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ASNT Level III Study Guide

Infrared an TherDlai Testing Me od by Herbert Kaplan

The American Society for Nondestructive Testing, Inc.

ASNT Level III Study Guide

Infrared an TherDlai Testing Me by Herbert Kaplan

The American Society for Nondestructh'e Testing, In c.

ii

ASNT Level III Study Guide: Infrared and Thermal Testing Method

Published by American Society for Nondestructive Testing, Inc. 17 11 Arling.te L.ne Columbus, OH 43228-0518 (800) 222-2768 © 2001 by American Society for Nondestructive Testing,Inc. All rights reserved. Published 200 I Printed in the United States of America No part of this book may be reproduced or transmitted in any form, by any means electronic or mechanical including photocopying, recording, or otherwise, without the expressed prior written permission of the publisher. ASNT is not responsible for the authenticity or accuracy of information herein, and published opinions or statements do not necessaril y reflect the opinion of ASNT. Products and/or services that may appear in thi s book do not carry the endorsement or recommendation of ASNT. ASNT assumes no responsibility for the safety of persons usi ng the information in thi s book.

Library of Congress Cataloging-in-Publication Data Kaplan , Herbert. ASNT level UI study guide. Infrared and thermal testing method I Herbert Kaplan. p. cm. Includes bibliographical references. ISBN 1-57117-015-4 I. Infrared testing. 1. Title: ASNT level 3 study gu ide. Infrared and thermal testing method. n. Title: ASNT level three study guide. Infrared and thermal testing method. 1Il. Title. TA417.5 .K37 2001 620. 1' 127--dc21 2001005701

first printing 1110 I

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Table of Contents

Chapler I - Introduction to Principlesffheory ...... •• • • ••• • . . •• • •• •• •• •• • • . • • • • .• • . • • • •••..• 1 Fundamentals of Temperature and Heat Transfer .................•. . .... 1 Temperature and Temperature Scales ......•..................•. . .... 1 Conductive Heat Transfer . ............ ........ ......... . .... 2 Convcctive Heat Transfer ..... 2 ..........................•. ............... . .... 3 Radiative Heat Transfer Fundamentals of Radiative Heat Row ......... ...... • ... . . .. . . .....•. . ... .5 Radiation Exchange at the Target Surface . . . . .•. . .. . . . . .•. . .5 Reflections off Specular and Diffuse Surfaces ........ .. . ... . . . .... . ... . ..... .5 Transient Heat Exchange .......... .. ....... . . ........ . ... ....... .. .. . .. . . ... . . .... .6 Radiant Energy Related to Target Surface Temperature .... . . . . . • . . • . . . .. . . . ..... .6 Practical Infrared Measurements ......... .... .. .. . ...... . . . . . • . . .... 7 Characteristics of the Target Surface . .. ..... . . ..... 7 Characteristics of the Transmitting Medium . ... . . . . 8 Chapter I Review Questions ......... ....... . ..15

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Chapter 2 -

Materials Characteristics "', • • •••••. ............•...•. .. • ".,., •• • • • •• • •••... 19

Surface Properties o f Material s ............. Emissivity ............ ........... .. . • .. . . • .. . Reflectivity ........ ....... Transmissivity ......... View Angle ... . ......•. Heat Conducting Properties of Materials . •. . . Thermal Conductivity . .. ................ .. Heat Capacity . ...... ... ............... .. Thennal Diffusivity ........ . . . . . Chapter 2 Review Questions .. .. . .......... .....

.... ... .... . . •. .•. . . . . . . . . . . . . . . . .. . ........... .•. . . . . . .... , , .. . . . ... . .. . .. ....... . . . . . . .,. . . • . .. . . , .,•. ........

..,.. .

..,. . ..,.. ... ..... ...

. .19 . . . . . . . . .19 . ... ....... . 19 . . . .20 . . ..... 20 . ..... .20 . .......... .. . .20 . . .. .. ..... 20 . .. .. ..... 20 . ........... ... 27

Chapter 3 - Thermal Instrumentation Overview ••.. • ...... • •.. • ... • ......• ,., • ••• • ••••••... 29 Contacting Thermal Measuring Devices . . ....... . . . . . .. . . .. • . . .. . . . . . . . ... 29 .... . , . . . ....... . .............. 29 Bimetallic Thermometers Thennochromic Liquid Crystals ........... .. . .. . ........ . . .......... . .. 29 T hcnnocouplesfrhermopiles .. ....... . . . . . . . . . . , . . , , .. .. . . . . . . , . . , , • . . . . . . .... .29 Resistance Thermometers . . . . . . . . . , • . , , .. .. . . . . . . , . . , , .... .. . . ....... 30 Thermistors ........... ... . ............... . . . . . . . . . . . . . . ........... .30 Heat Rux Indicators ..... .. ............. ..... ......•...... . . .......... .. .30 Optical Pyrometers ......... ... ............. .... ...........,.•. . ........... 30 Basic Configurations of Infrared Sensing and Imaging Instruments ...... ... . . . . . . . . . . . . . .. 30 Infrared Detector ........ ... ..... ......... . ............ ..... . . ........ .. .. .30 The Infrared Optics - Lenses, Mirrors and Filters ... ........ . . .• .. . . . . . . , . . . .3 1 The Processing Electronics ............ .... .... . .. • . .. ......,...,. .. . . .32

AS NT Level III Study Guide: Infrared and Thermal Testing Method Scanning and Imaging ................ ..... . . .......... . .......... 32 Line Scanning ............ ............ ..... . . . . . . . . . . . . . . . . . . . . . . . . . ... 32 Two-dimensional Scanning - Thcrmal Imaging . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . ... 33 Optomechanical Scanning ..... . .... ........ ........ ....... • ... . ........ ........... .33 Eleclronic Scanning - Pyroelcclric Vidicon Thermal Imagers ...... . . .... ... ....... 33 Focal Plane Array Imaging ... .... . ...... ............ . ... .. ....... 34 Performance Parameters of Infrared Sensing and Imaging Instruments ......... . ..... 34 Qualitative Versus Quantitative Thermography .............. ............. . ......... 34 Performance Characteristics of Pointsensing Instruments (Radiation Thermometers) ... .......... .34 Temperature Range ................................... . .... .34 ....................................... . ... .34 Absolute Accuracy .... .. . Repeatability ... ..... .. . ............ ....... • ...•... . ........... .35 Temperature Sensitivity ....... ............ ........ ...... . . ...... 35 Speed of Response .......... ........... .. . • ... . ..... •. . • . . ... . . . . . . ..• ...... 36 Target Spot Size and Working Distance ................ . .... ......•. . . . . ........ 36 Output Requirements ......... ....... ............ .. • .. . ......... • ... . .... .. .. 37 Sensor Environment ............ ....... ...... .. •. . . ... ... . . . . . . . . . . . . . . .. .... 37 Speclral Range ............................. .. • . . . ... . . . . . .. . • ... . .. . . .. . . .. 37 Performance Characteristics of Scanners and Imagers . ............ . ... . ................... 38 Total Field of View . . . . . . . . .. . . . . . . . . . . . . . . . . •. . . . . . . . . . . •. .. •. . .38 Instantaneous Field of View .................. .. . • .. . . .. . ... . . .•...•... . •.. ...... 38 Measurement Spatial Resolution ..... ............. ..•...•. . ...... .39 . . . . . . . . . ............ . . . . • . . ... . . ....40 Frame Repetition Rate ....... Minimum Resolvable Temperature Difference ................ ... . ... • .. . . .40 Thermal Imaging Display and Diagnostic Software Overview ... ......• . • . . .....40 Descriptions of Thermal Sensing and Imaging Equipment .... ........... .. . ... • ... . . ...... .40 Point Sensors (Radiation Thermometers) . ....... ...... ............ .... . ...... . .40 Temperature Probes .. ................. ......... . ... . .40 Portable Handheld Devices ................... . . . . . . . • . . . . . . . . .. .40 Online Process Monitoring and Control Devices ...... . .......... • ... . .. . . ... ... .41 Devices with Special Configurations ........ ....... . ... .. .....•... . .. . . .... 41 Line Scanners .. . .......... ......... ...... ...... . . . . . . . . . • .. . • .. . ... . . ....42 Online Process Control Devices ........ .. .. . . .. .. . ... . . . . • .. .• . . . . .. . . . . . . .... 42 Special Purpose Devices .... ................•.......... . .. .42 Imagers (Thermographic lnstruments) ......... . . . . . •. . . . . . . . . . . . . . ...... .42 Qualitative Thermal Imagers ... . ... ........ ... . ... . . . . • .. . • .. . . . . . . . ... .. .42 Mechanically Scanned Thermal Viewers . . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . .42 Electronically Scanned Viewers ..................•....... .43 Staring Infrared Focal Plane Array Thermal Viewers ....... . . ... . .......... • . .43 Quantitative Thermal Imagers ....... ..... ............. .. ...•. .. . . . ...43 Mechanically Scanned Thermal Imagers ............... . . . . .. .. •. . ....43 Focal Plane Array Radiometers ............. • ......... ... .. • . . ..... ...44 Thermal Imaging Display and Diagnostic Software ....... . . . . . . . . . •. . . . . . . . . .... ..44 Quantitative Thermal Measurements ............ . . .. ..• . . •. . •. . . . . •. . .....44 Image Recording, Storage and Recovery ......... . . . . . . . . . . . . . . . . ....... .. .45 Database and Documentation ...... .......... .•... . ... . . . . . ...... ... .45 Calibration Accessories ..... ........................ . ... . .. . . . . .. . ..... .46 Photorccording Accessories for Hard Copies ....... . • . , . , .. . , . •. . ...... 46 ......... . ..... . .. . .......•.... . .. •..... .47 Chapter 3 Review Questions. . . . . . .

Chapter 4 - Operating Equipment and Understanding Results .•... .. • .. •..••••• • •.• • ..••.... . .51 Temperature Changes .................. ....... ............. . , . . . .. . . . ..... 5 1 Causes of Apparent Temperature Changes ... .... ............ .... . ............. .. .... 5 1 Emissivity Differences . . . . . . . . . . .. . . •.. . •.. . . •.. . •. . . . . . ....... .•.... .. 51

Table of Contents Reflectivity Differences ....... . , ... . ................................ 51 Transmissivity Differences ...... .... . • . . . . . . . .... . . . ...... .51 Target Geometry Differences ............... . . .. . . . . .. .. .. . • . . . . . . . . . .. . .. . .. .51 Causes of Real Temperature Changes ................... . . . . . . .. .. .. ....... .51 Mass Transport Differences (Fluid Flow) .......... . ... . ... .. ... .. .. . .. •. . .... .51 Phase Change Differences (Physical State) . . . ..... . . . ....•... . .. . , ........ .51 Thennal Capacitance Differences ......... .... . •.. . ....... ....... 52 Induced Heating Differences . . . . . . . . . .•. . .•. . . . .. .. . . ......... 52 Energy Conversion Differences ........ . .......... . ......... .. . .. ........ 52 ............. ........... . . .52 Direct Heat Transfer Differences Combination of Heat Transfer Mechanisms .............. ... . •. . . . . . . . . ..... . .53 Image Interpretation ............................... . .. . . ......... . .53 Spectral Considerations in Product and Process Applications ...... .... .. ... . ..... ... .53 Using Line Scanners for Monitoring Continuous Processes .. .. .• . . .. .. ... 54 Infrared Thennographic Equipment Operation .................... .• . .. .. .. . . ......... 55 Preparation of Equipment for Operation .... ... ...... .. . . . ........ 56 Procedures for Checking Critical Instrument Perfonnance Parameters ... . . .... ..... . . ...... .57 Thennal Resolution .................................. . ... . . .57 Imaging Spatial Resolution .... ... ............... ... .. . .... . ................ 57 Measurement Spatial Resol ution .. .. ....... ............ . ........... . .. 59 Common Mistakes in Instrument Operation .... . ... . . . . .•. . . . .. ... .59 Learning the Startup Procedure ... ... ............. .... . ....... . ..... 59 Memorizing the Default Values .... .. ........ ......... . . . . . .......... .. .. .... 59 Selling the Correct Effective Emissivity ........................ .......... . . .60 Measuring and Reporting Temperature Accurately ~ Filling the £FOV .. . . .. .60 . ...... 60 Aiming Nonnal to the Target ...................... .. ....... .. .. Recognizing and Avoiding Reflections from External Sources .. . ................... . .. .61 Measuring the Appropriate Background Temperature Using the Instrument ....... ..... ... . .61 Avoiding Radiant Heat Damage to the Instrument . . . . . . . . . . . .... . . . ...... 61 Temperature Differences Between Similar Materials ....... . . . . . . . . . . ....... 62 Safety and Health ...... .... . . . . . . . . . . . . . . . . . . ........ . . . . . . . .......... 62 Liquid and Compressed Gases . . . . . . . . . . . . . . . . . .. .......... . ... . .......... 62 Batteries .......... ........•..............•. . • .. . . . , . . . • . . ... 62 . ........ . .. . . ... ............. 62 Electrical Safety ............... . . . .. • . .. . ... .. .. Record Keeping ...... ..... ... . ... . . ........ . ........ . ...... . . . ... . . ...... 63 Chapter 4 Review Questions . . . . . . . . . . . ....... . •.. . . . . . . . • ........ .. ... .65

Chapter 5 - Applications, , , ................... ... .. • • ..• . .. ...... .. . ..... , . , , , . , .. , .....67 Overview of Applications . . . . . . . . . .... ........ ... , . . ........ .. . . . . .. . . . . .... .67 Exothermic and Endothennic Investigations ..... ... ........... .... .... ..... . ..... 67 Electrical Applications ................ .. . . . . . . .. . . .. . .•. . . . . . . . ..... 67 Moisture in Airframes ................. . ................... . . . .......... 68 Process Control and Product Monitoring .... . . .. ...... . ............... . . . ...... 69 Line Scanners or Imagers for Mapping of Continuous Processes ...... 69 Spectral Considerations in Product and Process Applications ....... .. . . ..... . . ..... ...... 69 Night Vision. Search, Surveillancel Security and Fire Detection ............................ . . . . .•. . . . . . . . . . . .. .. .70 Animal Studies .......... .......... . • .. . .. . . • ... . .. ... . . . . . .. . . .. 70 Friction Investigations . ..... . ........ . ................ • . . . . . . ....... ... .. .. . . . ... 70 Fluid Flow Investigations .... ...... .... . . .71 Thennal Resistance Investigations . ... ..... . . .72 Building Insulation and Other Factors ...... . . •. .72 Jndustrial Roof Moisture Detection .........•.. . ..... ..... 72 Refractory Systems ..... ... ............ • ........ ...... . . . ......... • . ..• . .. ..... 73

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ASNT Level III Study Guide: Infrared and Thermal Testing Method Subsurface Discontinuity Detection in Materials .. . . . . .. ... .. . ................ 73 The Unstimulated Measurement Approach to Infrared Materials Raw Detection .... ... . . . ...... 74 The Stimulated Measurement Approach to Infrared Materials Flaw Detection .... ... . .. . ... ..... 74 Stimulated Thennography Using Pulsed or Thcnnal Wave Injection ........... . ... . .... .. .. 76 Thermal Capacitance Investigations . . . ... ..... . . ....... ........... • ...•........ 77 Industrial Roof Moisture Detection .......... .. ... ............. .......... • . • . . .. ...... 77 Liquid Level Detection ........ .............. .................. . ... ...78 Unstimulated and Stimulated Approaches to Infrared Materials Flaw Detection ......... .... . .78 Underground Void Detection ..................... ... ......... .... ... ... •. ..• ....... .78 .......... . ... ••. . . .. ......79 Subsurface Discontinuity Detection in Materials ....... .•. . . . .•. . .. •• .. . • . ....... 81 C hapter 5 Review Questions .....................

Answers to Review Questions .........••••••••••......•...•...•.. . • .. •. .. • ...•...••....... 83 Appendix A - Glossary •••••........•.•••..••.... ..... ........... . • • •• • •• • • • • • • •• • ...... 85 Appendix B - Cost Benefit Determination ........... ... . . ....•• •• ..... •• .. • ..• • ... • .... . . .. 95 Appendix C - Commonly Used Infrared Specifications and Sta ndards •••... • ... • .•.••.. • . .... ... 97

References

References I.

Maldague, X.PV, technical editor, Patrick O. Moore, editor, Nondestructive Testing Handbook third edition, Volume 3, Infrared and Themral TesTing, American Society for Nondestructive Testing, Inc. , Columbus. Ohio, 2001.

2.

Spicer, Jane, Themrographic NDT, presented at SprE International Symposium on Optical Engineering and Photonics in Aerospace and Remote Sensing, Orlando, Rorida, 9 April 1996.

3.

Maldague, X.PY, NondeSTructive Evaluation of Materials by Infrared Thennography, Springer-Verlag, London, 1993.

4.

National Fire Protection Association NFPA 70E, Standard for Electrical Safety Reqlliremellfs for Employee Workplace, Quincy, Massachusetts, 1995.

5.

National Fire Protection Association NFPA 708, Recommended Practice for Electrical Equipment Maintenance, Quincy, Massachusetts, 1994.

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1

Chapter 1 PrincipleslTheory Introduction to Principlesffheory

Fundamentals of Temperature and Heat Transfer

Infrared/thermal testing involves the use of temperature and heat now measurement as a means to predict or d iagnose failure. This may involve the use of contacting or noncontacting devices, or a combination of both. A fundamental knowledge of heat now and the thermal behavior of materials is necessary to understand the significance o f temperalUre and temperature changes on a leSI sample. Contacting devices include thermometers of various types, thermocouples. thermopiles and thennochromic coatings. Noncontacting devices include convection (heal nux) devices, optical pyromClers, infrared radiation thermometers. infrared line scanners and infrared thermal imaging (thermographic) equipment. Infrared thermography is the nondestructive. non intrusive. noncontact mapping of thennal patterns on the surface of objects. h is usually used to diagnose thennal behavior and. thereby. to assess the perfonnance of equ ipment and the integrity o f materials, products and processes. The infrared thennal imaging equipment used in infrared thermography is available in numerous configurations and with varying degrees of complexity. The thennal maps produced by infrared thennal imaging instruments are called thennograms. To understand and interpret thennograms. the thennographer must be familiar with the fundamentals o f temperature and heat transfer. infrared radiative heat flow and the perfonnance of infrared thennal imaging instruments and other thennal instruments. An understanding of the equipment. materials and processes being observed is also important to effectively assess the full significance of infrared/thennal measuremenls. A more detai led discussion of the perfonnancc parameters of infrared thennal imaging instruments is provided in Chapter 3.

Heat is a transient fonn of energy in which thennal energy is transient. What is often referred to as a heat source (such as an oil furnace or an electric heater) is really one fonn or another of energy conversion - the energy slored in one object being converted to heat and flowing to another object. Heat flow is thennal energy in transit and heat always flows from wanner objects to cooler objects. Temperature is a measure of the thennal energy contained in an object - the degree o f hotness or coldness of an object that is measurable by any of a number o f relative scales. The three modes of heat transfer arc conductive. convective and radiative. All heat is transferred by one of these three modes. In most situations. heat is transferred by a combination of two or all three modes. Of these three modes of heat transfer. infrared thennography is mOSI closely associated with the radiative process. bul it is essential 10 sludy all three to understand the meaning of thennograms and to pursue a successful program of thennography. As a result of heat transfer. objects tend to increase or decrease their temperature until they come to thennal equilibrium with their surroundings. To mainlain a steadystatc heat flow condition. energy must be continuously supplied by some means of energy conversion so that the temperature differential. and hence the heal flow, remains constant.

Temperature and Temperature Scales Temperature is expressed in either absolute or relative tcnns. There are two absolute scales called Rankine (English system) and Kelvin (metric system). There arc two corresponding rclalive scales called fahre nheit (English system) and celsius or centigrade (metric system). Absolute zero is the temperature at which no molecular action takes place. This is expressed as zero Kelvin or zero degrees Rankine (0 K or 0 OR). Relative temperature is expressed as degrces celsius or degrees