . . . . . . . . .. Subsurface Discontinuities . . . . . . . . . . . . . .. Effect of Discontinuity Orientation Formation of Indications PART 5: ELECTRICALLY INDUCED MAGNETISM. . . . . . . . . . . . . . . . . . . . . . . . . .. Circular Magnetization . . . . . . . . . . . . . . . . .. Magnetic Field Direction . . . . . . .. Longitudinal Magnetization Multidirectional Magnetization. . . . . . . . . .. .. PART 6: MAGNETIC PARTICLE TEST SYSTEMS Stationary Magnetic Particle Test Systems .,. Power Packs

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258 258 258

259 259 259 260 262 263 263 263 266 266 267 267 267 268 268 270 270 270 271 271 272 272 273 273 273 274 275 276 277 277

Mobile and Portable Testing Units, , ' , , ,.. Prods and Yokes ., PART 7: FERROMAGNETIC MATERIAL CHARACTERISTICS , ,. Magnetic Flux and Units of Measure . . . . . .. Magnetic Hysteresis .......,............ Magnetic Permeability ,.......... PART 8: TYPES OF MAGNETIZING CURRENT. Alternating Current ,............. Half-Wave Direct Current Full-Wave Direct Current ,....... Three-Phase Full-Wave Direct Current .... , PART 9: DEMAGNETIZATION PROCEDURES. Justification for Demagnetizing ,.... Methods of Demagnenzanon , " Demagnetization Practices .. . , . . . . . . . . . ., PART 10: MEDIA AND PROCESSES IN MAGNETIC PARTICLE TESTING ,.. Magnetic Particle Properties , ... ,'....... Effects of Particle Size ,..,....,.......... Effect of Particle Shape ,....... Visibility and Contrast. . . . . . . . . . . . . . .. . . .. Particle Mobility , . . . . . . . . .. Media Selection .. ,.................... Magnetic Particle Testing Processes .. ,.... Conclusion , ,.. BIBLIOGRAPHY , , . . . . . .. SECTION 9: ACOUSTIC EMISSION TESTING . . . . . . . . . . . . . . . . . . • . . . . . ..

J

PART 1: FUNDAMENTALS OF ACOUSTIC EMISSION TESTING , ... , ... ,........... The Acoustic Emission Phenomenon . . . . . . Acoustic Emission Nondestructive Testing. .. Application of Acoustic Emission Tests ..... Successful Applications .... , . . . . . . . . . . . .. Acoustic Emission Testing Equipment . . . . .. Microcomputers in Acoustic Emission Test Svstems Characteristics of Acoustic Emission Techniques " Acoustic Emission Test Sensitivity Interpretation of Test Data ' , , The Kaiser Effect ., " PART 2: BUCKET TRUCK AND LIFT INSPECTION , . . .. Acoustic Emission Inspection Development . Instrumentation for Bucket Truck Inspection. Test Procedure for Bucket Truck Inspection . T:pical Test Data ,............... Acceptance Criteria PART 3: ACOUSTIC EMISSIO\, TESTS OF FIBER REINFORCED PLASTIC VESSELS ..

Testing Procedures for Pressure, Storage and Vacuum Vessels , , , . . . .. Applications in the Chemical Industries . .. Composite Pipe Testing Applications , Effect of Acoustic Emission Tests of Fiber Reinforced Plastic Structures .,........ Zone Location in Fiber Reinforced Plastics ,. Felicity Effect in Fiber Reinforced Plastics .. Acceptance of Acoustic Emission Techniques for Testing of Fiber Reinforced Plastics ,. PART 4: INDUSTRIAL GAS TRAILER TUBE APPLICATIONS " Recertification of Gas Trailer Tubing . . . . . .. Test Procedure for Trailer Tubing Tests ..... Advantages of Acoustic Emission Testing of Trailer Tubes , , ,.. PART 5: RESISTANCE SPOT WELD TESTING . Resistance Spot Welding , ,. Principles of Acoustic Emission Weld Monitoring , Weld Quality Parameters That Produce Acoustic Emission .. ,................ Acoustic Emission Instrumentation for Resistance Spot Welding , . . . . . .. Typical Applications of the Acoustic , ,. Emission Method. , Monitoring Coated Steel Alternating Current Welds............. Alternating Current Spot Welding Galvanized Steel Detecting the Size of Adjacent Alternating Current Welds ," Control of Spot Weld Nugget Size .. . . . . . .. ,. Conclusions :., PART 6: ACOUSTIC EMISSION APPLICATIONS IN UNDERSEA REPEATER MANUFACTURE , , . . . . . . . . . . . .. High Voltage Capacitor in the Repeater Circuitry Unit , ,.............. Instrumentation and Analvsis .. Tubulation Pinchweld on the Repeater Housing , , .. " BIBLIOGRAPHY , , . . . . ..

277 278 278 278 278 280 281 281 281 282 282 284 284 284

286 288

288 289 289 290 290 291 291 292 294

297

298 298 298 300 300 301 302 302 303 303

310

310 312 314 314

316 317 318 318 319 321 322 322 323 324 324

326 327 327 329

329 330

331 331 332

334 339

SECTION 10: INTRODUCTION TO ULTRASONIC TESTING . . . . . . . . .. . . . .. 345

304

PART 1: BASIC ULTRASONIC TESTING Advantages of Ultrasonic Tests ,. Limitati~ns of Ultrasonic Tests " Criteria for Successful Testing PART 2; ULTRASONIC WAVES IK ~IATERIALS. Definition of Wave and Wave Properties .... Ultrasonic Attenuation , ,............. Nonlinear Elastic Waves , ..

30.5 30,5

306 307

308 309 310 xiv

346 346 347 348 :349 350 3.50 350

PART 3: IMPLEMENTATION OF ULTRASONIC TESTING Transmission and Reflection Techniques Ultrasonic Test Systems Ultrasonic Sources Typical Transducer Characteristics . . . . . . . .. Through-Transmission Systems . . . . . . . . . . .. Pitch and Catch Contact Testing Amplitude and Transit Time Systems . . . . . .. B-Scan Presentation C-Scan Presentation . . . . . . . . . . . . . . .. System Calibration ' Major System Parameters PART 4: ULTRASONIC TESTING EQUIPMENT. Basic Ultrasonic Test Systems . . . . . . . . . . . .. Portable Instruments Capabilities of General Purpose Ultrasonic Test Equipment . . . . . . . . . . . . . . . . . . . .. Modular Ultrasonic Equipment Special Purpose Ultrasonic Equipment Operation in Large Testing Systems . . . . . . .. PART 5: OTHER ULTRASONIC TECHNIQUES. Optical Generation and Detection of Ultrasound . . . . . . . . . . . . . . . . . . . . . . . .. Optical Generation of Elastic Waves Optical Detection of Ultrasound. Future Developments in Laser Ultrasonics .. Air Coupled Transducers . Low Frequency Transducers High Frequency Transducers Electromagnetic Acoustic Transducers . . . . .. BIBLIOGRAPHY. . . . . . . . . . . . . . . . . . . . . . . . . ..

351 351 351 352 353 354 354 356 358 359 359 361 363 363 364 367 367 368 369 370 370 370 370 371 371 371 372 373 378

SECTION 11: ULTRASONIC PULSE ECHO TECHNIQUES. . . . . . . . . . . . . . . . . . . . .. 379 PART 1; ULTRASONIC TESTING TECHNIQUES . . . . . . . . . . . . . . . . . . . . . . . . .. The A-Scan Method The B-Scan Method . . . . . . . . . . . . . .. The C-Scan Method .. . . . . . . . . . . . . . . . . .. PART 2: STRAIGHT BEAM PULSE ECHO TESTS. . . Instrumentation for Straight Beam Tests Straight Beam Test Procedures. . . . . . . . . . .. Applications of Straight Beam Contact Tests. Discontinuity Discrimination Discontinuities Detected by the Straight Beam Method . ~. . . . . .. Sizing Discontinuities . . . . . . . . . . . . . . . . . .. Mechanical Scanning Selection of Ultraso~ic Test Frequencies Effects of Ultrasonic Transducer Diameter .. Transducer Near Field

380 380 380 380

:382 382 382 :384 :38.5 386 386 3Ell) 388 388 389

Divergence of Ultrasonic Beams in the Far Field Focused Beam Immersion Techniques. . . . .. Ultrasonic Beam Attenuation by Scattering .. Selection of Test Frequencies . . . . . . . . . . . .. Effect of Discontinuity Orientation on Signal Amplitude Effect of Geometry of Discontinuity on Echo Signal Amplitude " Data Presentation . . " . . . . . . . . . . . . . . . . .. Tests of Multilayered Structures and Composites Dual-Transducer Methods PART 3: ANGLE BEAM CONTACT TESTING. " Verification of Shear Wave Angle Ranging in Shear Wave Tests. . . . . . . . . . . .. Ultrasonic Tests of Tubes Weld Testing . . . . . . . . . . . . . . . . . . . . . . . . .. PART 4: COUPLING MEDIA FOR CONTACT TESTS Use of Transducer Shoes Use of Couplant and Membranes . . . . . . . . .. Use of Delay Lines Selection and Use of Coupling Media Selection of Couplants Operator Techniques to Ensure Good - Coupling PART 5: IMAGING OF PULSE ECHO CONTACT TESTS Ultrasonic Imaging Procedures . . . . . . . . . . .. Contact Weld Tesis . . . . . . . . . . . . . . . . . . . .. PART 6: ULTRASONIC PULSE ECHO WATER COUPLED TECHNIQUES . . . . . . . . . . . . . . .. Immersion Coupling . . . . . . . . . . . . .. ..... Immersion Coupling Devices . . . . . . . . . . . .. Pulse Echo Immersion Test Parameters . . . .. Test Indications Requiring Special Consideration. . . . . . .. Location of Discontinuities. . . . . . . . . . . . . .. Grain Site Discontinuities Interpretation of Indications from Rotor Wheels. . . . . . . . . . . . . . . . . . . . . . . . . . .. PART 7: IMMERSION TESTING OF COMPOSITE MATERIALS . . . . . . . . . . . . . . .. Discontinuities in Composite Laminates .... Ultrasonic Testing of Composite Laminates .. Tests of Composite Tubing . . . . .. . . . . . . . . .. Laminate Test Indications. . . . . . . . . . . . . . Conclusion

SECTION 12: VISUAL TESTI:'\1G PART 1: DESCRIPTION OF VISUAL .AND OPTICAL TESTS .' '

389 390 392 393 394 394 395 395 395 397 397 397 398 398 400 400 400 401 401 402 402 404 404 405 407 407 408 410 411 412 413 414 419 419 419 420 423 423

, 425 426

Luminous Energy Tests Geometrical Optics . . . . . . . . . . . . . . . . . . . .. PART 2: VISION AND LIGHT . . The Physiology ~{s.ight .:::::::::::::::: Vision Acuity . . . . . . . . . . . . . . . . . . . . . . . . .. Vision Acuity Examinations . . ., . . . . . . . . . . .. Visual Angle Color Vision Fluorescent Materials . . . . . . . . . . . . . . . . . .. _ _ Safety for Visual and Optical Tests PART 3: BASIC VISUAL AIDS . . . . . . . . . . . . . . .. Environmental Factors .. , . . . . . . . . . . . . . .. Effects of the Test Object . . . . . . . . . . . . . . .. Magnifiers . . . . . . . . . . . . . . . . . . . . . . . . . . .. Low Power Microscopes . . . . . . . . . . . . . . . .. Photographic Techniques for Recording Visual Test Results . . . . . . . . . .....' . . . .. Image Enhancement. . . . . . . . . . . . . . . . . . .. PART 4: BORESCOPES Fiber Optic Boresoopes Rigid Boreseopes Special Purpose Borescopes . .. Typical Industrial Borescope Applications ... Borescope Optical Systems . . . . . . . . . . . . . .. Borescope Construction _ ..Photographic Adaptations . . . . . . . . . . . . . . .. PART 5: VIDEO TECHNOLOGY Photoelectric Devices : : : : : : : : : : : : :: Phctoemissive Devices Photoconductive Cells or Photodiodes Photovoltaic Devices . . . . . . . . . . . . . . . . . . .. Uses of Photoelectric Detectinz and MeasuringDevices ..... ~............. Photoelectric Imaging Devices . . . . . . . . . . .. Video Borescopes Video Borescope Applications. . . . . . . . . . . .. Principles of Scanning Television Camera Tubes Cathode Ray ViewingTube . . . . . . . . . . . . . Video Resolution . . . . . . . . . . . . . . . . . . . . . .. PART 6: REMOTE POSITIOI'\ING AND TRANSPORT SYSTEMS Fixed Systems ... : : : : : : : : : : : : : : : : : .: Automated Systems

426 426 428 428 429 430 432 432 435 435 440 440 441 443 445

Manual Systems System Selection and Application . . . . . . . . .. PART 7: MACHINE VISION TECHNOLOGY ... Lighting Techniques . . . . . . . . . . . . . . . .. . .. Optical Filtering. . . . . . . . . . . . . . . . . . . . . .. Image Sensors. . . . . . . . . . . . . . . . . . .

465 466 468 468 470 470

SECTION 13: THERMOGRAPHY AND OTHER SPECIAL METHODS •........ 473 PART 1: THE SPECIAL NONDESTRUCTIVE TESTING METHODS . . . . . . . . . . . . . . . . . . .. Relationship between Material Property and Material Behavior PART 2: PRINCIPLES OF INFRARED THERMOGRAPHY Heat Transfer . . . . . . . . . . . . . . . . . . .. Instrumentation and Techniques PART 3: THERMOGRAPHIC APPLICATIONS .. Composite Materials and Structures . . . . . . .. Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . .. Electric Power Distribution and Transmission Systems Pavement, Bridge Decks and Subterranean Surveys ' . . . . . . . . .. Automotive Applications . . . . . . . . . . . . . . . .. Bonded Materials and Structures ... . . . . . .. Diverse Applications . . . . . . . . . . . . . . . . . . .. PART 4: OPTICAL METHODS Grid and Moire Nondestructive Testing. . . .. Holography . . . . . . . . . . . . . . . . . . . . . . . . . .. Shearography Point Triangulation Profilometry PART 5: OTHER SPECIAL METHODS Alloy Identification . . . . . . . . . . . . .. Electromagnetic Special Methods Acoustic Methods .. . . . . . . . . . . . . . . . . . . .. Resistance Strain Gaging

446 447 449 449 450 452 452 453 454 455 457 457 457 457 457 458 458 459 461 461 462 462 463

474 475 478 478 482 486 486 490 491 491 492 493 495 497 49i 498 500 500 503 503 503 505 506

SECTION 14: NONDESTRUCTIVE TESTING GLOSSARy.. . . . . . . . . . . . . . . . . . . . ... 515

46.5 465 465

INDEX

xvi

..............

,.~~

~

.

567

SECTION

INTRODUCT·ION TO NONDESTRUCTIVE TESTING

1

2 / NONDESTRUCTIVE TESTING OVERVIEW

PART 1

NATURE OF NONDESTRUCTIVE TESTING

Definition of Nondestructive Testing Nondestructive testing (NDT) has been defined as comprising those test methods used to examine or ins-pect a part or material or system without impairing its future usefulness. The term is generally applied to nonmedical investigations of material integrity. . Strictly speaking, this definition of nondestructive testing does include noninvasive medical diagnostics. Xvrays, ultrasound and endoscopes are used by both medical and industrial nondestructive testing. In the 1940s, many members of the American Society for Nondestructive Testing (then the Society for Industrial Radiography) were medical X-ray professionals. Medical nondestructive testing, however, has come to be treated by a body of learning so separate from industrial nondestructive testing that today most physicians never use the word nondestructive. Nondestructive testing is used to investigate specifically the material integrity of the 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 to evaluate material properties specifically. Nondestructive testing is concerned in a practical way with the performance of the test piece - how long may the piece be used and when does it need to be checked again? Radar and sonar are classified as nondestructive testing when used to inspect dams, for instance, but not when they are used to chart a river bottom. Nondestructive testing asks "Is there something wrong with this material?" Various performance and proof tests, in contrast, ask "Does this component work?" This is the reason that it is not considered nondestructive testing when an inspector checks a circuit by running electric current through it. Hydrostatic pressure testing is usually proof testing and intrinsicallv not nondestructive ~ but acoustic: emission testing used to monitor changes in a pressure vessel's integrity dt!ring hydrostatic testing is nondestructive testing. Another gray area that invites various interpretations in deHning non-destructive testing is that of future usefulness. Some material investigations involve taking a sample of the inspected part for testing that is inherently destructive. A noncritical part of a pressure vessel ma>' be scraped or shaved 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 destructive and 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 quality control practice of sampling. Sampling (that is, the use of less than 100 percent inspection to draw inferences about the unsampled lots) is nondestructive testing if the tested sample is returned to service. If the steel is tested to verify the alloy in some bolts that can then be returned to service, then the test is nondestructive. In contrast, even if spectroscopy used in the chemical testing of many fluids is inherently nondestructive, the testing is destructive if the samples are poured down the drain after testing. Hardness testing by indentation provides an interesting test case for the definition of nondestructive testing. Hardness testing machines look somewhat like drill presses. The applied force is controlled as the bit is lowered to make a small dent in the surface of the test piece. Then the diameter or depth of the dent is measured. The force applied is correlated with the dent size to provide a measurement of surface hardness. The future usefulness of the test piece is not impaired except in rare cases when a high degree of surface quality is important. However, because the piece's contour is altered, the test is rarely considered nondestructive. A nondestructive alternative to this hardness test could be . to use electromagnetic nondestructive testing. Nondestructive testing is not confined to crack detection, Other discontinuities include porosity, wall thinning from corrosion and manv sorts of disbonds. Nondestructive material characterizatio~ is a grov\ling field concerned with material properties including material identification and microstructural characteristics - such as resin curing, case hardening and stress - that have a direct influence on the service life of the test object. Nondestructive testing has also been defined by listing or dassif}ing the variousmethods, 1.2 This approach is prac" tical in that it typically highlights methods in use by industry.

Purposes of Nondestructive Testing Since the 1920s, the art of testing without destroying the test object has developed from a laboratorv curiosity to an indispensable tool of production. No longer is visual exarnination of materials, parts and complete products the principal means of determining adequate quality. Nonclestmc:tive

INTRODUCTION TO NONDESTRUCTIVE TESTING I

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. The various nondestructive testing methods are covered in detail in the literature but it is always wise to consider objectives before plunging into the details of a method. What is the use of nondestructive testing? Why do thousands of industrial concerns buy the testing equipment, pay the subsequent operating costs of the testing and even reshape manufacturing processes to fit the needs and findings of nondestructive testing? Modem 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 (see 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 control

3

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

Ensuring the Integrity/Reliability of a Product The user of a fabricated product buys it with every expectation that it will give trouble-free service for a reasonable period of usefulness. Few of today's products are expected to deliver decades of service but they are required to give reasonable unfailing value. Year by year the public has learned to expect better service and longer life, despite the increasing complexity of our everyday electrical and mechanical appliances. America has always been a nation on the move. Today our railroads, automobiles, buses, aircraft and ships carry people to more places faster than ever before. And people expect to get there without delays due to mechanical failure. Meanwhile factories tum out more products, better, faster and with more automatic machinery. Management expects machinery to operate continuously because profits depend

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

4 I NONDESTRUCTIVE TESTING OVERVIEW

on such sustained output. The complexity of present-day products and the machinery which makes and transports them requires greater reliability from every part. If a product has one part that has a probability of failure of 1 in 1,000 before it has served a reasonable life, it may be satisfactory. This seems to be a very low chance of failure. Now suppose that a product is assembled from 100 critical parts of various kinds and that each part has a failure possibility of 1 in 1,000. 'What then is the possibility of failure of the assembled item? The overall reliability of any assembly is the mathematical product of the component reliability factors. Overall reliability of this example is then: R

=

0.999 100

'"

0.9057

The possibility of failure of the assembly is then:

(Eq. 1)

1.00 -

0.9057

;;;

0.0943

or almost 1 in 10. It is certain that the user of this product will be highly dissatisfied if lout of every 10 units fails prematurely. The point is that component integrity, and in turn, reliability must be immensely greater than the required reliabilityof the assembled product. Consider the ordinary V-8automobile engine. It has only one crankshaft but eight connecting rods, sixteen valve springs and hundreds of other parts. Theoretically, failure of anyone of these could make the motor useless. Yet how frequently does the car owner experience a part failure? This amazingly low incidence of service failure during the normal life of an automobile is a great tribute to the ability of the automotive engineers to design well, of metallurgists to develop the right materials, of production personnel to cast,

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

FROM BEN BAILEY. USEO WITH PERMISSION.

(Eq.2)

INTRODUCTION TO NONDESTRUCTIVE TESTING I 5

roll, forge, machine and assemble correctly, and of inspectors and quality control staff to set standards and see that the product meets those standards. Preventing Accidents and Saving Lives Ensuring product reliability is necessary because of the general increase in performance expectancy of the public. A homeowner expects the refrigerator to remain in uninterrupted service, indefinitely protecting the food investment, or the power lawnmower to start with one pull of the rope and to keep cutting grass for years on end. The manufacturer expects the lathe, punch press Or fork lift to stand up for years of continuous work even under severe loads. But reliability merely for convenience and profit is not enough. Reliability to protect human lives is a valuable end in itself. The railroad axle must not fail at high speed. The front spindle of the intercity bus must not break on the curve. The aircraft landing gear must not collapse on touchdown. The mine hoist cable must not snap with people in the cab. Such critical failures are rare indeed. And this is mostcertainly not the result of mere good luck. In large part it is the direct result of the extensive use of nondestructive testing and of the high order of nondestructive testing ability now available. Ensuring Customer Satisfaction While it is true that the most laudable reason for the use of nondestructive tests is that of safety, it is probably also true that the most comnwn reason is that of making a profit for the user. The sources of this profit are both tangrble and intangible. Toe intangible source of profit is ensured customer satisfaction. Its corollary is the preservation and improvement of the manufacturer's reputation. To this obvious advantage may be added that of maintaining the manufacturer's competitive position. It is generally true that the user sets the quality level, It is set in the market place when choosing among the products of several competing manufacturers. Certainly the manufacturer's reputation for high quality is only one factor. Others may be function, appearance, packaging, service and price. But in todays highly competitive markets, actual qualityand reputation for quality stand high in the consumer's mind. Aiding in Product Design Nondestructive testing aids Significantly in better product design. For example, the state of physical soundness as

revealed by such nondestructive tests as radiography, magnetic particle or penetrant inspection of a pilot run of castings often shows the designer that design changes are needed to produce a sounder casting in an important section. The design may then be improved and the pattern modified to increase the quality of the product. This example is not academic; it occurs almost daily in many plants. Somewhat outside the scope of discontinuity detection are nondestructive tests to determine the direction, amount and gradient of stresses in mechanical parts, as applied in the field of experimental stress analysis. These play a very important part in the design of lighter, stronger,-less costly and more reliable parts.' -

Controlling Manufacturing Processes Control is a basic concept in industry. Engineers, inspectors, operators .and production personnel know the problems of keeping any manufacturing process under control. The process must he controlled, and the operator must be trained and supervised. When any element of a manufacturing operation gets out of control, quality of the affected product is compromised and waste may be produced. Almostevery nondestructive testing method is applied in one way or another to assist in process control and so ensure a direct profit for the manufacturer. As one example of thousands which could he cited, consider a heat treating operation. The metallurgist sets up a procedure based on sound material of a given analysis. One nondestructive test, applied to all parts or to a few from each batch of parts, tells whether the chemical analysis of the material is so erratic that the procedure will fail to produce the desired hardness or induce cracking. A second test may show when and where cracking has occurred, Another test may show that the desired hardness has not been developed. If so, process variables may be corrected immediately. In these ways, cost and processing time are saved for the manufacturer.

Lowering Manufacturing Costs There are many other examples of both actual and potential cost savings possible through the use of nondestructive tests. Most manufacturers could cut manufacturing costs by deciding where to apply the following cost reduction principle: A nondestructive test can reduce manufacturing cost when it locates undesirable characteristics of a material or component at an early stage, thus eliminating costs offurther processing or assembly. -An example of this principle is the testing of forging blanks before the forging operation. The presence of seams, large inclusions or cracks in 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 hammer time involved in forming the material into the product. Another profit making principle is that a nondestructive test may save manufacturing cost when it produces desirable information at lower cost than some other destructive or nondestructive tests. An example of this principle is the substitution of a magnetic particle nondestructive test for acid pickling to detect seams or cracks. Asit has in many plants, a straightforward economic study of comparative costs of the two methods may show the cost savingadvantage of the nondestructive test over the pickling examination. -

Rapid Growth and Acceptance of Nondestructive Tests . The foregoing tangible and intangible reasons for widespread profitable use of nondestructive tests are sufficient in themselves. But parallel developments have contributed to their growth and acceptance.

Increased Complexity of Modern Machinery Maintaining Uniform Quality Level It seems obvious that improved product quality should be an invariable aim and result of nondestructive testing. Yetthis is not always the case, for there is such a thing as too high a quality level. The true function of testing is to control and maintain the quality level that engineers or design engineers establish for the particular product and circumstances. Quality conscious engineers and manufacturers have long recognized that perfection is unattainable and that even the attempt to achieve perfection in production is unrealistic and costly Sound management seeks not perfection but pursues excellence in management of workmanship from order entry to product delivery. The desired quality level is the one which is most worthwhile, all things considered. Quality below the specified requirement can ruin sales and reputation. Quality above the specified requirement can swallow up profits through excessive production and scrap losses. Management must decide what quality level it wants to produce and support Once the quality level has been established, production and testing personnel should aim to maintain this level and not to depart from it excessively either toward lower or higher quality. In blunt language, a nondestructive test does not improve quality. It can help to establish the quality level but only management sets the quality standard.1f management wants to make a nearly perfect product or wants at the other extreme to make junk, then nondestructive tests will help make what is wanted, no more and no less. In making a drawing for a part, the designer sets tolerances on dimension and finish. If a drawing specifies a certain dimension as 31.8 mm (1.25 in.) but failsto specify the tolerance, the machine shop supervisor rejects the drawing as incomplete or assumes the standard tolerance. In nondestructive testing, a quality tolerance (the tolerance on the characteristic being determined) or criteria for acceptance or rejection must also be specified. The lack of appreciation for this obvious requirement has caused more misunderstanding of nondestructive testing and more objections to nondestructive tests than any other factor. Perhaps it is the cause of more confusion than all other factors combined.

Consider the present-day automobile. First, the manual choke became obsolete. The old rod from the dashboard to a butterfly valve in the carburetor has been replaced by more reliable and efficient metered fuel injection. The mechanically connected brake pedal and brake shoe have given way to hydraulic and antiloek braking systems. The old manual windshield wipers are now powered by vacuum Or electricity and complicated by washer jets and variable timers. Today's components include complex ventilation, heating, defrosting and air conditioning systems, power seats, power actuated windows and sun roofs, expanded electronics, emission controls, cruise controls, stereo equipment, digital gaging and automatic transmissions. The automobile industry, while carrying design complexity to great lengths, has also tremendously raised component reliability. Otherwise, most people would never dare to take their car from the garage for fear of serious failure. As an even more startling example of component reliability arithmetic, consider computers. They require complex microprocessors, chips, resistors, wire connections, counters and other parts whose functioning demands operational reliability in each component. The automobile and the electronic instrument industries are examples of complexity that could never have been achieved without parallel advances in nondestructive testing.

Increased Demand on Machines Within a lifetime, average speeds of railway passenger and freight trains have doubled. The speed of commercial air transport has quintupled. Transonic speeds for rocket powered missiles and for piloted aircraft are not unusual. Automobile. bus and truck speeds have increased and their engines tum twice as fast. Elevators in tall buildings are fully automatic and much faster. with speeds limited only by the comfort of the passengers. The stress applied to parts in these vehicles often increases as the square or cube of the increased velocitv, In the interest of greater speed and rising costs of materials, the design engineer is always under pressure to reduce

INTRODUCTION TO NONDESTRUCTIVE TESTING I 7

weight. This can sometimes be done by substituting aluminum or magnesium alloys for steel or iron, but such light alloyparts are not of the same size or design as those they replace. The tendency is also to reduce the size. These pressures on the designer have subjected parts of all sorts to increased stress levels. Even such commonplace objects as sewing machines, sauce pans and luggage are also lighter and more heavily loaded than ever before. The stress to be supported is seldom static. It often fluctuates and reverses at low or high frequencies. Frequency of stress reversals increases with the speeds of modem machines and thus parts tend to fatigue and fail more rapidly. Another cause of increased stress on modem products is a reduction in the safety factor. An engineer designs with certain known loads in mind. On the supposition that materials and workmanship are never perfect, a safety factor of 2,3, .5 or 10 is applied. Because of other considerations though, a lower factor is often used, depending on the importance of lighter weight or reduced cost or risk to consumer. New demands on machinery have also stimulated the development and use of new 'materials whose operating characteristics and performance are not completely known. These new materials create greater and potentially dangerous problems. As an example, there is a record of an aircraft's being built from an alloy whose work hardening, notch resistance and fatigue life were not well known. After relativelyshort periods of service some of these aircraft suffered disastrous failures. Sufficient and proper nondestructive tests could have saved manv lives. As technology improves and as service requirements increase, machines are subjected to greater variations and to wider extremes of all kinds of stress, creating an increasing demand for stronger materials.

Engineering Demands for Sounder Materials Another justification for the use of nondestructive tests is the designer's demand for sounder materials. As size and weight decrease and the factor of safety is lowered, more and 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 of raw material or of a finished product frequently does not improve quality or performance until that improvement is demanded by the customer. The pressure of the customer is transferred to implementation .ofimproved design or manufacturing. Nondestructive testing is frequently caned on to deliver this new qualitv level.

Public Demands for Greater Safety The demands and expectations of the public for greater safety are apparent evervwhere, Review the record of the

courts in granting higher and higher awards to injured persons. Consider tne outcry for greater automobile safety, as evidenced by the required use of auto 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 Environmental Protection Agency and the Federal Aviation Administration in the United States, and the work of similar agencies abroad, are only a few of the ways in which this demand for safety is expressed. It has been expressed directly by the many passengers who cancel reservations immediately following a serious aircraft accident. This demand for personal safety has been another strong force in the development of nondestructive tests.

Rising Costs of Failure Aside from awards to the injured or to estates of the deceased, consider briefly other factors in the rising costs of mechanical failure. These costs are increasing for many reasons. Some important ones are: L 2. 3. 4.

greater costs of materials and labor; greater costs of complex parts; greater costs due to the complexity of assemblies; 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; and I. failure of a part within an automatic production machine may shut down an entire high speed, integrated, production line. '\.Then production was carried out on many separate machines, the broken one could be bypassed until repaired. Today, one machine is tied into the production of several others. Loss of such production is one of the greatest losses resulting from part failure.

Responsibilities of Production Personnel and Inspectors

Labor today often means a machinery operator. Formerly, a laborer in a shop manually made a part and the work piece received individual attention. Today the laborer may be just as skilled but the skill is directed toward the operation of a machine. The machine requires attention rather 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 some sort of inspection. even if cursory. Today that is seldom the case. Many production operations are covered hy hoods,

8 I NONDESTRUCTIVE TESTING OVERVIEW

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

!

---------..fI QUALITY

PRODUCT DESIGN

SPECIFICATIONS

MANUFACTURING METHODS

CHIEF INSPECTOR

I I

I _ _ J!

PRODUCT SPECIFICATIONS

SAFETY ENGINEEr intervals which make equations easy to manipulate, Scientific Notation. Leakage rates covering many orders of magnitude have been expressed in powers often, e.g" 6 x 10-5, I X 10-9 etc.

Derived 51 Units for Leak Testing The follOWing derived 51 units were adopted for leak testing. Gas quantity. Pascal cubic meter (Pa.m3), The quantity of gas stored in a container Orwhich has passed through a leak is described by the derived 51 unit of pascal cubic meter, the product of pressure and volume. To be strict, the temperature should be specified for the gas volume 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, 101 kPa, and a temperature of 20 °C(293 K). 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. 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~I). Use of the word standard in units such as std cm3·s- I requires that gas leakage rate be converted to standard ternperature and pressure conditions (293 K and 1Ol.325 kPa), often even during the process of collecting data during leak. age rate tests, Expressing leakage rates in the 51 units of Pa·m3·s~1 provides a leakage rate valid at any pressure. Leakage rates given in 51 units of Pa,m3·s- 1 can be converted to units of std cm3·s~1 at any time by simply multiplying the 51 leakage rate by 10 or (more precisely) by 9.87. For conversions, 1 Pa·m',s-l ¢ 10 std cm3·s- l . Gas permeation rate. Pascal cubic meter per second per square meter per meter (Pa.m3·s-I )/(m 2.m- 1 ). Permeation is

INTRODUCTION TO NONDESTRUCTIVE TESTING I 21

the leakage of gas through a (typically solid) substance that is not impervious to gas Row. The permeation rate is larger with an increased exposed area, a higher pressure differential across the substance (membrane,gasket etc.), and is smaller with an increasing thickness of permeable substance. In vacuum testing, the pressure differential is usually considered to be one atmosphere (101 kPa). One sometimes finds units of permeation rate where the gas quantity is expressed in units of mass and where the differential pressure is- expressed in various units. Equation 4 expresses an equivalence for conversion of measurements:

(Eq.4)

Rounding. Many tables and graphs were obtained from researchers and scientists who did their work in the English system. In the conversion, some numbers have been rounded drastically but some were left as irrational numbers in the metric version, especially where quotes were made to specific entries.

a hypothetical wire one meter (1 m) long and one square millimeter (I mm'') in cross section. This comparison is immaterial because no actual wire is involved. Hence, for conformance to S1, this unit could be changed to mlQ·m 2, which reduces to l/Q·m. Because l/Q is also conductivity in siemens (S), material conductivity could be expressed in S/m:

1m

(Eq.6)

Resistivity has sometimes been given in Q·cm, where 1 Q·cm '" 0.01 Q·m.

51 Units for Other Nondestructive Testing Methods Optical Units

51 Units for Electrical and Magnetic Testing Magnetism Units The SI unit for magnetic flux is the weber (Wb), which replaces the maxwell: 1 wb = 108 maxwells. The density of magnetic flux (i.e., how much flux passes perpendicularly through a unit of area) is measured in tesla (T); 1 T = 1 Wb·m- 2 . The older unit is the maxwell per square centimeter, or gauss (G); 10 4 G = 1 T. The gauss meter used in nondestructive testing is now called the tesla meter. Magnetic field strength, formerly expressed in oersted (Oe, a nonexisting physical agent enabling analysis of complex magnetic field problems), is ex-pressed in SI by ampere per meter (A.m~I): lA'm- 1

_

4n:

x

_ L2.57

10-:' Oe X

1O~2

(Eq.5)

Oe

Vision requires a source of illumination. The light source is the candela (cd), defined as the luminous intensity in a given direction of a source that emits monochromatic radiation of 540 x 10 12 hertz (Hz) at a radiant intensity of 1/683 watt per steradian (W·sr~I). ' The luminous flux in a steradian (sr) is measured in lumens (Irn). The measurement in lumens is the product of candela and steradian (11m", Lcd-sr), A light [lux of one lumen (11m) striking one square meter (1 m 2) on the surface of the sphere around the source illuminates it with one lux (1 lx), the unit of illuminance. If the source itself is scaled to one square meter (1 m2 ) and emits one candela (1 ed), the luminance (formerlv called brightness) of the source is 1 cd·m-2 . ' Some terms have been replaced. Illumination is now illuminance; brightness is luminance; transmission factor ,is transmittance. Meter-candle is now lux and nit is candela per square meter (cd-rrrJ and tertiary creep. See also deformation. 8 . creep strength: The constant nominal stress that will a specified creep rate at constant temperature.f crevice corrosion: See corrosion, crevice. critical angle: .The in._c.i~ent angle of an u.ltrasoun.d bearp].:. above which a specific mode of refracted energy n : longer exists.7JO .,.: cross line grating: In moire and grid nondestructive testing, a grating with bars, furrows or lines parallel orthogonal xy axes.? cross talk: The unwanted signal leakage (acoustical or electrical) across an intended barrier, such as leak between the transmitting and receiving elements of dual transducer. Also called cross noise and cross c piing. i,12 CRT: See cathode ray tube.'~ crush: A casting discontinuity caused by a partial destruc . •J tion of the mold before the metal was poured.' crushing: T.he pushin.g out of shape of a sand core or sanl.'.•.•. .•.~ mold when two parts of the mold do not fit properl.J where they meet. 3 ." crystal: See transducer: crystal mosaic: Multiple crystals mounted in the plane on one holder and connected so as to cause all vibrate as one unit,i,12 crystal, X-cut: A cut such that the cut face isperpendicu I~ lar to the X-direction of the piezoelectric crystal. In , . 1 quartz slice so cut, a thickness mode of vibration occurs when the slice is electrically stimulated in th(' \ X-direction.7,12:1 crystal, Y-cut: In Y-cut, the cut face of the piezoelectric # crystal is perpendicularto the Y-direction. In quartz, shear mode of vibration is obtained when the slice electrically stimulated in the Y~direction.7.l2 cumulative bursts: The number of bursts detected from the beginning of the test. 5 ..

.

526 I NONDESTRUCTIVE TESTING OVERVIEW

cumulative characteristic distribution: A display of the number of times an acoustic emission signal exceeds a preselected characteristic as a function of the eharacteristic.P

cumulative count: The number of times the amplitude of an acoustic emission signal has exceeded the threshold since the start of a test. 5 cumulative events: The number of events detected from the beginning of a test. Use of this term is restricted in the same way as event counting," cup fracture: Fracture, frequently seen in tensile test places of a ductile material, in which the surface of failure on one portion shows a central flat area of failure in tension, with an exterior extended rim of failure in shear. Also called cup-and-cone fracture. 2 Curie point; The temperature at which ferromagnetic materials lose residual magnetism and can no longer be magnetized by outside forces (between 650 and 870°C [1,200 and 1,600 OF] for most metals).6.16 current flow technique: Magnetizing by passing current through an object using prods or contact heads. The current may be alternating current or rectified alternating current.6.16 curre.nt in~uction tec~~iq.uei M.a.gne~z.ation in Which a . circulating current IS induced m a nng component by the influence of a fluctuating magnetic field. 6.l6 cutoff frequency: Upper or lower spectral response of a filter or amplifier, at a specified amount less (usually 3 or 6 dB) than the maximum response.' cycle: A single period of a waveform or other variable. See 1 period.:

I

o damping: (1) Limiting the duration or decreasing the amplitude of vibrations, as when damping a transducer element.P (2) A deliberate introduction of energy v absorbers to reduce vibrations.' damping capacity: A measure of ability of a material to dissipate mechanical energy.7.1S damping material; A highly absorbent material used to I cause rapid decay of vibration.' ldamping, transducer: A material bonded to the back of the piezoelectric element of a transducer to limit the duration of vibrations.'.l° damping, ultrasonic: Decrease or decay of ultrasonic wave amplitude with respect to time or distance.v'? dark adaptation: (1) Adjustment of the eye over time to reduced illumination, including increased retinal sensitivity, dilation of the pupil and other reflex physical changes. 2 .6.16 (2) Process by which the retina becomes adapted to luminance less than about 0.034 cd·m-2. 8.2o

dark adapted vision: See scotopic vision. daubing: The act offilling cracks in cores' dead zone: In ultrasonic contact testing, the interval following the initial pulse at the surface-of a test object to the nearest inspectable depth. lO Any interval following a reflected Signal where additional Signals cannot be detected.' deburrlng: Removing burrs, sharp edges or fins from metal objects by flling, grinding or rolling the work in a barrel with abrasives suspended in a suitable liquid medium. Sometimes called burring. 2.3 decarburization: The loss of carbon from the surface of a ferrous alloy as a result of heating in a medium that reacts with the carbon at the surface.f decibel: A unit for expressing power relationships in sonic and acoustic measurements. Equal to ten times the base ten logarithm of the ratio of two powers. The unit for voltages is twenty times the base ten logarithm of the ratio Oftwo voltages, provided the voltages are measured across equal impedances.' deep drawing: The forming of deeply recessed parts by means of plastic flow of the materialf deep etching: Severe etching of a metallic surface for examination at a magnification of ten diameters or less to reveal gross features such as segregation, cracks, porosity or grain flow. 2 defect: A discontinuity whose size, shape, orientation or location make it detrimental to the useful service of its host object or which exceeds the accept/reject criteria of an applicable specification.v'? Note that some discontinuities mav not affect serviceability and are therefore not defe~ts.2 All defects are dIscontinuities. 2 Compare discontinuity and indication. 8.19 deformation: Change of shape under load. See also creep and elastic deformation. S degasifier: A substance that can be added to molten metal to remove soluble gases that might otherwise be occluded or entrapped in the metal during solidification.? degassing: Removing gases from liquids or solids.P degreasing fluid: Solvents or cleaners employed to remove oil and grease from test surfaces before the liquid penetrant is applied. 2 delamination: A laminar discontinuity, generally an area of unbonded materials.' ' , delay line: A material (liquid or solid) placed in front of a transducer to cause a time delay between the initial pulse and the front surface reflection.'.l2 delayed sweep: An A-scan or B-scan sweep, the start of which has been delayed, thereby eliminating the appearance of early response data on the screen. 7.2.1 delayed time base: See delayed sweep.

NONDESTRUCTIVE TESTING GL.OSSARY 1527

detector probe: An adjustable or fixed device delta effect: Reradiation of energy from a discontinuity.12 which air and/or tracer gas is drawn into the leak test The reradiated energy may include waves of both inciinstrument and over the sensing element or de1:ecl:~81' dent mode and converted modes (longitudinal and shear)," Also called a sampling probe or a sniffer probe. 1 detector probe test: A pressure leak test in which delta ferrite: Solid solution with body centered cubic leakage of a component, pressurized with a tracer ri . structure and iron as solvent. Also called delta iron. 8 mixture, is detected by scanning the test object bou delta iron: See delta ferrite. ary surface with a sniffer probe connected to an e delta t (At): The time interval between the detected arrival .. . tronic leak detector. Leakage tracer gas is pulled from of an acoustic emission wave at two sensors.P demagnetization: The reduction of residual magnetism to " . an acceptable leveL6.l6 the' real< test instrument.' Also called sniffer test. demagnetizing coil: A coil of conductive material carrying detergent r.emove.r: A penetrant re.mover that is a. sOl.Util·· •.· . • .•. alternating current used for demagnetization. 6,15 of a detergent in water. 2 ); demodulation: A modulation process wherein a wave developer: (1) In penetrant testing, a material that IS resulting from previous modulation is employed to applied to the test piece surface after the excess pen~ derive a wave having substantially the characteristics of trant has been removed and that i~d~si~ed to enham 1 the original modulating wave.v!" the penetrant bleedout to form indications. May be J dendrite: A crystal that has a treelike branching pattern, fine powder, a solution that dries to form a dry powder being most evident in cast metals slowlycooled through or a..susp..e~sio~ (in solvent or w.ater) tfat dries l~avi1"··.l.• . the solidification range. 2.3 an absorptive film on the test surface.f (2) In radiogr I deoxidizing: (1) The removal of oxygen from molten metphy,a chemical solution that reduces exposed silver als by use of suitable deoxidizers. (2) Sometimes refers halide crystals to metallic silver.l l . to the removal of undesirable elements other than oxydeveloper, dry: A dry, fine powder applied to the test piec J gen by the introduction of elements or compounds th~t after the excess penetrant is removed and the surface readily react with them. (3) In metal finishing, the dried in order to increase the bleedout by means of removal of oxide films from metal surfaces bv chemical capillary action.f .. or electrochemical reaction.' developer, nonaqueous: See developer, solvent. developer, soluble: Fine particles completely soluble in its depth compensation: See distance amplitude correction. depth of field: In photography, the range of distance over carrier (not a sus p. ension of powder .in a liquid) th".·.!:.l.• dries to form an adsorptive coatmg." ,I which an imaging system gives satisfactory definition developer, solvent: Fine particles suspended in a volatile when its lens is in the best focus for a specific distance." solvent. The volatile solvent helps to dissolve the penedepth of fusion: The depth to which the base metal melted trant out of th~ dis~o.ntinui~ a~d ~rin~s it to the su during welding.s face. It then dries, flXlng the indication.f depth of penetration: In electromagnetic testing, the developer, wet: A penetrant developer usually supplied as depth at which the magnetic field strength or intensity ~ry particle~ tha~ is mixed with water to form a suspeJj of induced eddy currents has decreased to 37 percent sion of partlcles.-. . "J of its surface value. The square of the depth of penetradeveloping time: Elapsed time necessary for the applied tion is inversely proportional to the frequency of the de.v.eloper to abso~b and show indications from. pene-.·.. signal, the conductivity of the material and the permetrant entrapments.' ;~l ability of the material. Synonymous terms are standard dewaxing: Removing the expendable wax pattern from a:ti depth of penetration and skin depth. See joint penetrainvestment mold by heat or solvent," tion, root penetration and skin effect. 2.4.13 dewetting: The flow and retraction of liqu_id on a surfaei ] descallng: Removing the thick layer of oxides formed on caused by contaminated surfaces or dissolved surfac "I some metals at elevated temperatures.i coatings." deseaming: Analogous to chipping, the discontinuities diamagnetic material: A material whose relative perm€' being removed by gas cutting. 2 . ability is less than unity. The intrinsic induction B; detail: In radiography, the degree of sharpness of outline of oppositely directed to applied magnetizing force the image. If a radiograph does not show a clear definiA material with magnetic permeability less than 1.6 tion of the object or a discontinuity in the object, it is of die casting: (1) A casting made in a die. (2) A casting pH little value although it may have sufficient contrast and cess where molten metal is forced under high pressUl density.!l into the cavity of a metal mold. 3 detector coil: See sensing coil.4 difference cylinder: See background cylinder.

~ ~:J:~~~r~~11e~~ ~~:bl~n~~~~~: St~:si~~~I:t~:I;']

528 / NONDESTRUCTNE TESTING OVERVIEW

differential amplifier: An amplifier whose output signal is proportional to the algebraic difference between two input signals. 4 ,14

!!:;t~idiffe~:~~y ~:~~~pi::c~~s~:::e~;:;~~~~ri:~j~~;~~i~;~

such that an unbalance between them, causing a signal,

will be produced only when the electromagnetic conditions are different in the regions beneath two of the coils. In contrast, comparator coils are not adjacent.' differential measurement: In electromagnetic testing, the imbalance in the system is measured using differential coils ~ in contrast to absolute measurement and comparative measurement. 4,13

j;~n::~~d ;~~:~~~~let~tr~:ak;~~ ~~;~~' :~t:u~f

change with respect to time. 4.13 ~'r'racoon: In ultrasonic testing, the deflection of a wave•. fro.nt w~en passing the edge of an ultrasonically opaque

'

obJectI~

l.

diffuse indications: Indications that are not clearly defi~ed. as, for example, indications from surface con• tamination." diffuse reflection: Scattered, incoherent reflections from rough surfaces. 7.l O

frrusion: The process b~ which ~olecules intermingl~ as.~ result of concentration gradients or thermal motion.Spreading ofa gas through other gases within a volume. ",. UIa~on: In image pr?ces~ing, the c,' on~.ition ?f a b.inary j Image where the pixel m the output Image IS a 1 If any of its eight closest neighbors is a 1 in the input image. ' \. See also closing, erosion and opening. 8 p rin~e: A means o~ removin~ exces~ surface penetr~nt in which the test objects are dipped into a tank of.agitated water or remover. 2 rec~ contact magnetization: See current flow techtuque. direct' current: An electric current flowing continually in t one direction through a conduetor.v'? ;rect current field: Ail active magnetic field produced by direct current flowing in a conductor or COil. 6,I7

r

"l.•

.r"rec,t pho",tome,try: Sim,ultan,e~us comparI,8,20 'son of a, s"tandard lamp and an unknown light source. ect substitution alloy: Alloy in which the atoms of the alloying element Can occupy the crystal lattice spaces normally occupied by the atoms of the parent metal," !.I·ect viewing: Viewing of a test object in the viewer's immediate-presence. The term direct viewing is used in the fields of robotics and surveillance to distinguish \ conventional from remote viewing.8 direct vision instrument: Device offering a view directly forward. A typical scene is about 19 rnrn (0.75 in.) wide , at 25 mm (1 in.) from the objective lens." .Jrectional lighting: lighting provided on the work plane or object predominantly from a preferred direction. s,2o .

I

directional properties: Properties whose magnitudes depend on the relation of the test axis to the specific direction in the metal, resulting from preferred orientation or from fibering in the structure. See anisotropy. 2 directional solidification: The solidification of molten metal in a casting in such manner that feed metal is always available for that portion that is just solidifying.3 dlscernible image: Image capable of being recognized by sight without the aid of magnification. 2 discontinuity: An intentional or unintentional interruption in the physical structure or configuration of a part. 6•8,16.22 After nondestructive testing, unintentional discontinuities interpreted as detrimental in the host object may be called flaws or defects," Compare defect, dislocation and indication. discontinuity, artificial: Reference discontinuities such as holes, indentations, cracks, grooves or notches that are introduced into a reference standard to provide accurately reproducible indications for determining sensitivity Ievels.? discontinuity, inherent: Material anomaly originating from solidification of cast metal. Pipe and nonmetallic inclusions are the most common and can lead to other types of discontinuities in fabrication.f-'? discontinuity, primary processing: Material anomaly produced from the hot or cold working of an ingot into forgings, rod and bar.8 .l 9 discontinuity, secondary processing: Material anomaly produced during machining, grinding, heat treating, plating or other finishing operations. S,19 discontinuity, service induced: Material anomaly caused by the intended use of the part. 8 dislocation: Void or discontinuity in the lattice of a metal crystalline structure.f Two basic linear types are recognized (edge dislocation and screw dislocation) but combinations and partial dislocations are most prevalent.i dispersion: The variation of phase velocity with frequency. 7 dispersive medium: A medium in which propagation velocity depends on the wave frequency.' displacement resolution: In moire and grid nondestructive testing, measurement precision expressed as the smallest displacement that can be determined with reasonable reliability" dissociation: The breakdown of a substance into two or more constituents.t distal: In a manipulative or interrogating system, of or pertaining to the end opposite from the eyepiece and farthest from the person using the system. Objective; tip.8 distance amplitude correction (DAC): Compensation of gain as a function of time for difference in amplitude of reflections from equal reflectors at different sound travel distances. Refers also to compensation by electronic means such as swept gain, time corrected gain, time variable gain and sensitivity time controP,12

NONDESTRUCTIVE TESTING GLOSSARY I

divergence: A term used to describe the spreading of ductility: The ability of a material to deform plastical ultrasonic waves beyond the near field. It is a function without fracturing, being measured by elongation or of transducer diameter and wavelength in the :eductio? of area in ate.n.isile test, by height of cuppinru,;.',.:.• medium.' III an Erichsen test or by other means.2;",~ domain: A saturated macroscopic substructure in ferrodwell time: The total time that the penetrant or emulsifier magnetic materials where the elementary particles is in contact with the test surface, including the (electron spins) are aligned in one direction by interrequired for application and the drain time. 2 atomic forces. A saturated permanent magnet. 6.l O dynamic creep: Creep that occurs under conditions dose: The amount of ionizing radiation energy absorbed" fluctuating load or fluctuating temperature.f per unit mass of irradiated material at a specific loca- " od.yn:;j,~ic r:mge: The ratio ~f ~aXi:num to minimum refJe(.·.·•.-•. •.~•. tion, such as part of the human body. Measured in rems tive 'are~s that can be distinguished on the cathode' ra.~ and rads. ll tube'at a constant gain setting.'·23.M dose rate: The radiation dose delivered per unit time and measured, for instance, in rems per hour. See also E dose. 11 dosimeter: A device that measures radiation dose, such as a echo: A signal indicating reflected acoustic energy.'_. film badge or ionization chamber.lECT: Eddy current testing. 1 eddy current: An electrical current induced in a conducte! double crystal method: A method of ultrasonic testing that uses two transducers, one transmitting and the by a time varying magnetic field. 4 7 10 other receiving. . . eddy current testing: A nondestructive testing method drag: The bottom section of a flask, mold or pattern. 3 which eddy current flow is induced in the test objec . • •. Changes in the flow caused by variations in the object dragout: The carryout or loss of penetrant materials as a are reflected into a nearby coil, coils, Hall effect device result of their adherence to the test pieces." drain time: That portion of the dwell time during which or .other ~agnetic f1u~ sensor forsu?sequent analysis 1.1··. suitable instrumentation and techmques. 4•I3 ; the excess penetrant, emulsifier, detergent remover or developer drains off the test piece.? edge or end effect: In electromagnetic testing, the disturdrop: A discontinuity in a casting due to a portion of the banceorof. th.e magne.. tic field and eddy cUrrents due. tl.l.·•. sand dropping from the cope or overhanging section of the proximity of an abrupt change in geometry. The ... effect generally results in the masking of discontinuities the mold.3 drop out: The falling away of green sand from the walls of a 1 within the affected region. 4 ,13 mold cavity when the mold is closed.' effe~tive dep~ .of penetration: In elec~romagnetictest, dross: The scum that forms on the surface of molten metals mg, the mmrmum depth beyond which a test system' largely because of Oxidation but sometimes because of can no longer practically detect a further increase in object thickness. If the minimum thickness for the fre the rising of impurities to the surface. 3 quency used is not exceeded or the object thickness dry bulb temperature: Alternate term for ambient or atnot rigidly controlled, the test may be influenced by the mospheric temperature. 1 object thickness.P Depending on the criteria, this min " dry powder: Finely divided ferromagnetic particles select. ed and prepared for magnetic particle testing. 6.10 imum thickness is three to seven times the skin depth.~O material at which discontinuities can be) \ powder form. 6,16 effective throat: In welding, the weld throat including th6. J drying oven: An oven used for drying rinse water from test pieces.r amount of weld penetration but ignoring excess metal between the theoretical face and the actual face.8 drying time: The time allotted for a rinsed or cleaned test piece to dry.Z elastic constants: Modulus of elasticity, either in tension, compression or shear and Poisson's ratio. 2 dual response penetrant: A penetrant that produces discontinuity indications that can be seen under either elastic deformation: Temporary change in shape under a load. The material returns to its original size and shape I ultraviolet light or visible light. 2 after the load is removed. Elastic deformation is the .1 dual transducer: A single transducer containing two piezostate in which most metal components are used in serelectric elements, one for transmitting and one for vice.8 receiving.'·12 ductile crack propagation: Slow crack propagation that is elastic limit: The maximum stress to which a material accompanied by noticeable plastic deformation and be subjected without any permanent strain remaining on complete release of stress." requires energy to be supplied from outside the body.2 I.'.,.;.i.1 ....

il·.

•

Q

I NONDESTRUCTIVE TESTING OVERVIEW

·~.~!rlasticity: The

ability of a material to resume its former shape after deformation.f electric arc welding: Joining of metals by heating with 111 electric arc. Also called arc welding. 8 >pen sand casting: Any casting made in a mold that has no I cope or other covering.' rning~ I~age. pr,ocessing operati~:>n. of er~sion foll~wed by dilation. A smgle opemng eliminates Isolated smgle . pixels. See also closing.S ~in: See visual purple. :ltic disk: Area in the retina through which the fibers from the various receptors cross the inner (vitreous humor) ! side of the retina and pass through it together in the optic .J . nerve bundle. This transitional area is completely blind.s ptimum frequency: The frequency that provides the highest signal-to~noise ratio compatible with the detection of a specific discontinuity. Each combination of discontinuity type and material may have a different optimum frequency.7.l2

b

'. J

organoleptic: Relying on or using sense organs, such as the human eye. s orientation: The angular relationship of a surface, plane, discontinuity or axis to a reference plane or surface. 7.IO orthicon: See image orthicon. oscillogram: Common term for a record or photograph of data displayed on the cathode ray tube face.7.l2 ounces per year (oz/yr): Units defining the size of a leak as the weight of refrigerant gas that will pass through the leak in one year.l outgassing: Forms of gas coming from material in a vacuum system. Includes gases adsorbed on the surface, dissolved in material, trapped in pockets and those due to evaporation or condensation. 1 overall integrated leakage rate: The total leakage through all leakage paths including containment welds, valves, fittings and components that penetrate a primary reactor containment system, expressed in weight . percent of contained air mass per day. I

p pancake coil: A probe coil whose axis is normal to the surface of the te-st material and whose length is not larger than the radius." parafoveal vision: See scotopic vision. parallax: The apparent difference in position of an imaged point according to two differently positioned sensors." parallel mag-netization: A magnetic field induced in magnetizable material placed parallel to a conductor carrying an electric current. 10 Not a recommended practice for magnetic particle testing." paramagnetic material: In electromagnetic testing, a material that has a relative permeability slightly greater than unity and is practically independent of the magnetizing force. 4 ,l .3 parameter distribution: A display of the number of times the acoustic emission parameter falls between the values x and x -+ Ox as a function of x. Typical parameters are amplitude, rise time and duration." parasitic echo: See spurious echo. particle motion: Mov~ment of particles of material during wave propagation.' parting line: The mark left on the casting where the die halves meet. Also, the surface between the cover and ejector portions of the die.3 parting sand: Fine sand for dusting on sand mold surfaces that are to be separated.' parts per million (ppm): Concentration of a specific gas in another gas or gas mixture, For example, a tracer gas concentration might be 10 ppm in air Or nitrogen. The mare specific term JlUL is often used, with ppm to indicate proportion by volume.'

NONUJ:~ I KU\.IIVI:: 11:.3! " ..... "".........., ....

pass: In welding, a single bead along the entire weld length penetration time: The time allowed, after penetrant or the process of laying down that bead. S . been applied to a surface, for the penetrant to enter pattern: A form of wood, metal or other material, around continuities that may be present. The length of which a molding material is placed to make a mold for elapsing between the application of the penetrant casting metals. 3 · · the test object and the removal of the penetrant.f pearlite: Platelet mixture of cementite and ferrite in steels penetration, ultrasonic: Propagation of ultrasonic enl~rE··~·~ or in alpha and beta phases in nonferrous alloys." into a material. See also effective penetration.' peeling: (1) The dropping. away of sand from the casting period: The absolute value of the minimum inteVlrv,aal·~tbril which the same characteristics of a periodic v' d. uring shakeout. I (2) The detaching of one layer of a .. coating from another or from the basic metal, because .'._ . or a periodic feature return.t-l" of pQoradherence.? . perip'11eral vision: The seeing of objects displaced t.he.p.p'ffiary line of Sight and outside the central pencLI source: An arti ficial source using the fracture 0 f a field.8.~ brittle graphite lead in a suitable fitting to simulate an . . . acoustic emission event. 5 permanent magnet: An object possessing the ability retain an applied magnetic field for a long period penetrability: The condition of being penetrable so that time after the active power of the field has liquid can enter into very fine openings such as cracks. removed.v-? Often erroneously used to describe the property of a permanent mold: A metal mold of two or more parts pene~ran\ that causes it to find its way into very fine repeatedly for the production of many castings of t opemngs.same form.' penetrameter: A strip of metal the same composition as permeabili.·ty: (1) A ?en.eral. t~.rm for various r~l~tionshi.c.-c.".l.'. that of the metal being tested, representing a percent-between magnetic induction and magnetIzmg fonl. age of object thickness and provided with a combmaThese relationships are: (a) absolute permeability (the tion of steps, holes or slot or alternatively made as a quotient of a change in magnetic induction divided wire, When placed in the path of the rays, its image the corresponding change in magnetizing force):, provides a check on the radiographiC technique (b) specific (relative) permeability (a pure number that employed. 3 .11 Also called im.age quality-indicator. is the same in all unit systems). The value and dim~~penetrant: A liquid capable of entering discontinuities Sio~ of absolute permea?ility d~pend ~n. the syste.n:.. . ·..1f open to the test surface and that is adapted to the peneunits employed. In anisotropic media, permeabf trant test process by being made highly visible in small becomes a rnatrix.v'" (2) The characteristic of materials traces. Fluorescent penetrants fluoresce brightly under th.at ..allows .ga.ses or liqUi~. S. to pass throub.~~ the.r~.'.~. ultraviolet light and visible penetrants are intensely col(3) The ratio of flux density B to magnetizing fI F ored to be readily visible on developer backgrounds strength H. High permeability materials are easiertfo when illuminated with visible light 2 magnetize than low permeability materials.f penetrant comparator: See comparator; penetrant. phantom: A reference standard used to verify the perf penetrant leak testing: A technique of penetrant testing mance of ultrasound systems. t . in which the penetrant is applied to one surface of a test phase: In metallurgy, a physically homogeneous portion of a material system, specifically the portion of an a material while the opposite surface is tested for indications that would identify a through leak or void passing characterized by its microstructure at a particular . perature during melting or solidification.s through the material thickness.f penetrant testing: Nondestructive testing method using phase analy.sis.: .An an~yt·.ical. :e.chnique. th~t dis.Crim.in,.. •·. . ·.•. .•~~s between variables m an ob]ect undergom£:~ electron: : penetrant. netic testing by the different phase angle changes that penetrant, fluorescent: A penetrant characterized by its h di d' h al S 1 ability to fluoresce when excited bv ultraviolet lizht." te.se con·ti.·on.s pro.uce m t e test sign. ee a.•...~.o • • v phase detection.4j., .! penetrant, post emulsifiable: A penetrant that requires phase angle: The angular equivalent of the time displ~t~the application of a separate emulsifier to render the ment between corresponding points on two sine waves of the same frequencyv'" . excess surface penetrant water washable.f penetrant, visible: A penetrant characterized by an intense phase contrast microscope: See microscope, phase visible color dye that allows it to give contrasting indicatrast. tions on a white developer background.? phase detection: 'The derivation of a Signal whose arr~i. penetrant, water washable: A penetrant with built in tude is a function of the phase angle between two alk emulsifier that makes it directly water washable.f nating currents, one of which is used as a reference.";~3 j

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NONDESTRUCT'VE TEST'NG OVERVIEW

diagram: Graph showing the temperature, pressure and composition limits of phase fields in a material system. Also called a constitution diagram. Compare equilibrium diagram. 8 shift: A change in the phase relationship between two alternating quantities of the same frequency.4.l3 ehase velocity: The velocity of a single frequency continuous wave." Ii ase-sensitive system: A system whose output signal is - dependent on the phase relationship between the volt-

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age retume.d. 4fr,?m a pickup or sensing coil and. a reference voltage. ,l cl . phased array: A mosaic of transducer elements in which .. the timing of the elements' excitation can be individually controlled to produce certain desired effects, such as steering the beam axis or focusing the beam.' phasor quantity: Any quantity that is expressed as a com1 plex number. See impedance. 4.15 FPtoconduction: Method by which a vidicon television camera tube produces an electrical image, in which conductivity of the photosensitive surface changes in relation to intensity of the light reflected from the scene focused onto the surface. Compare phatoemission. 8 f>J:t?toelasticity: The effect of a material's elastic properties I on the way that it refracts or reflects light. s ) htoelecmc effect: Emission of electrons from a surface bombarded by sufflciently energetic photons. Such . 'll.emissions :nay be, used i~ an illuminance meter and may be calibrated m IlLX.8._0 . )notoemission: Method by which an image orthicon television camera tube produces an electrical image, in 1,,:hich .a photosensitive. surface ~mi~s electrons when J light reflected from a viewed object IS focused on that surface. Compare photoconduction. 8 I~ )tometer: The basic measuri~g inst~ment of p~10t?me­ J try. Accurate meters measunng radiant energy Incident on a receiver, producing measurable electrical quanti. 8 . I ties. ] J1tometric brightness: The luminance of a light souroe.f h •tometry: The science and practice of the measurement of light or photon-emitting electromagnetic radiation. 1See also relative photometry. 8 I .lton: Particle of light,S hotopie vision: Vision adapted to daylight and mediated [mainiy by the cones. Vision is wholly photopic when the jluminance of the. test surface is above 0.034 cd-rn? (0.0032 cd·ft-'!). Also known as foveal vision and light jadapted vision. Compare mesopic vision and scotopic luision. S,20 ~vtoreceptor: Light sensor," . iysical properties: Nonmechanical properties such as \densitY, electrical conductivity, heat conductivity and !thermal expansion, 2 eture element: See pixel.

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picture processing: See image processing. piezoelectric effect: The ability of certain materials to convert electrical energy into mechanical energy and vice versa, i.12 pinhole porosity: Porosity, in either castings or metal .. formed by electrodeposition, resulting from numerous small holes distributed throughout the metal." pipe: (1) The central cavity formed dUring solidification of metal, especially ingots, by thermal contraction. (2) The discontinuity in wrought or cast products resulting from such a cavity. (3) An extrusion discontinuity due to the Oxidized surface of the billet flowing toward the center of the rod at the back end. (4) A cast, wrought or welded metal tube. 2 pitch and catch: Test technique in which ultrasonic energy is emitted by one transducer and received by another on the same or opposite surface.P Also called pitch-catch, two transducer technique or dual crystal method.' pitting: Discontinuity consisting of surface, cavities. See also cavitation fatigue and pitting fatigue. S pitting fatigue: Discontinuity consisting of surface cavities . typically due to fatigue and abrasion of contacting surfaces undergoing compressive loading. See also cavitation fatigue and pitting. 8 pixel: A lighted point on the screen of a digital image. Picture element. S Planck's Distribution Law: The distribution criterion for blackbody radiation. plane of focus: See focus, principal plane of plane wave: A wave in which points of same phase lie on parallel plane surfaces.U" plaster molding: Molding where a gypsum bonded aggre~ gate flour in the form of a water slurry is poured over a pattern, permitted to harden and is thoroughly dried after removal of the pattern. The technique is used to make smooth nonferrous castings of accurate size.3 plastic deformation: Deformation that does or will remain permanent after removal of the load that caused it. 2 plate wave: See Lamb wave. platelet: Flat crystallites in certain phases of steel," plunger machines: Die casting machines having a plunger in continuous contact with molten metal.' point of incidence: In ultrasonic testing, the point at which the center of the sound beam leaves the plastic wedge of an angle beam transducer and enters the test object. 12 See probe index.' polarizing microscope: See microscope, polarizing. pole: See magnetic pole. poling: The process of reorienting crystal domains in certain materials by applying a strong electric field at elevated temperatures. Materials (usually ceramics) so treated exhibit piezoelectric behavior,"

NONDESTRUCTIVE TESTING GLOSSARY I

pores: (1) Small voids within a metal. (2) Minute cavities, some~mes intenti0r:al, i~ a powder metallurgy ~om.ract. (3) Minute perforations in an electroplated coating.~ porosity: A discontinuity in metal resulting from the ereation or coalescence of gas. Very small pores are called pinholes. S.19 positive sliding: The rolling and sliding of meshing gears or rollers when directions of rolling and sliding are the same. s postcleaning: The removal of penetrant testing residues from the test piece after penetrant test processing is

completed.'

-

postemulsification: A penetrant removal technique employing a separate emulsifier applied over the surface penetrant to make it removable with water spray.2 poultice corrosion: See corrosion, poultice. pouring basin: A basin on top of a mold to receive the molten metal before it enters the sprue or downgate. 3 pouring: Transferring molten metal from a furnace or a ladle to a rnold.' powder: See dry powder: powder blower: A compressed air device used to apply dry magnetic particles over the surface of a test object. 6,16 practical examination: In certification of nondestructive testing personnel, a hands-on examination using test equipment and sample test objects. Compare general examination and specific examination. S precleaning: The removal of surface contamination or smeared metal from the test piece so that it cannot interfere with the penetrant testing process.f pressure testing:. A technique ofleak testing objects pressurized with a tracer gas with the subsequent detection and location of any existing leaks with a sampling probe (a qualitative test). Tests performed by increasing the pressure inside a test boundary to a level greater'than the surrounding atmosphere and detecting leakage by svstematic examination of the outside of the test surf~ce. Leaks are located at time of detection; however, it is impossible to accurately determine a total leakage . rate for the object being tested. 1 prewash technique: Penetrant system in which major por~ tion of a nonwater washable penetrant is removed with a water spray prior to application of the remover' primary creep: First stage of creep, marked by elastic . strain plus plastic strain.f primary radiation: Radiation emitting directly from the target of an X-ray tube or from a radioactive source. 11 primary reference response level: The ultrasonic response from the basic calibration reflector at the specified sound path distance, electronically adjusted to a specified percentage of full screen height. 7 principal plane of focus: See focus, principal. plane of

probe: In leak testing, the physical means for sensing gaseous leak, typically a tube having a fine opening one end, used for directing or collecting a stream of tracer gas. Dete.ctor probes are used or pr~ssure testin•.... ·.•.'•.:t and tracer probes are used for vacuum testing. I In ultra-ir;ttli sonic testing, see search unit. 7 probe coll: In electromagnetic testing, a small coil or assembly that is placed on or near the surface of . objects.4,l3 probe coil clearance: The perpendicular distance between J", adJilcen~ surfaces of the probe and test object. See .fI.

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probe gilS: A tracer gas that issues from a fine orifice so as to impinge on a restricted (small) test area. probe index: The point on.a shear wave or surface waV:f. transducer through which the emergent beam axis ~

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passes.il" process: Repeatable sequence of actions to bring about desired result." process control: Application of quality control principles ~, to the management of a repeated process." process testing: Initial produet testing to establish correc.:.• manufacturing procedures and then by periodic tests to ensure that the process continues to operate correctly.~, prod magnetization: See currentflow technique. ] prods: Handheld electrodes for transmitting magnetizing'" current from a generating source to a test object,6.15 production string: See tubing string. propagation: Advancement of a wave through medium.i-'? . :. be.: A. probe that can vary the tr,ace.:. r.· .ga..".·. I•. .• prop.o.m.·onin~ p.ro concentration In the sample at the sensor, typically b mixing pure air with sample gas from the probe inlet' port. Ratios of mixture between 100 percent pure (obt~ned.· from a.n outdoors source or by filtering am.. bi._ ent air through charcoal) and 100 percent leak sampl\",)1 gas are attainable without great changes in total flow from the probe. The proportioning probe used in halo)~ gen leak testing lets the user operate in an atmospher'jl with up to 1,000 IlUL (ppm) tracer gas background contamination. It proportions the amount of atmort sp~ere allowe? to enter the probe with its own (recircul lating) fresh air s u p p l y . l " " , pseudocolor: Image enhancement technique wherein colors are assigned to an image at several gray scale intervals. 8 pseudoisochromatic plates: Color plates used for coloL,~ vision examinations. Each plate bears an image which may be difficult for the examinee to see if his or herl color vision is Impaired." }I psychophysics: Interaction between vision performand:'!'~ and physical or psychological factors. One example i~ the so-called vigilance decrement, the degradation reliability based on performing visual andlor repetitivLI activities over a period of time. 8

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I NONDESTRUCTIVE TESTING OVERVIEW

Liquid penetrant testing. cracks: In a casting, cracks caused by residual stresses produced by cooling because of the object shape." ~m~lulse: A transient electrical or ultrasonic signal that has a rapid increase in amplitude to its maximum value, followed by an immediate return. 7 •21 An example is the

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pulse echo method: An ultrasonic -test method in which discontinuities are detected bv return echoes of the ""J transmitted pulses.' ~ulse length: A measure of tmlse duration expressed in time or number of cycles.'·-I -.,ulse magnetization: Direct or indirect application ofa 1 high field intensity, usually by the capacitor discharge method," ~p'ulse method: Multifrequency technique in which a .• broadband excitation such as an impulse is used. Either .1 the frequency components are extracted and analyzed or the interpretation is based directly on characteristics -I of the time domain waveform." tulse repetition frequency: See repetition rate. pulse tuning: Control of pulse frequency to optimize sys, tern response. 7 }ulser transducer: In .a~~ustic emission tes?ng, a trans..' ducer used as an artificial source of acoustic energy.s fupil: Aperture in the center of an eye's iris, through which .. l' light focused by the lens passes. S .'" ure air supply: In leak testing, air that has been cleaned of halogen contamination by means of an activated charcoal filter. This term is sometimes also used to describe any nonreactive gas, such as nitrogen, that contains no halogen contamination and to which the leak detector is not sensitive. I jurple: See visual purp~e. ' . . . . r1yrometry: Type of radiation thermometer, glVmgreadings for one point at a time, rather than imaging a scene in the manner of an infrared video camera. The word pyrometry means fire measurement. As the name implies, pyrometers are used for hot applications, such as the monitoring of furnace or foundry conditions. Pyrometers today are digital devices with liquid crystal temperature readouts. They may be mounted in place or available as hand held unitsf .t

Q

Q of a coil: Ratio of reactance to resistance measured at the . operating frequency.4,14 iuadrature: The relation between two periodic functions when the phase difference between them is one-fourth of a period. 4.14

qualification: Process of demonstrating that an individual has the required amount and the required type of training, experience, knowledge and capabilities. See also qualified. 8 qualified: Having demonstrated the required amount and the required type of training, experience, knowledge and abilities. See also qualification. S quality: The ability of a process or product to meet specifications or to meet the expectations of its users in terms of efficiency, appearance, longevity and ergonomics.f quality assurance: Administrative actions that specify, enforce and verify a quality program. s quality control: Physical and administrative actions required to ensure compliance with the quality assurance program. May include nondestructive testing in the manufacturing cycle." quality of lighting: Level of distribution of luminance in a visual task or environment. S quartz Bourdon tube gage: High precision pressure measuring instrument containing a -quartz helical Bourdon tube) quasilongitudinal wave: A wave in which the direction of particle motii'n is not parallel to the direction of energy propagation. quasishear wave: A wave in which the direction of particle motion is no! perpendicular to the direction of energy propagation. i quenching of fluorescence: The extinction of fluorescence by causes other than removal of the ultraviolet light (the exciting radiationj.? quick break: A sudden interruption of magnetizing current. Used in magnetic particle tests for materials with high residual longitudinal magnetism and limited to three-phase fullwave rectified alternating current.6,I6 I

R rad: Radiation absorbed dose. A unit of absorbed dose of ionizing radiation. One rad is equal to the absorption of 10- 5 J (100 ergs) of radiation energy per gram of matter.!I Replaced by the gray (Gy). radiance: Radiant flux per unit solid angle and per unit projected area of the source. Measured in watts per square meter steradian. Compare irradiance," .. radiant energy: Energy transmitted through a medium by electromagnetic waves. Also known as radiation.8 radiant flux: .Badiant energy's rate of flow, measured in watts." radiant intensity: Electromagnetic energy emitted per unit time per unit solid angle. Measured in watts per steradian.f radiant power: Total radiant energy emitted per unit time."

NONDESTRUCTIVE TESTING GLOSSARY I

radiation safety officer: An individual engaged in the practice of providing radiation protection, The representative appointed by the licensee for liaison with the applicable regulatory agency.ll radio frequency display: The 'presentation of unrectified signals on a display screen. i,l2 Also called RF display. See also video presentation. radiographic interpretation: The determination of the cause and significance of subsurface discontinuities indicated on a radiograph. The evaluation as to the acceptability or rejectability of the material is based on the judicious application of the radiographic specifications and standards governing the material.l! radiographic screens: Metallic or fluorescent sheets used to intensify the radiation effect on films.ll radiographic testing (RT): The use of radiant energy in the form of Xsrays or gamma rays for nondestructive testing of opaque objects in order to produce graphical records on a medium that indicates the comparative soundness of the object being tested.!' radiography: Radiographic testing. radiology: That branch of medicine which uses ionizing radiation for diagnosis and therapy. 11 radiometer: Instrument for measuring radiant power of specified frequencies. Different radiometers exist for different frequencies.f radiometric photometer: Radiometer for measuring radiant power over a variety ofwavelengths," radioscopy: A radiographic testing technique in which gamma rays or X-rays are used to produce an instantaneous image on a video or screen display as opposed to a latent image on a film. The test object may be remotely manipulated in real time to present a moving radiographic image. ramoff: A casting discontinuity resulting from the movement of sand away from the pattern because of improper ramming? range: In ultrasonic testing, the maximum path length that is displayed. See also sweep length. 7.12 rarefaction: The thinning or separation of particles in a propagating medium due to the relaxation phase of an ultrasonic cycle, Opposite of compression. A compressional wave is composed of alternating compressions and rarefactions. no . raster: A repetitive pattern whereby a directed element (a robotic arm or a flying dot on a video screen) follows the path of a series of adjacent parallel lines, taking them successively in tum, always in the same direction (from top to bottom or from left to right), stopping at the end of one line and beginning again at the start of the next line. Following a raster pattern makes it possible for electron beams to form video pictures or frames and for a sensor bearing armature to cover a predetermined part of the surface of a test object."

rat's tooth principle: (1) The tendency for hard materti~l< on a tooth's front surface to wear more slowly than material on the back surface, keeping the edge sharp. (2) Mechanism of wear whereby adjacent hard and stt surfaces wear at different rates, producing a self sha1),,':ill ening edge. s ' Rayleigh wave: An ultrasonic wave that propagates ala the surface of a test object. The particle motion is ell tical in a plane perpendicular to the surface, decrea . . ~ 'rapidly with depth below the surface, The effective ~p.th ..of penetration is considered to be about wa\:,~,eftgth.7

real gnltitlg: In moire and grid nondestructive testing, a

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physical g,ra,ti~g, ,on glass. or other substrate. Two ~].i,., are the amplttude gratzng (or bar-and-space gratin, consisting of opaque bars and clear spaces for use with transmitted light, or reflective bars and nonrefleCtij' spaces for use with reflected light; and the phase gn' ing consisting of an array of furrows on the surface m: transparent or opaque body? recarhu~ze: (1) To increas~ the carbon.content of. mol:','.".',.~.l.• cast Iron or steel by adding carbonaceous material, h16,' carbon pig iron or a high carbon alloy. (2) To carburize ~n;;tal object to return surface carbon lost in proce~J receiver: The section of an ultrasonic instrument tha! amplifies echoes returning from the test object. Also:"l" transducer that picks up the echoes.' • recommended practice: A set of guidelines or recons' mendations.f Recommended Practice SNT~TC-IA: See ASNT RecOJ ·.·. •l mended Practice No. SNT-TC-1A. '~ recovery: Reduced stress level and increased ductility of metal after work hardening. See creep. 8 recovery time: The time required for a test system return to its original state after it has received a nal. 4•13 , recrystallization: (1) The change.from one ~rainstructl to another, as occurs on heating or cooling througlrA critical temperature. (2) The formaticn of a new, str~~ free grain structure from that existing in cold work?des. of the contacting ~etaJ~.r offretting wear, mixed WIth 011 or grease and retained !~ or near the site of its formation. See also cocoa. 8 . ,.! reference blocks: A block of material containing artific~expressed as functions of the complex fri'~ quency.4.l4 retentivity materials to trap magnetic particles and indicate discontinuities." retentivity: A material's property of retaining residual residual technique: Ferromagnetic particles are applied netism to a greater or lesser degree. 6.1o to a test object after the magnetizing force has been disretina: In the eye, the tissue that senses light.s eontinued.f retinene: See visual purple. resolution: An aspect of image quality pertaining to a sysRF display: See radio frequency display. tem's ability to reproduce objects, often measured by rhodopsin: See visual purple. resolving a pair of adjacent objects or parallel lines. See ring standard: See test ring. also minimum line pair and resolving power. s ringdown count: See acoustic emission count. resolution, discontinuity: The property of a test system ringing method: A test method for bonded structures that enables the separation of indications due to disconwhich disbonds are indicated by increased amplitude of tinuities located in close proximity to each other in a ,.. •. ringing signalS.',12 2 test object. ringing signals: (1) Closely spaced multiple signalseaus resolution test: Procedure wherein a line is detected to by multiple reflections in a thin material. (2) Signals verify a system's sensitivity." caused by continued vibration of a transducer.'·12 resolution threshold: Minimum distance between a pair of ringing time: The time that the mechanical vibrations 0 points or parallel lines when they can be distinguished as transducer continue after the electrical pulse two, not one, expressed in minutes of arc. Vision acuity stopped.,,12 in such a case is the reciprocal of one half of the period rinse: Th 7 process . o.f re.m._oving .liq.uid p~netrant testi . expressed in minutes.8 .2o matenals from the surface of a test object by means . J resolving power: The ability of detection systems to sepawashing or flooding with another liquid, usually water. rate two points in time or distance. Resolving power wash, 2 Also called depends on the angle of vision and the distance of the riser: A reservoir of molten metal connected to the casti sensor from the test surface. Resolving power in vision to provide additional metal to the casting, required systems is often measured using parallel lines. Compare the result of shrinkage before and during solidification' 8 resolution. robotic system: Automated system programmed to pi .~ resonance: The condition in which the frequency of a forcform purposeful movements in variable sequences. 1l 1 ing vibration (ultrasonic wave) is the same as the naturod: Retinal receptor that responds. at low levels of lumiral vibration frequency of the propagation body (test nance even below the threshold for cones. At these object), resulting in large amplitude responses at that els.there is no basis for perceiving differences in frequency.7,10 . and saturation. No rods are found in the foveacenresonance method: A method using the resonance princi8 •20 tralis. ple for determining velocity, thickness or presence of roof angle: In a dual element delay line transducer, laminar discontinuities.' . angle by which the top surfaces of the delay line resonant frequency: The frequency at which a body vitilted horizontally to direct the beams of the two ele:;brates, that frequency being sympathetic to the energy ments to intersect at a specified zone in the medium. II causing the vibration. root crack: A crack in either the weld or heat affected zo.,"~ response or response time: The time (time-constant) at the root of a we1d. 2 required for a leak detector or leak testing system to yield root penetration: The depth to which weld metal a signal output equal to 63 percent of the maximum siginto the root of a joint. 2 nal attained when tracer gas is applied continuously for RT: Radiographic testing. an indefinitely long period to the leak detector probe. 1

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NONDESTRUCTIVE TESTING OVERVIEW

!i't'unner: (1) A channel through which molten metal flows from one receptacle to another. (2) The portion of the gate assembly that connects the downgate sprue or riser with the casting. (3) Parts of patterns and finished castings corresponding to the described portion of the gate

assembly' ""r"nner box: A distribution box that divides the molten !.

metal Jnto several streams before it enters the mold cavity."

'r~f~;: t~:~::~~~~ a casting caused by the escape

5 salvage tests: Testing after salvage operations or testing objects that can be repaired," ... amp~ng prob~: See de.tector probe. sampling, partial: Testmg of less than one hundred per_ cent of a production lot. See one hundred percent testJ ing. 8 Jampling, random partial: Partial sampling that is fully random.f .... ]ampling, specified partial: Partial sampling in which a j particular frequency or sequence of sample selection is prescribed. An example of specified partial sampling is ,,' the testing of every fifth unit. s ' land: A granular material resulting from the disintegration I of rock. Foundrv sands are mainlv silica. Bank sands are found in sedimentary deposits and contains less than .5 percent clay. Dune sand occurs in wind blown deposits near large bodies of water and is very high in silica content. Molding sand contains more than 5 percent clay, usually between 10 and 20 percent. Silica sand is a granular material containing at least 95 percent silica and often more than 99 percent. Sand core is nearly pure silica. Miscellaneous types of sand include zircon, . olivine, calcium carbonate, lava and titanium minerals:" laturation: (1) A condition in which high amplitude signals on a display screen do not increase with increased gain and appear flattened.' (2) Relative or comparative color characteristic resulting from a hue's dilution with white light. s "jaturation level: See magnetic saturation. Icab: A flat volume of metal joined to a casting through a J small area. Usually set in a depression, a flat side being separated from the metal of the casting proper by a thin , layer of sand.' icalar: A quantity completely specified by a single number. 4 .14 lcale: Oxide formed on metal by chemical action of the sur. face metal with oxygen from the air.2 ~cale pit: Shallow surface depression in metal, caused by scale.f

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scaling: (1) Forming a layer of oxidation product on metals, usually at high temperatures. (2) Deposition of insoluble constituents on a metal surface, as in cooling tubes and water boilers. S.l 9 scanning: Movement of the transducer over the surface of the test object in a controlled manner so as to achieve complete coverage. May be either contact or immersion method.' scarfing: Cutting surface areas of metal objects, ordinarily by using a gas torch. The operation permits surface discontinuities to be cut from ingots, billets or the edges of plate that is to be beveled for butt welding. 3 scattering: (1) Random reflection and refraction of radiation caused by interaction with material it strikes or penetrates. (2) Random reflection of ultrasonic waves by small discontinuities or surface irregularities.' Schlieren system: An optical system used for visual display of an ultrasonic beam passing through a transparent medium.'·9J2 ' .. scoring: (1) Marring or scratching of any formed part by metal pickup on a punch, die or guide. (2) Reducing the thickness of a part along a line to weaken it purposely at a specific location. S.l 9 scotopic vision: Dark adapted vision, using only the rods in the retina, where differences in brightness can be detected but differences in hue cannot. Vision is whollv scotopic when the luminance of the test surface is below 3 X 10-5 cd·m-z (2.7 x 10-6 cd-fr"). Also known as parafoveal vision. Compare mesopic vision and photopic vision. S scrap: (1) Manufactured materials not suitable for sale. (2) Discarded metallic material that may be reclaimed through melting and refining.' scuffing: A type of adhesive wear. sea level atmospheric pressure or sea level barometric pressure: See atmospheric pressure. sealing: (1) Closing pores in anodic coatings to render them less absorbent. (2) Plugging leaks in a casting by introducing thermosetting plastics into porous areas and subsequently setting the plastic with heat.' seam: (1) On the surface of metal, an unwelded fold or lap that appears as a crack, usually resulting from a discontinuity obtained in casting or working. (2) Mechanical or welded joints.' (3) Longitudinal surface discontinuity on metal originating from a surface crack or blowhole near the surface of the ingot, that is drawn out during rolling and follows the rolling direction. Also due to overfill while rolling.'After forging, seams generally follow the direction of flow lines. 2 search coil: A detection coil that is usually smaller than the excitation coil." '

NONDESTRUCTIVE TESTING GLOSSARY I

search unit: An assembly comprising a piezoelectric element, backing material (damping), wear plate or wedge (optional) and leads enclosed in a hous.ing. Also called transducer or probe.' second stage replica: A positive replica made from the first cast to produce a duplicate of the original surface.f secondary creep: Second stage of creep, where deformation proceeds at a constant rate and less rapidly than as in 'primary creep. Essentially an equilibrium condition between the mechanisms of work hardening and recovery.s secondary magnetic flux: magnetic flux due to induced flow of eddy currents.f seeability: The characteristic of an indication that enables an observer to see it against the adverse conditions of background, outside light etc. 2 segregation: Nonuniform distributio,? of alloying elements, impurities or microphases.V' selectivity: The characteristic of a test system that is a measure of the extent to which an instrument is capable of differentiating between the desired Signal and disturbances of other frequencies or phases. o 3 self emulsifiable: Describes a penetrant that spontaneouslyemulsifies into water, a property that allows it to be rinsed off with water, with more control than if it actually dissolved in the rinse water. Also called water washable. See penetrant, water washable. 2 self inductance: The property of an electric circuit whereby an electromotive force is induced in that circuit by a change of current in the circuit. 4 .l 4 semipermanent mold: A permanent mold in which sand or plastic cores are used:' send/receive transducer: A transducer consisting of two piezoelectric elements mounted side by side separated by an acoustic barrier. One element transmits, one receives.i'? sensing coils A coil that detects changes in the magnetic field produced by the flow of eddy currents in a test specimen, induced by an excitation coil. Sensing and excitation coils can be one and the same." sensitivity: A measure of a sensor's ability to detect small Signals. Limited by the signal-to-noise ratio. 7 sensitivity of leak. detector: Response of a leak detector to tracer gas leakage (typically panel meter pointer deflection in scale divisions; leak sensitivity is measured in units ofPa·m3·s-1 or std cm 3·s-l ) .1 sensitivity of leak test: The smallest leakage rate that an instrument, technique or system can detect under specified conditions (implies minimum detectable leakage rate).' sensitivity panel: A plated metal panel with cracks of known depth induced into the plating. Used to evaluate and compare penetrant sensitivity.-

sensitization: Precipitation of chromium carbides in grain boundaries of a corrosion resistant alloy, in intergranular corrosion that would otherwise resisted. 8 settling test: A procedure used to determine the co:nct~}i tration of particles in a magnetic particle bath. 6 SH wave: See shear horizontal wave. 70~ shadow: A region in a test object that cannot be reached Iii . ultrasonic energy traveling in a given direction. Caused ~ ~~ti~::~3or the presence of intervening large

j]

shadow;'~isting:

Nondestructive technique of vapor depositing a thin metal film onto a replica at an Obliq•.. .,. angle in order to obtain a micrograph of a test surface.f an opaque specimen. S •••• 3 shakeout: Removing castings from a sand mold. ., shallow discontinuity: A discontinuity open to the surfa ~ of a solid object that possesses little depth in proportk.~ to the width of this opening. A scratch or nick may be a shallow discontinuity in this sense. 2 shear: A force that tends to cause two contiguous parts the same body to slide in a direction parallel to their plane of contact. 2 shear break: Open break in metal at the periphery of bolt, nut, rod or member at approximately a 45 degree angle to the app.li.·.ed stress. Occurs. m._o.st often Wi:t.. ~.• . flanged products. Also called shear crack. S,l9 shear crack: See shear break.

J

:. l

shear horizon.talw ..ave: A shear wave.. in wh.. ich.the p.artie.If vibration is parallel to the incidence surface. Abbre . ated SH wave. .. .. shear vertical wave: A shear wave in which the particle vibration is perpendicular to the direction of wal propagation but essentially normal to the incidence SL.J face. Abbreviated SV wave. I shear wave: A type of wave in which the particle motion perpendicular to the direction of propagation. ' ,12 shear wave transducer: An angle beam transducer or straight beam transducer designed to cause mode verted shear waves to J?ropagate at a nominal angle specified test medium. • shell core: A shell molded sand core. 3 I shell molding: Forming a mold from thermosetting ref slag lines: Elongated cavities containing slag or other foreign matter in fusion welds.2.,3 . slide: Part of a die generally arranged to move parallel to the parting line, the inner end forming a part of the die cavity wall and involving one or more undercuts and sometimes including a core or cores.f sliver: A discontinuity consisting of a very thin elongated piece of metal attached by only one end to the parent metal into whose surface it has been rolled.? slurry: A free-flawing pumpable suspension of a fine solid in a liquid. 6 . slush casting: A casting made by pouring an alloy into a metal mold, allowing it to remain long enough to form a thin shell and then pouring out the remaining liquid. 3 smoothing: In image processing, use of positive coefficients in a linear combination of pixel values to smoothen abrupt transitions in a digital image. Also called lou; passfiltering.8 snap flask: A hinged flask removed from the mold after the mold is made.' Snell's law: The physical law that defines the relationship between the angle of incidence and the angle of refraction.' sniffer probe: See detector probe. sniffer test: See detector probe test. SNT-TC-IA: See ASNT Recommended Practice No. SNT-TC-1A. soak time: The period of time when the emulsifier remains in contact with the liquid penetrant on the surface of the test object. Soak time ceases when the penetrant emulsifier is quenched with water or completely removed by water rinsing. Also Called emulsification time. 2 soaking: Prolonged holding at a selected temperature.I soldiers: Wooden blocks or sticks used to reinforce bodies of sand in the cope. They usually overhang the mold cavity. 3

NONDESTRUCTIVE TESTING GLOSSARY I

solidification shrinkage: The decrease in volume of a metal during solidiflcation.2•s solution heat treatment: A heat treatment that causes the hardening constituent of an alloy to go into solid solution, followed by a quench to retain it temporarily in a

electromagnJ~I("

spectroradiometry: Measurement of radiant power and spectral emittance, used particularl' to examine colors and to measure the spectral tance of light sources." spectroscope: Instrument used for spectroscopy. S

I.'•

supersaturated solution state at lower temperatures.' spectr.~scopy: spectrop.hotometry o.r spect.rora.diometIY.r.•:. ·.,.n.. solvent action: The ability of a liquid to dissolve another which the spectrum, rather than bemg analyzed onl}.::y materialf a processing unit, is presented in a visible form toz e solvent cleaning: The process of removing excess pene~", . operator for organoleptic examination." trant from the surface of a test object by hand wiping ';>,. spebtrum.... ..'0: (!) The amplitude.distributi.?n.' of freqUe?Cie:.".•.•.·.' 1 with a solvent dampened cloth.2 a SIgnaL! (2) Representation of radiant energy m aci" solvent developer: A developer for penetrant tests in cent .'bands of hues in sequence according to the .·. 'sxamelengths or frequenc.ies. A rainbow is a ,,1 which the developing powder is applied as a suspension ene.rgy or solution in a quick drying solvent.f known example ofa visible spectrum." •.••••: solvent remover: A volatile liquid that can dissolve penespectrum response: The amplification (gain) of a receiver trant and that is used to remove excess surface peneover a range of frequencies.' specular: Pertaining to a. mirror-like reflective finish, as ( trant from test objects by appropriate hand Wiping techniques.? ' metal. Compare lambertian. s s source: The location where an event takes place. specular reflection: When reflected waves and incident source location: The computed origin of acoustic emission waves form equal angles at the reflecting surface. S ""1 s signals. speed of light: The speed of all radiant energy, incIudlg spalIing: Cracking or flaking of small particles of metal, light, is 2.997925 x 10 8 m- S-l in vacuum (approximately usuallyin thin layers, from the surface of an object. 2 8 000 1) "all al th d I ~ spalIing fatigue: See subcasefiatigue. ~'. .mi. s- . In '•.. ~.at~ri s e spee ,is ess