ASM Metals HandBook Vol. 17 - Nondestructive Evaluation and Quality Control

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ASM

INTERNATIONAL ®

The Materials

Information Company

Publication Information and Contributors

Nondestructive Evaluation and Quality Control was published in 1989 as Volume 17 of the 9th Edition Metals

Handbook. With the second printing (1992), the series title was changed to ASM Handbook. The Volume was prepared

under the direction of the ASM Handbook Committee.

Authors and Reviewers

• LAMET UFRGS

• D.A. Aldrich Idaho National Engineering Laboratory EG&G Idaho, Inc.

• Craig E. Anderson Nuclear Energy Services

• Gerald L. Anderson American Gas and Chemical Company

• Glenn Andrews Ultra Image International

• Bruce Apgar DuPont NDT Systems

• R.A. Armistead Advanced Research and Applications Corporation

• Ad Asead University of Michigan at Dearborn

• David Atherton Queen's University

• Yoseph Bar-Cohen Douglas Aircraft Company McDonnell Douglas Corporation

• R.C. Barry Lockheed Missiles & Space Company, Inc.

• John Bassart Iowa State University

• George Becker DuPont NDT Systems

• R.E. Beissner Southwest Research Institute

• Alan P. Berens University of Dayton Research Institute

• Harold Berger Industrial Quality, Inc.

• Henry Bertoni Polytechnic University of New York

• R.A. Betz Lockheed Missiles & Space Company, Inc.

• Craig C. Biddle United Technologies Research Center

• Kelvin Bishop Tennessee Valley Authority

• Carl Bixby Zygo Corporation

• Dave Blackham Consultant

• Gilbert Blake Wiss, Janney, Elstner Associates

• James Bolen Northrop Aircraft Division

• Jim Borges Intec Corporation

• J.S. Borucki Ardox Inc.

• Richard Bossi Boeing Aerospace Division The Boeing Company

• Byron Brendan Battelle Pacific Northwest Laboratories

• G.L. Burkhardt Southwest Research Institute

• Paul Burstein Skiametrics, Inc.

• Willard L. Castner National Aeronautics and Space Administration

Lyndon B. Johnson Space

Center

• V.S. Cecco Atomic Energy of Canada, Ltd. Chalk River Nuclear Laboratories

• Francis Chang General Dynamics Corporation

• Tsong-how Chang University of Wisconsin, Milwaukee

• F.P. Chiang Laboratory for Experimental Mechanics Research

State University of New York at

Stony Brook

• D.E. Chimenti Wright Research & Development Center Wright-Patterson Air Force Base

• P. Cielo National Research Council of Canada Industrial Materials Research Institute

• T.N. Claytor Los Alamos National Laboratory

• J.M. Coffey CEGB Scientific Services

• J.F. Cook Idaho National Engineering Laboratory EG&G Idaho, Inc.

• Thomas D. Cooper Wright Research & Development Center Wright-Patterson Air Force Base

• William D. Cowie United States Air Force Aeronautical Systems Division

• L.D. Cox General Dynamics Corporation

• Robert Cribbs Folsom Research Inc.

• J.P. Crosson Lucius Pitkin, Inc.

• Darrell Cutforth Argonne National Laboratory

• William Dance LTV Missiles & Electronics Group

• Steven Danyluk University of Illinois

• Oliver Darling Spectrum Marketing, Inc.

• E.A. Davidson Wright Research & Development Center Wright-Patterson Air Force Base

• Vance Deason EG&G Idaho, Inc.

• John DeLong Philadelphia Electric Company

• Michael J. Dennis NDE Systems & Services General Electric Company

• Richard DeVor University of Illinois at Urbana-Champaign

• Robert L. Ditz GE Aircraft Engines General Electric Company

• Kevin Dooley University of Minnesota

• Thomas D. Dudderar AT&T Bell Laboratories

• Charles D. Ehrlich National Institute of Standards & Technology

• Ralph Ekstrom University of Nebraska Lincoln

• Robert Erf United Technologies Research Center

• K. Erland United Technologies Corporation Pratt & Whitney Group

• J.L. Fisher Southwest Research Institute

• Colleen Fitzpatrick Spectron Development Laboratory

• William H. Folland United Technologies Corporation Pratt & Whitney Group

• Joseph Foster Texas A&M University

• Kenneth Fowler Panametrics, Inc.

• E.M. Franklin Argonne National Laboratory Argonne--West

• Larry A. Gaylor Dexter Water Management Systems

• David H. Genest Brown & Sharpe Manufacturing Company

• Dennis German Ford Motor Company

• Ron Gerow Consultant

• Scott Giacobbe GPU Nuclear

• Robert S. Gilmore General Electric Research and Development Center

• J.N. Gray Center for NDE Iowa State University

• T.A. Gray Center for NDE Iowa State University

• Robert E. Green, Jr. The Johns Hopkins University

• Arnold Greene Micro/Radiographs Inc.

• Robert Grills Ultra Image International

• Donald Hagemaier Douglas Aircraft Company McDonnell Douglas Corporation

• John E. Halkias General Dynamics Corporation

• Grover L. Hardy Wright Research & Development Center Wright-Patterson Air Force Base

• Patrick G. Heasler Battelle Pacific Northwest Laboratories

• Charles J. Hellier Hellier Associates, Inc.

• Edmond G. Henneke Virginia Polytechnic Institute and State University

• B.P. Hildebrand Failure Analysis Associates, Inc.

• Howard E. Housermann ZETEC, Inc.

• I.C.H. Hughes BCIRA International Centre

• Phil Hutton Battelle Pacific Northwest Laboratories

• Frank Iddings Southwest Research Institute

• Bruce G. Isaacson Bio-Imaging Research, Inc.

• W.B. James Hoeganaes Corporation

• D.C. Jiles Iowa State University

• Turner Johnson Brown & Sharpe Manufacturing Company

• John Johnston Krautkramer Branson

• William D. Jolly Southwest Research Institute

• M.H. Jones Los Alamos National Laboratory

• Gail Jordan Howmet Corporation

• William T. Kaarlela General Dynamics Corporation

• Robert Kalan Naval Air Engineering Center

• Paul Kearney Welch Allyn Inc.

• William Kennedy Canadian Welding Bureau

• Lawrence W. Kessler Sonoscan, Inc.

• Thomas G. Kincaid Boston University

• Stan Klima NASA Lewis Research Center

• Kensi Krzywosz Electric Power Research Institute Nondestructive Evaluation Center

• David Kupperman Argonne National Laboratory

• H. Kwun Southwest Research Institute

• J.W. Lincoln Wright Research & Development Center Wright-Patterson Air Force Base

• Art Lindgren Magnaflux Corporation

• D. Lineback Measurements Group, Inc.

• Charles Little Sandia National Laboratories

• William Lord Iowa State University

• D.E. Lorenzi Magnaflux Corporation

• Charles Loux GE Aircraft Engines General Electric Company

• A. Lucero ZETEC, Inc.

• Theodore F. Luga Consultant

• William McCroskey Innovative Imaging Systems, Inc.

• Ralph E. McCullough Texas Instruments, Inc.

• William E.J. McKinney DuPont NDT Systems

• Brian MacCracken United Technologies Corporation Pratt & Whitney Group

• Ajit K. Mal University of California, Los Angeles

• A.R. Marder Energy Research Center Lehigh University

• Samuel Marinov Western Atlas International, Inc.

• George A. Matzkanin Texas Research Institute

• John D. Meyer Tech Tran Consultants, Inc.

• Morey Melden Spectrum Marketing, Inc.

• Merlin Michael Rockwell International

• Carol Miller Wright Research & Development Center Wright-Patterson Air Force Base

• Ron Miller MQS Inspection, Inc.

• Richard H. Moore CMX Systems, Inc.

• Thomas J. Moran Consultant

• John J. Munro III RTS Technology Inc.

• N. Nakagawa Center for NDE Iowa State University

• John Neuman Laser Technology, Inc.

• H.I. Newton Babcock & Wilcox

• G.B. Nightingale General Electric Company

• Mehrdad Nikoonahad Bio-Imaging Research, Inc.

• R.C. O'Brien Hoeganaes Corporation

• Kanji Ono University of California, Los Angeles

• Vicki Panhuise Allied-Signal Aerospace Company Garrett Engine Division

• James Pellicer Staveley NDT Technologies, Inc.

• Robert W. Pepper Textron Specialty Materials

• C.C. Perry Consultant

• John Petru Kelly Air Force Base

• Richard Peugeot Peugeot Technologies, Inc.

• William Plumstead Bechtel Corporation

• Adrian Pollock Physical Acoustic Corporation

• George R. Quinn Hellier Associates, Inc.

• Jay Raja Michigan Technological University

• Jack D. Reynolds General Dynamics Corporation

• William L. Rollwitz Southwest Research Institute

• A.D. Romig, Jr. Sandia National Laboratories

• Ward D. Rummel Martin Marietta Astronautics Group

• Charles L. Salkowski National Aeronautics and Space Administration

Lyndon B. Johnson Space

Center

• Thomas Schmidt Consultant

• Gerald Scott Martin Marietta Manned Space Systems

• D.H. Shaffer Westinghouse Electric Corporation Research and Development Center

• Charles N. Sherlock Chicago Bridge & Iron Company

• Thomas A. Siewert National Institute of Standards and Technology

• Peter Sigmund Lindhult & Jones, Inc.

• Lawrence W. Smiley Reliable Castings Corporation

• James J. Snyder Westinghouse Electric Company Oceanic Division

• Doug Steele GE Aircraft Engines General Electric Company

• John M. St. John Caterpillar, Inc.

• Bobby Stone Jr. Kelly Air Force Base

• George Surma Sundstrand Aviation Operations

• Lyndon J. Swartzendruber National Institute of Standards and Technology

• Richard W. Thams X-Ray Industries, Inc.

• Graham H. Thomas Sandia National Laboratories

• R.B. Thompson Center for NDE Iowa State University

• Virginia Torrey Welch Allyn Inc.

• James Trolinger Metro Laser

• Michael C. Tsao Ultra Image International

• Glen Wade University of California, Santa Barbara

• James W. Wagner The Johns Hopkins University

• Henry J. Weltman General Dynamics Corporation

• Samuel Wenk Consultant

• Robert D. Whealy Boeing Commercial Airplane Company

• David Willis Allison Gas Turbine Division General Motors Corporation

• Charles R. Wojciechowski NDE Systems and Services General Electric Company

• J.M. Wolla U.S. Naval Research Laboratory

• John D. Wood Lehigh University

• Nello Zuech Vision Systems International

Foreword

Volume 17 of Metals Handbook is a testament to the growing importance and increased sophistication of methods used to

nondestructively test and analyze engineered products and assemblies. For only through a thorough understanding of

modern techniques for nondestructive evaluation and statistical analysis can product reliability and quality control be

achieved and maintained.

As with its 8th Edition predecessor, the aim of this Volume is to provide detailed technical information that will enable

readers to select, use, and interpret nondestructive methods. Coverage, however, has been significantly expanded to

encompass advances in established techniques as well as introduce the most recent developments in computed

tomography, digital image enhancement, acoustic microscopy, and electromagnetic techniques used for stress analysis. In

addition, material on quantitative analysis and statistical methods for design and quality control (subjects covered only

briefly in the 8th Edition) has been substantially enlarged to reflect the increasing utility of these disciplines.

Publication of Volume 17 also represents a significant milestone in the history of ASM International. This Volume

completes the 9th Edition of Metals Handbook, the largest single source of information on the technology of metals that

has ever been compiled. The magnitude, respect, and success of this unprecedented reference set calls for a special tribute

to its many supporters. Over the past 13 years, the ASM Handbook Committee has been tireless in its efforts, ASM

members have been unflagging in their support, and the editorial staff devoted and resourceful. Their efforts, combined

with the considerable knowledge and technical expertise of literally thousands of authors, contributors, and reviewers,

have resulted in reference books which are comprehensive in coverage and which set the highest standards for quality. To

all these men and women, we extend our most sincere appreciation and gratitude.

Richard K. Pitler

President, ASM International

Edward L. Langer

Managing Director, ASM International

Preface

The subject of nondestructive examination and analysis of materials and manufactured parts and assemblies is not new to

Metals Handbook. In 1976, Volume 11 of the 8th Edition--Nondestructive Inspection and Quality Control--provided what

was at that time one of the most thorough overviews of this technology ever published. Yet in the relatively short time

span since then, tremendous advances and improvements have occurred in the field--so much so that even the

terminology has evolved. For example, in the mid-1970s the examination of an object or material that did not render it

unfit for use was termed either nondestructive testing (NDT) or nondestructive inspection (NDI). Both are similar in that

they involve looking at (or through) an object to determine either a specific characteristic or whether the object contains

discontinuities, or flaws.

The refinement of existing methods, the introduction of new methods, and the development of quantitative analysis have

led to the emergence of a third term over the past decade, a term representing a more powerful tool. With nondestructive

evaluation (NDE), a discontinuity can be classified by its size, shape, type, and location, allowing the investigator to

determine whether or not the flaw is acceptable. The title of the present 9th Edition volume was modified to reflect this

new technology.

Volume 17 is divided into five major sections. The first contains four articles that describe equipment and techniques used

for qualitative part inspection. Methods for both defect recognition (visual inspection and machine vision systems) and

dimensional measurements (laser inspection and coordinate measuring machines) are described.

In the second section, 24 articles describe the principles of a wide variety of nondestructive techniques and their

application to quality evaluation of metallic, composite, and electronic components. In addition to detailed coverage of

more commonly used methods (such as magnetic particle inspection, radiographic inspection, and ultrasonic inspection),

newly developed methods (such as computed tomography, acoustic microscopy, and speckle metrology) are introduced.

The latest developments in digital image enhancement are also reviewed. Finally, a special six-page color section

illustrates the utility of color-enhanced images.

The third section discusses the application of nondestructive methods to specific product types, such as one-piece

products (castings, forgings, and powder metallurgy parts) and assemblies that have been welded, soldered, or joined with

adhesives. Of particular interest is a series of reference radiographs presented in the article "Weldments, Brazed

Assemblies, and Soldered Joints" that show a wide variety of weld discontinuities and how they appear as radiographic

images.

The reliability of discontinuity detection by nondestructive methods, referred to as quantitative NDE, is the subject of the

fourth section. Following an introduction to this rapidly maturing discipline, four articles present specific guidelines to

help the investigator determine the critical discontinuity size that will cause failure, how long a structure containing a

discontinuity can be operated safely in service, how a structure can be designed to prevent catastrophic failure, and what

inspections must be performed in order to prevent failure.

The final section provides an extensive review of the statistical methods being used increasingly for design and quality

control of manufactured products. The concepts of statistical process control, control charts, and design of experiments

are presented in sufficient detail to enable the reader to appreciate the importance of statistical analysis and to organize

and put into operation a system for ensuring that quality objectives are met on a consistent basis.

This Volume represents the collective efforts of nearly 200 experts who served as authors, contributors of case histories,

or reviewers. To all we extend our heartfelt thanks. We would also like to acknowledge the special efforts of Thomas D.

Cooper (Wright Research & Development Center, Wright-Patterson Air Force Base) and Vicki E. Panhuise (Allied-

Signal Aerospace Company, Garrett Engine Division). Mr. Cooper, a former Chairman of the ASM Handbook

Committee, was instrumental in the decision to significantly expand the material on quantitative analysis. Dr. Panhuise

organized the content and recruited all authors for the section "Quantitative Nondestructive Evaluation." Such foresight

and commitment from Handbook contributors over the years has helped make the 9th Edition of Metals Handbook--all 17

volumes and 15,000 pages--the most authoritative reference work on metals ever published.

The Editors

General Information

Officers and Trustees of ASM International

Officers

• Richard K. Pitler President and Trustee Allegheny Ludlum Corporation (retired)

• Klaus M. Zwilsky Vice President and Trustee National Materials Advisory Board

National

Academy of Sciences

• William G. Wood Immediate Past President and Trustee Kolene Corporation

• Robert D. Halverstadt Treasurer AIMe Associates

Trustees

• John V. Andrews Teledyne Allvac

• Edward R. Burrell Inco Alloys International, Inc.

• Stephen M. Copley University of Southern California

• H. Joseph Klein Haynes International, Inc.

• Gunvant N. Maniar Carpenter Technology Corporation

• Larry A. Morris Falconbridge Limited

• William E. Quist Boeing Commercial Airplanes

• Charles Yaker Howmet Corporation

• Daniel S. Zamborsky Consultant

• Edward L. Langer Managing Director ASM International

Members of the ASM Handbook Committee (1988-1989)

• Dennis D. Huffman (Chairman 1986-; Member 1983-) The Timken Company

• Roger J. Austin (1984-) ABARIS

• Roy G. Baggerly (1987-) Kenworth Truck Company

• Robert J. Barnhurst (1988-) Noranda Research Centre

• Peter Beardmore (1986-1989) Ford Motor Company

• Hans Borstell (1988-) Grumman Aircraft Systems

• Gordon Bourland (1988-) LTV Aerospace and Defense Company

• Robert D. Caligiuri (1986-1989) Failure Analysis Associates

• Richard S. Cremisio (1986-1989) Rescorp International, Inc.

• Gerald P. Fritzke (1988-) Metallurgical Associates

• J. Ernesto Indacochea (1987-) University of Illinois at Chicago

• John B. Lambert (1988-) Fansteel Inc.

• James C. Leslie (1988-) Advanced Composites Products and Technology

• Eli Levy (1987-) The De Havilland Aircraft Company of Canada

• Arnold R. Marder (1987-) Lehigh University

• John E. Masters (1988-) American Cyanamid Company

• L.E. Roy Meade (1986-1989) Lockheed-Georgia Company

• Merrill L. Minges (1986-1989) Air Force Wright Aeronautical Laboratories

• David V. Neff (1986-) Metaullics Systems

• Dean E. Orr (1988-) Orr Metallurgical Consulting Service, Inc.

• Ned W. Polan (1987-1989) Olin Corporation

• Paul E. Rempes (1986-1989) Williams International

• E. Scala (1986-1989) Cortland Cable Company, Inc.

• David A. Thomas (1986-1989) Lehigh University

• Kenneth P. Young (1988-) AMAX Research & Development

Previous Chairmen of the ASM Handbook Committee

• R.S. Archer (1940-1942) (Member, 1937-1942)

• L.B. Case (1931-1933) (Member, 1927-1933)

• T.D. Cooper (1984-1986) (Member, 1981-1986)

• E.O. Dixon (1952-1954) (Member, 1947-1955)

• R.L. Dowdell (1938-1939) (Member, 1935-1939)

• J.P. Gill (1937) (Member, 1934-1937)

• J.D. Graham (1966-1968) (Member, 1961-1970)

• J.F. Harper (1923-1926) (Member, 1923-1926)

• C.H. Herty, Jr. (1934-1936) (Member, 1930-1936)

• J.B. Johnson (1948-1951) (Member, 1944-1951)

• L.J. Korb (1983) (Member, 1978-1983)

• R.W.E. Leiter (1962-1963) (Member, 1955-1958, 1960-1964)

• G.V. Luerssen (1943-1947) (Member, 1942-1947)

• G.N. Maniar (1979-1980) (Member, 1974-1980)

• J.L. McCall (1982) (Member, 1977-1982)

• W.J. Merten (1927-1930) (Member, 1923-1933)

• N.E. Promisel (1955-1961) (Member, 1954-1963)

• G.J. Shubat (1973-1975) (Member, 1966-1975)

• W.A. Stadtler (1969-1972) (Member, 1962-1972)

• R. Ward (1976-1978) (Member, 1972-1978)

• M.G.H. Wells (1981) (Member, 1976-1981)

• D.J. Wright (1964-1965) (Member, 1959-1967)

Staff

ASM International staff who contributed to the development of the Volume included Joseph R. Davis, Manager of

Handbook Development; Kathleen M. Mills, Manager of Book Production; Steven R. Lampman, Technical Editor;

Theodore B. Zorc, Technical Editor; Heather J. Frissell, Editorial Supervisor; George M. Crankovic, Editorial

Coordinator; Alice W. Ronke, Assistant Editor; Jeanne Patitsas, Word Processing Specialist; and Karen Lynn O'Keefe,

Word Processing Specialist. Editorial assistance was provided by Lois A. Abel, Wendy L. Jackson, Robert T. Kiepura,

Penelope Thomas, and Nikki D. Wheaton. The Volume was prepared under the direction of Robert L. Stedfeld, Director

of Reference Publications.

Conversion to Electronic Files

ASM Handbook, Volume 17, Nondestructive Evaluation and Quality Control was converted to electronic files in 1998.

The conversion was based on the fifth printing (1997). No substantive changes were made to the content of the Volume,

but some minor corrections and clarifications were made as needed.

ASM International staff who contributed to the conversion of the Volume included Sally Fahrenholz-Mann, Bonnie

Sanders, Marlene Seuffert, Gayle Kalman, Scott Henry, Robert Braddock, Alexandra Hoskins, and Erika Baxter. The

electronic version was prepared under the direction of William W. Scott, Jr., Technical Director, and Michael J.

DeHaemer, Managing Director.

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 written permission of the copyright owner.

First printing, September 1989

Second printing, May 1992

Third printing, May 1994

Fourth printing, January 1996

Fifth printing, December 1997

ASM Handbook is a collective effort involving thousands of technical specialists. It brings together in one book a wealth

of information from world-wide sources to help scientists, engineers, and technicians solve current and long-range

problems.

Great care is taken in the compilation and production of this Volume, but it should be made clear that no warranties,

express or implied, are given in connection with the accuracy or completeness of this publication, and no responsibility

can be taken for any claims that may arise.

Nothing contained in the ASM Handbook shall be construed as a grant of any right of manufacture, sale, use, or

reproduction, in connection with any method, process, apparatus, product, composition, or system, whether or not covered

by letters patent, copyright, or trademark, and nothing contained in the ASM Handbook shall be construed as a defense

against any alleged infringement of letters patent, copyright, or trademark, or as a defense against any liability for such

infringement.

Comments, criticisms, and suggestions are invited, and should be forwarded to ASM International.

Library of Congress Cataloging-in-Publication Data (for Print Volume)

Metals handbook.

Includes bibliographies and indexes.

Contents: v. 1. Properties and selection--v. 2. Properties and selection--nonferrous alloysand pure metals--[etc.]--v. 17.

Nondestructiveevaluation and quality control.

1. Metals--Handbooks, manuals, etc.

I. ASM Handbook Committee.

II. ASM International. Handbook Committee.

TA459.M43 1978 669 78-14934

ISBN 0-87170-007-7 (v. 1)

SAN 204-7586

Visual Inspection

Introduction

VISUAL INSPECTION is a nondestructive testing technique that provides a means of detecting and examining a variety

of surface flaws, such as corrosion, contamination, surface finish, and surface discontinuities on joints (for example,

welds, seals, solder connections, and adhesive bonds). Visual inspection is also the most widely used method for detecting

and examining surface cracks, which are particularly important because of their relationship to structural failure

mechanisms. Even when other nondestructive techniques are used to detect surface cracks, visual inspection often

provides a useful supplement. For example, when the eddy current examination of process tubing is performed, visual

inspection is often performed to verify and more closely examine the surface disturbance.

Given the wide variety of surface flaws that may be detectable by visual examination, the use of visual inspection may

encompass different techniques, depending on the product and the type of surface flaw being monitored. This article

focuses on some equipment used to aid the process of visual inspection. The techniques and applicability of visual

inspection for some products are considered in the Selected References in this article and in the Section "Nondestructive

Inspection of Specific Products" in this Volume.

The methods of visual inspection involve a wide variety of equipment, ranging from examination with the naked eye to

the use of interference microscopes for measuring the depth of scratches in the finish of finely polished or lapped

surfaces. Some of the equipment used to aid visual inspection includes:

• Flexible or rigid borescopes for illuminating and observing internal, closed or otherwise inacc

essible

areas

•

Image sensors for remote sensing or for the development of permanent visual records in the form of

photographs, videotapes, or computer-enhanced images

• Magnifying systems for evaluating surface finish, surface shapes (profile and contour ga

ging), and

surface microstructures

•

Dye and fluorescent penetrants and magnetic particles for enhancing the observation of surface cracks

(and sometimes near-surface conditions in the case of magnetic particle inspection)

This article will review the use of the equipment listed above in visual inspection, except for dye penetrants and magnetic

particles, which are discussed in the articles "Liquid Penetrant Inspection" and "Magnetic Particle Inspection,"

respectively, in this Volume.

Acknowledgements

ASM International would like to thank Oliver Darling and Morley Melden of Spectrum Marketing, Inc., for their

assistance in preparing the section on borescopes. They provided a draft of a textbook being developed for Olympus

Corporation. Thanks are also extended to Virginia Torrey of Welch Allyn, Inc., for the information on videoscopes and to

Peter Sigmund of Lindhult and Jones, Inc., for the information on instruments from Lenox, Inc.

Visual Inspection

Borescopes

A borescope (Fig. 1) is a long, tubular optical device that illuminates and allows the inspection of surfaces inside narrow

tubes or difficult-to-reach chambers. The tube, which can be rigid or flexible with a wide variety of lengths and diameters,

provides the necessary optical connection between the viewing end and an objective lens at the distant, or distal, tip of the

borescope. This optical connection can be achieved in one of three different ways: